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ASME Conference Presenter Attendance Policy and Archival Proceedings

2017;():V002T00A001. doi:10.1115/ICEF2017-NS2.
FREE TO VIEW

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presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.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

Emissions Control Systems

2017;():V002T04A001. doi:10.1115/ICEF2017-3537.

The catalytic generation of ammonia from a liquid urea solution is a critical process determining the performance of SCR (Selective Catalytic Reduction) systems. Solid deposits on the catalyst surface from the decomposition of urea have to be avoided, as this leads to reduced system performance or even failure. At present, reactor design is often empirical, which poses a risk for costly iterations due to insufficient system performance. The presented research project proposed a performance prediction and modelling approach for SCR hydrolysis reactors generating ammonia from urea. Different configurations of hydrolysis reactors were investigated experimentally. Ammonia concentration measurements provided information about parameters influencing the decomposition of urea and the system performance. The evaporation of urea between injection and interaction with the catalyst was identified as the critical process driving the susceptibility to deposit formation. The spray of urea solution was characterised in terms of velocity distribution by means of particle-image velocimetry. Results were compared with theoretical predictions and calculation options for processes in the reactor were determined. Numerical simulation was used as an additional design and optimisation tool of the proposed model. The modelling approach is presented by a step-by-step method which takes into account design constraints and operating conditions for hydrolysis reactors.

Topics: Modeling
Commentary by Dr. Valentin Fuster
2017;():V002T04A002. doi:10.1115/ICEF2017-3550.

Due to current and future exhaust emissions regulations, oxidation catalysts are increasingly being added to the exhaust streams of large-bore, 2-stroke, natural gas engines. Such catalysts have been found to have a limited operational lifetime, primarily due to chemical (i.e. catalyst poisoning) and mechanical fouling resulting from the carry-over of lubrication oil from the cylinders. It is critical for users and catalyst developers to understand the nature and rate of catalyst deactivation under these circumstances. This study examines the degradation of an exhaust oxidation catalyst on a large-bore, 2-stroke, lean-burn, natural gas field engine over the course of 2 years. Specifically this work examines the process by which the catalyst was aged and tested and presents a timeline of catalyst degradation under commercially relevant circumstances. The catalyst was aged in the field for 2 month intervals in the exhaust slipstream of a GMVH-12 engine and intermittently brought back to the Colorado State Engines and Energy Conversion Laboratory for both engine testing and catalyst surface analysis. Engine testing consisted of measuring catalyst reduction efficiency as a function of temperature as well as the determination of the light-off temperature for several exhaust components. The catalyst surface was analyzed via SEM/EDS and XPS techniques to examine the location and rate of poison deposition. After 2 years on-line the catalyst light-off temperature had increased ∼55°F (31°C) and ∼34 wt% poisons (S, P, Zn) were built up on the catalyst surface, both of which represent significant catalyst deactivation.

Commentary by Dr. Valentin Fuster
2017;():V002T04A003. doi:10.1115/ICEF2017-3572.

Motivated by increasingly strict NOx limits, engine manufactures have adopted selective catalytic reduction (SCR) technology to reduce engine-out NOx below mandated levels. In the SCR process, nitrogen oxides (NOx) react with ammonia (NH3) to form nitrogen and water vapor. The reaction is influenced by several variables, including stored ammonia on the catalyst, exhaust gas composition, and catalyst temperature. Currently, measurements from NOx and/or NH3 sensors upstream and downstream of the SCR are used with predictive models to estimate ammonia storage levels on the catalyst and control urea dosing.

This study investigated a radio frequency (RF) -based method to directly monitor the ammonia storage state of the SCR catalyst. This approach utilizes the SCR catalyst as a cavity resonator, in which an RF antenna excites electromagnetic waves within the cavity to monitor changes in the catalyst state. A mmonia storage causes changes in the dielectric properties of the catalyst, which directly impacts the RF signal. Changes in the RF signal relative to stored a mmonia (NH3) were evaluated over a wide frequency range as well as temperature and exhaust conditions. The RF response to NH3 storage, desorption, and oxidation on the SCR was observed to be well-correlated with changes in the catalyst state. Calibrated RF measurements demonstrate the ability to monitor the adsorption state of the SCR to within 10 % of the sensor full scale. The results indicate direct measurement of SCR ammonia storage levels, and resulting catalyst feedback control, via RF sensing to have significant potential for optimizing the SCR system to improve NOx conversion and decrease urea consumption.

Topics: Catalysts , Storage
Commentary by Dr. Valentin Fuster
2017;():V002T04A004. doi:10.1115/ICEF2017-3640.

In this work, engine-out particulate matter (PM) mass emissions from an off-highway diesel engine measured using a low-cost photometer, scanning mobility particle sizer, elemental versus organic carbon analysis, and a photo-acoustic analyzer are compared. Tested engine operating modes spanned the range of those known to result in high semi-volatile particle concentration and those that emit primarily solid particles. Photometer measurements were taken following a primary dilution stage and a sample conditioner to control relative humidity prior to the instrument. Results of the study show that the photometer could qualitatively track total particle mass trends over the tested engine conditions though it was not accurate in measuring total carbon mass concentration. Further, the required photometric calibration factor (PCF) required to accurately measure total PM mass changes with the organic carbon (OC) fraction of the particles. Variables that influence PCF include particle effective density, which changes both as a function of particle diameter and OC fraction. Differences in refractive index between semi-volatile and solid particles are also significant and contribute to high error associated with measurement of total PM using the photometer. This work illustrates that it may be too difficult to accurately measure total engine PM mass with a photometer without knowing additional information about the sampled particles. However, removing semi-volatile organic materials prior to the instrument may allow the accurate estimation of elemental carbon mass concentration alone.

Commentary by Dr. Valentin Fuster
2017;():V002T04A005. doi:10.1115/ICEF2017-3658.

Environmental regulations have put stringent requirements on NOx emissions in the transportation industry, essentially requiring the use of exhaust after-treatment on diesel fueled light and heavy-duty vehicles. Urea-Water-Solution (UWS) based Selective Catalytic Reduction (SCR) for NOx is one the most widely adopted methods for achieving these NOx emissions requirements. Improved understanding and optimization of SCR after-treatment systems is therefore vital, and numerical investigations can be employed to facilitate this process. For this purpose, detailed and numerically accurate models are desired for in-cylinder combustion and exhaust after-treatment. The present paper reports on 3-D numerical modeling of the Urea-Water-Solution SCR system using Computational Fluid Dynamics (CFD). The entire process of Urea injection, evaporation, NH3 formation and NOx reduction is numerically investigated. The simulation makes use of a detailed kinetic surface chemistry mechanism to describe the catalytic reactions. A multi-component spray model is applied to account for the urea evaporation and decomposition process. The CFD approach also employs an automatic meshing technique using Adaptive Mesh Refinement (AMR) to refine the mesh in regions of high gradients. The detailed surface chemistry NOx reduction mechanism validated by Olsson et al. (2008) is applied in the SCR region. The simulations are run using both transient and steady-state CFD solvers. While transient simulations are necessary to reveal sufficient details to simulate catalytic oxidation during transient engine processes or under cyclic variations, the steady-state solver offers fast and accurate emission solutions. The simulation results are compared to available experimental data, and good agreement between experimental data and model results is observed.

Commentary by Dr. Valentin Fuster

Instrumentation, Controls, and Hybrids

2017;():V002T05A001. doi:10.1115/ICEF2017-3521.

Electrically-assisted engine boosting systems lend themselves to better throttle response, wider effective operating ranges, and can provide the ability to extract excess energy during deceleration and high-load events (and store it in a vehicle’s onboard batteries). This can lead to better overall vehicle performance, emissions, and efficiency while allowing for further engine downsizing and increased power density.

In this research effort, a hybrid-electric turbocharger, variable-frequency drive (VFD), and novel sensorless control algorithm were developed. An 11kW permanent-magnet machine was coupled to a commercial turbocharger via an in-line, bolt-on housing attached to the compressor inlet. A high-efficiency, high-temperature variable-frequency drive, consisting of custom control and power electronics, was also developed. The variable-frequency drive uses SiC MOSFETS to achieve high-switching frequency and can be cooled using an existing engine coolant loop operating at up to 105 °C at an efficiency greater than 98%. A digital sliding mode-observer (DSMO) sensorless speed control algorithm was created to command and regulate speed and achieved ramp rates of over 68,000 rpm/sec.

A two-machine benchtop motor/generator test stand was constructed for initial testing and tuning of the VFD and sensorless control algorithm. A gas blow-down test stand was constructed to test the mechanical operation of the hybrid-electric turbocharger and speed control using the VFD. In addition, a liquid-pump cart was assembled for high-temperature testing of the VFD. Initial on-engine testing is planned for later this year. This paper intends to present a design overview of the in-line, hybrid-electric device, VFD, and performance characterization of the electronics and sensorless control algorithm.

