ASME Conference Presenter Attendance Policy and Archival Proceedings

2018;():V002T00A001. doi:10.1115/ICEF2018-NS2.

This online compilation of papers from the ASME 2018 Internal Combustion Engine Division Fall Technical Conference (ICEF2018) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

Emissions Control Systems

2018;():V002T04A001. doi:10.1115/ICEF2018-9528.

Tightening global emissions regulations are motivating interest in the development and implementation of Selective Catalytic Reduction + Filtration (SCRF) systems, which are designed to reduce the concentration of tailpipe particulate matter (PM) and NOx emissions. These systems allow designers to combine the NOx reduction capability of an SCR with the filtration capability of a particulate filter on a single unit. Practical implementation of these systems requires reliable measurement and diagnosis of their state — both with respect to trapped particulate matter as well as adsorbed ammonia. Currently, these systems rely on a variety of gas sensors, mounted upstream or downstream of the system, that only provide an indirect inference of the operation state.

In this study, a single radio frequency (RF) sensor was used to perform simultaneous measurements of soot loading and ammonia inventory on an SCRF. Several SCRF core samples were tested at varying soot and ash loads in a catalyst reactor bench. Soot levels were measured by monitoring changes in the bulk dielectric properties within the catalyst using the sensor, while ammonia levels were determined by feeding selected regions of the RF spectrum into a pretrained generalized regression neural network model. Results show the RF sensor is able to directly measure the instantaneous ammonia inventory, while simultaneously providing soot loading measurements within 0.5 g/L. These results confirm that simultaneous measurements of both the PM and ammonia loading state of an SCRF are possible using a single RF sensor via analysis of specific features in the full RF spectrum. The results indicate significant potential to remove the control barriers typically associated with the implementation of advanced SCRF systems.

Commentary by Dr. Valentin Fuster
2018;():V002T04A002. doi:10.1115/ICEF2018-9627.

Recent particulate regulations for gasoline passenger cars have prompted the utilization of Gasoline Particulate Filters (GPF’s) to mitigate particulate emissions. This study overviews a comprehensive experimental methodology for examination of essential GPF parameters: spatial exothermic temperature rise, particulate trapping efficiency, and the pressure rise versus particulate loading. A GDI vehicle equipped with a subfloor catalytically washcoated GPF downstream of the three-way catalyst was operated on a chassis dynamometer for data collection. Accelerated soot accumulation procedures were developed to expedite the testing while avoiding passive particulate regeneration based on both particulate concentration and size distributions. Soot concentrations pre and post GPF were used to measure the soot trapping efficiency and total soot accumulation. Fuel-cut coast events, common in real-world driving, were utilized to initiate worst case GPF regenerations, namely regenerations which produce maximum temperature rise due to the limited exhaust flow through the GPF. CO2 measurements simultaneously measured before and after the GPF were examined to calculate the quantity of soot burned during each regeneration event. Thermocouples located inside the GPF were implemented to obtain the spatially disparate, transient temperature traces and analyzed to obtain insights on the soot distribution inside the GPF. The maximum exothermic temperature rise within the GPF was tracked for different soot loadings and regeneration temperatures to ensure GPF substrate and catalytic washcoat health. Most initial soot loadings required multiple ‘fuel-cut coast’ regenerations for complete soot oxidation of all trapped particulate mass.

Additionally, externally supplied oxygen was utilized to obtain complete GPF regeneration in a single event. This purpose built system created O2 availability while maintaining constant GPF temperatures, similar to actively commanding lean A/F ratios during vehicle operation. Emissions measurements indicated that this system successfully regenerated all GPF soot. However, due to magnitude disparity between exhaust flow and total exothermic heat released, the thermocouples inside the GPF recorded only minimal exothermic temperature rises, providing confidence that lean active regeneration strategies pose little threat to GPF health.

Commentary by Dr. Valentin Fuster
2018;():V002T04A003. doi:10.1115/ICEF2018-9644.

Reduction of particulate matter (PM) is important issues even for shipping industry since PM harms the environment and human health. In order to reduce PM from marine diesel engines, we focused on components forming PM, elemental carbon (EC), organic carbon (OC), sulfate, and “others” (nitrate, bound water associated with sulfate, metal, ash and hydrogen associated with OC), and investigated the reduction effect of each component by changing fuel injection pressure of a four-stroke marine diesel engine at the two engine load points of 25% and 50%. At 50% load, the PM emissions decreased with increasing the fuel injection pressure, the reduction in the PM emissions which reflected the decrease in EC. At 25% load, the PM emissions did not decrease simply with the injection pressure since OC, sulfate, “others” components in addition to EC contributed to the injection pressure dependence of PM. The results suggest that behaviors of each component of PM should be grasped to achieve the appropriate reduction method of PM.

Commentary by Dr. Valentin Fuster
2018;():V002T04A004. doi:10.1115/ICEF2018-9687.

Gasoline particulate filters (GPFs) are the most promising and practically applicable devices to reduce Particulate Matter (PM) and Particulate Number (PN) emissions from gasoline direct ignition engines. A model that can predict internal GPF temperature dynamics during regeneration events can then be implemented online to maintain GPF health and aide in exotherm control algorithms without the associated instrumentation costs. This work demonstrates a control-oriented model, which captures the thermal dynamics in a catalyzed, ceria-coated GPF in the axial direction. The model utilizes soot oxidation reaction kinetics to predict internal GPF temperature dynamics during regeneration events using three finite volume cells.

A model methodology initially proposed by Arunachalam et al [18] is utilized with the GPF of this work, validating the broad applicability of that methodology. Then, the model’s temperature prediction fidelity is improved through axial discretization. The zonal model parameters are identified via a Particle Swarm Optimization using experimental results from the instrumented GPF. Identified parameters from the various data sets are used to develop a linear parameter varying model for prediction of the axial temperature distribution within the GPF. The resulting model is then validated against an experimental data set utilizing the exhaust temperature entering the GPF. The spatial discretization methodology employed both enables the prediction of spatial temperature variation within the GPF and improves the accuracy of the peak temperature prediction by a factor ranging from 2–10x.

Commentary by Dr. Valentin Fuster
2018;():V002T04A005. doi:10.1115/ICEF2018-9763.

NOx pollution from Diesel engines causes over 10 000 premature deaths annually and the trend is increasing. In order to decrease this growing global problem, exhaust after-treatment systems for Diesel engines have to be improved.

The most common SCR systems in the market place inject an aqueous Urea solution, DEF that evaporates prior the catalytic surface of the SCR-catalyst. Due to a catalytic reaction within the catalyst, NOx is converted nominally into Nitrogen and Water.

Currently, the evaporative process is enhanced by aggressive mixer plates and long flow paths; these, negatively, create extra exhaust back pressure and cool the exhaust gases decreasing engine and catalyst efficiency. To achieve future emission legislation targets SCR efficiency has to be improved especially under low catalyst temperature conditions, plus Ammonia slip has to be avoided as it is now legislated against.

Swedish Biomimetic’s novel μMist® platform technology, inspired by the Bombardier Beetle, injects a hot, effervescent, finely atomised, highly dispersed spray plume of DEF into the exhaust stream. This is achieved by raising the temperature of the DEF, in a closed volume, above its saturated vapour pressure. The DEF is then rapidly released creating effervescent atomisation.

This study investigates a back to back study of the evaporating and mixing behaviour of the μMist® injector and a class leading DEF injector. The test conditions are with and without a mixer plate and the use of two different flow path designs. Spray distribution across the face of the catalyst is assessed by measuring NOx conversion whilst Ammonia slip is also measured post catalyst. This report describes how the novel μMist® injector significantly increases NOx conversion and catalyst surface usage whilst considerably reducing Ammonia slip.

Commentary by Dr. Valentin Fuster
2018;():V002T04A006. doi:10.1115/ICEF2018-9777.

The purpose of this study is evaluate emission characteristics, such as nitrogen oxides (NOx), hydrocarbon, carbon monoxide, and particulate matter (PM), of excavator with Tier-4f level diesel engine in the real work conditions. The test excavator has an engine power of 124 kW at an engine speed of 1800rpm, and it has various after-treatment devices, such as exhaust gas recirculation (EGR), selective catalytic reduction (SCR), and diesel oxidation catalyst (DOC), to reduce the engine-out emissions. The emissions including carbon monoxide (CO), carbon dioxides (CO2), and NOx, were measured by portable emission measurement system (PEMS). The PEMS device conducted a correlation analysis with the emission bench on the engine dynamometer before being used to measure the real-work to confirm the reliability of the equipment. The tests were carried out in four categories: idling, driving, excavations and flattening.

It revealed that the average power output for each operation mode was higher in the order of flattening, excavation, and drive. On average, those are higher than that for the non-road transient cycle (NRTC) certification mode as 1.5 to 1.9 times. It may be determined that the power output is higher in conditions where there are more boom and bucket movements than the movement of the vehicle itself. In emission analysis, NOx and HC emission in driving mode are higher than other two modes: excavation and flattening. The real time NOx have been low in most test conditions, but large quantities of NOx have been released due to the deactivation of the SCR catalyst during cold start period or immediately after the non-working.

Commentary by Dr. Valentin Fuster

Instrumentation, Controls, and Hybrids

2018;():V002T05A001. doi:10.1115/ICEF2018-9507.

Measuring and analyzing combustion is a critical part of the development of high efficiency and low emitting engines. Faced with changes in legislation such as Real Driving Emissions and the fundamental change in the role of the combustion engine with the introduction of hybrid-electric powertrains, it is essential that combustion analysis can be conducted accurately across the full range of operating conditions. In this work, the sensitivity of five key combustion metrics is investigated with respect to eight necessary assumptions used for single zone Diesel Combustion analysis. The sensitivity was evaluated over the complete operating range of the engine using a combination of experimental and modelling techniques. This provides a holistic understanding of combustion measurement accuracy.

