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ASME Conference Presenter Attendance Policy and Archival Proceedings

2017;():V001T00A001. doi:10.1115/ICEF2017-NS1.
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This online compilation of papers from the ASME 2017 Internal Combustion Engine Division Fall Technical Conference (ICEF2017) 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presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.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

Large Bore Engines

2017;():V001T01A001. doi:10.1115/ICEF2017-3522.

The North American oil and gas industry has experienced a market pull for dual fuel (DF) engines that can run on any ratio of fuels ranging from 100% diesel to a high proportion of field gas relative to diesel, while also meeting the US Tier 4 Nonroad emissions standards. A DF engine must meet complex and at times competing requirements in terms of performance, fuel tolerance, and emissions. The challenges faced in designing a DF engine to meet all of the performance and emissions requirements require a detailed understanding of the trade-offs for each pollutant. This paper will focus on the details of NOx formation for high substitution DF engines.

Experimental results have demonstrated that NOx emission trends (as a function of lambda) for DF engines differ from both traditional diesel engines and lean burn natural gas engines. For high energy substitution (>70%) conditions, NOx emissions are a function of the premixed gas lambda (λng) and contain a local minimum, with NOx increasing as lambda is either leaned or rich-ened beyond the local minimum which occurs from approximately λng = 1.7–1.85.

It is hypothesized that at richer conditions (λng < 1.7), NOx formed in the burning of gaseous fuel results in increased total NOx emissions. At leaner conditions (λng > 1.85) the NOx formed in the diesel post flame regions, as a result of increased oxygen availability, results in increased total NOx emissions. Between these two regions there are competing effects which result in relatively constant NOx.

Commentary by Dr. Valentin Fuster
2017;():V001T01A002. doi:10.1115/ICEF2017-3531.

This paper presents the application of the Ganser CRS common rail injectors with the proprietary poppet valve, the state of the art hydraulic switching device for common rail injectors. Due to its unique design, the combustion process is optimized by stable and rapid injection rate profiles, which are allowing for reliable multiple injection driving strategies to further reduce the fuel consumption and in-cylinder emissions. Due to its flexible characteristics, the poppet valve is applicable in numerous fields. Two applications are specifically presented in this paper.

The first application of the poppet valve is the common rail retrofit of a V16 GE® 7FDL locomotive engine with a power output of 4000HP. In this retrofit project, the existing mechanical fuel injection system is replaced by a common rail system. The injector design is such that no changes to the cylinder head are required. The injector includes an integrated accumulator for maximized and constant injection pressures during the whole injection process. Each cylinder bank is equipped with its own slim rail attached to the engine structure and a dedicated high pressure pump, allowing for a freely configurable injection event up to 1600bar. The resulting significant reduction of fuel consumption over the locomotive duty cycle as well as emissions reductions are discussed in detail in this paper.

The poppet valve is also successfully applied in the field of micro pilot injection for new dual fuel engines, in the marine and power-gen sectors, as a second application of this injector design principle. On these engines, the micro pilot injection quantity to ignite the gas is typically 0.5–2% of the total energy input. This maximized diesel fuel substitution is possible because of the accurate switching characteristics of the poppet valve at smallest injection quantities. With the application of the proprietary Wave Dynamics and Dampening System (WDD) [1] and injector-integrated accumulators, the rail can be replaced completely by so-called jumper lines, while maintaining a slim outer shape on the overall injector size.

Commentary by Dr. Valentin Fuster
2017;():V001T01A003. doi:10.1115/ICEF2017-3549.

Dual-Fuel (DF) engines offer great fuel flexibility since they can either run on gaseous or liquid fuels. In the case of Diesel pilot ignited DF-engines the main source of energy is provided by gaseous fuel, whereas the Diesel fuel acts only as an ignition source. Therefore, a proper autoignition of the pilot fuel is of utmost importance for combustion in DF-engines. However, autoignition of the pilot fuel suffers from lower compression temperatures of Miller or Atkinson valve timings. These valve timings are applied to increase efficiency and lower nitrogen oxide engine emissions. In order to improve the ignition, it is necessary to understand which parameters influence the ignition in DF-engines. For this purpose, experiments were conducted and the influence of parameters such as injection pressure, pilot fuel quantity, compression temperature and air-fuel equivalence ratio of the homogenous natural gas-air mixture were investigated. The experiments were performed on a periodically chargeable combustion cell using optical high-speed recordings and thermodynamic measurement techniques for pressure and temperature. The study reveals that the quality of the Diesel pilot ignition in terms of short ignition delay and a high number of ignited sprays significantly depends on the injection parameters and operating conditions. In most cases, the pilot fuel suffers from too high dilution due to its small quantity and long ignition delays. This results in a small number of ignited sprays and consequently leads to longer combustion durations. Furthermore, the experiments confirm that the natural gas of the background mixture influences the autoignition of the Diesel pilot oil.

Commentary by Dr. Valentin Fuster
2017;():V001T01A004. doi:10.1115/ICEF2017-3554.

Large bore reciprocating internal combustion engines are used in a wide variety of applications such as power generation, transportation, gas compression, mechanical drives, and mining. Each application has its own unique requirements that influence the engine design & control strategy. The system architecture & control strategy play a key role in meeting the requirements. Traditionally, control design has come in at a later stage of the development process, when the system design is almost frozen. Furthermore, transient performance requirements have not always been considered adequately at early design stages for large engines, thus limiting achievable controller performance. With rapid advances in engine modeling capability, it has now become possible to accurately simulate engine behavior in steady-states and transients. In this paper, we propose an integrated model-based approach to system design & control of reciprocating engines and outline ideas, processes and real-world case studies for the same. Key benefits of this approach include optimized engine performance in terms of efficiency, transient response, emissions, system and cost optimization, tools to evaluate various concepts before engine build thus leading to significant reduction in development time & cost.

Commentary by Dr. Valentin Fuster
2017;():V001T01A005. doi:10.1115/ICEF2017-3577.

This paper discusses chemical kinetic modeling used to analyze the formation of pollutant emissions in large-bore, lean-burn gas reciprocating engines. Pollutants considered are NOx, CO, HCHO, and UHC. A quasi-dimensional model, built as a chemical reactor network (CRN), is described. In this model, the flame front is treated as a perfectly stirred reactor (PSR) followed by a plug flow reactor (PFR), and reaction in the burnt gas is modeled assuming a batch reactor of constant-pressure and fixed-mass for each crank angle increment. The model treats full chemical kinetics. Engine heat loss is treated by incorporating the Woschni model into the CRN. The mass burn rate is selected so that the modeled cylinder pressure matches the experiment pressure trace. Originally, the model was developed for large, low speed, two-stoke, lean-burn engines. However, recently, the model has been formatted for the four-stroke, open-chamber, lean-burn engine. The focus of this paper is the application of the model to a four-stroke engine. This is a single-cylinder non-production variant of a heavy duty lean-burn engine of about 5 liters cylinder displacement Engine speed is 1500 RPM. Key findings of this work are the following. 1) Modeled NOx and CO are found to agree closely with emission measurements for this engine over a range of relative air-fuel ratios tested. 2) This modeling shows the importance of including N2O chemistry in the NOx calculation. For λ = 1.7, the model indicates that about 30% of the NOx emitted is formed by the N2O mechanism, with the balance from the Zeldovich mechanism. 3) The modeling shows that the CO and HCHO emissions arise from partial oxidation late in the expansion stroke as unburned charge remaining mixes into the burnt gas. 4) Model generated plots of HCHO versus CH4 emission for the four-stroke engine are in agreement with field data for large-bore, lean-burn, gas reciprocating engines. Also, recent engine tests show the correlation of UHC and CO emissions to crevice volume. These tests suggest that HCHO emissions also are affected by crevice flows through partial oxidation of UHC late in the expansion stroke.

Commentary by Dr. Valentin Fuster
2017;():V001T01A006. doi:10.1115/ICEF2017-3580.

Slow-steaming operation and an increased pressure in the combustion chamber have contributed to increased sulfuric acid (H2SO4) condensation on the cylinder liners in large two-stroke marine diesel engines, thus causing increased corrosion wear. To cope with this, lube oils are formulated with overbased detergent additives present as CaCO3 reverse micelles to neutralize the condensing H2SO4. In this present work, a mixed flow reactor (MFR) setup aims to investigate the neutralization reaction by varying Ca/S molar ratio, stirrer speed, H2SO4 inlet concentration, and residence time. Lube oil samples from the outlet of the MFR were analysed by use of Fourier Transform Infrared Spectroscopy (FTIR) and a titration method. The MFR results indicate that the CaCO3-H2SO4 reaction is very fast in a real engine, if the cylinder liner is well-wetted, the oil-film is well-mixed, and contains excess of CaCO3 compared to the condensed H2SO4. The observed corrosion wear in large two-stroke marine diesel engines could consequently be attributed to local molar excess of H2SO4 compared to CaCO3 reverse micelles on the cylinder liners.

Topics: Diesel engines
Commentary by Dr. Valentin Fuster
2017;():V001T01A007. doi:10.1115/ICEF2017-3601.