Commentary by Dr. Valentin Fuster
2017;():V002T05A002. doi:10.1115/ICEF2017-3526.

This research study focuses on determining optimal points of operation for the engine-generator system and regenerative braking at the wheels in a plug-in series hybrid electric Chevrolet Camaro. The goal is to improve overall fuel economy of the vehicle as well as reducing overall tail-pipe emissions. An abstract mathematical model of the series hybrid electric Chevrolet Camaro is being used to simulate the overall energy consumption of the vehicle. Previously tested and published control algorithms and strategies are studied, discussed and a viable scheme is chosen for optimization. The results from the optimal strategy considered are compared against the unoptimized results. An improvement of ∼ 8.9% in fuel economy and ∼ 8.2% reduction in tail-pipe emissions is estimated.

Commentary by Dr. Valentin Fuster
2017;():V002T05A003. doi:10.1115/ICEF2017-3534.

Electric turbochargers offer an additional degree of freedom in engine design to meet the conflicting needs of emissions, fuel consumption and performance targets. This paper presents a simulation study of the application of a mechanically decoupled electric turbocharger to a 2.0L Gasoline engine. The aim of this work is to investigate and quantify how the sizing of the turbine influences performance and efficiency both in steady state and over homologation and on-road duty cycles. Steady state simulations are performed in a GT Power 1D gas dynamics model that includes a simplified model of the electric turbocharger. The 1D model was used to create a mean value engine model for the drive cycle simulations. The turbine diameter was varied from 58mm to 78mm (representing 50%–150% of the baseline turbine size). In steady state conditions, the electric turbocharger achieved a maximum of 1.5% improvement in system efficiency. Larger turbines can improve efficiency by reducing the engine pumping loss, however, they compromise the amount of electrical energy that can be harvested in the low engine speed region. This is problematic as this represents a key area of engine operation in a passenger vehicle. A series of mean value engine models were created for different sized turbines to predict BMEP, turbine power generation and overall system efficiency — these were used to evaluate performance over key duty cycles. The mechanically-decoupled electric turbocharger can generate up to 0.38kW average power in the real road driving simulation which can greatly increase the engine fuel economy. In NEDC and WLTP cycles, the e-turbo system can always generate energy and store it into battery (0.21kW and 0.23kW average power in the whole cycle respectively). In several real road driving tests, the energy consumption of the compressor exceeds that of the turbine due to significant running in the low speed/high torque region (A 0.04kW in specific on-road cycle simulation). The sensitivity of these results to vehicle gear ratios and electrical system efficiency is also presented.

Commentary by Dr. Valentin Fuster
2017;():V002T05A004. doi:10.1115/ICEF2017-3555.

This paper is one of the first publications documenting the performance optimization of a port fuel injected, spark ignited, internal combustion engine for an unmanned aerial vehicle hybrid powertrain. An optimized hybrid powertrain enables long-duration quadcopter flight and provides vertical takeoff and landing capability for fixed-wing aircraft. This technology can improve flight times and lessen runway requirements, helping to solve two of the biggest problems faced by the booming UAV industry.

The main activities contributing to this hybrid powertrain effort are the development of a small engine test facility, design of powertrain vehicle integration hardware, and the testing and characterization of both electric motor-generators and fuel-injected two-stroke engines. This paper investigates engine testing completed to date including experimental setup, testing procedures, data post processing, and results.

Commentary by Dr. Valentin Fuster
2017;():V002T05A005. doi:10.1115/ICEF2017-3568.

Diesel engine control strategies use complex injection patterns which are designed to meet the increasing request for engine-out emissions and fuel consumption reduction. As a result of the large number of tuneable injection parameters in modern injection systems (such as start and duration of each injection), injection patterns can be designed with many degrees of freedom. Each variation of the injection parameters modifies the whole combustion process and, consequently, engine-out emissions.

Aging of the injection system usually affects injection location within the cycle as well as the amount of injected fuel (compared to the target value), especially for small pre-injections. Since Diesel combustion is very sensitive to injection pattern variations, aging of injectors strongly affects engine behavior, both in terms of efficiency and pollutant emissions production. Moreover, such variations greatly affect other quantities related to the effectiveness of the combustion process, such as noise radiated by the engine.

This work analyses the effects of pre-injection variations on combustion, pollutant emissions and noise radiated by the engine. In particular, several experimental tests were run on a 1.3L Common Rail Diesel engine varying the amount of fuel injected in pre-injections. Torque delivered by the engine and center of combustion (MFB50) were kept constant using a specifically designed closed-loop combustion controller. During the tests, noise radiated by the engine was measured by properly processing the signal coming from a microphone faced to the engine block. The investigation of the correlation between the combustion process and engine noise can be used to set up a closed-loop algorithm for detecting and recentering injectors’ drifts over time.

Commentary by Dr. Valentin Fuster
2017;():V002T05A006. doi:10.1115/ICEF2017-3672.

A novel decentralized control architecture is developed based on a feedback from the pressure difference across the engine which is responsible for the pumping losses and the Exhaust Gas Recirculation (EGR) flow in diesel engines. The controller is supplemented with another feedback loop based on NOx emissions measurement. Aiming for simple design and tuning, the two control loops are designed and discussed; one manipulates the Variable Geometry Turbine (VGT) actuator and the other manipulates the EGR valve. An experimentally validated mean-value diesel engine model is used to analyze the best pairing of actuators and set points. Emphasis is given to the robustness of this pairing based on gain changes across the entire operating region, since swapping the pairing needs to be avoided. The VGT loop is designed to achieve fast cylinder air charge increase in response to a rapid pedal tip-in by a feedforward term based on the real-time derivative of the desired boost pressure. The EGR loop relies on a feedback measurement from a NOx sensor and a real-time estimation of cylinder oxygen ratio, χcyl. The engine model is used for evaluating the designed controllers over the federal test procedure (FTP) for heavy duty vehicles. Results indicate that the control system meets all targets, namely fast air charge and χcyl control during torque transients, robust NOx control during steady state operation and controlled pumping losses in all conditions.

Commentary by Dr. Valentin Fuster
2017;():V002T05A007. doi:10.1115/ICEF2017-3679.

At a given speed and load, the spark advance (SA) is tuned to reach the maximum break torque (MBT) timing to maximize efficiency. The use of exhaust gas recirculation (EGR) can further improve fuel economy at the same speed and load. As EGR increases, MBT moves towards a more advanced timing that can be limited by the high variability in the combustion process, reflected in unacceptable torque fluctuations. This variability is rapidly increased by the random occurrence of partial burns and/or misfires. In order to operate close to the misfire limit, a stochastic misfire controller has been designed to momentarily move from an undesired to an allowable misfire rate, without significantly increasing variability in the combustion process. Control-oriented models for the combustion process and misfire events are discussed. Simulation of the closed-loop system shows that the feedback misfire controller, on average, stays closer to the misfire limit than a more conventional controller designed to react when a misfire is detected.

Topics: Combustion , Cycles , Feedback
Commentary by Dr. Valentin Fuster

Numerical Simulation

2017;():V002T06A001. doi:10.1115/ICEF2017-3527.

In an earlier publication [1] the authors compared numerical predictions of the mean cylinder pressure of diesel and dual-fuel combustion, to that of measured pressure data from a medium-speed, large-bore engine. In these earlier comparisons, measured data from a flush-mounted in-cylinder pressure transducer showed notable and repeatable pressure oscillations which were not evident in the mean cylinder pressure predictions from CFD. In this paper, the authors present a methodology for predicting and reporting the local cylinder pressure consistent with that of a measurement location. Such predictions for large-bore, medium-speed engine operation demonstrate pressure oscillations in accordance with those measured. The temporal occurrences of notable pressure oscillations were during the start of combustion and around the time of maximum cylinder pressure. With appropriate resolutions in time steps and mesh sizes, the local cell static pressure predicted for the transducer location showed oscillations in both diesel and dual-fuel combustion modes which agreed with those observed in the experimental data. Fast Fourier Transform (FFT) analysis on both experimental and calculated pressure traces revealed that the CFD predictions successfully captured both the amplitude and frequency range of the oscillations. Resolving propagating pressure waves with the smaller time steps and grid sizes necessary to achieve these results required a significant increase in computer resources.

Commentary by Dr. Valentin Fuster
2017;():V002T06A002. doi:10.1115/ICEF2017-3530.