For several metrics, it was found that the sensitivity at the mid speed/load condition was not representative of sensitivity across the full operating range, in particular at low speeds and loads. Peak heat release rate and indicated mean effective pressure were found to be most sensitive to the determination of top dead center (TDC) and the assumption of in-cylinder gas properties. An error of 0.5° in the location of TDC would cause on average a 4.2% error in peak heat release rate. The ratio of specific heats had a strong impact on peak heat release with an error of 8% for using the assumption of a constant value.

A novel method for determining TDC was proposed which combined a filling and emptying simulation with measured data obtained experimentally from an advanced engine test rig with external boosting system. This approach improved the robustness of the prediction of TDC which will allow engineers to measure accurate combustion data in operating conditions representative of in-service applications.

Commentary by Dr. Valentin Fuster
2018;():V002T05A002. doi:10.1115/ICEF2018-9534.

The combustion resonance is a focal point of the analysis of combustion and thermodynamic processes in diesel engines, such as detecting ‘knock’ and predicting combustion noise. Combustion resonant frequency is also significant for the estimation of in-cylinder bulk gas temperature and trapped mass. Normally, the resonant frequency information is contained in in-cylinder pressure signals. Therefore, the in-cylinder pressure signal processing is used for resonant frequency calculation. Conventional spectral analyses, such as FFT (Fast Fourier transform), are unsuitable for processing in-cylinder pressure signals because of its non-stationary characteristic. Other approaches to deal with non-stationary signals are Short-Time Fourier Transform (STFT) and Continue Wavelet Transform (CWT). However, the choice of size and shape of window for STFT and the selection of wavelet basis for CWT are totally empirical, which is the limit for precisely calculating the resonant frequency. In this study, an approach based on Empirical Wavelet Transform (EWT) and Hilbert Transform (HT) is proposed to process in-cylinder pressure signals and extract resonant frequencies. In order to decompose in-cylinder pressure spectrum precisely, the EWT are applied for separating the frequency band corresponding combustion resonance mode from other irrelevant modes adaptively. The signals containing combustion resonant mode is processed by HT, so that the instantaneous resonant frequency and amplitude can be extracted. Validation is performed by four in-cylinder pressure signals with different injection timing. And the effects of injection timing on resonant frequency are discussed.

Commentary by Dr. Valentin Fuster
2018;():V002T05A003. doi:10.1115/ICEF2018-9540.

Cycle-to-cycle combustion variability (CV) in spark ignition internal combustion engines is amplified at high levels of exhaust gas recirculation (EGR) by sporadic partial burn and misfire events. A non-equiprobable cycle classification method, based on the magnitude of the indicated mean effective pressure (IMEP), was developed to discern and study the deterministic and stochastic components of cyclic CV. The time series analysis of experimental combustion cycles suggested that the occurrence of high energy release cycles right after misfires is the only deterministic component between consecutive cycles. This predictable behavior results from the retained air and fuel from the incomplete combustion cycle to the next. On the other hand, this study shows that the occurrence of partial burn and misfire cycles is the product of the stochastic component of cyclic CV with statistical properties similar to a multinomial probability distribution. It is demonstrated that observation of partial burns can increase the probability of observing a misfire when the conditional probability is used as the metric. Based on these findings, future work will be able to use the observation of partial burns alone to control the upper bound on the probability of misfire events. To this end, different metrics are proposed to control directly and indirectly the probability of misfires, and their advantages and disadvantages for feedback combustion control are discussed.

Commentary by Dr. Valentin Fuster
2018;():V002T05A004. doi:10.1115/ICEF2018-9545.

The integration of sensors in engine components has been a long-standing wish of engine manufacturers and researchers. Conventional probes are particularly difficult to mount in moving engine parts and require time-intensive and costly preparation, while often still not reaching the site of interest close enough. The advances recently made in the field of printed electronics enable new possibilities for sensor integration that previously were not possible. Particularly, crankshaft engine bearings are an interesting component to apply those new sensors to.

An important enabling factor for the successful sensor integration has been the increasing market penetration of polymer overlays for crankshaft bearings. The driving force behind this development was the pressure from legislation to reduce CO2 emissions, which in turn brought about new technologies such as start-stop and mild hybrids. Engine components now have to operate in much more aggressive environments, which in many cases only polymer overlays withstand. The unique application process of those coatings together with their material properties, such as robustness and non-conductivity, now allow embedding of electronic components right at the running surface of the bearings.

This paper details the development of a printed sensor that has been integrated into the bearing polymer overlay coating. Various results from respective rig testing of the sensor feedback throughout different load and speed conditions during operation are reported.

Topics: Sensors , Engines , Bearings
Commentary by Dr. Valentin Fuster
2018;():V002T05A005. doi:10.1115/ICEF2018-9549.

According to current worldwide trends for homologation vehicles in real driving conditions, is forced to test the engines in altitude and in highly dynamic driving cycles in order to approach nowadays and next future emissions standard. Up to now, there were two main options to perform this type of tests: round-robin tests of the whole vehicle or hypobaric chambers, both with high costs and low repeatability.

In this paper a new device is described, which can emulate ambient conditions at whatever altitude between sea level and 5000m high. Even it can be used to emulate ambient conditions at sea level when test bench is placed up to 2000 m high. The main advantages of the altitude simulation equipment are: dynamic emulation of all the psychrometric variables affecting the vehicles during round-robin tests; lower space usage and low energy consumption.

The altitude simulator has been validated comparing with results from a hypobaric chamber at different altitudes. Previously a research about the dispersion in the measurements of both testing devices has been done for assessing the results of the comparison experiment. Final conclusion resulted in the same operating performance and emissions of the studied engine with both types of testing equipments for altitude simulation.

Commentary by Dr. Valentin Fuster
2018;():V002T05A006. doi:10.1115/ICEF2018-9570.

Skip-firing (or cylinder de-activation) was assessed as a method of sampling CO2 from directly in the cylinder at higher speeds than previously possible. CO2 was directly sampled from one cylinder of a 1-litre 3-cylinder gasoline engine to determine the residual gas fraction using a fast response CO/CO2 analyser. Acquisition of data for similar measurements is typically limited to engine speeds of below 1300 rpm to allow full resolution of the sample, through the analyser that has an 8 millisecond finite response time. In order to sample in-cylinder CO2 at higher engine speeds a skip-firing method is developed. By shutting off ignition intermittently during engine operation, the residual CO2 from the last firing cycle can be measured at significantly higher engine speeds. Comparison of residual gas fraction CO2 at low speeds for normal and skip-fire operation shows good correlation. This suggests that skip-firing is a suitable method for directly measuring internal exhaust gas recirculation up to at least 3000 rpm. The measurements obtained may provide a useful tool for validating internal exhaust gas recirculation models and could be used to calculate combustion air-fuel ratio from the CO and CO2 content of the burned gas. These are typically complicated parameters to predict due to the slow response time and sensitivity to hydrocarbons of wide-band oxygen sensors. A differing pattern of residual gas fraction change with increasing speed was seen between normal and skipfire operation.

Commentary by Dr. Valentin Fuster
2018;():V002T05A007. doi:10.1115/ICEF2018-9583.

The electrification of powertrains is now the accepted roadmap for automotive vehicles. The next big step in this area will be the adoption of 48V systems, which will facilitate the use of technologies such as electric boosting and integrated startergenerators. The introduction of these technologies gives new opportunities for engine airpath design as an electrical energy source may now be used in addition to the conventional mechanical and exhaust thermal power used in super- and turbochargers. This work was conducted as part of the EU funded project “THOMSON” which aims to create a cost effective 48V system enabling engine downsizing, kinetic energy recovery, and emissions management to reduce the environmental impact of transportation. The paper presents a study on an electrified airpath for a 1.6L diesel engine. The aim of this study is to understand the design and control trade-offs which must be managed in such an electrified boosting system. A two-stage boosting system including an electric driven compressor (EDC) and a variable geometry turbocharger (VGT) is used. The air path also include low and high pressure EGR loops. The work was performed using a combination of 1D modelling and experiments conducted on a novel transient air path test facility.

The simulation results illustrate the trade-off between using electrical energy from in the EDC or thermal energy in the turbocharger to deliver the engine boost pressure. For a same engine boost target, the use of the EDC allows wider VGT opening which leads to lower engine backpressure (at most 0.4bar reduction in full load situation) and reduced pumping losses. However, electricity consumed in EDC either needs to be provided from the alternator (which increases the load on the engine) or by depleting the state of charge of the battery. The location of charge air coolers (pre- or post-EDC) is also investigated. This changes the EDC intake temperature by 100K and the intake manifold by 5K which subsequently impacts on engine breathing. An experimentally validated model of a water charge air cooler model has been developed for predicting flow temperature.

Topics: Tradeoffs
Commentary by Dr. Valentin Fuster
2018;():V002T05A008. doi:10.1115/ICEF2018-9601.

A diesel engine electrical generator set (’gen-set’) was instrumented with in-cylinder indicating sensors as well as acoustic emission microphones near the engine. Air filter clogging was emulated by progressive restriction of the engine’s inlet air flow path during which comprehensive engine and acoustic data were collected. Fast Fourier Transforms (FFTs) were analyzed on the acoustic data. Dominant FFT peaks were then applied to supervised machine learning neural network analysis with MATLAB based tools. The progressive detection of the air path clogging was audibly determined with correlation coefficients greater than 95% on test data sets for various FFT minimum intensity thresholds. Further, unsupervised machine learning Self Organizing Maps (SOMs) were produced during normal-baseline operation of the engine. Application of the degrading air flow engine sound data was then applied to the normal-baseline operation SOM. The quantization error of the degraded engine data showed clear statistical differentiation from the normal operation data map. This unsupervised SOM based approach does not know the engine degradation behavior in advance, yet shows clear promise as a method to monitor and detect changing engine operation. Companion in-cylinder combustion data additionally shows the degrading nature of the engine’s combustion with progressive airflow restriction (richer and lower density combustion).