To enable sustainable power generation through increasing shares of renewable energy, it is necessary to find flexible solutions that use conventional fossil fuels to compensate for volatile energy production from the wind and sun in order to stabilize the electrical grid. Modern large bore engines fueled by gas are already able to ramp up or shut down production quickly and also provide high efficiency throughout all load conditions. Nevertheless, transient capabilities of these engines must be improved even more in order to compete with diesel engines in applications with the highest transient requirements. To meet these demands, sophisticated actuators and control strategies are required. Testing of these components and strategies should already be conducted in an early development phase using rapid prototyping simulation and measurements on single cylinder engines instead of expensive multicylinder engine tests.

The first section of this paper shows how engine controller functions for transient operation based on rapid prototyping models and real-time capable models can be derived and tested. This enables the capabilities of different control strategies to be quantified in order to improve transient performance in an early stage of development.

The second section of the paper presents a methodology for transferring the transient behavior of a large multicylinder engine to a single cylinder test bed using a hardware-in-the-loop (HiL) approach with real time capable simulation models. A description of the demands on hardware and software is provided followed by a description of the overall system, after which the application of the real-time capable models on the real-time controllers of the test bed system is introduced.

Finally, the models with measurement data from the single cylinder engine are compared with the multicylinder engine with a special focus on block loads and ramping the engine at constant speed.

Commentary by Dr. Valentin Fuster
2017;():V001T01A008. doi:10.1115/ICEF2017-3608.

Industrial natural gas engines are used in a wide range of applications, each with unique requirements in terms of power density, initial cost, thermal efficiency, and other factors. As a result of these requirements, distinct engine designs have evolved to serve various applications. Heavy-duty spark-ignited engines can generally be divided into two broad categories based on their charge characteristics and method of emissions control.

Stoichiometric engines are widely used in applications where first cost, absolute emissions and relative engine simplicity are more important than fuel consumption. In most of the developed world, stoichiometric engines are equipped with a three-way catalyst to control emissions of nitrogen oxides (NOx) as well as products of incomplete combustion and raw unburned fuel.

Dilution of the charge mixture with excess air reduces the peak combustion gas temperature and associated heat rejection. As a result, lean burn engines are generally able to achieve higher efficiency and power density without inducing excessive component temperatures or end gas knock. NOx formation is mitigated by the reduced gas temperatures, such that most regulatory standards can currently be met in-cylinder. Significant obstacles exist to meeting more stringent future emissions regulations in this manner, however.

Another possible strategy is to dilute the charge mixture with recirculated exhaust gas. This offers similar benefits as air dilution while maintaining the ability to use a three-way catalyst for emissions after-treatment. While similar principles apply in either case, the choice of diluent can have a significant impact on knock resistance, emissions formation, thermal efficiency, and other parameters of importance to engine developers and operators.

This work aimed to examine the unique characteristics of EGR and air dilution from a thermodynamic and combustion perspective. A combination of cycle simulation tools and experimental data from a single-cylinder test engine was applied to demonstrate the impact of diluent properties on a fundamental level, and to illustrate departures from idealized behavior and practical considerations specific to the development of combustion systems for spark-ignited natural gas engines.

Commentary by Dr. Valentin Fuster
2017;():V001T01A009. doi:10.1115/ICEF2017-3642.

Natural gas/diesel dual fuel engines used in oil and gas drilling operations must be able to meet NOx emissions limits across a wide range of substitution percentage, which affects the air to natural gas ratio or gas lambda. In a dual fuel engine operating at high substitution, premixed, propagating natural gas flames occur and the NOx formed in such premixed flames is known to be a strong function of gas lambda. Consequently there is interest in understanding how NOx formation in a dual fuel engine is affected by gas lambda. However, NOx formation in a dual fuel engine is complicated by the interaction with the non-premixed diesel jet flame. As a result, previous studies have shown that enriching the air-fuel ratio can either increase or decrease NOx emissions depending on the operating conditions investigated. This study presents multi-dimensional combustion simulations of an air-fuel ratio sweep from gas lambda 2.0 to 1.5 at 80% substitution, which exhibited a minimum in NOx emissions at a natural gas lambda of 1.75. Images from the simulations are used to provide detailed explanations of the physical processes responsible for the minimum NOx trend with natural gas lambda.

Commentary by Dr. Valentin Fuster
2017;():V001T01A010. doi:10.1115/ICEF2017-3652.

The work conducted in this paper presents a novel experimental setup to study sulfuric acid cold corrosion of cylinder liners in large two-stroke marine diesel engines. The process is simulated in a motored light duty BUKH DV24 diesel engine where the charge air contain known amounts of H2SO4 and H2O vapor.

Liner corrosion is measured as iron accumulation in the lube oil. Similarly sulfuric acid condensation is assessed by measuring the accumulation of sulfur in the lube oil. To clarify the corrosive effect of sulfuric acid the lube oil utilized for experiments is a sulfur free neutral oil without alkaline additives (Chevron Neutral Oil 600R).

Iron and sulfur accumulation in the lube oil is analyzed with an Energy Dispersive X-Ray Fluorescence (ED-XRF) apparatus. Three test cases with different H2SO4 concentrations are run. Results reveal good agreement between sulfuric acid injection flow and the accumulation of both iron and sulfur in the oil.

Commentary by Dr. Valentin Fuster
2017;():V001T01A011. doi:10.1115/ICEF2017-3693.

Tunnels represent one of the most severe operating conditions for diesel engines in diesel-electric locomotive applications, specifically for non-ventilated tunnels located at high elevation. High ambient air temperatures are observed in these tunnels due to heat rejected from the locomotive engines through the exhaust and engine cooling and lubrication systems. Engine protection algorithms cause the maximum allowable engine horsepower to be reduced due to these conditions leading to a reduction in train speed and occasionally train stall. A first law based model was developed to simulate the performance of a train pulled by GE diesel-electric locomotives equipped with medium speed diesel engines in a high altitude and non-ventilated tunnel. The model was compared against and calibrated to actual tunnel operation data of EPA Tier 2 compliant locomotives. The model was then used to study the impact of engine design changes required for EPA Tier 4 compliant locomotives, specifically the introduction of exhaust gas recirculation (EGR), on engine, locomotive, and train performance in the tunnel. Simulations were completed to evaluate engine control strategies targeting same or better train performance than the EPA Tier 2 compliant locomotive baseline case. Simulation results show that the introduction of EGR reduces train performance in the tunnel by increasing the required reduction in engine horsepower, but is slightly offset by improved performance from other engine design changes. The targeted engine and train performance could be obtained by disabling EGR during tunnel operation.

Commentary by Dr. Valentin Fuster
2017;():V001T01A012. doi:10.1115/ICEF2017-3695.

Heat rejected with the exhaust gas, EGR, engine coolant and other engine components is a major source of efficiency loss in internal combustion engines. One important technology to recover some of this “wasted” heat is turbocompounding. The US Environmental Protection Agency (EPA) estimates that turbocompounding provides a 1.8% efficiency improvement, is already a commercial technology and a penetration rate of 10% is estimated by 2027. Line haul sleeper cab applications are the most likely to see the highest market penetration rates.

This paper presents an overview of mechanical turbocompounding for heavy-duty truck engines. For these applications, series turbocompounding is the most suitable configuration and a number of applications have used it since the early 1990s. Unlike other WHR technologies, turbocompounding interacts significantly with the engine through a higher exhaust backpressure. EGR makes it more challenging to realize an efficiency benefit from turbocompounding. It also makes emission control using aftertreatment technology more challenging due to a lower exhaust temperature.

Commentary by Dr. Valentin Fuster

Fuels

2017;():V001T02A001. doi:10.1115/ICEF2017-3509.

The generation of particulate matter (PM) is one problem with gasoline direct-injection engines. PM is generated in high-density regions of fuel that are formed by non-uniform air/fuel mixtures, coarse droplets generated during end-of-injection, and fuel adhering to the nozzle body surface and piston surface. Uniform air/fuel mixtures and short fuel-spray durations with multiple injections are effective in enabling the valves of fuel injectors to not wobble and dribble. We previously studied what effects the opening and closing of valves had on fuel spray behavior and found that valve motions in the opening and closing directions affected spray behavior and generated coarse droplets during the end-of-injection. We focused on the effects of valve wobbling on fuel spray behavior in this study, especially on the behavior during the end-of-injection. The effects of wobbling on fuel spray with full valve strokes were first studied, and we found that simulated spray behaviors agreed well with the measured ones. We also studied the effects on fuel dribble during end-of-injection. When a valve wobbled from left to right, the fuel dribble decreased in comparison with a case without wobbling. When a valve wobbled from the front to the rear, however, fuel dribble increased. Surface tension significantly affected fuel dribble, especially in forming low-speed liquid columns and coarse droplets. Fuel dribble was simulated while changing the wetting angle on walls from 60 to 5 degrees. We found that the appearance of coarse droplets in sprays decreased during the end-of-injection by changing the wetting angles from 60 to 5 degrees.

Commentary by Dr. Valentin Fuster
2017;():V001T02A002. doi:10.1115/ICEF2017-3551.