Recent experimental studies on a production heavy-duty diesel engine have shown that gasoline compression ignition (GCI) can operate in both conventional mixing-controlled and low-temperature combustion modes with similar efficiency and lower soot emissions compared to diesel at a given engine-out NOx level. This is primarily due to the high volatility and low aromatic content of high reactivity, light-end fuels. In order to fully realize the potential of GCI in heavy-duty applications, accurate characterization of gasoline sprays for high-pressure fuel injection systems is needed to develop quantitative, three-dimensional computational fluid models that support simulation-led design efforts. In this work, the non-reacting fuel spray of a high reactivity gasoline (research octane number of ∼60, cetane number of ∼34) was modeled under typical heavy-duty diesel engine operating conditions, i.e., high temperature and pressure, in a constant-volume combustion chamber. The modeling results were compared to those of a diesel spray at the same conditions in order to understand their different behaviors due to fuel effects. The model was developed using a Lagrangian-Particle, Eulerian-Fluid approach. Predictions were validated against available experimental data generated at Michigan Technological University for a single-hole injector, and showed very good agreement across a wide range of operating conditions, including ambient pressure (3–10 MPa), temperature (800–1200 K), fuel injection pressure (100–250 MPa), and fuel temperature (327–408 K). Compared to a typical diesel spray, the gasoline spray evaporates much faster, exhibiting a much shorter liquid length and wider dispersion angle which promote gas entrainment and enhance air utilization. For gasoline, the liquid length is not sensitive to different ambient temperatures above 800 K, suggesting that the spray may have reached a “saturated” state where the transfer of energy from the hot gas to liquid has already been maximized. It was found that higher injection pressure is more effective at promoting the evaporation process for diesel than it is for gasoline. In addition, higher ambient pressure leads to a more compact spray and fuel temperature variation only has a minimal effect for both fuels.

Commentary by Dr. Valentin Fuster
2017;():V002T06A003. doi:10.1115/ICEF2017-3533.

In this paper, a multidimensional computational fluid dynamics (CFD) model coupled with detailed chemistry calculations was used to analyze dual-fuel combustion based on high pressure direct injection of natural gas. The main focus was to analyze the capability of predicting pressure curve and heat release rate (HRR) for different injection strategies. Zero-dimensional homogeneous constant volume reactor calculations were used to select a reaction mechanism for the temperature range below 800 K. As the best-performing mechanism, the Chalmers mechanism was chosen. To validate the numerical model, the setup was first split into a single gas injection and a single Diesel injection. They were validated individually using shadowgraphs obtained from a Rapid Compression Expansion Machine (RCEM). Diesel ignition timing and position in the combustion chamber were close to experimental results. Gas direct injection showed good agreement with regard to penetration and mixing. In the dual-fuel setup, the injection timing of natural gas was varied to create a first case with mainly diffusive combustion and a second case with mainly premixed combustion of natural gas. For both setups good agreement with pressure curve and heat release rate were achieved. A qualitative comparison of shadowgraphs with the density field highlights the important points to predict dual-fuel combustion.

Commentary by Dr. Valentin Fuster
2017;():V002T06A004. doi:10.1115/ICEF2017-3538.

The improved fuel economy and low pollutant emissions are highly demanded for internal combustion engines. Gasoline Direct Injection (GDI) engine is the one of promising devices for highly efficient engine. However, GDI engines generally tend to emit more Particulate Matter (PM) than Port Fuel Injection (PFI) engine because the fuel sprayed from the injector can easily attach to the wall, which is the major origin of PM. Therefore, the precise analysis of the fuel/air mixture formation and the prediction of emissions are required. From the view of industrial use, Computational Fluid Dynamics (CFD) becomes a necessary tool for the various analyses including the fuel/air mixture formation, spray attachment on the cylinder wall, the in-cylinder turbulence formation, the combustion and emission etc.

In our previous study, the flow and spray simulation in internal combustion engine has been conducted using OpenFOAM®, the open-source CFD toolbox. Since the engine involves the dynamic motion such as valve and piston, the morphing and mapping approach was employed. Furthermore, by virtue of open-source code, we have developed the methodology of the hybrid simulation from the internal nozzle flow to the fuel/air mixture in order to take into account detailed breakup process nearby injector nozzle.

We expand the above research to the combustion simulation. For the combustion model, the Hyperbolic Tangent Approximation (HTA) model is adopted. The HTA model has a simple form of equation and one can easily implement; moreover, the HTA model has the following features: 1. capability of both laminar and turbulent flow, 2. the clearness of analytical derivation based on the functional approximation of the reaction progress variable distribution in a one-dimensional laminar flame. In the current study, the premixed flame is studied on a gasoline combustion engine. The simulations for in-cylinder engine are conducted with different Air/Fuel (A/F) ratio conditions, and the results are compared with the experimental results. The in-cylinder pressure agrees well with experimental results and the validity of the current methodology is confirmed.

Commentary by Dr. Valentin Fuster
2017;():V002T06A005. doi:10.1115/ICEF2017-3542.

Fuel efficiency is the key buying factor in the non-road diesel engine market, because the engine mainly operates in the high torque region and consumes relatively large amount of fuel in a short term. A compression ratio of diesel engine is deeply related to a thermal efficiency and it is one of the key design parameter influencing on the fuel efficiency. In this paper, the new approach to select compression ratio is described and the design constrains such as in-cylinder max allowable pressure, max allowable temperature at turbine front end and max allowable temperature at compressor back end were considered. The base engine is 3.4 liter non-road diesel engine without EGR (Exhaust Gas Recirculation) system for Stage V emission standards and is originated from the same engine system with EGR system to meet Tier 4 Final emission standards. Its official compression ratio is 17.0. The purpose of this study is to select an optimal compression ratio for non-road diesel engine system with non-EGR system to meet Stage V emission standards. The methodology to be presented in this study is based on the 1-D engine performance simulations, the 3-D CFD (Computational Fluid Dynamics) combustion simulations, and the engine bench test. In these simulations, a compression ratio and a SOI (Start of Injection) were considered for sweeping parameters. With analyzing the results of parameter studies and engine design constraints, an optimal compression ratio is found to be 18.0. As a result of many engine bench tests, a fuel consumption has been improved by 1.5% with new piston bowl of which compression ratio is 18.0, meeting Stage V emission standards.

Commentary by Dr. Valentin Fuster
2017;():V002T06A006. doi:10.1115/ICEF2017-3548.

In this paper, a numerical investigation of the ignition process of dual fuel engines is presented. Optical measurements revealed that a homogeneous natural gas charge ignited by a small diesel pilot comprises the combustion phenomena of compression ignition of the pilot fuel as well as premixed flame propagation. The 3-Zones Extended Coherent Flame Model (ECFM3Z) was selected, since it can treat auto-ignition, pre-mixed flame propagation and diffusion flame aspects. Usually combustion models in multi-dimensional computational fluid dynamics (CFD) software packages are designed to handle only one reactive species representing the fuel concentration. In the context of the ECFM3Z model the concept of a multi-component fuel is applied to dual fuel operation. Since the available ignition models were not able to accurately describe the ignition characteristics of the investigated setup, a new dual fuel auto-ignition model was developed. Ignition delay times of the fuel blend are tabulated using a detailed reaction mechanism for n-heptane. Thereby, the local progress of pre-ignition reactions in the CFD simulation can be calculated. The ignition model is validated against experiments conducted with a periodically chargeable constant volume combustion chamber. The proposed model is capable to reproduce the ignition delay as well as the location of the flame kernels. The CFD simulations show the effect of temperature stratification and variations in the injection pressure on the apparent ignition delay of the micro pilot.

Commentary by Dr. Valentin Fuster
2017;():V002T06A007. doi:10.1115/ICEF2017-3552.

In 2027, the fully phased-in EPA/NHTSA Phase-2 greenhouse gas (GHG) emission legislation for heavy-duty (HD) diesel engines will mandate a 5.1% reduction in fuel consumption for MY2017 tractor engines and a 4.2% reduction in fuel consumption for MY2017 vocational engines. Along with improvements in engine efficiency, manufacturers are likely to face a simultaneous challenge to achieve a significant reduction in tailpipe NOx emissions, as the ARB is expected to implement an ultra-low NOx emission standard in the 2024–27 timeframe. With this consideration, technology solutions for Phase-2 GHG will have to be NOx neutral or provide additional reduction in NOx emissions which is typically contrary to a reduction in fuel consumption.