Commentary by Dr. Valentin Fuster
2018;():V002T05A009. doi:10.1115/ICEF2018-9638.

Diesel engine emission cycle data shows that major portions of cycle emissions are produced at the beginning of the test, when the aftertreatment is not at operational temperature (prior to “light-off”) [1]. To reduce diesel emissions, aggressive combustion phasing retard via injection timing can be used to achieve faster aftertreatment light-off, but this method is limited because of vibration and harshness concerns associated with the combustion variability induced by the late combustion phasing. In order to achieve aggressive exhaust heating while mitigating combustion variability concerns, the premise of controlling combustion variability is explored. In particular, a controller will use real-time measurements of combustion features and control injection timing to maintain an acceptable level of combustion variability. The closed loop controller tuning requires an understanding of combustion variability behavior as a function of combustion phasing retard. The characterization of combustion variability using engine experiments is presented, and the findings are used to develop a control-oriented combustion variability model consisting of regressions of the statistics of IMEP as a function of fuel and timing offsets.

Commentary by Dr. Valentin Fuster
2018;():V002T05A010. doi:10.1115/ICEF2018-9651.

Due to the direct connection between the engine and the compound power split hybrid transmission (CPSHT) in hybrid electric vehicle (HEV), engine ripple torque (ERT) can result in obvious jerks in engine starting process (ESP). In order to improve the riding comfort, two wet clutches are mounted in this novel CPSHT. This research developed a new coordinated control strategy and its effectiveness was verified in simulation. Firstly, the mechanical and hydraulic parts of the CPSHT were introduced, and the riding comfort problem during ESP in primary design was illustrated. Secondly, the dynamic plant model including ERT, driveline model and clutch torque was deduced. Thirdly, a coordinated control strategy was designed to determine the target engine torque, motor torque, clutch torque and the moment of fuel injection. A Kalman filter based clutch torque estimator was applied with the help of electric motors information. The simulation result indicates that proposed coordinated control strategy can indeed suppress vehicle jerk and improve the riding comfort in ESP.

Commentary by Dr. Valentin Fuster
2018;():V002T05A011. doi:10.1115/ICEF2018-9714.

Over the past years, the increasingly stringent emission regulations for Internal Combustion Engines (ICE) spawned a great amount of research in the field of combustion control optimization. Nowadays, optimal combustion control has become crucial, especially to properly manage innovative Low Temperature Combustion (LTC) strategies, usually characterized by high instability, cycle-to-cycle variability and sensitivity to slight variations of injection parameters and thermal conditions.

Many works demonstrate that stability and maximum efficiency of LTC strategies can be guaranteed using closed-loop control strategies that vary the standard injection parameters (mapped during the base calibration activity) to keep engine torque and center of combustion (CA50) approximately equal to their target values. However, the combination of standard base calibration and closed-loop control is usually not sufficient to accurately control Low Temperature Combustions in transient conditions. As a matter of fact, to properly manage LTC strategies in transient conditions it is usually necessary to investigate the combustion methodology of interest and implement specific functions that provide an accurate feed-forward contribution to the closed-loop controller.

This work presents the experimental analysis performed running a light-duty compression ignited engine in dual-fuel RCCI mode, the goal being to highlight the way injection parameters and charge temperature affect combustion stability and ignition delay. Finally, the paper describes how the obtained results can be used to define the optimal injections strategy in the analyzed operating points, i.e. the combination of injection parameters to be used as a feed-forward for a closed-loop combustion control strategy.

Commentary by Dr. Valentin Fuster
2018;():V002T05A012. doi:10.1115/ICEF2018-9776.

In this study, a variety of piezoelectric pressure transducer designs and mounting configurations were compared for measuring in-cylinder pressure on a heavy-duty single-cylinder diesel engine. A unique cylinder head design was used which allowed cylinder pressure to be measured simultaneously in two locations. In one location, various piezoelectric pressure transducers and mounting configurations were studied. In the other location, a Kistler water-cooled switching adapter with a piezoresistive pressure sensor was used. The switching adapter measured in-cylinder pressure during the low pressure portion of the cycle. During the high pressure portion of the cycle the sensor is protected from the high pressure and high temperature gases in the cylinder. Therefore, the piezoresistive sensor measured in-cylinder pressure highly accurately, without the impacts of short term thermal drift, otherwise known as thermal shock. Additionally, the piezoresistive sensor is an absolute pressure sensor which does not require a baseline or “pegging” on every engine cycle. With this measurement setup, the amount of thermal shock and induced measurement variability was accurately assessed for the piezoelectric sensors. Data analysis techniques for quantifying the accuracy of a piezoelectric cylinder pressure measurements are also presented and discussed. It was observed that all the piezoelectric transducers investigated yielded very similar results regarding compression pressure, start of combustion, peak cylinder pressure, and the overall heat release rate shape. Differences emerged when studying the impact of the transducer mounting (e.g., recessed vs. flush-mount). Recessed-mount transducers tended to yield a more accurate measurement of the cycle-to-cycle variability when compared to the baseline piezoresistive sensor. This is thought to be due to reduced levels of thermal shock, which can vary from cycle-to-cycle.

Commentary by Dr. Valentin Fuster

Numerical Simulation

2018;():V002T06A001. doi:10.1115/ICEF2018-9506.

As the reduction of the nozzle hole diameter in diesel injectorsleads to a better vaporization and mixture generation, thenozzle geometry is considered as a key factor to face stricteremission standards. Many researches have been conductedconcerning the inner nozzle flow and especially the cavitationformation in the nozzles. In these studies, the geometricalinfluence of the nozzle shape on flow development is analyzednumerically. To reduce simulation time, sector models are used.One nozzle is simulated separately and the flow in the sac holeis assumed to follow symmetric boundaries. In this work, a newdesign of diesel nozzle is presented using 12 spray holes withalternating diameters (6 big and 6 small nozzles). The goal is toenhance air utilization during the combustion process byincreasing the spray covered volume in the piston bowl. Withthis design symmetric boundaries can only be set by simulatingtwo nozzles simultaneously. To analyze the influence of usingalternating nozzle hole diameters in one model severalsimulation are conducted. Three nozzle designs with 8, 12 and6+6 holes are examined and three types of models simulatingup to 6 nozzles simultaneously are applied. All nozzles have thesame hydraulic flow rate. In transient simulations the innerflow of these nozzles is analyzed, including the needlemovement. Compared to a sector model of an 8-hole nozzle,the flow field shows differences using alternating diameters ofspray holes at various needle positions. Since the flow field atthe nozzle outlet can be used as initial conditions forcontinuative spray simulations this effect may influence thespray angle and spray penetration.

Commentary by Dr. Valentin Fuster
2018;():V002T06A002. doi:10.1115/ICEF2018-9531.

The widths of fuel plumes around nozzle outlets expanded due to flash boiling during the nozzle flow. In some sprays, the length (penetration) of the air/fuel mixture increased due to the flash boiling. A cavitation model was incorporated in a simulation of the fuel spray integrating a simulation of the nozzle flow with a simulation of the air/fuel mixture. The simulation was applied to fuel sprays from a gasoline direct-injection injector; six nozzles were placed on an orifice cup in axial symmetry. Expansions of the plumes (in terms of width) around the nozzle outlets due to flash boiling and extension of spray penetration qualitatively agreed with the measured ones. Effects of the expansions of the plumes due to flash boiling on spray-penetration distance were also studied. The result of that study indicated that interactions between the expanded plumes around the nozzle outlets cause the spray shape of the air/fuel mixtures to thin, thereby extending the penetration of the spray.

Commentary by Dr. Valentin Fuster
2018;():V002T06A003. doi:10.1115/ICEF2018-9532.

Since the beginning of this century, Liquefied Natural Gas (LNG) has been attracting more and more attention as a cleaner energy alternative to other fossil fuels, mainly due to the possibility to transport it over longer distances than natural gas in pipelines and lower environmental impact than other liquid fuels. It is expected that this trend in the use of LNG will lead to steady increases in demand over the next few decades.

At present, in the automotive sector, natural gas is employed as fuel in spark-ignited (SI) engines in the gas phase (CNG) adopting port-fuel injection system (PFI) in the intake manifold, with the main result of reducing CO2 emissions by up to 20%, compared with gasoline operation. However, SI engines which are operated in this manner suffer loss of peak torque and power due to a reduction in volumetric efficiency. Direct-Injection (DI) inside the cylinder can overcome this drawback by injecting CNG after intake valve closure. Another strategy could be the injection of natural gas in the liquid phase, both in PFI or DI mode. The injected fuel evaporation cools down the intake air; increasing the charge density with a substantial improvement in the engine volumetric efficiency and delivered power. However, at present, injection systems dedicated to cryogenic injection of natural gas are still in the prototype state.

In the present study, the volumetric efficiency and performance of a turbocharged, LNG fuelled SI-ICE were numerically analysed both in the cases of DI and PFI modes and compared with the results of a conventional CNG system. Various fuel injection timings and injector position were analysed. The engine performance was evaluated by means of a one-dimensional model developed with the simulation program GT-Power, while the verification of the LNG-air mixture characteristics was carried out with the commercial code Aspen HYSIS.

The numerical activity has shown that gaseous DI, before inlet valves closing, gives the worst result since methane, once injected into the cylinder, expands hindering the entry of air. On the other side, liquid PFI represents the best configuration to maximize the volumetric efficiency and therefore the engine power. All the technological issues related to a cryogenic liquid methane injection system were not taken into consideration in this study.

Commentary by Dr. Valentin Fuster
2018;():V002T06A004. doi:10.1115/ICEF2018-9550.