Blending cellulosic biofuels with traditional petroleum-derived fuels results in transportation fuels with reduced carbon footprints. Many cellulosic fuels rely on processing methods that produce mixtures of oxygenates which must be upgraded before blending with traditional fuels. Complete oxygenate removal is energy-intensive and it is likely that such biofuel blends will necessarily contain some oxygen content to be economically viable. Previous work by our group indicated that diesel fuel blends with low levels (<4%-vol) of oxygenates resulted in minimal negative effects on short-term engine performance and emissions. However, little is known about the long-term effects of these compounds on engine durability issues such as the impact on fuel injection, in-cylinder carbon buildup, and engine oil degradation. In this study, four of the oxygenated components previously tested were blended at 4%-vol in diesel fuel and tested with a durability protocol devised for this work consisting of 200 hrs of testing in a stationary, single-cylinder, Yanmar diesel engine operating at constant load. Oil samples, injector spray patterns, and carbon buildup from the injector and cylinder surfaces were analyzed. It was found that, at the levels tested, these fuels had minimal impact on the overall engine operation, which is consistent with our previous findings.

Commentary by Dr. Valentin Fuster
2017;():V001T02A003. doi:10.1115/ICEF2017-3556.

Technology developments in directional drilling and hydraulic fracturing have led to increased natural gas reserves. Development of these unconventional resources is an energy intensive process. Prime-movers of unconventional well development were previously identified to be over-the-road trucks, drilling engines, and hydraulic stimulation engines. Diesel engines dominate these markets but industry is attempting to cut costs by using dual fuel and dedicated natural gas engines. On-road engines are subject to the transient FTP cycle for certification and off-road engines are subject to the 5-mode ISO 8178 D-2 cycle. It is well known that in-use activity can differ from certification activity. Significant in-use activity data for each prime-mover were collected and a Markov-Chain Monte-Carlo Simulation with a genetic algorithm was used to develop test cycles for each.

The developed test cycles allowed for operation of a smaller yet similar engine within a controlled laboratory environment. Laboratory tests utilized a Cummins 8.9L ISL-G to analyze the emissions of new cycles compared to certification cycles and to examine the effects of fuel quality on emissions. The ISL-G is a spark-ignited engine used for heavy-duty trucks and could see market penetration in fleets serving the well development industry. It is similar in technology to the Waukesha LI7044, which is used in drilling operations — both employ air fuel ratio control and three-way catalysts. For the case of “pump” quality fuel, compressed natural gas was used. The developed OTR truck cycle produced higher brake-specific emissions of CO2, CO, NOx, and lower HC emissions compared to the FTP. The drilling and fracturing cycles tended to have lower CO2 and HC emissions but higher CO emissions when compared to the D-2 cycle. Two additional fuel blends were used on the new cycles and represented blends with higher ethane and propane fractions — which are common to shale gases that could fuel prime-movers in the future. The minimum recommended methane number for this engine was 75 and additional fuel blends had methane numbers of 75.5 (propane blend) and 75.3 (ethane blend). As expected, CO2 emissions increased with increased alkane concentration, while opposite trends were shown for THC and CH4. NOx emissions also tended to decrease with higher ethane and propane blends, across all cycles. For all cycles and fuels, HC emissions were predominately CH4 - 94–97%. Variations in activity and the effects of different fuels should be addressed when estimating emissions since using standard certification or emissions factors may not be representative of in-use emissions.

Commentary by Dr. Valentin Fuster
2017;():V001T02A004. doi:10.1115/ICEF2017-3569.

Precise control of the spray behavior is key to fully realize the potential benefits of modern GDI engines. Flash boiling is known to alert the spray behavior significantly; and thus, a complete understanding of its mechanism is essential. In this work, a study of the effect of the fuel properties on the near-nozzle flow characteristics of a single-hole GDI injector under the flash boiling conditions is presented. The performance of hexane and a typical gasoline surrogate iso-octane has been studied both experimentally and numerically. Fuel temperature varied from 20 and 100 °C with ambient pressures of 20, 50 and 100 kPa. For the experiment, microscopic imaging was conducted with a high-speed camera coupled with a long-distance microscope; and a convex lens was used to provide enough illumination to the interested area. The numerical studies were performed at the maximum needle lift using OpenFOAM, an open-source Computational Fluid Dynamics (CFD) code. Phase change was captured with the Homogeneous Relaxation Model (HRM); and turbulence was modeled using RNG k–ε model. The results have shown that while the near-field flow behavior of hexane and isooctane was similar under ambient conditions, a significant difference was observed between the two under the flash boiling conditions. The onset and development of flash boiling of isooctane was retarded compared to hexane due to its much lower vapor pressure. Spray contraction has been observed in the down-stream due to fuel vaporization and air entrainment. The CFD results were shown to agree well with the experimental data.

Commentary by Dr. Valentin Fuster
2017;():V001T02A005. doi:10.1115/ICEF2017-3589.

Recent gas engines developments tend to use more excess air to reduce NOx emissions. Under these circumstances the ignition in a single cylinder research gas engine with micro pilot injection of highly ignitable fuels has been investigated. Three igniting fuels, Hydrogenated Vegetable Oil (HVO), 2-ethoxyethyl ether (2-EEE) and a Diesel/2-ethylhexyl nitrate blend have been selected by a systematical assessment and their properties have been analyzed. These fuels have been evaluated concerning their aptitude as igniting fuels and compared with diesel as reference fuel. A higher ignitability of igniting fuel reduced the ignition delay of the injected fuel and enabled the diminution of the igniting fuel fraction. A significant share of NOx emissions have been attributed to the ignition injection, therefore micro pilot injection is necessary to reach emission targets. The micro pilot injection of 2-EEE as a highly ignitable fuel with the highest Cetane Number showed favorably low ignition delay. Depending on the selected fuel and the igniting fuel fraction, the combustion phasing can be controlled directly by the injection timing. In the last section, the results for pilot injection with 2-EEE as an igniting fuel have been compared with the results using a conventional spark plug. Advantages and disadvantages for both ignition systems have been identified at constant Air Fuel Ratio (AFR). A thermodynamical comparison with each ignition system has been performed to explain the different effects on combustion.

Topics: Fuels , Ignition , Gas engines
Commentary by Dr. Valentin Fuster
2017;():V001T02A006. doi:10.1115/ICEF2017-3614.

Due to the high cost and time required to synthesize alternative fuel candidates for comprehensive testing, an Artificial Neural Network (ANN) can be used to predict fuel properties, allowing researchers to preemptively screen desirable fuel candidates. However, the accuracy of an ANN is limited by its error, measured by the root mean square error (RMSE), standard deviation, and r-squared values derived from a given input database. The present work improves upon an existing model for predicting the Cetane Number (CN) by changing the neuron activation function of the ANN from sigmoid to rectified linear unit (ReLU). This change to the ANN’s architecture provides an increase in accuracy by reducing the RMSE by 21.4% (1.35 CN units), the average standard deviation across models by 28%, and increasing the r-squared value by 0.0492 across a wide range of molecular structures. Additionally, by using the ReLU activation function, input data is not required to be normalized, which reduces the likelihood of an inaccurate prediction on future fuel candidates which may have input parameters outside the range of normalization. Increasing the accuracy of the predictive ANN in this way will allow researchers to obtain more accurate fuel property predictions for promising fuel candidates.

Commentary by Dr. Valentin Fuster
2017;():V001T02A007. doi:10.1115/ICEF2017-3620.

Particulate matter (PM) emissions from gasoline direct injection (GDI) engines are a concern due to the health effects associated with ultrafine PM. This experimental study investigated sources of PM emissions measurement variability observed in previous tests and also examined the effect of ethanol content in gasoline on PM emissions. Some engine operating parameters (fuel and oil temperature, PCV filtration) and test conditions (dilution air conditions) were studied and controlled but could not account for the level of measurement variability observed. Fourier Transform Infrared Spectrometry (FTIR) measurements of gas phase hydrocarbon emissions provided evidence that changes in fuel composition were responsible for the variability. Exhaust emissions of toluene and ethanol were correlated positively with PM emissions, while emissions of isobutylene correlated negatively. Exhaust emissions of toluene and isobutylene were interpreted as markers of gasoline aromatic content and gasoline volatility respectively. Tests conducted with gasoline containing added toluene (10% v/v) supported this hypothesis and led to the overall conclusion that the PM emissions variability observed can be attributed to changes in the composition of the pump gasoline being used. Tests conducted with gasoline containing added ethanol (10% and 30% v/v) found that increasing ethanol fuel content increased PM emissions at the steady-state operating condition utilized.

Commentary by Dr. Valentin Fuster
2017;():V001T02A008. doi:10.1115/ICEF2017-3647.

This research work investigates the performance, combustion and emission characteristics of a low heat rejection engine operated on diesel and diethyl ether blends. The combustion chamber walls of the diesel engine insulated by ceramic material were referred to as low heat rejection (LHR) engine. In the LHR engine, an improvement in fuel economy would be obtained by recovering the waste heat rejected to the cooling system as useful work. Initially, the diesel fuel was tested in the conventional engine as a baseline reading for comparison. Then the engine was insulated by coating the engine components of the piston crown and the cylinder liner with aluminum titanate using plasma spray method. In this work, the experiments are conducted using diesel and diethyl ether blends in a conventional and low heat rejection engine at constant speed condition. The experimental results indicate that the brake thermal efficiency increases with increased percentage of diethyl ether in the blends. The maximum brake thermal efficiency was found to be 33.24% for LHR engine using diesel-diethyl ether blend (Diesel 85% & Diethyl ether 15% by volume) at full load condition. The emissions of carbon monoxide and hydrocarbon are decreased due to better combustion characteristics and higher NOx emissions are observed with low heat rejection engine (LHR) compared to the conventional engine using diesel and blended fuels.