In this study, various advanced engine technologies — such as engine downsizing and downspeeding, variable compression ratio, cylinder deactivation and turbocompounding — have been evaluated to improve engine efficiency with a goal to reach Phase-2 GHG engine requirements. Simultaneously, the impact of these technologies on engine-out NOx emission and aftertreatment inlet temperature has also been evaluated. The technologies were evaluated with a GT-Power model of a 7.7 liter medium HD diesel engine applied in vocational vehicles at steady-state operating conditions as well as over transient operating profiles. Significant fuel consumption reductions were observed with engine downsizing and engine downspeeding at the same engine-out NOx emissions as the baseline engine. Cylinder deactivation showed a moderate impact on fuel consumption while variable compression ratio and turbocompounding had a much lower impact on fuel consumption. In general, exhaust gas temperatures decreased with a reduction in fuel consumption, except in the case of cylinder deactivation where significant increase in exhaust gas temperatures was observed. The results of the study show that engine efficiency improvements beyond what has been mandated by the Phase-2 GHG regulations are possible without increasing the engine-out NOx emissions of a Phase-1 GHG compliant engine. However, if an ultra-low NOx emission standard is implemented as expected, some of the efficiency gains demonstrated in this study will need to be offset to achieve higher exhaust gas temperatures and lower engine-out NOx emissions.

Commentary by Dr. Valentin Fuster
2017;():V002T06A008. doi:10.1115/ICEF2017-3561.

Accurate and efficient simulation of unsteady turbulent in-cylinder flow process of the piston engine is essential in better understanding the physical process and better designing the cylinder scavenging system. The engineering RANS method is dominated by second order. This paper studies the performance of the high order method in the numerical simulation of the cylinder scavenging under the RANS framework. The current study is with a 2-D setup to simulate tumble flow during the intake process of an SI engine. We adopt the monotonicity preserving(MP) scheme from fifth order (MP5) to up to ninth order (MP9) with SST turbulence model equipped. The simulation results are compared between conventional second order and high order ones with a same resolution of mesh grid. It is shown that the vorticity resolving ability of RANS method can be better improved by using the high order scheme. Different reconstruction variables such as primary variable, conservative variable and characteristic variable can also influence the capturing of these details to a certain extent. For flow processes that do not have strong discontinuities, the use of primary variable reconstruction provides the best simulation precision. In terms of computational efficiency, the high order scheme is comparable to the second order scheme. Therefore, the high order scheme is very applicable in RANS method for the simulation and design purpose of the cylinder.

Commentary by Dr. Valentin Fuster
2017;():V002T06A009. doi:10.1115/ICEF2017-3563.

Large-eddy simulation (LES) of diesel spray and combustion was performed to study its improvement in the simulation of engine in-cylinder dynamics compared to the Reynolds-averaged simulation. For the LES, the dynamic structure approach was used to model the sub-grid turbulence and its interaction with the moving droplets in the spray. A multicomponent vaporization model (MCV) based on the continuous thermodynamics approach and a gamma distribution to describe the distribution of the numerous fuel components, was used to simulate the vaporization of diesel fuel droplets. The MCV model was imbedded into the LES framework in the KIVA-4 program. Using this LES model, a non-evaporative spray in a constant-volume chamber was first simulated. More realistic spray structures and improved agreements in the spray penetration with the experimental data were obtained by the LES compared to a Reynolds-averaged simulation of the same spray. A further simulation of an evaporative diesel spray and the subsequent combustion process using both LES and MCV models was also performed. Improved agreements with the experimental data in the spray structures and soot distributions were also observed using both models.

Commentary by Dr. Valentin Fuster
2017;():V002T06A010. doi:10.1115/ICEF2017-3565.

Numerical study on the combustion chemical reaction of biodiesel fuel for the improvement of compression ignition combustion performance was studied in this work. The constant volume closed homogeneous reactor model was applied, at the same time, analysis conditions were set to 700∼900K of ambient temperature, and 15atm of ambient pressure. Also, the equivalence ratio was changed from 0.5 to 1.4 under the various mixing ratio, respectively. The results of analysis were compared in terms of ignition delay, combustion temperature, combustion pressure, NOx and CO emissions. Also, the total mass and the mass densities of the reactants were compared in the constant volume chamber. It was revealed that the value of ignition delay became shorter and combustion temperature and pressure were increased under the rich combustion conditions (Φ > 1.0). Furthermore, the CO emission was decreased under the lean combustion conditions (1.0 > Φ). Maximum value of NOx emission was observed when the equivalence ratio was 0.8 condition since the nitrogen and oxygen chemical reactions became actively than other cases.

Commentary by Dr. Valentin Fuster
2017;():V002T06A011. doi:10.1115/ICEF2017-3566.

The objective of this study is to investigate the effect of water injection into intake port on the performance of small CI engine. The ECFM-3Z model was applied for the combustion analysis model, and the amount of injected water were varied 10%, 20% and 30% of injected fuel mass. The results of this work were compared in terms of cylinder pressure, rate of heat release (ROHR), and the ISNO and soot emissions. It was found that the cylinder pressure was decreased from 1.2% to 9.2% when the amount of injected water was increased from 10% to 30%. In the results, NO emission significantly decreased from about 24% to about 85% when the amount of injected water increased due to the specific heat and latent heat of water. Considering the test results, the best conditions for the simultaneous reduction of NO and soot is the BTDC 05deg of injection timing and 30% of water injection mass. It can be expected the best IMEP and ISFC characteristics.

Commentary by Dr. Valentin Fuster
2017;():V002T06A012. doi:10.1115/ICEF2017-3583.

One of the attractive alternatives to traditional spark ignition engines is the gasoline compression ignition (GCI) engine technology. Fuels with octane numbers lower than those of market gasolines have been identified as a viable option for GCI engine applications. Their longer ignition delay time characteristics compared to diesel fuel and their similar volatility features compared to gasoline fuels make them interesting to be explored. In this study, we have numerically investigated the effect of different injection timings at part-load conditions using a research octane number (RON) 75 fuel in gasoline compression ignition single cylinder engine. Full cycle GCI computational fluid dynamics (CFD) engine simulations have been successfully performed while changing the start of injection (SOI) timing from −60° to −10° CAD aTDC at 5bar net indicated mean effective pressure (IMEPn). The effect of SOI on mixing, combustion phasing and engine-out emissions is investigated using detailed equivalence ratio-temperature maps. Also, the effects of different rates of exhaust gas recirculation (EGR) on the combustion and emissions characteristics are investigated. Rebreathing valves profiles along with double injection strategies are also examined in the current study. Fuel consumption, soot, nitric oxides (NOx), hydrocarbon (HC) emissions and combustion phasing (CA50) are the targeted parameters throughout this study. Optimum engine parameters to obtain the best combination of the targeted properties were identified.

Commentary by Dr. Valentin Fuster
2017;():V002T06A013. doi:10.1115/ICEF2017-3586.

The automotive industry is subjected to increasing pressure in order to improve fuel efficiency and reduce the CO2 emissions of internal combustion (IC) engines. The power cylinder system (piston, piston ring, and liner) contributes significantly to the friction losses, engine oil consumption and gas leakage called blow-by. The role of cylinder bore shape in engine performance has been the subject of several studies in recent years. High bore distortion must be avoided because it can lead to ring conformability issues, which leads to inadequate sealing resulting in increased blow-by and oil consumption. It also leads to asperity contact between the piston skirt and cylinder bore increasing friction causing abnormally high surface wear. Although bore distortion cannot be eliminated, engine manufacturers strive to contain it within acceptable limits. Therefore, numerical analysis of the power cylinder with physically based mathematical models becomes very essential to the engine and component manufacturer in order to reduce engine development lead time and minimize the number of engine tests.

The integrated ring-pack modeling methodology developed by the authors [1] is used to investigate the piston ring-pack performance. Although the modeling approach can be used for extensive parameter analysis of piston, piston rings and lubrication oil consumption, the influence of the bore distortion on the ring conformability and its impact on blow-by, friction and wear is highlighted in this study. Piston tilting, piston ring twist and surface roughness of the piston ring and liner have been taken into consideration.

Commentary by Dr. Valentin Fuster
2017;():V002T06A014. doi:10.1115/ICEF2017-3588.

The spatial and temporal distribution of fuel and air within the combustion chamber directly influences ignition, combustion and emissions formation in diesel engines. These fuel-air interactions are affected by details of the combustion chamber geometry and fuel injection parameters. This paper investigates the effects of piston bowl geometry and spray targeting on combustion behaviour in a single cylinder diesel engine. Closed cycle computational fluid dynamics simulations are performed on a sector mesh at various load points using the 3 Zones Extended Coherent Flame Model coupled with adaptive mesh refinement. The computational fluid dynamics model is validated experimentally at the baseline conditions at each test point after-which, parametric sweeps of bowl geometry, exhaust gas recirculation rate and nozzle tip protrusion are conducted. Results indicate that appropriately pairing fuel injection strategy and piston geometry is essential.

Commentary by Dr. Valentin Fuster
2017;():V002T06A015. doi:10.1115/ICEF2017-3591.