Turbocharged engines are the standard powertrain type of internal combustion engines for both spark ignition and compression ignition concepts. Turbochargers modeling traditionally rely in look up tables based on turbocharger manufacturer provided maps. These maps as the only secure source of information. They are used both for the matching between reciprocating engine and the turbocharger and for the further engine optimization and performance analysis. In the last years have become evident that only these maps are not being useful for detailed calculation of variables like after-treatment inlet temperature (turbine outlet), intercooler inlet temperature (compressor outlet) and engine BSFC at low loads. This paper shows a comprehensive study that quantifies the errors of using just look up tables compared with a model that accounts for friction losses, heat transfer and gas-dynamics in a turbocharger and in a conjugated way. The study is based in an Euro 5 engine operating in load transient conditions and using a LP-EGR circuit during steady state operation.

Commentary by Dr. Valentin Fuster
2018;():V002T06A005. doi:10.1115/ICEF2018-9552.

The Los Alamos turbulent reactive flow researchers, our modelers and simulation code developers have succeeded in providing the engine research and development community an encompassing, robust, accurate and easy to use software for engine modeling or simulations. This software is now known as the FEARCE Toolkit.

In this paper we discuss the physics present in the engine by discussion the methods we’ve employed to solve the model equations within the toolkit. Provided are background on what has been developed recently at LANL for internal combustion engine modeling.

Commentary by Dr. Valentin Fuster
2018;():V002T06A006. doi:10.1115/ICEF2018-9553.

Shear-driven cavitation plays an important role in many technological applications, including fuel injectors and power generators. Cavitation affects the performance of components and hence it is desirable to understand and predict its behavior since it can have favorable as well as adverse consequences. Although there have been a vast number of studies, a full understanding or theoretical framework describing its behavior has not yet been achieved. This is in part due to the complexities associated with cavitating flows including, internal flow physics, turbulence, two-phase flow and non-equilibrium thermodynamics. Further, experimental techniques are limited in their ability to visualize the phenomena with sufficient resolution for a detailed analysis. In this work, an unstructured, finite volume, computational fluid dynamic (CFD) code coupled to the Eulerian-Eulerian multi-fluid model is utilized to study cavitation phenomena in a nozzle. The well-reported Winkhlofer nozzle at a range of conditions including ΔP = 20, 40, 60, 70, 75, 80, and 85 bar is modeled using n-dodecane reference fuel properties. Three cavitation sub-models were investigated and the results compared with previous experimental and simulation flow data. The flow turbulence was modeled using Reynolds Averaged Navier Stokes Equation (RANS) and Large Eddy Simulation (LES) models and the results evaluated. A mesh sensitivity analysis was conducted with minimum cell sizes of 13.40, 9.48, 7.55, and 6.13 μm were considered to show grid convergence. Further, a novel erosion model was also integrated to identify the potential vulnerability damage zones with respect to the nozzle flow operating conditions. The results were in good agreement with experimental data from optical nozzles as well as previous simulation results. The models capture the cavitation near the solid boundary region and were able to predict the critical cavitation as well as the chocked flow regions. This was consistent with all the models. The results from the erosion model revealed a direct relationship between surface erosion, in terms of Mean Depth of Penetration Rate (MDPR) and incubation time, to higher pressure drops across the nozzle. These findings can be useful to develop future injector nozzle designs that can better mitigate cavitation induced material damage for improved engine endurance.

Commentary by Dr. Valentin Fuster
2018;():V002T06A007. doi:10.1115/ICEF2018-9574.

In the present paper, a comprehensive ignition system model (VTF ignition model) accounting for the practical module and working mechanism of a spark plug was developed, aiming to provide enhanced capability for the 3D combustion simulation of spark ignition engines. In this model, an electrical circuitry model is used to represent the ignition coil, spark plug, and air column. The air column is represented by a set of Lagrangian particles that move with the local flow field. Flame propagation is directly calculated using SAGE model with a reduced isooctane reaction mechanism. The new ignition system model is further implemented into CONVERGE through user defined functions and is verified by comparing with the conventional DPIK model. It is found that the VTF ignition model predicts slower combustion than the DPIK model, mainly due to more realistic energy deposit method and energy discharging rate. Furthermore, the VTF model also has the capability of predicting the arc motion and restrike phenomena associated with spark ignition processes. It is expected that with more validation with experiments, the new VTF model has the great potential to better serve the needs of engine combustion simulation.

Commentary by Dr. Valentin Fuster
2018;():V002T06A008. doi:10.1115/ICEF2018-9579.

An efficient computational fluid dynamics model for predicting high pressure dual-fuel combustion is one of the most essential steps in order to improve the concept, to reduce the number of experiments and to make the development process more coste-efficient. For Diesel and natural gas such a model developed by the authors is first used to analyze the combustion process with respect to turbulence chemistry interaction and to clarify the question whether the combustion process is limited by chemistry or the mixing process. On the basis of these findings a reduced reaction mechanism is developed in order to save up to 35% of computing time. The prediction capability of the modified combustion model is tested for different gas injection timings representing different degrees of premixing before ignition. Compared to experimental results from a rapid compression expansion machine, the shape of heat release rate, the ignition timing of the gas jet and the burnout are well predicted. Finally, misfiring observed at different geometric configurations in the experiment are analyzed with the model. It is identified that in these geometric configurations at low temperature levels the gas jet covers the preferred ignition region of the diesel jet. Since the model is based on the detailed chemistry approach, it can in future also be used for other fuel combinations or for predicting emissions.

Commentary by Dr. Valentin Fuster
2018;():V002T06A009. doi:10.1115/ICEF2018-9581.

A dual fuel engine concept with lean premixed methane-air charge ignited by a diesel pilot flame is highly promising for reducing NOx and soot emissions. One drawback of this combustion method, however, is the high nitric dioxide (NO2) emissions observed at certain operating points. NO2 is a toxic gas, which is identifiable by its yellow color.

In this paper the conditions leading to increased NO2 formation have been investigated using a batch reactor model in Cantera. In a first step, it has been found that the high emission levels of NO2 can be traced back to the mixing of small amounts of quenched CH4 with NO from the hot combustion zones followed by post-oxidation in the presence of O2, requiring that the temperatures are within a certain range.

In the second step, NO2 formation in the exhaust duct of a test engine has been modeled and compared to the experimental results. For that purpose a well-stirred reactor model has been used that calculates the steady-state of a uniform composition for a certain residence time. An appropriate reaction mechanism that considers the effect of NO/NO2 on methane oxidation at low temperature levels has been used.

The numerical results of NO to NO2 conversion in the duct at low temperature and pressure levels show good agreement with the experimental results for various temperatures and concentrations of unburned methane. The partial oxidation of CH4 can be predicted well. It can be shown that methane oxidation in the presence of NO/NO2 at low temperature levels is enhanced via the reaction steps CH3 + NO2 ⇌ CH3O + NO and CH3O2 + NO ⇌ CH3O + NO2. In addition the elementary reaction HO2 + NO ⇌ NO2 + OH is the important NO oxidizing step.

Topics: Fuels , Engines , Methane
Commentary by Dr. Valentin Fuster
2018;():V002T06A010. doi:10.1115/ICEF2018-9587.

The ignition mechanism of a lean premixed CHVair mixture by a hot turbulent jet issued from the pre-chamber combustion is investigated using 3D combustion CFD. The turbulent jet ignition experiments conducted in the rapid compression machine (RCM) at Michigan State University (MSU) were simulated. A full simulation was carried out first using RANS model for validation, the results of which were then taken as the boundary condition for the detailed simulations using both RANS and LES. To isolate the thermal and chemical kinetic effects from the hot jet, two different inlet conditions of the chamber were considered: inert case (including thermal effects only) and reactive case (accounting for both thermal and chemical kinetic effects). It is found that the chemical kinetic effects are important for the ignition in the main chamber. Comparison of OH and HRR (heat release rate) computed by RANS and LES shows that RANS predicts slightly faster combustion, which implies higher predicted turbulent flame speed. Correlations between vorticity, mixing field, and temperature field are observed, which indicate that the flow dynamics strongly influence the mixing process near the flame front, and consequently affect flame propagation.

Commentary by Dr. Valentin Fuster
2018;():V002T06A011. doi:10.1115/ICEF2018-9597.

It is known that low-temperature combustion (LTC) strategies can help simultaneously reduce nitrogen oxides (NOx) and particulate matter (PM) emissions from diesel engines to very low levels. However, it is also known that LTC may cause emissions of unburned hydrocarbons (UHC) to rise — especially in low load operating conditions. Recent studies indicate that end-of-injection (EOI) processes may support ignition recession back to injector nozzle thereby helping to reduce these emissions. This paper contributes to the physical understanding of this EOIphe-nomenon, combustion recession, using computational fluid dynamics studies at LTC conditions. Simulations are performed on a single-hole injection of n-dodecane under a range of Engine Combustion Network’s “Spray A” conditions. The primary objective of this paper is to assess the ability of a Flamelet Generated Manifold (FGM) combustion model to predict and characterize combustion recession. First, a baseline condition FGM simulation is compared with two other combustion models namely the Well Stirred model (WSR), the Representative Interactive Flamelet model (RIF) using the commercially-available CFD solver, CONVERGE. Further studies were carried out for FGM model alone including: varying ambient temperature conditions and chemical mechanisms. Two chemical kinetics mechanisms with low temperature chemistry for n-dodecane are employed to help to predict the occurrence of combustion recession. All simulations are performed under the Reynolds-Averaged Navier-Stokes (RANS) framework in a grid-converged Lagrangian spray scenario. The simulation of combustion recession is qualitatively validated against experimental data from literature and the efficacy of each model in predicting combustion recession is evaluated. Overall, it was found that the FGM model was able to capture the combustion recession phenomenon well — showing particular strength in predicting distinct auto-ignition events in the near nozzle region.

Topics: Combustion , Sprays , Diesel
Commentary by Dr. Valentin Fuster
2018;():V002T06A012. doi:10.1115/ICEF2018-9605.