Commentary by Dr. Valentin Fuster
2017;():V001T02A009. doi:10.1115/ICEF2017-3660.

The goal of this investigation is to compare the validation of Sasol-IPK and its surrogate fuel in the IQT and in an actual diesel engine. The surrogate fuel is composed of three components (46% iso-cetane, 44% decalin and 10% n-nonane on a volume basis). IQT experiments were conducted as per ASTM D6890-10a. Engine experiments were conducted at 1500 RPM, two engine loads, and two injection timings. Analysis of the ignition delay, peak pressure, peak RHR and other combustion phasing parameters, showed a closer match in IQT than in the diesel engine. This investigation suggests that validation in a single cylinder diesel engine should be a part of the surrogate validation, particularly for low ignition quality fuels.

Commentary by Dr. Valentin Fuster
2017;():V001T02A010. doi:10.1115/ICEF2017-3664.

Gasoline compression ignition (GCI) offers the potential to reduce criteria pollutants while achieving high fuel efficiency in heavy-duty diesel engines. This study aims to investigate the fuel chemical and physical properties effects on GCI operation in a heavy-duty diesel engine through closed-cycle, 3-D computational fluid dynamics (CFD) combustion simulations, investigating both mixing-controlled combustion (MCC) at 18.9 compression ratio (CR) and partially premixed combustion (PPC) at 17.3 CR.

For this work, fuel chemical properties were studied in terms of the primary reference fuel (PRF) number (0–91) and the octane sensitivity (0–6) while using a fixed fuel physical surrogate. For the fuel physical properties effects investigation, PRF70 was used as the gas-phase chemical surrogate. Six physical properties were individually perturbed, varying from the gasoline to the diesel range.

Combustion simulations were carried out at 1375 RPM and 10 bar brake mean effective pressure (BMEP). Reducing fuel reactivity (or increasing PRF number) was found to influence ignition delay time (IDT) more significantly for PPC than for MCC due to the lower charge temperature and higher EGR rate involved in the PPC mode. 0-D IDT calculations suggested that the fuel reactivity impact on IDT diminished with an increase in temperature. Moreover, higher reactivity gasolines exhibited stronger negative coefficient (NTC) behavior and their IDTs showed less sensitivity to temperature change. When exploring the octane sensitivity effect, ignition was found to occur in temperature conditions more relevant to the MON test. Therefore, increasing octane sensitivity (reducing MON) led to higher reactivity and shorter ignition delay.

Under both MCC (TIVC: 385K) and PPC (TIVC: 353K), all six physical properties showed little meaningful impact on global combustion behavior, NOx and fuel efficiency. Among the physical properties investigated, only density showed a notable effect on soot emissions. Increasing density resulted in higher soot due to deteriorated air entrainment into the spray and the slower fuel-air mixing process. When further reducing the IVC temperature from 353K to 303K under PPC, the spray vaporization and fuel-air mixing were markedly slowed. Consequently, increasing the liquid fuel density created a more pronounced presence of fuel-rich and higher reactivity regions, thereby leading to an earlier onset of hot ignition and higher soot.

Commentary by Dr. Valentin Fuster
2017;():V001T02A011. doi:10.1115/ICEF2017-3674.

The combustion in an experimental medium duty direct injected engine was investigated in a dual mode process known as partially premixed compression ignition (PPCI). Both a common rail fuel injection system and port fuel injection (PFI) system have been custom designed and developed for the experimental single cylinder engine in order to research the combustion and emissions characteristics of Fischer Tropsch synthetic paraffinic kerosene (S8) with PFI of n-butanol in a low temperature combustion mode (LTC). Baseline results in single fuel (ULSD) combustion were compared to dual fuel strategies coupling both the low and high reactivity fuels. The low reactivity fuel, n-butanol, was port fuel injected in the intake manifold at a constant 30% fuel mass and direct injection of a high reactivity fuel initiated the combustion. The high reactivity fuels are ULSD and a gas to liquid fuel (GTL/S8). Research has been conducted at a constant speed of 1500 RPM at swept experimental engine loads from 3.8 bar to 5.8 bar indicated mean effective pressure (IMEP). Boost pressure and exhaust gas recirculation (EGR) were added at constant levels of 3 psi and 30% respectively. Dual fuel combustion with GTL advanced ignition timing due to the high auto ignition quality and volatility of the fuel. Low temperature heat release (LTHR) was also experienced for each dual-fuel injection strategy prior to the injection of the high reactivity fuel. Peak in-cylinder gas temperatures were similar for each fueling strategy, maintaining peak temperatures below 1400°C. Combustion duration increased slightly in ULSD-PPCI compared to single fuel combustion due to the low reactivity of n-butanol and was further extended with GTL-PPCI from early ignition timing and less premixing. The effect of the combustion duration and ignition delay increased soot levels for dual fuel GTL compared to dual fuel ULSD at 5.8 bar IMEP where the combustion duration is the longest. NOx levels were lowest for GTL-PPCI at each load, with up to a 70% reduction compared to ULSD-PPCI. Combustion efficiencies were also reduced for dual fuel combustion, however the atomization quality of GTL compared to ULSD increased combustion efficiency to reach that of single fuel combustion at 5.8 bar IMEP.

Topics: Compression , Ignition
Commentary by Dr. Valentin Fuster
2017;():V001T02A012. doi:10.1115/ICEF2017-3689.

This paper presents the engine performance, combustion process, and exhaust emissions from of a turbocharged spark ignition (SI) WP-10 off-road engine developed to operate on gaseous fuels applicable to a wide range of the higher heating value (HHV) (900 to 1400 BTU). The HHV of the fuels was varied by blending of propane or carbon dioxide (CO2) into natural gas (NG). The developed engine was designed to operate at 1800 rpm and 175 kW.

A new method of calculating the specific heat ratio of the bulk gases with the calculated bulk gas temperature and composition was proposed. The specific heat ratio calculated using this method was lower than the value derived from the conventional Log P-Log V method. The application of the specific heat ratio calculated in calculating the heat release process increased the heat release rate (HRR) and the total heat released during combustion. In addition, it also resulted in retarded phasing of CA50 and CA95 defined as the crank angle location when 50% and 95% of total energy was released.

The effects of the fuel composition on engine performance, combustion process, and exhaust emissions were experimentally investigated. It achieved a brake thermal efficiency of about 32.8%. The exhaust emissions are in compliance with both EPA and CARB regulations. The addition of propane to NG increased the HRR, accelerated the combustion process, and shortened the combustion duration. This was the result of the quicker flame propagation property of propane. The HRR observed with propane blending was featured with two heat release peaks. The peak HRR observed with 1400 BTU fuel was about 10% higher than that observed with NG only operation. As expected, the blending of CO2 to NG was shown to slow down the combustion process, and retarded the combustion phasing, especially during the completion of combustion.

Commentary by Dr. Valentin Fuster
2017;():V001T02A013. doi:10.1115/ICEF2017-3691.

Bio-butanol has been widely investigated as a promising alternative fuel. However, the main issues preventing industrial-scale production of butanol are its relatively low production efficiency and high cost of component recovery from the acetone-butanol-ethanol (ABE) fermentation process. Therefore, ABE has attracted a lot of interest as an alternative fuel for the reason that it not only has positive characteristics of oxygenated fuels, but also reduces the production cost during fermentation. This investigation is focused on the regulated and unregulated emissions of a single cylinder port-fuel injection (PFI) spark-ignition (SI) engine fueled with ABE (volumetric concentration of A:B:E = 3:6:1) and gasoline blends. Blends of gasoline with various ABE content (0 vol.%, 10 vol.%, 20 vol.% ABE referred to as G100, ABE10, ABE20) were used as test fuels. Experiments were performed at an engine speed of 1200 rpm, and at engine loads of 3 and 5 bar brake mean effective pressures (BMEP) and under various equivalence ratios (Φ = 0.83–1.25). Exhaust gases measured included nitrogen oxides (NOX), carbon monoxide (CO) and unburned hydrocarbons (UHC). Additionally, benzene, ethylbenzene, toluene and xylenes (BTEX) concentrations were also measured by a gas chromatograph coupled with a mass spectrometer (GC/MS) and a flame ionization detection (GC/FID). The results show that with an increase of ABE in the blended fuel, there are reductions of UHC, CO and NOx. For the unregulated emissions, ABE addition leads to decreases in benzene, toluene and xylene emissions but an increase in ethylbenzene.

Commentary by Dr. Valentin Fuster

Advanced Combustion

2017;():V001T03A001. doi:10.1115/ICEF2017-3524.