In spark ignition (SI) engines, high efficiencies are typically obtained near limits of stable operation which may result in high cycle-to-cycle variations (CCV). Traditional computational fluid dynamics (CFD) tools like Reynolds-averaged Navier-Stokes simulations (RANS) may not predict the CCV in engines. Higher fidelity CFD tools like large-eddy simulations (LES) have been shown to capture these CCV. In this paper, LES of a motored transparent combustion chamber (TCC) engine is performed to simulate the CCV introduced during the gas exchange process. A grid convergence study is performed, and it is shown that using a 1 mm in-cylinder grid size leads to similar flowfield statistics as compared to using a 0.5 mm in-cylinder grid size. The phase-averaged mean and root mean square (RMS) flowfields predicted by LES are validated comprehensively using particle image velocimetry (PIV) measurements. The validation is performed for 4 different crank angles, corresponding to the intake, compression, expansion and exhaust strokes, and for three different measurement planes. It is shown that LES is able to accurately predict the mean velocities, whereas the RMS velocity magnitudes are under-predicted. The inaccuracy in the RMS velocities are largest during the intake stroke, whereas good agreement with the measurements is observed during the expansion and exhaust strokes. A similarity index analysis provides a quantitative measure of the number of cycles that are required to be simulated to capture the flowfield statistics. This analysis is applied to both the PIV dataset and CFD dataset. It is shown that approximately 20 cycles are sufficient to obtain converged mean and RMS flowfields from the simulations, whereas the PIV measurements require approximately 40 cycles. Faster convergence for the LES results is because the simulations do not take into account additional uncertainties in the rpm, plenum pressures, boundary temperatures and so on, which are present in the experiments.

Topics: Cycles
Commentary by Dr. Valentin Fuster
2017;():V002T06A016. doi:10.1115/ICEF2017-3596.

The stiffness of large chemistry mechanisms has been proved to be a major hurdle towards predictive engine simulations. As a result, detailed chemistry mechanisms with a few thousand species need to be reduced based on target conditions so that they can be accommodated within the available computational resources. The computational cost of simulations typically increase super-linearly with the number of species and reactions. This work aims to bring detailed chemistry mechanisms within the realm of engine simulations by coupling the framework of unsteady flamelets and fast chemistry solvers. A previously developed Tabulated Flamelet Model (TFM) framework for non-premixed combustion was used in this study. The flamelet solver consists of the traditional operator-splitting scheme with VODE (Variable coefficient ODE solver) and a numerical Jacobian for solving the chemistry. In order to use detailed mechanisms with thousands of species, a new framework with the LSODES (Livermore Solver for ODEs in Sparse form) chemistry solver and an analytical Jacobian was implemented in this work. Results from 1D simulations show that with the new framework, the computational cost is linearly proportional to the number of species in a given chemistry mechanism. As a result, the new framework is 2–3 orders of magnitude faster than the conventional VODE solver for large chemistry mechanisms. This new framework was used to generate unsteady flamelet libraries for n-dodecane using a detailed chemistry mechanism with 2,755 species and 11,173 reactions. The Engine Combustion Network (ECN) Spray A experiments which consist of an igniting n-dodecane spray in turbulent, high-pressure engine conditions are simulated using large eddy simulations (LES) coupled with detailed mechanisms. A grid with 0.06 mm minimum cell size and 22 million peak cell count was implemented. The framework is validated across a range of ambient temperatures against ignition delay and liftoff lengths. Qualitative results from the simulations were compared against experimental OH and CH2O PLIF data. The models are able to capture the spatial and temporal trends in species compared to those observed in the experiments. Quantitative and qualitative comparisons between the predictions of the reduced and detailed mechanisms are presented in detail. The main goal of this study is to demonstrate that detailed reaction mechanisms (∼1000 species) can now be used in engine simulations with a linear increase in computation cost with number of species during the tabulation process and a small increase in the 3D simulation cost.

Commentary by Dr. Valentin Fuster
2017;():V002T06A017. doi:10.1115/ICEF2017-3599.

Knock is a major impediment to achieving higher efficiency in Spark-Ignition (SI) engines. The recent trends of boosting, downsizing and downspeeding have exacerbated this issue by driving engines toward higher power density and higher load duty cycles. Apart from the engine operating conditions, fuel anti-knock quality is a major determinant of the knocking tendency in engines, as quantified by its octane number (ON). The ON of a fuel is based on an octane scale which is defined according to the standard octane rating methods for Research Octane Number (RON) and Motor Octane Number (MON). These tests are performed in a single cylinder Cooperative Fuel Research (CFR) engine. In the present work, a numerical approach was developed based on multidimensional computational fluid dynamics (CFD) to predict knocking combustion in a CFR engine. The G-equation model was employed to track the propagation of the turbulent flame front and a multi-zone model based on temperature and equivalence ratio was used to capture auto-ignition in the endgas ahead of the flame front. Furthermore, a novel methodology was developed wherein a lookup table generated from a chemical kinetic mechanism could be employed to provide laminar flame speed as an input to the G-equation model, instead of using empirical correlations. To account for fuel chemistry effects accurately and lower the computational cost, a compact 121-species primary reference fuel (PRF) skeletal mechanism was developed from a more detailed gasoline surrogate mechanism using the directed relation graph assisted sensitivity analysis (DRGASA) reduction technique. Extensive validation of the skeletal mechanism was performed against experimental data available in the literature for both homogeneous ignition delay and laminar flame speed. The skeletal mechanism was used to generate the lookup tables for laminar flame speed as a function of pressure, temperature and equivalence ratio. The engine CFD model incorporating the skeletal mechanism was employed to perform numerical simulations under RON and MON conditions for different PRFs. Parametric tests were conducted at different compression ratios and the predicted values of critical compression ratio (at knock onset), delineating the boundary between “no knock” and “knock”, were found to be in good agreement with the available experimental data. The virtual CFR engine model was, therefore, demonstrated to be capable of adequately capturing the sensitivity of knock propensity to fuel chemistry.

Commentary by Dr. Valentin Fuster
2017;():V002T06A018. doi:10.1115/ICEF2017-3600.

Cycle-to-cycle variability (CCV) is detrimental to IC engine operation and can lead to partial burn, misfire, and knock. Predicting CCV numerically is extremely challenging due to two key reasons. Firstly, high-fidelity methods such as large eddy simulation (LES) are required to accurately resolve the in-cylinder turbulent flowfield both spatially and temporally. Secondly, CCV is experienced over long timescales and hence the simulations need to be performed for hundreds of consecutive cycles. Ameen et al. (Int. J. Eng. Res., 2017) developed a parallel perturbation model (PPM) approach to dissociate this long time-scale problem into several shorter time-scale problems. The strategy is to perform multiple single-cycle simulations in parallel by effectively perturbing the initial velocity field based on the intensity of the in-cylinder turbulence. This strategy was demonstrated for motored engine and it was shown that the mean and variance of the in-cylinder flowfield was captured reasonably well by this approach. In the present study, this PPM approach is extended to simulate the CCV in a fired port-fuel injected (PFI) spark ignition (SI) engine. Two operating conditions are considered — a medium CCV operating case corresponding to 2500 rpm and 16 bar BMEP and a low CCV case corresponding to 4000 rpm and 12 bar BMEP. The predictions from this approach are also shown to be similar to the consecutive LES cycles. Both the consecutive and PPM LES cycles are observed to under-predict the variability in the early stage of combustion. The parallel approach slightly under-predicts the cyclic variability at all stages of combustion as compared to the consecutive LES cycles. However, it is shown that the parallel approach is able to predict the coefficient of variation (COV) of the in-cylinder pressure and burn rate related parameters with sufficient accuracy, and is also able to predict the qualitative trends in CCV with changing operating conditions. The convergence of the statistics predicted by the PPM approach with respect to the number of consecutive cycles required for each parallel simulation is also investigated. It is shown that this new approach is able to give accurate predictions of the CCV in fired engines in less than one-tenth of the time required for the conventional approach of simulating consecutive engine cycles.

Topics: Engines
Commentary by Dr. Valentin Fuster
2017;():V002T06A019. doi:10.1115/ICEF2017-3603.