Engine knock remains one of the major barriers to further improve thermal efficiency of Spark Ignition (SI) engines. Knock can be suppressed by lowering the compression ratio, or retarding the spark ignition timing, however, at an expense of efficiency penalty. SI engine is usually operated at knock-limited spark advance (KLSA) to achieve possibly maximum efficiency with given engine hardware and fuel properties, such as Research Octane Number (RON), Motor Octane Number (MON), and heat of vaporization, etc. Co-optimization of engine design and fuel properties is promising to improve the engine efficiency and predictive CFD models can be used to facilitate this optimization process. However, difficulties exist in predicting KLSA in CFD simulations. First, cyclic variability of SI engine demands that multi-cycle results are required to capture the extreme conditions. Secondly, Mach Courant-Friedrichs-Lewy (CFL) number of 1 is desired to accurately predict the knock intensity (KI), resulting in unaffordable computational cost, especially for multi-cycle simulations. In this study, a new approach to numerically predict KLSA using large Mach CFL number of 50 is proposed. This approach is validated against experimental data for a boosted Direct Injection Spark Ignition (DISI) engine at multiple loads and spark timings. G-equation combustion model coupled with well-mixed chemical kinetic model are used to predict the turbulent flame propagation and end-gas auto-ignition, respectively. Simulations run for 10 consecutive engine cycles at each condition. The results show good agreement between model predictions and experiments in terms of cylinder pressure, combustion phasing and cyclic variation. Engine knock is predicted with early spark ignition timing, indicated by significant pressure wave oscillation and end-gas heat release. Maximum Amplitude of Pressure Oscillation (MAPO) analysis is performed to quantify the KI, and the slope change point in KI extrema is used to indicate the KLSA accurately. Using a smaller Mach CFL number of 5 also results in the same conclusions thus demonstrating that this approach is insensitive to the Mach CFL number. The use of large Mach CFL number allows us to achieve fast turn-around time for multi-cycle engine CFD simulations.

Topics: Engines , Ignition
Commentary by Dr. Valentin Fuster
2018;():V002T06A013. doi:10.1115/ICEF2018-9612.

Computational fluid dynamics (CFD) plays a tremendous role in evaluating and visualizing the spray breakup, atomization and vaporization process. In this study, ANSYS Forte CFD tool was used to simulate the spray penetration length and spray morphology in a constant volume chamber at different grid size of a multi-hole injector. An unsteady gas jet model was coupled with Kelvin-Helmholtz (KH) and Rayleigh-Taylor (RT) model for multi-hole spray simulation. The effect of CFD cell size and ambient gas pressure on spray penetration length and spray morphology of fuel vapor mass fraction were investigated for both KH-RT and KH-RT with the unsteady gas jet model. It is found that KH-RT with the unsteady gas jet model shows mesh independent spray penetration length and spray morphology of fuel vapor mass fraction as compared to KH-RT model. This can be explained by the Lagrangian-Eulerian coupling of axial droplet-gas relative velocity is modeled on the principle of unsteady gas jet theory instead of discretizing very fine grid to the computational domain. This reduces the requirement of fine mesh near the nozzle and allows larger time step during spray injection. It is also observed that at higher ambient gas pressure, an aerodynamic force between the droplet and gas intensifies which reduces the overall spray penetration length and fuel vapor mass. The distorted spray morphology of fuel vapor mass fraction was accurately predicted at high ambient gas pressure using the KH-RT with an unsteady gas jet model which results in mesh independent drag predictions. The use of advanced spray model results in the mesh size dependency reduction and accurate drag prediction with less computational time and faster accurate solutions over all conventional spray breakup models.

Topics: Simulation , Ejectors , Sprays
Commentary by Dr. Valentin Fuster
2018;():V002T06A014. doi:10.1115/ICEF2018-9639.

The distribution of lubricating oil droplets in cylinder is one of main causes of abnormal combustion of natural gas engines. The evaporation of lubricating oil droplet is one of the key sub-processes controlling its auto-ignition event. The components of lubricating oil with different carbon number (16–50) shows significantly different evaporation and ignition characteristics from gasoline and diesel fuels. Even though there are many evaporation models focusing on the evaporation behaviors of multi-component droplets, most of them are limited to the liquid fuels, which are composed by more volatile hydrocarbons. Therefore, understanding the evaporation characteristics of lubricating oil droplets is very important for investigating the mechanism of abnormal combustion of natural gas engines. In this study, a multi-component evaporation model for lubricating oil was developed, which considers several key characteristics in the droplet evaporation process, including the finite heat conduction and limited mass diffusion in liquid phase, multi-component diffusion in gas phase, real vapor-liquid equilibrium at the droplet interface, as well as the nitrogen quantity dissolved in liquid phase. The simulation results by this model were compared with experimental results, and good agreements have been achieved. Then, this model was used to study the evaporation behaviors of different hydrocarbon droplets, including lubricating oil droplet. The influences of ambient temperatures and pressures, as well as methane concentration on evaporation characteristics (namely the heat up period, average evaporation rate, and droplet lifetime) were investigated. The results show that both heat up period and evaporation rate of lubricating oil droplets increase as the methane concentration increases. Besides, the droplet lifetime monotonically decreases as the ambient pressure decreases. This is different from the diesel and gasoline droplets, for which the effects of pressure on the droplet evaporation behaviors are depended on the ambient temperature.

Commentary by Dr. Valentin Fuster
2018;():V002T06A015. doi:10.1115/ICEF2018-9676.

In this study, CFD modeling capability of near-wall flow and heat transfer was evaluated against experimental data. Industry-standard wall models for RANS and LES (law of the wall) were examined against near-wall flow and heat flux measurements from the transparent combustion chamber (TCC-III) engine. The study shows that the measured, normalized velocity profile does not follow law of the wall. This wall model, which provides boundary conditions for the simulations, failed to predict the measured velocity profiles away from the wall. LES showed reasonable prediction in peak heat flux and peak in-cylinder pressure to the experiment, while RANS-heat flux was closer to experimental heat flux but lower in peak pressure. The measurement resolution is higher than that of the simulations, indicating that higher spatial resolution for CFD is needed near the wall to accurately represent the flow and heat transfer. Near-wall mesh refinement was then performed in LES. The wall-normal velocity from the refined mesh case matches better with measurements compared to the wall-parallel velocity. Mesh refinement leads to a normalized velocity profile that matches with measurement in trend only. In addition, the heat flux and its peak value matches well with the experimental heat flux compared to the base mesh.

Commentary by Dr. Valentin Fuster
2018;():V002T06A016. doi:10.1115/ICEF2018-9684.

The current work presents a recent development of the Extended Coherent Flamelet Model (ECFM) for 3D combustion modeling in spark-ignited gasoline engines. The reference-based ECFM model, originally published in 2003, computes the conditional unburned and burned gas species mass fractions from both real species and species tracers. This current work is motivated by two limitations of the reference-based model. First, the difference between convection of species tracers and convection of real species leads to small discrepancies between the two, due to high velocity gradients during gas exchange. This can lead to inaccurate estimation of the progress variable and consequently to negative conditional mass fractions in the burned gases after ignition. Second, the reference-based ECFM model assumes implicitly that the unburned and burned states correspond to the same mixture fraction. This assumption is valid for low stratification cases, but it can lead to substantial conditioning errors for highly stratified systems like gasoline direct injection (GDI) engines. To address these shortcomings, a new species-based ECFM (SB-ECFM) implementation is presented. In this species-based model, the unburned and burned gas states are entirely defined by the transported species in each zone. It is shown that SB-ECFM more reliably defines conditional quantities and the progress variable. This enhancement allows the use of a second-order central scheme in space when using full decoupling of auto-ignition and premixed flame progress variables as proposed in Robert et al., Proc. Comb. Inst, 2015, while the reference model is limited to the first-order upwind scheme in this case. Finally, simulations of a GDI engine are presented at different loads and rpm conditions. It is shown that, with the higher order scheme, SB-ECFM demonstrates very good agreement with measured pressure.

Commentary by Dr. Valentin Fuster
2018;():V002T06A017. doi:10.1115/ICEF2018-9686.

Low-pressure exhaust gas recirculation (LP-EGR) is an EGR configuration in which clean exhaust gas is taken downstream of the turbine and aftertreatment, and then reintroduced upstream of the compressor (1). Employing LP-EGR on Diesel engines can improve fuel economy by reducing pumping losses, lowering intake manifold temperature and facilitating advanced combustion phasing (2, 3). The LP-EGR can also improve compressor and turbine performance by moving their operating points towards higher flow rate and higher efficiency points, which is reflected as a net reduction in pumping losses of the engine. In this study, we focus on effects of introducing LP-EGR on the compressor pressure ratio, and isentropic total-to-total efficiency.

The flow field of LP-EGR and air mixing upstream of the compressor as well as the entire compressor stage were studied using a CFD RANS model. The model was validated against turbocharger gas stand measurements. A T-junction mixer was chosen as the design baseline, and various configurations of this mixer were evaluated. The impact of the geometric configuration of the mixer was studied by varying mixing length, EGR jet introduction angle, and EGR-to-air cross section area ratio over a wide range of relevant engine operating conditions.

The flow field upstream of the compressor is strongly affected by the dimensionless quantity EGR-to-air momentum ratio. At intermediate momentum ratios, stream-wise counter-rotating vortex pairs (4) are induced in the flow. These vortices can reach the impeller inlet, and depending on vorticity and length scale, perturb the local velocity triangle. At low and high momentum ratios, creeping or impinging jets respectively are formed. In addition prewhirl can be induced by eccentric introduction of EGR. The EGR-induced prewhirl acts similar to an inlet guide vane and can alter the incidence angle at the impeller inlet.

The performance of the compressor is altered by the EGR-induced flow field. Compressor pressure ratio is either increased or decreased depending on the direction of EGR-induced prewhirl with eccentric EGR introduction. The compressor efficiency decreases at low flow rates by introduction of concentric EGR due to perturbation of the velocity triangle at the impeller inlet. On the other hand, at low flow rates compressor efficiency can be improved by eccentric EGR introduction, which generates prewhirl in the direction of rotation of the impeller leading to improved incidence angle. The extent to which the compressor is influenced by the EGR-induced flow field is generally reduced by increasing the EGR mixing length, due to viscous damping and breakdown of large-scale EGR-induced vortices.