An internal combustion engine which is primarily designed for producing power can be utilized as a chemical reactor for a range of chemical processes given its inherent advantages including high throughput, high chemical conversion efficiency, and reactant/product handling benefits. For gas-phase processes requiring a catalyst, the ability to develop a fluidized bed reactor within the engine cylinder would greatly enhance gas/solid mixing, reducing mass transfer barriers and allowing the reactor to efficiently process large volumes of fluid. In addition, use of an engine could facilitate vibration and pulsed flow which may enhance fluidization quality. This work examines the fluidization behavior of particles within a cylinder of an internal combustion engine at various engine speeds using analytical and experimental methods. First, calculations were carried out to determine the maximum fluidization velocity and the corresponding engine speeds below which fluidization of a particle bed is possible given the properties of the particles and engine dimensions. Fluidization depends on particle properties as well as the engine used. For 40–63 micron diameter silica gel particles placed inside a modified Megatech Mark III transparent combustion engine (with a bore of 4.1 cm, stroke length of 5.1 cm and compression ratio of 2.4), calculations indicate that engine speeds of approximately 1.1 to 60.8 RPM would result in fluidization of the particles. For higher engine speeds, the fluidization behavior is expected to deteriorate as the maximum fluidization velocity is surpassed. Next, experiments were conducted using the transparent engine and video recording to obtain qualitative confirmation of the analytical predictions. Simulations were then performed using ANSYS Fluent to investigate pressure drop across the bed. Consistent with the calculations, for an engine speed of 48 RPM, fluidized behavior was observed. In contrast for an engine speed of 171 RPM, the fluidization was observed to deteriorate and result in a “cake” of particles that moved in a lumped manner. Overall, the investigation shows that a fluidized bed can be obtained within the cylinder of a reciprocating piston engine if the engine speed is within the range predicted by the maximum fluidization velocity.

Commentary by Dr. Valentin Fuster
2017;():V001T03A002. doi:10.1115/ICEF2017-3525.

Improved internal combustion (IC) engine simulations of natural gas (NG) combustion under conventional and advanced combustion strategies have the potential to increase the use of NG in the transportation sector in the United States. This study focused on the physics of turbulent flame propagation. The experiments were performed in a single-cylinder heavy-duty compression-ignition (CI) optical engine with a bowl-in piston that was converted to spark ignition (SI) NG operation. The size and growth rate of the early flame from the start of combustion until the flame filled the camera field-of-view were correlated to combustion parameters determined from in-cylinder pressure data, under low-speed, lean-mixture, and medium-load conditions. Individual cycles showed evidence of turbulent flame wrinkling, but the cycle-averaged flame edge propagated almost circular in the 2D images recorded from below. More, the flame-speed data suggested a different flame propagation inside a bowl-in piston geometry compared to a typical SI engine chamber. For example, while the flame front propagated very fast inside the piston bowl, the corresponding mass fraction burn was small, which suggested a thick flame region. In addition, combustion images showed flame activity after the end of combustion inferred from the pressure trace. All these findings support the need for further investigations of flame propagation under conditions representative of CI engine geometries, such as those in this study.

Commentary by Dr. Valentin Fuster
2017;():V001T03A003. doi:10.1115/ICEF2017-3529.

In this study, the influence of the charge motion on the internal combustion in a spark ignition sewage gas-driven engine (150 kW) for combined heat and power units was investigated. For this purpose, the geometry of the combustion chamber in the immediate vicinity to the inlet valve seats was modified. The geometrical modification measures were conducted iteratively by integrative determination of the swirl motion on a flow bench, by laser-optical methods and consecutively by combustion analysis on a test engine. Two different versions of cylinder heads were characterized by dimensionless flow and swirl numbers prior to testing their on-engine performance. Combustion analysis was conducted with a cylinder pressure indication system for partial and full load, meeting the mandatory NOx limit of 500 mg m−3. Subsuming the flow bench results, the new valve seat design has a significant enhancing impact on the swirl motion but it also leads to disadvantages concerning the volumetric efficiency. A comparative consideration of the combustion rate delivers that the increased swirl motion results in a faster combustion, hence in a higher efficiency. In summary, the geometrical modifications close to the valve seat result in increased turbulence intensity. It was proven that this intensification raises the ratio of efficiency by 1.6%.

Commentary by Dr. Valentin Fuster
2017;():V001T03A004. doi:10.1115/ICEF2017-3532.

In this paper, pilot-ignited high pressure dual-fuel (HPDF) combustion of a natural gas jet is investigated on a fundamental basis by applying two separate single-hole injectors to a rapid compression expansion machine (RCEM). A Shadowgraphy system is used for optical observations, and the combustion progress is assessed in terms of heat release rates. The experiments focus on the combined influence of injection timing and geometrical jet arrangement on the jet interaction and the impact on the combustion process. In a first step, the operational range for successful pilot self-ignition and transition to natural gas jet combustion is determined, and the restricting phenomena are identified by analyzing the shadowgraph images. Within this range, the combustion process is assessed by evaluation of ignition delays and heat release rates. Strong interaction is found to delay or even prohibit pilot ignition, while it facilitates a fast and stable onset of the gas jet combustion. Furthermore, it is shown that the heat release rate is governed by the time of ignition with respect to the start of natural gas injection — as this parameter defines the level of premixing. Evaluation of the time of gas jet ignition within the operability map can therefore directly link a certain spatial and temporal interaction to the resulting heat release characteristics. It is finally shown that controlling the heat release rate through injection timing variation is limited for a certain angle between the two jets.

Commentary by Dr. Valentin Fuster
2017;():V001T03A005. doi:10.1115/ICEF2017-3544.

A partially premixed combustion (PPC) approach was applied in a single cylinder diesel research engine in order to characterize engine power improvements. PPC is an alternative advanced combustion approach that generally results in lower engine-out soot and NOx emission, with a moderate penalty in engine-out unburned hydrocarbon (UHC) and carbon monoxide (CO) emissions. In this study PPC is accomplished with a minority fraction of jet fuel injected into the intake manifold, while the majority fraction of jet fuel is delivered directly to the combustion chamber near the start of combustion (SOC). Four compression ratios (CR) were studied. Exhaust emissions plus exhaust opacity and particulate measurements were performed during the experiments in addition to fast in-cylinder combustion metrics. It was seen that as CR increased the soot threshold equivalence ratio decreased for conventional diesel combustion, however this afforded an increased opportunity for higher levels of port injected fuel leading to power increases from 5 to 23% as CR increased from 14 to 21.5. PPC allowed for these power increases (defined by a threshold opacity level of 3%) due to smaller particles (and lower overall number of particles) in the exhaust that influence measured opacity less significantly than larger and more numerous conventional diesel combustion exhaust particulates. Carbon monoxide levels at the higher PPC driven power levels were only modestly higher, although NOx was generally lower due to the overall enriched operation.

Topics: Combustion , Diesel
Commentary by Dr. Valentin Fuster
2017;():V001T03A006. doi:10.1115/ICEF2017-3553.

Low energy content fuels such as landfill gas can contain a significant amount of diluents like CO2. Critical fuel properties including the lower heating value (LHV) and an anti-knock property, in particular the methane number (MN), should be considered to optimize operation of a spark ignited (SI) engine. The MN has been shown to be a good indicator of knock propensity in stoichiometric SI engines. However, this approach is not always as effective for lean burn SI engines. Two fuels with the same methane number, but with different compositions, may exhibit a different propensity to knocking in an advanced lean burn SI engine. This effect is particularly pronounced when comparing fuels that have different amounts of diluents. In this paper we propose an alternative calculation of the MN, which compensates for the effect of diluents. More specifically, we define a lean burn methane index (LBMI), which is calculated without the diluents. This approach was validated using chemical kinetics modeling. The analysis considered fundamental combustion properties, including laminar flame speed (LFS), adiabatic flame temperature (AFT) and the autoignition interval (AI). For this study, a baseline fuel was selected based on a typical US pipeline natural gas composition. CO2 was then added as a diluent to the baseline fuel to simulate low energy density fuel compositions. Lambda values were selected to provide the same AFT or engine-out NOx. Low energy content fuel were found to have very similar AI values (less than 2% relative difference) to the baseline fuel at the target lambda values. A key result of this study is that the LBMI is a much better predictor of knock propensity than the traditional MN, when comparing fuels with widely varying levels of dilution for advanced lean burn SI engines.

Commentary by Dr. Valentin Fuster
2017;():V001T03A007. doi:10.1115/ICEF2017-3574.

In-cylinder air flow structure makes significant impacts on fuel spray dispersion, fuel mixture formation, and flame propagation in spark ignition direct injection (SIDI) engines. While flow vortices can be observed during the early stage of intake stroke, it is very difficult to clearly identify their transient characteristics because these vortices are of multiple length scales with very different swirl motion strength. In this study, a high-speed time-resolved 2D particle image velocimetry (PIV) is applied to record the flow structure of in-cylinder flow field along a swirl plane at 30 mm below the injector tip. First, a discretized method using flow field velocity vectors is presented to identify the location, strength, and rotating direction of vortices at different crank angles. The transients of vortex formation and dissipation processes are revealed by tracing the location and motion of the vortex center during the intake and compression strokes. In addition, an analysis method known as the wind-rose diagram, which is implemented for meteorological application, has been adopted to show the velocity direction distributions of 100 consecutive cycles. Results show that there exists more than one vortex center during early intake stroke and their fluctuations between each cycle can be clearly visualized. In summary, this approach provides an effective way to identify the vortex structure and to track the motion of vortex center for both large-scale and small-scale vortices.

Topics: Engines , Vortices , Ignition
Commentary by Dr. Valentin Fuster
2017;():V001T03A008. doi:10.1115/ICEF2017-3584.

As an inexpensive and low carbon fuel, the combustion of natural gas reduces fuel cost and generates less carbon dioxide emissions than diesel and gasoline. Natural gas is also a clean fuel that generates less particulate matter emissions than diesel during combustion. Replacing diesel by natural gas in internal combustion engines is of great interest for industries. Dual fuel combustion is an efficient way to apply natural gas in internal combustion engines.