The use of Large-eddy Simulations (LES) has increased due to their ability to resolve the turbulent fluctuations of engine flows and capture the resulting cycle-to-cycle variability. One drawback of LES, however, is the requirement to run multiple engine cycles to obtain the necessary cycle statistics for full validation. The standard method to obtain the cycles by running a single simulation through many engine cycles sequentially can take a long time to complete. Recently, a new strategy has been proposed by our research group to reduce the amount of time necessary to simulate the many engine cycles by running individual engine cycle simulations in parallel. With modern large computing systems this has the potential to reduce the amount of time necessary for a full set of simulated engine cycles to finish by up to an order of magnitude. In this paper, the Parallel Perturbation Methodology (PPM) is used to simulate up to 35 engine cycles of an optically accessible, pent-roof Direct-injection Spark-ignition (DISI) engine at two different motored engine operating conditions, one throttled and one un-throttled. Comparisons are made against corresponding sequential-cycle simulations to verify the similarity of results using either methodology. Mean results from the PPM approach are very similar to sequential-cycle results with less than 0.5% difference in pressure and a magnitude structure index (MSI) of 0.95. Differences in cycle-to-cycle variability (CCV) predictions are larger, but close to the statistical uncertainty in the measurement for the number of cycles simulated. PPM LES results were also compared against experimental data. Mean quantities such as pressure or mean velocities were typically matched to within 5–10%. Pressure CCVs were under-predicted, mostly due to the lack of any perturbations in the pressure boundary conditions between cycles. Velocity CCVs for the simulations had the same average magnitude as experiments, but the experimental data showed greater spatial variation in the root-mean-square (RMS). Conversely, circular standard deviation results showed greater repeatability of the flow directionality and swirl vortex positioning than the simulations.

Commentary by Dr. Valentin Fuster
2017;():V002T06A020. doi:10.1115/ICEF2017-3604.

In this work, we have applied a machine learning (ML) technique to provide insights into the underlying causes of cycle-to-cycle variation (CCV) in a gasoline spark-ignited (SI) engine. The analysis was performed on a set of large eddy simulation (LES) calculations of a single cylinder of a four-cylinder port-fueled SI engine. The operating condition studied was stoichiometric, without significant knock, and represents a load of 16 bar brake mean effective pressure (BMEP), at an engine speed of 2500 revolutions per minute. A total of 123 cycles was simulated. Of these, 49 were run in sequence, while 74 were run in a parallel manner. For the parallel approach, each cycle is initialized with its own synthetic turbulent field (through perturbation of the base field) to generate CCV, as part of another work performed by us. In the current work, we post-processed three-dimensional information from all 123 cycles to compute various flame topology and pre-ignition flow-field metrics. We then evaluated correlations between these computed metrics, and peak cylinder pressure (PCP) employing an ML technique called random forest which was used to learn the correlation between PCP, and these flame topology and pre-ignition flow-field metrics. The computed metrics form the inputs to the random forest model developed, and PCP is the predicted output. The random forest model inherently captures the effect of all inputs, as well as interactions between them owing to its decision-tree structure. The goal of this work is to demonstrate (as a first step) that ML models can implicitly learn complex relationships between pre-ignition flow-fields, flame shapes, and the eventual outcome of the cycle (whether a cycle will be a high or a low cycle).

Commentary by Dr. Valentin Fuster
2017;():V002T06A021. doi:10.1115/ICEF2017-3613.

Homogeneous charge is a preferred operation mode of gasoline direct-injection (GDI) engines. However, a limited amount of work exists in the literature for combustion models of this mode of engine operation. Current work describes a model developed and used to study combustion in a GDI engine having early intake fuel injection. The model was validated using experimental data obtained from a 1.6L Ford EcoBoost® four-cylinder engine, tested at the U.S. EPA. The start of combustion was determined from filtered cycle-averaged cylinder pressure measurements, based on the local maximum of third derivative with respect to crank angle. The subsequent heat release, meanwhile, was approximated using a double-Wiebe function, to account for the rapid initial pre-mixed combustion (stage 1) followed by a gradual diffusion-like state of combustion (stage 2) as observed in this GDI engine. A non-linear least-squares optimization was used to determine the tuning variables of Wiebe correlations, resulting in a semi-predictive combustion model. The effectiveness of the semi-predictive combustion model was tested by comparing the experimental in-cylinder pressures with results obtained from a model built using a one-dimensional engine simulation tool, GT-POWER (Gamma Technologies). Model comparisons were made for loads of 60, 120, and 180 N-m at speeds ranging from 1500 to 4500 rpm, in 500 rpm increments. The root-mean-square errors between predicted cylinder pressures and the experimental data were within 2.5% of in-cylinder peak pressure during combustion. The semi-predictive combustion model, verified using the GT-POWER simulation, was further studied to develop a predictive combustion model. The performance of the predictive combustion model was examined by regenerating the experimental cumulative heat release. The heat release analysis developed for the GDI engine was further applied to a dual mode, turbulent jet ignition (DM-TJI) engine. DM-TJI is an advanced combustion technology with a promising potential to extend the thermal efficiency of spark ignition engines with minimal engine-out emissions. The DM-TJI engine was observed to offer a faster burn rate and lower in-cylinder heat transfer when compared to the GDI engine under the same loads and speeds.

Commentary by Dr. Valentin Fuster
2017;():V002T06A022. doi:10.1115/ICEF2017-3618.

This work presents a modeling approach for multidimensional combustion simulations of a highly dilute opposed-piston spark-ignited gasoline engine. Detailed chemical kinetics is used to model combustion with no sub-grid correction for reaction rates based on the turbulent fluctuations of temperature and species mass fractions. Turbulence is modeled using RNG k-ε model and the RANS-length scales resolution is done efficiently by the use of automatic mesh refinement when and where the flow parameter curvature (2nd derivative) is large. The laminar flame is thickened by the RANS viscosity and a constant turbulent Schmidt (Sc) number and a refined mesh (sufficient to resolve the thickened turbulent flame) is used to get accurate predictions of turbulent flame speeds. An accurate chemical kinetics mechanism is required to model flame kinetics and fuel burn rates under the conditions of interest. For practical computational fluid dynamics applications, use of large detailed chemistry mechanisms with 1000s of species is both costly as well as memory intensive. For this reason, skeletal mechanisms with a lower number of species (typically ∼100) reduced under specific operating conditions are often used. In this work, a new primary reference fuel chemical mechanism is developed to better correlate with the laminar flame speed data, relevant for highly dilute engine conditions. Simulations are carried out in a dilute gasoline engine with opposed piston architecture, and results are presented here across various dilution conditions.

Commentary by Dr. Valentin Fuster
2017;():V002T06A023. doi:10.1115/ICEF2017-3623.

Increased Particulate Matter (PM) emissions from Gasoline Direct Injection (GDI) engines compared to conventional Port Fuel Injection (PFI) engines have been raising concerns because of the PM’s detrimental health effects and the stringent emissions regulations. One of the widely accepted hypotheses is that local rich pockets inside the combustion chamber are the primary reason for the increased PM emissions. In this paper, we investigate the effects of injection strategies on the charge composition and local thermodynamic conditions of a light duty GDI engine, and determine their impact on PM emissions. The operation of a 1.6L GDI engine is simulated using a 3-D Computational Fluid Dynamics (CFD) code. Combustion characteristics of a 3-component gasoline surrogate (n-heptane/iso-octane/toluene) are analyzed and the effects of injection timing (300° vs 240° vs 180° BTDC) and injected fuel mass (globally stoichiometric vs fuel rich) are explored at 2000 rpm, 9.5 bar BMEP condition, focusing on the homogeneity of the charge and the formation of the gaseous species that are soot precursors. The results indicate that when the physical time for air/fuel mixing is not long enough, fuel-rich pockets are present until combustion occurs, where high concentrations of soot precursors are found, such as acetylene and pyrene. In addition, simulation results indicate that the location of wetted surface as well as the in-cylinder flow structure induced by the fuel jet hitting the piston bowl is significantly influenced by varying the injection timing, which affects subsequent air/fuel mixing. When the injected fuel mass is increased, the equivalence ratio distribution inside the combustion chamber shifts toward fuel-rich side, generating more mixtures with Φ > 1.5, where formation of acetylene and pyrene are favored.

Commentary by Dr. Valentin Fuster
2017;():V002T06A024. doi:10.1115/ICEF2017-3630.

Reliably starting the engine during extremely cold ambient temperatures is one of the largest calibration and emissions challenges in engine development. Although cold-start conditions comprise only a small portion of an engine’s typical drive cycle, large amounts of hydrocarbon and particulate emissions are generated during this time, and the calibration of cold-start operation takes several months to complete.

During the cold start period, results of previous cycle combustion event strongly influences the subsequent cycle due to variations in engine speed, residual fraction, residual wall film mass, in-cylinder charge and wall temperatures, and air flow distribution between cylinders. Include all these parameters in CFD simulation is critical in understanding the cold start process in transient and cumulative manner.

Measured cold start data of a production four cylinder spark-ignition direct-injection engine was collected for this study with an ambient temperature of −30 °C. Three-dimensional transient engine flow, spray and combustion simulation over first 3 consecutive engine cycles is carried out to provide a better understandings of the cold-start process. Measured engine speed and 1D conjugate heat transfer model are used to capture realistic in-cylinder flow dynamics and transient wall temperatures for more accurate fuel-air mixing predictions.