The LP-EGR configuration provides a potential pathway towards improvement of compressor performance, not only by increasing compressor flow rate, but also by manipulation of the flow field. Given that the engine pumping losses are strongly dependent on compressor performance, specifically the compressor efficiency, this study indicates that LP-EGR provides an important path towards reducing pumping loss and improving fuel conversion efficiency.

Commentary by Dr. Valentin Fuster
2018;():V002T06A018. doi:10.1115/ICEF2018-9690.

With the engine technology moving towards more challenging (highly dilute and boosted) operation, spark-ignition processes play a key role in determining flame propagation and completeness of the combustion process. On the computational side, there is plenty of spark-ignition models available in literature and validated under conventional, stoichiometric SI operation. Nevertheless, these models need to be expanded and developed on more physical grounds since at challenging operation they are not truly predictive.

This paper reports on the development of a dedicated model for the spark-ignition event at non-quiescent, engine-like conditions, performed in the commercial CFD code CONVERGE. The developed methodology leverages previous findings that have expanded the use and improved the accuracy of Eulerian-type energy deposition models. In this work, the Eulerian energy deposition is coupled at every computational time-step with a Lagrangian-type evolution of the spark channel. Typical features such as spark channel elongation, stretch, attachment to the electrodes are properly described to deliver realistic energy deposition along the channel during the entire ignition process.

The numerical results are validated against schlieren images from an optical constant volume chamber and show the improvement in the simulation of the spark channel during the entire ignition event, with respect to the most commonly used energy deposition approach. Further development pathways are discussed to provide more physics-based features from the developed ignition model in the future.

Commentary by Dr. Valentin Fuster
2018;():V002T06A019. doi:10.1115/ICEF2018-9696.

Gasoline compression ignition (GCI) engine technology has shown the potential to achieve high fuel efficiency with low criteria pollutant emissions. In order to guide the design and optimization of GCI combustion, it is essential to develop high-fidelity simulation tools. Building on the previous work in computational fluid dynamic (CFD) simulations of spray combustion, this work focuses on predicting the soot emissions in a constant-volume vessel representative of heavy-duty diesel engine applications for an ultra-low sulfur diesel (ULSD) and a high reactivity (Research Octane Number 60) gasoline, and comparing the soot evolution characteristics of the two fuels. Simulations were conducted using both Reynolds Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES) turbulence models. Extensive model validations were performed against the experimental soot emissions data for both fuels. It was found that the simulation results using the LES turbulence model agreed better with the measured ignition delays and liftoff lengths than the RANS turbulence model. In addition, two soot models were evaluated in the current study, including an empirical two-step soot formation and oxidation model, and a detailed soot model that involves poly-aromatic hydrocarbon (PAH) chemistry. Validations showed that the separation of the flame lift-off location and the soot lift-off location and the relative natural luminosity signals were better predicted by the detailed soot model combined with the LES turbulence model. Qualitative comparisons of simulated local soot concentration distributions against experimental measurements in the literature confirmed the model’s performance. CFD simulations showed that the transition of domination from soot formation to soot oxidation was fuel-dependent, and the two fuels exhibited different temporal and spatial characteristics of soot emissions. CFD simulations also confirmed the lower sooting propensity of gasoline compared to ULSD under all investigated conditions.

Commentary by Dr. Valentin Fuster
2018;():V002T06A020. doi:10.1115/ICEF2018-9699.

Stringent emission legislations, increasing environmental and health issues have driven extensive research in combustion engines to control pollutants. Modeling of emissions offers a cost saving alternative to experimental analysis for combustion chamber design and optimization. Soot modeling in diesel engines has evolved over four decades from simple empirical relations to detailed kinetics involving polycyclic aromatic hydrocarbons (PAH) and complex particle dynamics. Although numerical models have been established for predicting soot mass for parametric variations, there is a lack of modeling studies for predicting soot particle size distribution for parametric variations. This becomes important considering the inclusion of limits on soot particle count in recent emission norms. The current work aims at modeling the soot particle size distribution inside a heavy duty diesel engine and validating the results for a parametric variation of injection pressure and intake temperature. Closed cycle combustion simulations have been performed using CONVERGE, a 3D computational fluid dynamics (CFD) code. A sectional soot model coupled with gas phase kinetics has been used with source terms for inception, condensation, surface reactions and coagulation. Numerical predictions for soot mass and particle size distribution at the exhaust show good agreement with experimental data after increasing the transition regime collision frequency by a factor of 100.

Commentary by Dr. Valentin Fuster
2018;():V002T06A021. doi:10.1115/ICEF2018-9713.

The paper describes the results from a computational fluid dynamics (CFD) simulation campaign that is complementary to an ongoing experimental program to develop an opposed-piston (OP) two-stroke gasoline compression ignition (GCI) engine for application in light-duty trucks. The simulation workflow and results are explained. First, open-cycle 3-D CFD simulations (in Converge CFD) are performed to simulate the scavenging process—gas exchange through the intake ports, cylinder, and exhaust ports. The results from these scavenging calculations are then fed into a model of this engine built in the system-level simulation tool (in GT-POWER), which in turn provides initial conditions for closed-cycle 3-D CFD simulations. These simulations are used to assess combustion by employing standard spray models and a chemical kinetic mechanism for gasoline. Validation of a representative set of engine operating points is performed in this way to gain confidence in the CFD model setup. Six injectors were then screened according to metrics of wall-wetting, maximum pressure rise rate, combustion efficiency and emission levels. Further CFD simulations have been carried out with parameter sweeps applying design of experiments (DoE) methods to finalize on candidate injectors, piston-bowls and injection strategies. The intended outcome of this program is a three-cylinder OP GCI engine equipped with a turbocharger and a supercharger targeting a 30% improvement in brake thermal efficiency (BTE) over conventional light-duty diesel engines.

Commentary by Dr. Valentin Fuster
2018;():V002T06A022. doi:10.1115/ICEF2018-9722.

High cycle-to-cycle variation (CCV) is detrimental to engine performance, as it leads to poor combustion and high noise and vibration. In this work, CCV in a gasoline engine is studied using large eddy simulation (LES). The engine chosen as the basis of this work is a single-cylinder gasoline direct injection (GDI) research engine. Two stoichiometric part-load engine operating points (6 BMEP, 2000 RPM) were evaluated: a non-dilute (0% EGR) case and a dilute (18% EGR) case. The experimental data for both operating conditions had 500 cycles. The measured CCV in IMEP was 1.40% for the non-dilute case and 7.78% for the dilute case.

To estimate CCV from simulation, perturbed concurrent cycles of engine simulations were compared to consecutively obtained engine cycles. The motivation behind this is that running consecutive cycles to estimate CCV is quite time-consuming. For example, running 100 consecutive cycles requires 2–3 months (on a typical cluster), however, by running concurrently one can potentially run all 100 cycles at the same time and reduce the overall turnaround time for 100 cycles to the time taken for a single cycle (2 days).

The goal of this paper is to statistically determine if concurrent cycles, with a perturbation applied to each individual cycle at the start, can be representative of consecutively obtained cycles and accurately estimate CCV. 100 cycles were run for each case to obtain statistically valid results. The concurrent cycles began at different timings before the combustion event, with the motivation to identify the closest time before spark to minimize the run time. Only a single combustion cycle was run for each concurrent case. The calculated standard deviation of peak pressure and coefficient of variance (COV) of indicated mean effective pressure (IMEP) were compared between the consecutive and concurrent methods to quantify CCV.

It was found that the concurrent method could be used to predict CCV with either a velocity or numerical perturbation. A large and small velocity perturbation were compared and both produced correct predictions, implying that the type of perturbation is not important to yield a valid realization.

Starting the simulation too close to the combustion event, at intake valve close (IVC) or at spark timing, under-predicted the CCV. When concurrent simulations were initiated during or before the intake even, at start of injection (SOI) or earlier, distinct and valid realizations were obtained to accurately predict CCV for both operating points.

By simulating CCV with concurrent cycles, the required wall clock time can be reduced from 2–3 months to 1–2 days. Additionally, the required core-hours can be reduced up to 41%, since only a portion of each cycle needs to be simulated.

Commentary by Dr. Valentin Fuster
2018;():V002T06A023. doi:10.1115/ICEF2018-9726.

This work evaluates different optimization algorithms for Computational Fluid Dynamics (CFD) simulations of engine combustion. Due to the computational expense of CFD simulations, emulators built with machine learning algorithms were used as surrogates for the optimizers.

Two types of emulators were used: a Gaussian Process (GP) and a weighted variety of machine learning methods called SuperLearner (SL). The emulators were trained using a dataset of 2048 CFD simulations that were run concurrently on a supercomputer. The Design of Experiments (DOE) for the CFD runs was obtained by perturbing nine input parameters using a Monte Carlo method. The CFD simulations were of a heavy duty engine running with a low octane gasoline-like fuel at a partially premixed compression ignition mode.

Ten optimization algorithms were tested, including types typically used in research applications. Each optimizer was allowed 800 function evaluations and was randomly tested 100 times. The optimizers were evaluated for the median, minimum, and maximum merits obtained in the 100 attempts. Some optimizers required more sequential evaluations, thereby resulting in longer wall clock times to reach an optimum.

The best performing optimization methods were particle swarm optimization (PSO), differential evolution (DE), GENOUD (an evolutionary algorithm), and Micro-Genetic Algorithm (GA). These methods found a high median optimum as well as a reasonable minimum optimum of the 100 trials. Moreover, all of these methods were able to operate with less than 100 successive iterations, which reduced the wall clock time required in practice.

Two methods were found to be effective but required a much larger number of successive iterations: the DIRECT and MALSCHAINS algorithms. A random search method that completed in a single iteration performed poorly in finding 1 Currently at Southwest Research Institute, San Antonio, Texas optimum designs, but was included to illustrate the limitation of highly concurrent search methods. The last three methods, Nelder-Mead, BOBYQA, and COBYLA, did not perform as well.