An issue that to a certain extent offsets the advantage of lower carbon dioxide emissions in natural gas–diesel dual fuel engines is the higher methane emissions and low engine efficiency at low load conditions. In order to seek strategies to improve the performance of dual fuel engines at low load conditions, an experimental investigation was conducted to investigate the effect of diesel injection split on combustion and emissions performance of a heavy duty natural gas–diesel dual fuel engine at a low load. The operating conditions, such as engine speed, load, intake temperature and pressure, were well controlled during the experiment. The effects of diesel injection split ratio and timings were investigated. The engine efficiency and emissions data, including particulate matter, nitric oxides, carbon monoxide and methane were measured and analyzed. The results show that diesel injection split significantly reduced the peak pressure rise rate. As a result, diesel injection split enabled the engine to operate at a more optimal condition at which engine efficiency and methane emissions could be significantly improved compared to single diesel injection.

Commentary by Dr. Valentin Fuster
2017;():V001T03A009. doi:10.1115/ICEF2017-3585.

The combustion of natural gas reduces fuel cost and generates less emissions of carbon dioxide and particulate matter than diesel and gasoline. Replacing diesel by natural gas in internal combustion engines is of great interest for transportation and stationary power generation. Dual fuel combustion is an efficient way to burn natural gas in internal combustion engines.

In natural gas–diesel dual fuel engines, unburned hydrocarbon emissions increase with increasing natural gas fraction. Many studies have been conducted to improve the performance of natural gas–diesel dual fuel engines and reported the performance of combustion and emissions of regulated pollutants and total unburned hydrocarbon at various engine operating strategies. However, little has been reported on the emissions of different unburned hydrocarbon components. In this paper, an experimental investigation was conducted to investigate the combustion performance and emissions of various unburned hydrocarbon components, including methane, ethane, ethylene, acetylene, propylene, formaldehyde, acetaldehyde and benzaldehyde, at a low engine load condition. The operating conditions, such as engine speed, load, intake temperature and pressure, were well controlled during the experiment. The combustion and emissions performance of pure diesel and natural gas–diesel dual fuel combustion were compared. The effect of diesel injection timing was analyzed. The results show that appropriately advancing diesel injection timing to form a homogeneous charge compression ignition-like combustion is beneficial to natural gas–diesel dual fuel combustion at low load conditions. The emissions of different unburned hydrocarbon components changed in dual fuel combustion, with emissions of some unburned hydrocarbon components being primarily due to the combustion of natural gas, while those of others being more related to diesel combustion.

Commentary by Dr. Valentin Fuster
2017;():V001T03A010. doi:10.1115/ICEF2017-3607.

Experimental work on reactivity-controlled compression ignition (RCCI) in a small-bore, multi-cylinder engine operating on premixed iso-octane and direct-injected n-heptane has shown an unexpected combustion phasing advance at early injection timings, which has not been observed in large-bore engines operating under RCCI at similar conditions. In this work, computational fluid dynamics (CFD) simulations were performed to investigate whether spray-wall interactions could be responsible for this result. Comparison of the spray penetration, fuel film mass, and in-cylinder visualization of the spray from the CFD results to the experimentally measured combustion phasing and emissions provided compelling evidence of strong fuel impingement at injection timings earlier than −90 crank angle degrees (°CA) after top dead center (aTDC), and transition from partial to full impingement between −65 and −90°CA aTDC. Based on this evidence, explanations for the combustion phasing advance at early injection timings are proposed along with potential verification experiments.

Commentary by Dr. Valentin Fuster
2017;():V001T03A011. doi:10.1115/ICEF2017-3609.

In recent years, many engine manufacturers have turned to downsizing and boosting of gasoline engines in order to meet the ever more stringent fuel economy and emissions regulations. With an increase in the number of turbocharged gasoline engines, solutions are required to manage knock under a range of operating conditions. The charge air cooler has been introduced to mitigate knock. Moreover, the engine is required to operate with spark retard and/or boost reduction to provide knock reduction leading to reduced fuel economy.

Under some operating conditions water can condense in the charge air cooler (CAC). Corrugated plate separators have been widely used in gas-water separation and oil-water separation in many industries including marine diesel engines. However, this sort of separator has not been applied to gasoline engines in vehicles to separate the condensation in the charged air. In this paper, a 1-D condensation model to estimate the potential amount of water condensation and entrainment from the charge air coolers is presented. An approach to designing a unit to separate condensation in the flow from the charge air cooler while maintaining a low pressure drop is described. The design approach provides correlations of separator geometries versus separation and pressure drop performance. The study is developed using a 3-D computational model for analyzing charge air and condensation flow. The model results of the 1-D condensation model and the 3-D computational model have been validated by experiments on an engine-dynamometer based test cell. The set-up incorporates a 4 cylinder gasoline direct injection (GDI) turbocharged engine. An air-to-air charge air cooler is mounted under the engine. The intake air for the engine is supplied using a combustion air unit which enables the operators to control the temperature and humidity.

Test conditions have been identified to demonstrate the phenomenon of CAC water condensation. Measurements of water condensation and motion through the system confirm the results of models. A separator has been designed that achieves high separation efficiency and low pressure drop.

Topics: Condensation , Water
Commentary by Dr. Valentin Fuster
2017;():V001T03A012. doi:10.1115/ICEF2017-3616.

Pinnacle is developing multi-cylinder 1.2 L gasoline engine for automotive applications using high performance computing (HPC) and analysis methods. Pinnacle and Oak Ridge National Laboratory executed large-scale multi-dimensional combustion analyses at the Oak Ridge Leadership Computing Facility to thoroughly explore the design space. These HPC-led investigations show high fuel efficiency (∼46% gross indicated efficiency) may be achieved by operating with extremely high charge dilution levels of exhaust gas recirculation (EGR) at a light load key drive cycle condition (2000 RPM, 3 bar BMEP), while simultaneously attaining high levels of fuel conversion efficiency and low NOx emissions. In this extremely dilute environment, the flame propagation event is supported by turbulence and bulk in-cylinder charge motion brought about by modulation of inlet port flow. This arrangement produces a load and speed adjustable amalgamation of swirl and counter-rotating tumble which provides the turbulence required to support stable low-temperature combustion (LTC). At higher load conditions, the engine may operate at more traditional combustion modes to generate competitive power.

In this paper, the numerical results from these HPC simulations are presented. Further HPC simulations and test validations are underway and will be reported in future publications.

Commentary by Dr. Valentin Fuster
2017;():V001T03A013. doi:10.1115/ICEF2017-3619.

This paper experimentally investigates the effect of water injection in the intake manifold on a naturally aspirated, single cylinder, Gasoline Direct Injection engine to determine the combustion and emissions performance with combustion knock mitigation. The endeavor of the current study is to use water injection to attain the optimum combustion phasing without knocking. Further elevated intake air temperature tests were conducted to observe the effect of water injection with respect to combustion and emissions. Experiments were carried out at medium load condition (800 kPa NIMEP, 1500 RPM) at intake air temperatures between 30–90° C in 20° C increments. Two fuels, an 87 AKI and a 93 AKI were used in this study. Baseline tests were undertaken with the high-octane fuel (93 AKI) to achieve optimal combustion phasing corresponding to Maximum Brake Torque (MBT) without water injection. Water injection was utilized for the low octane fuel to achieve combustion phasing of 8–10° ATDC and within the controlled knock limit. Combustion phasing was achieved by controlling the ignition timing, water injection quantity and timing to the knock threshold. The results showed that water injection and the resultant charge cooling mitigates combustion knock and an optimum combustion phasing based on indicated fuel conversion efficiency is achieved with a water to fuel ratio of 0.6. Water injection reduces the NOx emissions while achieving better indicated thermal efficiency compared to the baseline tests. A detailed comparison is presented on the combustion phasing, indicated thermal efficiency, burn durations, HC, NOx and PN emissions in this paper.

Commentary by Dr. Valentin Fuster
2017;():V001T03A014. doi:10.1115/ICEF2017-3625.

Many studies have shown that gasoline compression ignition (GCI) can replace conventional diesel combustion (CDC) by achieving high efficiency and low smoke and toxic gaseous emissions simultaneously. This is due to the low cetane number of gasoline that results in long ignition delay, allowing very advanced injection timing. This gives even longer time for fuel-air mixing, thus resulting in locally lean combustion that produces low particulate matter (PM). However, GCI operation faces challenges at high engine load condition. At high load conditions, large amounts of fuel injected early for premixed combustion can lead to high combustion noise from premixed combustion. Meanwhile, more fuel late injected late leads to poor mixing, hence higher smoke. Multiple injections can offer the flexibility in controlling the in-cylinder fuel stratification level. In this study, moderate to high engine loads of 8 to 14 bar BMEP were accomplished by utilizing an optimal multiple injection scheme. Injection timing of pilot, main, and post injections was investigated individually for its effect on the emission and engine performance. A moderate level of exhaust gas recirculating (EGR) was used to achieve low temperature combustion (LTC) condition. While higher EGR reduced NOx significantly due to lower combustion temperature, it affected the maximum boost that could be acquired by the turbocharger due to the reduction in exhaust enthalpy. During the engine load/speed sweep, calculations of combustion, thermodynamics, gas exchange, and mechanical efficiencies were analyzed to identify factor that needs to be improved for GCI operation. This study also demonstrates the importance of injection strategy including high injection pressure to attain high load points with low smoke and low noise.