The CFD predicted cumulative heat release trend for the first 3 cycles matches the data from measured pressure analysis. The same observation can be made for the vaporized fuel mass as well. These observations are explained in the report.

Commentary by Dr. Valentin Fuster
2017;():V002T06A025. doi:10.1115/ICEF2017-3631.

The prospect of analysis-driven pre-calibration of a modern diesel engine is extremely valuable in order to significantly reduce hardware investments and accelerate engine designs compliant with stricter EPA fuel economy regulations. Advanced modeling tools, such as CFD, are often used with the goal of streamlining significant portions of the calibration process. The success of the methodology largely relies on the accuracy of analytical predictions, especially engine-out emissions. However, the effectiveness of CFD simulation tools for in-cylinder engine combustion is often compromised by the complexity, accuracy, and computational overhead of detailed chemical kinetics necessary for combustion calculations. The standard approach has been to use skeletal kinetic mechanisms (∼50 species) which consume acceptable computational time but with degraded accuracy.

In this work, a comprehensive demonstration and validation of the analytical pre-calibration process is presented for a passenger car diesel engine using CFD simulations with CONVERGE™ and a GPU-based chemical kinetics solver (Zero-RK, developed at Lawrence Livermore National Laboratory) on high performance computing resources to enable the use of detailed kinetic mechanisms. Diesel engine combustion computations have been conducted over 600 operating points spanning in-vehicle speed-load map, using massively parallel ensemble simulation sets on the Titan supercomputer located at the Oak Ridge Leadership Computing Facility. The results with different mesh resolutions have been analyzed to compare differences in combustion and emissions (NOx, Carbon Monoxide CO, Unburned Hydrocarbons UHC, and Smoke) with actual engine measurements. The results show improved agreement in combustion and NOx predictions with a large n-heptane mechanism consisting of 144 species and 900 reactions with refined mesh resolution; however; agreement in CO, UHC and Smoke remain a challenge.

Commentary by Dr. Valentin Fuster
2017;():V002T06A026. doi:10.1115/ICEF2017-3632.

With ever more stringent emissions and performance regulations, more emphasis and efforts have been made in accurate modeling of the combustion process and engine-out emissions in engine development. However, accurate modeling of the combustion process requires detailed chemistry. Highly detailed mechanisms typically include hundreds of species and thousands of reactions, and solution of such reaction set has been one of the largest bottlenecks in numerical modeling of the IC engine with CFD. Typically, the accuracy in chemistry modeling is sacrificed by reducing the mechanism size for the sake of computational efficiency. In this study, a lookup-table based approach is applied for modeling the combustion process in an HCCI engine. Instead of solving chemistry on-the-fly during the CFD simulations, the chemistry is solved for possible combination of thermodynamic and mixing conditions. The turbulence-chemistry interaction is considered using a flamelet approach. Then, the solution is stored in a table, such that chemistry information can be retrieved during the CFD simulation. The lookup-table method, referred to as Flamelet Generated Manifold (FGM), provides significant runtime reduction in CFD simulations with high fidelity chemistry modeling.

The FGM model was applied to a canonical HCCI experiment from Sandia National Laboratory. The experiment examined the effect of different levels of fuel stratification on ignition and combustion of a gasoline HCCI engine. The different levels of stratification were generated by controlling the amount of directly injected fuel. This case has been highly challenging for modeling using traditional modeling approaches. With FGM, it was possible to use the most detailed reaction mechanism to describe the chemistry as completely as one can. The effect of different surrogates on modeling results was investigated as well. It was found that the one proposed by Gauthier showed the most promising results in reproducing the highly complicated combustion with partial fuel stratification.

Commentary by Dr. Valentin Fuster
2017;():V002T06A027. doi:10.1115/ICEF2017-3688.

The burning of natural gas (NG) in compression ignition dual fuel engines has been highlighted for its fuel flexibility, higher thermal efficiency and reduced particulate matter (PM) emissions. Recent research has reported the significant impact of the introduction of NG to the intake port on nitrogen dioxide (NO2) emissions, particularly at the low loads. However, the research on the mechanism of NO2 formation in dual fuel engines has not been reported.

This research simulates the formation and destruction of NO2 in a NG-diesel dual fuel engine using commercial CFD software CONVERGE coupled with a reduced primary reference fuel (PRF) mechanism consisting of 45 species and 142 reactions. The model was validated by comparing the simulated cylinder pressure, heat release rate, and nitrogen oxides (NOx) emissions with experimental data. The validated model was used to simulate the formation and destruction of NO2 in a NG-diesel dual fuel engine. The formation of NO2 and its correlation with the local concentration of nitric oxide (NO), methane, and temperature were examined and discussed. It was revealed that NO2 was mainly formed in the interface region between the hot NO-containing combustion products and the relatively cool unburnt methane-air mixture. NO2 formed at the early combustion stage is usually destructed to NO after the complete oxidation of methane and n-heptane, while NO2 formed during the post-combustion process would survive and exit the engine. This was supported by the distribution of NO and NO2 in the equivalence ratio (ER)-T diagram.

A detailed analysis of the chemical reactions occurring in the NO2 containing zone consisting of NO2, NO, O2, methane, etc., was conducted using a quasi-homogeneous constant volume model to identify the key reactions and species dominating NO2 formation and destruction. The HO2 produced during the post combustion process of methane was identified as the primary species dominating the formation of NO2. The simulation revealed the key reaction path for the formation of HO2 noted as CH4->CH3->CH2O->HCO->HO2, with conversion ratios of 98%, 74%, 90%, 98%, accordingly. The backward reaction of OH+NO2 = NO+HO2 consumed 34% of HO2 for the production of NO2.

It was concluded that the increased NO2 emissions from NG-diesel dual fuel engines was formed during the post combustion process due to higher concentration of HO2 produced during the oxidation process of the unburned methane at low temperature.

Topics: Fuels , Engines , Diesel
Commentary by Dr. Valentin Fuster
2017;():V002T06A028. doi:10.1115/ICEF2017-3692.

The gasoline direct-injection compression-ignition (GDCI) combustion strategy is studied in this work based on the numerically constructed ignition phase curves. Previous research has shown that for GDCI operation, the engine efficiency can reach as high as that of diesel engines yet the NOx and soot emissions can be reduced simultaneously. A comparison between GDCI and diesel operation is made by investigating two combustion regimes, partially premixed combustion (PPC) and conventional direct-injection compression-ignition (DICI). The injection timing, which determines the controllability of GDCI operation, spans over a wide range to study its effect on the combustion phasing. Fundamental processes, such as fuel evaporation, transport, and ignition are used to explain the differences between these two operating regimes. Finally, the effects of heating intake air, boosting intake air pressure, applying warm EGR are also studied. The emissions are correlated to the instantaneous parameters of the mixture at the moment of ignition, providing insights about the fundamental mechanisms of the emission reduction by adopting GDCI combustion.

Commentary by Dr. Valentin Fuster

Engine Design and Mechanical Development

2017;():V002T07A001. doi:10.1115/ICEF2017-3511.

The characteristic of coolant flow field in the water jacket of a cylinder head plays an important role in heat exchange, which could even influence the diesel engine’s performance and service life. Measurements and analysis methods to coolant flow field are limited by the complex internal geometrical structure of the cylinder head. In this paper, flow fields in a small and complicated spatial structure are measured by particle image velocimetry (PIV) system and the data are analyzed using proper orthogonal decomposition (POD) method. Time varying coolant flow structures located among two valve seats, a fuel injector seat and a side wall in a real cylinder head are measured by a two dimensional PIV system. PIV results of three measuring planes are displayed in different ways to show flow structures in the water jacket. Distinctive areas can be recognized easily in distributions of different flow parameters. A snapshot POD method is employed to analyze PIV data. Flow structures, which contain different amount of energy, are decomposed into different modes by POD method. POD Mode 1 and ensemble mean flow field are compared together and the relevance index shows a relatively high similarity between these two flow fields. The results also indicate a significant convergence of energy distribution. Energy contained in Mode 1 varies from 22% to 61% of the total energy in different measuring planes. 90% of the total energy is captured in top 10% of the total modes which belong to low-order modes. Energy in high-order modes, which occupy more than 60% of the total modes, contains less than 1% of the total energy. In summary, this paper presents the application of PIV measurements to coolant flow field in a real cylinder head and data processing using a snapshot POD method to analyze PIV results. A set of comprehensive properties showing the spatial and temporal characteristics of coolant flow structure is discussed and concluded detailedly. The data obtained can be used to build an experimental database to optimize coolant flow field structures and verify CFD numerical simulations in order to promote coolant flow passage design and simulation credibility of the diesel engine cooling system.