Commentary by Dr. Valentin Fuster
2018;():V002T06A024. doi:10.1115/ICEF2018-9739.

To meet the demand for greater fuel efficiency in passenger vehicles, various strategies are employed to increase the power density of light-duty SI engines, with attendant thermal or system efficiency increases. One approach is to incorporate higher-performance alloys for critical engine components. These alloys can have advantageous thermal or mechanical properties at higher temperatures, allowing for components constructed from these materials to meet more severe pressure and temperature demands, while maintaining durability. Advanced alloys could reduce the need for charge enrichment to protect certain gas-path components at high speed and load conditions, permit more selective cooling to reduce heat-transfer losses, and allow engine downsizing, while maintaining performance, by achieving higher cylinder temperatures and pressures. As a first step in investigating downsizing strategies made possible through high-performance alloys, a GT-Power model of a 4-cylinder 1.6L turbocharged direct-injection SI engine was developed. The model was tuned and validated against experimental dynamometer data collected from a corresponding engine. The model was then used to investigate various operating strategies for increasing power density. Results from these investigations will provide valuable insight into how new materials might be utilized to meet the needs of future light-duty engines and will serve as the basis for a more comprehensive investigation using more-detailed thermo-mechanical modeling.

Commentary by Dr. Valentin Fuster
2018;():V002T06A025. doi:10.1115/ICEF2018-9758.

The use of 3D CFD combustion models based on tabulated chemistry is becoming increasingly popular. Especially the runtime benefit is attractive, as the tabulated chemistry method allows to include state-of-the-art chemical reaction schemes in CFD simulations. In this work, the Tabkin FGM combustion model in AVL FIRE™ is used to assess the predictivity on a large database of a light-duty Diesel engine measurements. The AVL TABKIN™ software is used to create the chemistry look-up tables for the Tabkin FGM model.

The TABKIN software has been extended with the kinetic soot model, where the soot mass fraction calculation is done during the chemistry tabulation process, as well as an NO model using a second progress variable. From recent validation studies, a best-practice and nearly automated workflow has been derived to create the look-up tables for Diesel engine applications based on minimal input. This automated modeling workflow is assessed in the present study.

A wide range of parameter variations are investigated for 5 engine load points, with and without EGR, in total 186 cases. This large number of CFD simulations is run in an automated way and the parameters of the CFD sub-models are kept equal as well as all numerical settings.

Results are presented for combustion and emissions (NO and soot). Combustion parameters and NO emissions correlate very well to the experimental database with R2 values above 0.95. Soot predictions give order-of-magnitude agreement for most of the cases; the trend however is not always respected, which limits the overall correlation for all cases together, as reported by other authors. Further fundamental research on modeling soot formation and oxidation process remains required to improve the models. In terms of CPU time, the present study was executed on an off-the-shelf HPC cluster, using 8 CPU cores per case and requiring around 3 hrs of wall-time per case, e.g. such a large set of calculations can be simulated overnight on a standard HPC cluster.

Commentary by Dr. Valentin Fuster

Engine Design and Mechanical Development

2018;():V002T07A001. doi:10.1115/ICEF2018-9522.

Downsizing of engines is a major area of interest in the combustion engines sector due to a variety of reasons, chief among which is the CO2 emission reduction due to increased power to weight ratio. Furthermore, the introduction of various auxiliary devices into an automotive product, as well as increased acoustic insulation, necessitate continuous trimming of the engine packaging space. In this paper, the potential and limitations of downsizing diesel engines to very small displacements is studied. The goal of the article is to determine the minimum displacement a diesel engine can achieve, given the limitations posed by state-of-the-art technology. At the same time, the objective is the maximization of power density with acceptable levels of fuel consumption. While the investigations focused on the thermodynamic behavior of downsizing, structural aspects were also considered.

On the basis of a literature study, the article illustrates the benchmarking of existing small gasoline and diesel engines for different applications. Thereafter, a matrix of engine configurations, which were relevant to the investigations, was generated. This included, among others, various bore / stroke combinations, compression ratios, piston and nozzle geometries, as well as valve diameters. Further, the influence of injection pressure, swirl and air-fuel ratio were included in the study. With the aid of the 1D simulation software GT-Power and the 3D CFD code Kiva-3V, a detailed thermodynamic analysis was performed on the chosen variants.

In the results detailed in this article, a promising downsizing potential for a cylinder displacement well below 200cm3/cylinder has been established. Further, best-in-class power densities at acceptable fuel consumption levels could be achieved. This opens up the possibility for the application of such small diesel engines in a new range of applications. The challenges on the thermodynamic and structural fronts, which need to be met in order to achieve targets, are also highlighted.

Topics: Diesel engines
Commentary by Dr. Valentin Fuster
2018;():V002T07A002. doi:10.1115/ICEF2018-9539.

For efficient modeling of engine (or powertrain) supported by non-linear elastic mounts, a special methodology has been elaborated. Based on it, software tool has been developed to analyze the motion of rigid body and elastic mounts, which comprises of three modules:

• Non-linear static analysis;

• Modal analysis (undamped and damped);

• Forced response (in frequency domain).

Application example of a large V12 marine engine illustrates the suggested workflow.

The results are verified against other software tools and validated by measurements.

Commentary by Dr. Valentin Fuster
2018;():V002T07A003. doi:10.1115/ICEF2018-9541.

Variable valve timing technologies for internal combustion engines are used to improve power, torque, reduce emissions and increase fuel efficiency. Firstly, the paper presents a new electrohydraulic FVVA system which can control the seating velocity of engine valve flexibly. Secondly, based on the NSGA-II genetic algorithm, outlines multi-objective optimization strategy, the paper designs the parameters of FVVA system to make the system easier to implement. Thirdly, the paper builds the combined FVVA engine simulation model. The combined simulation and experimental are executed to validate the designed FVVA engine. Simulation results show brake power is improved between 1.31% and 4.48% and torque is improved by 1.32% to 4.47%. Brake thermal efficiency and volumetric efficiency also show improvement. Experimental results have good agreement with simulation results. The research results can provide a basis for engine modification design.

Commentary by Dr. Valentin Fuster
2018;():V002T07A004. doi:10.1115/ICEF2018-9567.

Different air systems such as turbochargers (TC), hybrid boosting, turbo compounding and exhaust gas recirculation (EGR) are increasingly used to improve the thermal efficiency of internal combustion engines (ICE). One dimensional (1D) gas dynamic codes supports their development and integration by modelling the engine and air systems and reducing testing time. However, this approach currently relies on steady flow characteristic maps which are inaccurate for simulating transient engine conditions. This is a key weakness of using gas-stand measured maps in engine simulations. Performing TC mapping on an engine would in principle solve this problem, however engine-based mapping is limited by the engine operating range and on these facilities, high-precision measurements are challenging.

In addition, simple turbocharging can no longer be constrained to an individual TC supplying boost air to an engine. Instead, modern downsized engines require air-path system making use of multiple components including TCs, mechanical superchargers, electrically driven compressors (EDCs), EGR paths and control valves. Thus studying multiple air systems requires an experimental test facility to understand how they work in synergy. This is also useful in developing empirical models to minimize test time. Therefore the aim of this paper is to present a novel experimental facility that is flexibly designed for evaluating air systems individually and also at the system level representing a complicated air path both in steady and transient condition.

The advanced test facility is built around a 2.2 l diesel engine to test the above air systems which can isolate the thermal and load transients from engine pulsating flows. Removing the flow pulsation allows study of the system characteristics in a steady state. Several examples of component and system level tests including a two-stage air path comprising of a VGT (variable geometry turbine) TC and a 48V EDC with typical operating condition (provided by 1D modeling) are discussed.

Commentary by Dr. Valentin Fuster
2018;():V002T07A005. doi:10.1115/ICEF2018-9616.

Following the successful commercial use of a 9.0L, V-8 automotive-derivative engine for stationary power generation, a new 4.5L, four-cylinder engine has been developed utilizing a modular family design approach. Substantial commonality of power cylinder components has been achieved including the complete power cylinder and cylinder head. This paper describes the design and development approach to the engine family.

These spark-ignited engines are typically used for standby emergency power and demand response applications utilizing commercial grade natural gas or propane. Driving a synchronous electrical generator operating at 60 HZ or 50Hz, engine speeds are either 1800 rpm/3600 rpm or 1500 rpm/3000 rpm respectively, depending upon selection of either a 2-pole or 4-pole alternating current generator. Designed for stoichiometric combustion, the engine configurations can include naturally-aspirated, turbocharged or turbocharged and after-cooled versions. Depending upon end-use applications, exhaust emissions technology and regulatory compliance can be met solely through engine calibration or inclusion of a 3-way catalyst with active air-fuel ratio control.

Since the 9.0L engine version was successfully introduced in 2012, significant efforts have been undertaken to achieve commonality of desired features between the existing veeengine and the future in-line versions, including optimization of performance characteristics in consideration of future power rating structures. Starting from 9.0L commercial introduction, the content herein specifically describes the development of the new 4.5L engine with regard to design and analysis.

Commentary by Dr. Valentin Fuster
2018;():V002T07A006. doi:10.1115/ICEF2018-9621.

Composite pistons are often used in heavy duty diesel engines due to its good reliability and durability. Owing to the alternating loads, fretting wear usually happens on the mating surfaces between piston crown and skirt. In this paper, a fretting wear finite element model is developed to analyze the mating surface wear of composite piston of heavy duty diesel engine. The fretting wear model predicts the wear depth evolution for each working cycle based on Archard model and mesh updating technique, which is validated by previous pin and disk contact experiments. The wear evolution of the top contact surface of piston skirt is simulated according to engine operating condition, and fretting wear life is estimated by the decreasing process of crown-skirt connecting bolt preload. Effects of the shape of piston skirt top surface is also evaluated. In the end, the rationality of fretting wear model is validated by durability tests of diesel engine.