Commentary by Dr. Valentin Fuster
2017;():V001T03A015. doi:10.1115/ICEF2017-3636.

Since fossil fuels will remain the main source of energy for power generation and transportation in next decades, their combustion processes remain an important concern for the foreseeable future. For liquid or gaseous fuels, flame velocity that propagates normal to itself and relative to the flow into the unburned mixture is one of the most important quantities to study. In a non-uniform flow, a curved flame front area changes continually which is known as flame stretch. The concept becomes more important when it is realized that the stretch affects the turbulent flame speed.

The current research empirically studies flame stretch under engine-like conditions since there has not been enough experimental studies in this area. For this reason, a one-cylinder, direct-injection, spark-ignition, naturally-aspirated optical engine was utilized to image the flame propagation process inside an internal combustion engine cylinder on the tumble plane. The flame front was found by processing high speed images which were taken from the flame inside the cylinder.

Flame front propagation analysis showed that after the flame kernel was developed, during flame propagation period, the stretch rate decreased until the flame front touches the piston surface. This trend was common among stoichiometric, lean, and rich mixtures. In addition, the fuel-air mixture with λ = 0.85 showed lower stretch rate compared to stoichiometric or lean mixture with λ = 1.2. However, based on previous studies, further enrichment may result in the flame stretch rate become greater than that of the stretch rates for stoichiometric or lean mixtures. Also, comparing the stretch rate at two different engine speeds revealed that as the speed increased the stretch rate also increased; especially during the early flame development period. Therefore, according to previous studies which discussed flame stretch as a mechanism for flame extinguishment, the probability of the flame extinction is higher when the engine speed is higher.

Topics: Engines , Flames
Commentary by Dr. Valentin Fuster
2017;():V001T03A016. doi:10.1115/ICEF2017-3653.

Conventional Navy jet fuel ‘5’ (JP-5) was operated in a Waukesha single cylinder diesel Cooperative Fuels Research (CFR) engine with intake port jet fuel injection under a range of compression ratios (CR). At the lowest CR of 12, a small range of engine loads in the lower torque or gross indicated mean effective pressure (gIMEP) range could be attained. As the engine CR was increased only a very limited range of loads were attained since heavy engine ‘knocking’ occurred. Navy jet fuel is a reactive fuel (cetane number 46), and thus could not tolerate higher CRs without premature combustion. Intake port water injection was then applied in order to cool the intake air charge and delay the jet fuel HCCI start of combustion. As a result, a range of HCCI operation (gIMEP from 1 to 5 bar) could be attained across a range of CRs. In general, with this approach, combustion phasing with port fuel and water injection advanced with increasing CR resulting in lower efficiencies at the higher CRs. Exhaust carbon monoxide (CO) was minimum in mid-HCCI operating range suggesting a trade-off of poor light load lean combustion, and the steadily diluted higher load operation with increasing water content. Companion analysis suggests that the thermal energy for water evaporation was principally provided by the engine walls. Further, the dilution effect of the water resulted in lower overall charge temperatures which further lowered the overall reactivity of jet fuel in the engine allowing reasonable HCCI operation.

Commentary by Dr. Valentin Fuster
2017;():V001T03A017. doi:10.1115/ICEF2017-3657.

With the advancement of spark ignition engines, lean or diluted in-cylinder charge is often used to improve the engine performance. Enhanced in-cylinder charge motion is widely applied under such conditions to promote the flame propagation, which raise challenges for the spark ignition system. In this work, the spark discharging process is investigated under different flow conditions via both optical diagnosis and electrical measurement. Results show that the spark plasma channel is stretched under flow conditions. A higher discharge current can maintain the stretched spark plasma for a longer duration. Re-strikes are observed when the spark plasma is stretched to a certain extent. The frequency of re-strikes increases with increased flow velocity and decreased discharge current level. The discharge duration reduces with the increased flow velocity. The effects of gas flow on the ignition and flame kernel development are studied in a constant volume optical combustion chamber with premixed lean and stoichiometric methane air mixture. Two spark strategies with low and high discharge current are used for the ignition. The flame propagation speed of both lean and stoichiometric mixtures increases with the increased gas flow velocity. A higher discharge current level retains a more stable spark channel and improves the flame kernel development for both lean and stoichiometric conditions, especially under the higher gas flow velocity of 20 m/s.

Topics: Flow (Dynamics)
Commentary by Dr. Valentin Fuster
2017;():V001T03A018. doi:10.1115/ICEF2017-3661.

The present paper represents a small piece of an extensive experimental effort investigating the dual-fuel operation of a light-duty spark ignited engine. Natural gas (NG) was directly injected into the cylinder and gasoline was injected into the intake-port. Direct injection of NG was used in order to overcome the power density loss usually experienced with NG port-fuel injection as it allows an injection after intake valve closing. Having two separate fuel systems allows for a continuum of in-cylinder blend levels from pure gasoline to pure NG operation. The huge benefit of gasoline is its availability and energy density, whereas NG allows efficient operation at high load due to improved combustion phasing enabled by its higher knock resistance. Furthermore, using NG allowed a reduction of carbon dioxide emissions across the entire engine map due to the higher hydrogen-to-carbon ratio. Exhaust gas recirculation (EGR) was used to (a) increase efficiency at low and part-load operation and (b) reduce the propensity of knock at higher compression ratios (CR) thereby enabling blend levels with greater amount of gasoline across a wider operating range. Two integral engine parameters, CR and in-cylinder turbulence levels, were varied in order to study their influence on efficiency, emissions and performance over a specific speed and load range. Increasing the CR from 10.5 to 14.5 allowed an absolute increase in indicated thermal efficiency of more than 3% for 75% NG (25% gasoline) operation at 8 bar net indicated mean effective pressure and 2500 RPM. However, as anticipated, the achievable peak load at CR 14.5 with 100% gasoline was greatly reduced due to its lower knock resistance. The in-cylinder turbulence level was varied by means of tumble plates as well as an insert for the NG injector that guides the injection “spray” to augment the tumble motion. The usage of tumble plates showed a significant increase in EGR dilution tolerance for pure gasoline operation, however, no such impact was found for blended operation of gasoline and NG.

Commentary by Dr. Valentin Fuster
2017;():V001T03A019. doi:10.1115/ICEF2017-3662.

Homogeneous Charge Compression Ignition (HCCI) combustion has the potential for high efficiency with very low levels of NOx and soot emissions. However, HCCI has thus far only been achievable in a laboratory setting due to the following challenges: 1) there is a lack of control over the start and rate of combustion, and 2) there is a very limited and narrow operating range. In the present work, the injection of water directly into the combustion chamber was investigated to solve the aforementioned limitations of HCCI. This new advanced combustion mode is called Thermally Stratified Compression Ignition (TSCI).

A 3-D CFD model was developed using CONVERGE CFD coupled with detailed chemical kinetics to gain a better understanding of the underlying phenomena of the water injection event in a homogeneous, low temperature combustion strategy. The CFD model was first validated against previously collected experimental data. The model was then used to simulate TSCI combustion and the results indicate that injecting water into the combustion chamber decreases the overall unburned gas temperature and increases the level of thermal stratification prior to ignition. The increased thermal stratification results in a decreased rate of combustion, thereby providing control over its rate. The results show that the peak pressure and gross heat release rate decrease by 37.8% and 83.2%, respectively, when 6.7 mg of water were injected per cycle at a pressure of 160 bar. Finally, different spray patterns were simulated to observe their effect on the level of thermal stratification prior to ignition. The results show that symmetric patterns with more nozzle holes were generally more effective at increasing thermal stratification.

Commentary by Dr. Valentin Fuster
2017;():V001T03A020. doi:10.1115/ICEF2017-3668.

Mixed mode combustion strategies have shown great potential to achieve high load operation but soot emissions were found to be problematic. A recent study investigating soot emissions in such strategies showed that delaying the load extension injection sufficiently late after the primary heat release makes the soot production dependent solely on the temperature field inside the combustion chamber and eliminates any dependence on mixing time and oxygen availability. The current study focuses on furthering this research to identify a feasible operating space to operate in and enable high load operation with this mixed mode combustion strategy.

A PCI combustion event was achieved using a premixed charge of gasoline (early cycle injection) and a load extension injection of gasoline was added near top dead center. CFD modeling considering polycyclic aromatic hydrocarbon (PAH) chemistry up to pyrene was used to perform a full factorial design of experiments (DOE) to study the effects of premixed fuel fraction (fraction of total fuel that is premixed), load extension injection timing and exhaust gas recirculation (EGR). The early injection timings for EGR rates less than 40% showed a soot-NOx tradeoff which constrained operating with SOI timings before TDC. The late injection timings showed reductions in soot and NOx at the expense of gross indicated efficiency (GIE). GIE increased with increasing premixed fuel until the premixed fuel quantity reached 80% of the total fuel mass. Premixed fuel quantities higher than 80% resulted in an efficiency penalty due to increased wall heat transfer losses resulting from early combustion phasing. However, at premixed fuel quantities close to 80%, the peak pressure rise rate became the dominating constraint. This confined the feasible operating space to a premix fuel mass range of 70% to 80%. For this premix fuel mass range, the feasible operating space had two regions; one in the early SOI regime before TDC at EGR rates higher than 38% and the other in the late SOI regime (SOI > 15° ATDC) across the entire EGR space. The study was repeated by splitting the premixed fuel into an early cycle injection and a stratified injection with SOI timing of −70° ATDC. The ratio of fuel in the two injections was varied in the DOE. The results showed that adding a stratified injection increases the ignition delay due to in-cylinder equivalence ratio stratification and relaxes the pressure rise rate effect on the operating space. This allows operation at high premix fuel quantities of 70% and higher with EGR rates less than 40% which yields significant increase in GIE. It was also identified that by targeting the fuel from the stratified injection into the squish region, there is improved oxygen availability in the bowl for the load extension injection, which results in the reduction of soot emissions. This allows the load extension injection to be brought closer to TDC while meeting the soot constraint, which further improves the GIE. Finally, the results from the study were used to demonstrate high load operation at 20 bar and 1300 rpm.

Topics: Combustion , Stress
Commentary by Dr. Valentin Fuster
2017;():V001T03A021. doi:10.1115/ICEF2017-3669.

Increasingly restrictive limits on NOx levels are driving the change from lean-burn to stoichiometric combustion strategies on heavy-duty on-highway natural gas engines in order to take advantage of inexpensive and effective three-way catalyst technology. The change to stoichiometric combustion has led to increased tendency for engine knock due to higher in-cylinder temperatures. Exhaust Gas Recirculation (EGR) has been proposed as a method to suppress knock via charge dilution while maintaining a stoichiometric air-fuel ratio. Two of the more common EGR driving architectures and the challenges associated with each architecture are described.

A series of engine tests were devised and performed on a 7-liter heavy-duty natural gas engine to explore the relationships between EGR knock suppression and engine backpressure. A unique concept for an external EGR pumping cart which allowed for the exploration of higher EGR rates independent of backpressure is also described. Results showed that for the conditions tested, increasing EGR rates beyond a certain point did not result in decreased knock tendency. 1D Simulation showed that the effectiveness of the EGR is limited by trapped hot residual gasses which resulted in higher in-cylinder temperatures and nullified the cooling effects of the EGR. These results suggest that attention must be paid to reducing backpressure via efficient EGR system architecture design in order to achieve the highest possible efficiency.

Commentary by Dr. Valentin Fuster
2017;():V001T03A022. doi:10.1115/ICEF2017-3671.

Jet-A was investigated in RCCI (Reactivity Controlled Compression Ignition) given that the fuel is readily available and has a similar cetane number compared to ultra-low sulfur diesel (ULSD#2). To promote emissions’ control, RCCI was conducted with direct injection (DI) of Jet-A and PFI (port fuel injection) of n-butanol. Combustion and emission characteristics of Jet-A RCCI were investigated for a medium duty DI experimental engine operated at constant boost and 30% EGR rate and compared to ULSD#2 RCCI and single-fuel ULSD#2 operation. DI fuel was injected at 5 CAD ATDC and constant rail pressure of 1500 bar. A 20% pilot by mass was added and investigated at timings from 15 to 5 CAD BTDC for combustion stability. The results showed that the effect of the pilot injection on Jet-A combustion was not as prominent as compared to that of ULSD#2, suggesting a slightly different spray and mixture formation. Ignition delay for Jet-A was 15–20% shorter compared to ULSD#2 in RCCI. When the pilot was set to 5 CAD BTDC, CA50 phased for ULSD#2 RCCI by 3 CAD later when compared to Jet-A RCCI. After TDC, the local pressure maximum for ULSD#2 RCCI decreased by 3 bar, resulting from a 15% difference in peak heat release rate between ULSD#2 and Jet-A in RCCI at the same pilot timing. NOx and soot levels were reduced by a respective maximum of 35% and 80% simultaneously in Jet-A RCCI mode compared to single-fuel ULSD#2, yet, were higher compared to ULSD#2 RCCI. Ringing intensity was maintained at similar levels and energy specific fuel consumption (ESFC) improved by at least 15% for Jet-A compared to ULSD#2 in RCCI. Mechanical efficiencies additionally improved at earlier pilot timing by 2%. In summary, Jet-A RCCI allowed for emissions control and increased fuel efficiencies compared to single fuel ULSD#2, however, injection should be further tweaked in order to reach lower soot levels.

Topics: Combustion , Emissions
Commentary by Dr. Valentin Fuster
2017;():V001T03A023. doi:10.1115/ICEF2017-3676.

Homogeneous Charge Compression Ignition (HCCI) has been considered as an ideal combustion mode for compression ignition engines due to its superb thermal efficiency and low emissions of nitrogen oxides (NOx) and particulate matter (PM). However, a challenge that limits practical applications of HCCI is the lack of control over the combustion rate, which either deteriorates thermal efficiency at low engine load, or produces excessive pressure rise rate and combustion noise at high engine load. Fuel stratification and partially premixed combustion (PPC) have considerably improved the control over the heat release profile with modulations of the ratio between premixed fuel and directly injected fuel, as well as injection timing for ignition initiation. It leverages the advantages of both conventional direct injection compression ignition and HCCI. Compared with those of HCCI, the ignition ability and combustion efficiency of PPC are significantly enhanced at low engine load, and the low emissions of NOx and PM are maintained with lower pressure rise rate. In this study, neat n-butanol is employed to generate the fuel stratification and partially premixed combustion in a single cylinder compression ignition engine. A fuel such as n-butanol can provide additional benefits of even lower emissions, and can potentially lead to a reduced carbon footprint and improved energy security if produced appropriately from biomass sources. Intake port fuel injection (PFI) of neat n-butanol is used for the delivery of the premixed fuel, while the direct injection (DI) of neat n-butanol is applied to generate the fuel stratification. Effects of PFI-DI fuel ratio, DI timing, and intake pressure, on the combustion, are studied in detail. Different conditions are identified at which clean and efficient combustion can be achieved at a baseline load of 6 bar IMEP. An extended load of 14 bar IMEP is demonstrated using stratified combustion with combustion phasing control.

Commentary by Dr. Valentin Fuster
2017;():V001T03A024. doi:10.1115/ICEF2017-3683.

Dual fuel combustion has garnered attention in recent years because of its potential for reducing emissions of oxides of nitrogen (NOx) and particulate matter (PM) while sustaining diesel-like fuel conversion efficiencies. However, most dual fuel combustion strategies suffer from higher engine-out hydrocarbon (HC) and carbon monoxide (CO) emissions, leading to poor combustion efficiencies, especially at low loads. The present work examined computationally the effect of in-cylinder swirl on diesel-ignited methane dual fuel combustion with a focus on devising strategies for improving part-load combustion efficiencies. For this purpose, diesel-methane dual fuel combustion was studied on a heavy-duty single cylinder research engine (SCRE) platform using CONVERGE computational fluid dynamics (CFD) software. A typical low load condition (IMEP = 5.1 bar) was selected at an engine speed of 1500 rpm and a relatively high methane percentage energy substitution (PES) of 80 percent (because experiments show poorer combustion efficiencies at high methane PES) at a nominal diesel injection timing of 2 degrees BTDC (358 CAD). The closed cycle simulation was first validated with experimental results (cylinder pressure and heat release histories as well as engine-out exhaust emissions) for neat diesel and diesel-methane dual fuel combustion, respectively. Subsequently, the influence of increasing swirl ratio from 0 to 1.5 on diesel-methane dual fuel combustion was characterized. Analysis of the computational results showed that peak cylinder pressure and heat release rate increased with increasing swirl ratio while the combustion duration (as determined by CA10-80) decreases from 25 CAD at a swirl ratio of 0.05 to nearly 15 CAD at a swirl ratio of 1.5. Indicated-specific hydrocarbon (ISHC) and indicated-specific carbon monoxide (ISCO) emissions decreased by about 60 percent and 50 percent, respectively, when swirl ratio was increased from 0.05 to 1.2; however, these reductions were accompanied by a 26 percent increase in indicated-specific NOx (ISNOx) emissions under these conditions. Therefore, the present study indicates that swirl optimization is a potentially viable strategy for reducing engine-out HC and CO emissions and for improving low-load combustion efficiencies in dual fuel engines, assuming additional NOx mitigation strategies are also employed simultaneously.

Commentary by Dr. Valentin Fuster
2017;():V001T03A025. doi:10.1115/ICEF2017-3696.

The design and development of high efficiency spark-ignition engines continues to be limited by the consideration of knock. Although the topic of spark knock has been the subject of comprehensive research since the early 1900s, little has been reported on the coupling of the engine thermodynamics and knock. This work uses an engine cycle simulation together with a sub-model for the knock phenomena to explore these connections. First, the autoignition characteristics as represented by a recent (2014) Arrhenius expression for the reaction time of the end gases is examined for a range of temperatures and pressures. In spite of the exponential dependence on temperature, pressure appears to dominate the ignition time for the conditions examined. Higher pressures (and higher temperatures) tend to enhance the potential for knock.

Second, knock is determined as functions of engine design and operating parameters. The trends are consistent with expectations, and the results provide a systematic presentation of knock occurrence. Engine parameters explored include compression ratio, engine speed, inlet pressure, start of combustion, heat transfer, and exhaust gas recirculation (EGR). Changes of cylinder pressures and temperatures of the unburned zone as engine parameters were varied are shown to be directly responsible for the changes of the knock characteristics.

Topics: Engines , Simulation , Cycles
Commentary by Dr. Valentin Fuster

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