Commentary by Dr. Valentin Fuster
2018;():V002T07A007. doi:10.1115/ICEF2018-9646.

Electrical efficiency is an important factor for most of the owners of gas engines. To reach a high electrical efficiency, engine manufacturers use four valve cylinder head technology on new designed engines. The change from two valve to four valve technology, in combination with optimized charge motion, can achieve an increase of electrical efficiency up to 2.5%. A significant number of engines in the market are only equipped with two valve cylinder heads, thus leaving potential to reduce carbon emissions and fuel consumption.

The scope of the paper applies to the modernization of an already well established gas engine series available on the market with a power range of 500–1100kW [1].

In the first step, the potentials were considered purely in the context of a change in configuration of the spark plug, to pre-chamber spark plug. As second step an optimization of the ports was examined. Due to the pre-existing high level of development of the combustion stage, combined with an adaption of the boost charging system, an improvement of almost 2.5% was achieved. According to data sheets, modern gas engines within this power range have efficiencies in the range of ηe ∼ 44%. The project team therefore proceeded to develop a new cylinder head along with new design leading to a better combustion. Minimizing changes around the periphery of the engine was a prerequisite in order to complete these on site as part of the 30.000-hour service. Intake- as well as exhaustport geometries were optimized with the aid of CFD tools, such that swirl and flow capacity values achieved their specified objectives. The geometries of the water jacket and valve train were also optimized through a similar methodology. These changes led to a 7% reduction in gas exchange work, which directly reflect within improved efficiency levels. Altogether, the various measures (including combustion optimization) resulted in an efficiency improvement of about 2.5% leading to an electric efficiency of 42.9%. The first endurance run shows that the mechanics match the expected technical requirements. Very low wear rates despite the increased masses of the valve train could be reached due to higher qualities in terms of materials.

The paper focuses particularly on the flow optimization in conjunction with the variables surrounding the mechanic design. Finally, the test results of the pilot engines are presented alongside an economic analysis.

Topics: Engines , Valves , Cylinders
Commentary by Dr. Valentin Fuster
2018;():V002T07A008. doi:10.1115/ICEF2018-9659.

IC engine spray evaporative cooling system design is discussed starting with a review of existing evaporative cooling systems that automotive applications are required to address. A component-level system design is proposed culminating in a simulation model of a PID strategy used to control transient gasside metal temperatures with varying engine load. The model combines a spray evaporation correlation model with 1D finite-difference equations to model the transient heat transfer through a 7 mm thick metal slab which represents the wall of a cylinderhead. Based on the simulation results, the particular changes required of existing engine cooling jacket designs are discussed.

Commentary by Dr. Valentin Fuster
2018;():V002T07A009. doi:10.1115/ICEF2018-9703.

Integrated Turbocompounding, Electrification and Supercharging (ITES) is a novel approach for integrated implementation of technologies aimed at reduction of fuel consumption in a single unit. The ITES system optimally manages the power flow between the turbocompound turbine, secondary compressor, 48V electric motor/generator and engine by employing a planetary gear set. The unified approach delivers a substantial reduction in both expense and space claim while improving the overall system efficiency in comparison to the independent implementation of each of these individual technologies.

As part of a previous development effort the ITES system functionality was validated through engine drive cycle simulation primarily utilizing the 48V motor generator unit for power split turbocompounding, power split supercharging and engine torque assist. In this latest development phase, the functionality of ITES system has been evaluated on a vehicle level model through a vehicle drive cycle simulation. First, a supervisory control strategy was developed for the ITES system to facilitate start-stop, regenerative braking and engine torque assist functionality using the ITES motor/generator unit. Next, a GT-Suite engine model developed for a downsized engine with the ITES unit applied, along with an appropriate control strategy, was integrated in to a class 6/7 vocational vehicle 1D model. The model was then simulated over the GHG Phase 2 ARB cycle and the fuel economy was compared to that of vehicle model with only the baseline engine configuration. Finally, the battery capacity was optimized to maximize vehicle fuel economy and battery life.

Topics: Vehicles , Cycles
Commentary by Dr. Valentin Fuster
2018;():V002T07A010. doi:10.1115/ICEF2018-9708.

With the increasing focus on reducing emissions and making fuel efficient vehicles within the automotive industry over the past few years, new methods are constantly being investigated to improve the efficiency of the powertrain. One such method is recovering waste heat from the exhaust gases as well as the coolant using a thermodynamic cycle such as a Rankine cycle. However, most studies looking into low temperature or coolant heat recovery investigate the use of a separate secondary cycle for the recovery of waste heat itself. This has the disadvantage of having the working fluid at a lower temperature than the coolant which reduces the recovery efficiency. This paper investigates the potential of an integrated Rankine cycle waste heat recovery system where the coolant also acts as the refrigerant and is integrated with the exhaust gas recirculation waste heat recovery. The refrigerant/coolant used for this study is ethanol, while being used in two modes for low temperature/coolant recovery: using the engine as the preheater and using it as an evaporator. Using a combination of GT Power and Matlab, a Scania D13 engine was simulated in partially premixed combustion operation with a waste heat recovery system. For the engine load-speed range, the coolant flow rate, pressure ratio and superheat were swept for determining the optimal values for maximizing output power. It was seen that while using the engine both as a preheater and as an evaporator the recoverable power increased in comparison to using only the exhaust gas recirculation heat for recovery. When using the engine for preheating, the recoverable power increased marginally with an indicated efficiency gain of less than 0.5 percentage points whereas when using the engine for the evaporation of the coolant, the indicated efficiency showed gains of up to 1.7 percentage points in comparison to using EGR-only heat recovery with a total gain in indicated efficiency of up to 5.5 percentage points. This larger gain in recoverable power while using the engine as an evaporator in comparison to as a preheater is due to the location of the pinch point in analyzing the heat exchange process. The system behavior was also studied with regards to the pressure ratio, the mass flow rate of coolant and the superheat. It was generally observed that at higher loads and speeds these parameters increased as more waste heat was available for recovery for the system.

Commentary by Dr. Valentin Fuster
2018;():V002T07A011. doi:10.1115/ICEF2018-9766.

The work presented here seeks to compare different means of providing uniflow scavenging for a 2-stroke engine suitable to power a US light-duty truck. Through the ‘end-to-end’ nature of the uniflow scavenging process, it can in theory provide improved gas-exchange characteristics for such an engine operating cycle; furthermore, because the exhaust leaves at one end and the fresh charge enters at the other, the full circumference of the cylinder can be used for the ports for each flow and therefore, for a given gas exchange angle-area demand, expansion can theoretically be maximized over more traditional loop-scavenging approaches. This gives a further thermodynamic advantage.

The three different configurations studied which could utilize uniflow scavenging were the opposed piston, the poppetvalve with piston-controlled intake ports and the sleeve valve. These are described and all are compared in terms of indicated fuel consumption for the same cylinder swept volume, compression ratio and exhaust pressure, for the same target indicated mean effective pressure and indicated specific power.

A new methodology for optimization was developed using a one-dimensional engine simulation package which also took into account charging system work. The charging system was assumed to be a combination of supercharger and turbocharger to permit some waste energy recovery.

As a result of this work it was found that the opposed-piston configuration provides the best attributes since it allows maximum expansion and minimum heat transfer. Its advantage over the other two (whose results were very close) was of the order of 8.3% in terms of NSFC (defined as ISFC net of supercharger power). Part of its advantage also stems from its requirement for minimum air supply system work, included in this NSFC value.

Interestingly, it was found that existing experiential guidelines for port angle-area specification for loop-scavenged, piston-ported engines using crankcase compression could also be applied to all of the other scavenging types. This has not been demonstrated before. The optimization process that was subsequently developed allowed port design to be tailored to specific targets, in this case lowest NSFC. The paper therefore presents a fundamental comparison of scavenging systems using a new approach, providing new insights and information which have not been shown before.

Topics: Engines , Light trucks
Commentary by Dr. Valentin Fuster
2018;():V002T07A012. doi:10.1115/ICEF2018-9774.

The conventional internal combustion engines driven by crankshafts and connecting rod mechanisms are restrained by combustion, thermal and mechanical inefficiencies. The Oscillating Free Piston Linear Engine Alternator (OFPLEA) produces electric power with no need to modify the reciprocating motion to rotary motion. In the most common geometry it consists of a linear alternator driven cyclically by one or two internal combustion engines. With the elimination of crankshaft mechanism linkages, the free piston engine offers potential benefits over crankshaft engines in terms of total mechanical losses. A significant proportion of 5% to 12% of total fuel energy in conventional engines is consumed to overcome the frictional losses. This research investigation addresses an analytical and numerical model to simulate the tribological performance of piston rings in an OFPLEA engine. The results are then compared with results from an equivalent conventional crankshaft driven engine. This axisymmetric, mixed lubrication tribological model is developed on the hydrodynamic process defined by Patir and Cheng’s modified Reynolds equation and an asperity contact process as defined by Greenwood and Tripp’s rough surface dry contact model. The asperity contact pressure distribution, hydrodynamic pressure distribution, lubricant oil film thickness, frictional force and frictional power losses are calculated using an explicit finite difference approach. In the absence of spring-dominated OFPLEA system, dissimilarity in the piston motion profile for compression and power stroke exhibited two different oil film thickness peaks. Whereas a similar oil film thickness peaks are observed for conventional engine due to the controlled and stable operation maintained by crankshaft mechanism. The simulation results state that the frictional losses due to piston ring - cylinder liner contact are found to be lower for a free piston engine than for those of a corresponding crankshaft engine. The simulated piston ring frictional power losses are found to be 342.8 W for the OFPLEA system and 382.6 W for the crankshaft engine. Further, an overall system efficiency improvement of 0.6 % is observed for an OFPLEA engine due to these reduced frictional losses from piston rings.

Commentary by Dr. Valentin Fuster

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