Commentary by Dr. Valentin Fuster
2017;():V002T07A002. doi:10.1115/ICEF2017-3513.

Single-cylinder diesel engines usually employ mechanically actuated or time-type electrically controlled fuel injection systems. But due to the lack of flexibility to provide high pressure and fully varying injection parameters, fuel efficiency and emissions are poor. Although modern multi-cylinder engines have employed high pressure common rail fuel injection system for a long time, this technology has not been demonstrated in single-cylinder diesel engines. Due to the small installation space and little fuel injection amount of single cylinder diesel engine, high pressure common rail fuel injection system cannot be employed directly. In this study an electrically controlled high pressure fuel injection system of time-pressure-type (PTFS) for single-cylinder diesel engine was demonstrated. PTFS integrated the fuel pump and pressure reservoir (PR) to reduce installation space, which enabled it to match various kinds of single-cylinder diesel engines. However, the volume of the PR of PTFS is still limited, leading to obvious pressure fluctuation induced by periodic fuel pumping and injection. Pressure fluctuation might affect the stability and consistency of fuel injection, deteriorating the combustion and emissions of the engine further. This work established a mathematical model for the system, and studied the effect of the main parameters of the PR to the pressure fluctuations in the PR. The structure and dimensions of the system were optimized and a damping mechanism was proposed to reduce the pressure fluctuation. The optimized pressure fluctuation of PTFS achieved an acceptable level which can support steady and effective fuel injection. As a result, the fuel consumption efficiency and emission level of single cylinder diesel engine were enhanced.

Commentary by Dr. Valentin Fuster
2017;():V002T07A003. doi:10.1115/ICEF2017-3515.

Measurement of film thickness between piston ring and cylinder bore has been a challenge for decades; laser induced fluorescence method (LIF) was used by several groups and promising results are obtained for the investigation of lubricant film transport. In this study, blue light generated by a laser source is transmitted to a beam splitter by means of a fiber optic cable and combined with another fiber optic line, then transmitted to the piston ring and cylinder bore conjunction. The light causes the fluorescence dye present in the lubricant to emit light in a longer wavelength, i.e. green. Reflected light is recollected; blue wavelength components are filtered out using a narrow band pass optical filter, and only components in the florescence wavelength is transmitted to a photomultiplier tube. The photomultiplier produces a voltage proportional instantaneous lubricant film thickness. Then, the photomultiplier signal is calibrated for lubricant film thickness using a laser textured cylinder bore with known geometries. Additional marks were etched on the liner for calibration. The LIF system is adapted to a piston ring and cylinder bore friction test system simulating engine conditions. Static piston ring and reciprocating liner configuration of the bench test system allows the collection of continuous lubricant film thickness data as a function of crank angle position. The developed system has potential to evaluate new designs, materials and surface properties in a controlled and repeatable environment.

Commentary by Dr. Valentin Fuster
2017;():V002T07A004. doi:10.1115/ICEF2017-3519.

For past decades, substantial developments have been accomplished in internal combustion (IC) engine technology, but there still remain some possible improvements. The combustion in an IC engine is a highly intricate phenomenon, thus, numerous factors correlated with different forms of loss decides the efficiency of an engine. In spark-ignition (SI) engines, the combustion duration is considered important because it plays a key role in determining the combustion phasing for best possible energy conversion. The geometry of engine components may directly change the burning rate of air-fuel mixture, therefore, it should also be considered as significant as other aspects like exhaust gas recirculation (EGR) rate or boosting in investigation of the engine performance. This is the reason the development engineers are putting their effort to design an engine with optimized flow motion. Tweaking the flow dynamics via design modification or use of auxiliary device influences the turbulence level inside the combustion chamber, thus, the burning rate as well. Intake port orientation, masking, and piston shape are one of the typical design parameters manipulated for such purpose, and profound understanding on the effect of these design parameters on burning rate is encouraged in order to assist the optimization process.

The design optimization process should be based on a fundamental understanding of how the design parameters affect the flow motion and combustion characteristics. This study aims for a simpler and faster method to investigate the consequences of design modifications. As a base model, a physics-based quasi-dimensional (QD) engine model is developed for simulation of SI combustion phenomenon. It is modeled to consider the change in flow motion and turbulence properties via simplified modeling. The advantages of such QD model is that it requires much less computational resource compared to 3D CFD model, and allows a greater degree of freedom within the simulation process which facilitates parametric studies. A zero-dimensional (0D) turbulence submodel is used to describe energy cascade mechanism, and turbulence intensity is calculated reflecting the effect cause by design modification. According to the sensitivities drawn from parametric study, the results of each effect on burning rate and other engine performance properties are compared individually and collectively.

A qualitative analysis suggests how sensitive each effect are at given operating conditions. The result infers that the flow concentration by port design modification boosts the burning rate, but it is advantageous in terms of fuel economy to enhance the breathing ability by valve masking. The product of this comparative study assists an intuitive understanding on how the design modification would affect the engine operations, and it is encouraged to develop the model further via validation with experiment data to provide more reliable output. It is believed that it can be utilized as a good reference in engine design process.

Commentary by Dr. Valentin Fuster
2017;():V002T07A005. doi:10.1115/ICEF2017-3536.

A design process was defined and implemented for the rapid development of purpose-built, heavy-fueled engines using modern CAE tools. The first exercise of the process was the clean sheet design of the 1.25 L, three-cylinder, turbocharged AMD45 diesel engine. The goal of the AMD45 development program was to create an engine with the power density of an automotive engine and the durability of an industrial/military diesel engine. The AMD45 engine was designed to withstand 8000 hours of operation at 4500 RPM and 45 kW output, while weighing less than 100 kg. Using a small design team, the total development time to a working prototype was less than 15 months.

Following the design phase, the AMD45 was fabricated and assembled for first prototype testing. The minimum-material-added design approach resulted in a lightweight engine with a dry weight 89 kg for the basic engine with fuel system. At 4500 RPM and an intake manifold pressure of 2.2 bar abs., the AMD45 produced 62 kW with a peak brake fuel-conversion efficiency greater than 34%. Predictions of brake power and efficiency from the design phase matched to within 5% of experimental values. When the engine is detuned to 56 kW maximum power, the use of multi-pulse injection and boost pressure control allowed the AMD45 to achieve steady state emissions (as measured over the ISO 8178 C1 test cycle) of CO and NOx+NMHC that met the EPA Tier 4 Non-road standard without exhaust after-treatment, with the exception of idle testing. PM emissions were also measured, and a sulfur-tolerant diesel particulate filter has been designed for PM after-treatment.

Topics: Diesel , Roads
Commentary by Dr. Valentin Fuster
2017;():V002T07A006. doi:10.1115/ICEF2017-3543.

The flywheel motor is one of the best ways to improve the power-to-weight ratio of heavy fuel helicopter that equipped with compression ignition heavy fuel aircraft piston engine (CIHFAPE). In this paper, a flywheel system is designed, engine start, power demand of helicopter and rotation landing with flywheel motor are studied. Design characteristic of flywheel motor is studied for the application background of the helicopter designed by us, and the design indexes are given. The design method of the flywheel motor is proposed based on this Design characteristic, and the design is given. Finally, the performance of the flywheel motor designed by this method is verified by finite element method (FEM).

Topics: Engines , Flywheels , Design
Commentary by Dr. Valentin Fuster
2017;():V002T07A007. doi:10.1115/ICEF2017-3545.

The move to lead-free bearing materials is well known and upcoming legislation, such as the Restriction of Hazardous Substances (RoHS), is increasing the drive to extend this trend towards heavy duty diesel truck and off-highway applications.

During the development of lead-free systems, new electroplated overlays and bronze-based substrates have been developed by various suppliers, but little attention has been given to the interlayer or diffusion barrier between the overlay and substrate materials. This interlayer is particularly necessary for tin-based solutions as it prevents the rapid diffusion of overlay species into the bronze substrate.

The present development focuses on improving this often overlooked element in the system and provides a further robustness that could even be adapted to lead-based systems where increased performance is required.

The incorporation of hexagonal boron nitride as a solid lubricant in the nickel interlayer changes dramatically the interlayer properties and provides more typical bearing-like behavior for seizure resistance scuff performance compared to nickel alone.

The paper details findings of respective rig tests as well as an actual engine test supporting the change in material characteristics and the associated improvement in seizure resistance.

Commentary by Dr. Valentin Fuster
2017;():V002T07A008. doi:10.1115/ICEF2017-3557.

Two-stroke engines are often used for their low cost, simplicity, and power density. However, these engines suffer efficiency penalties due to fuel short-circuiting. Increasing power density has previously been an area of focus for performance two-stroke engines — such as in dirt bikes. Smaller-displacement engines have also been used to power remote controlled cars, boats, and aircraft. These engines typically rely on gasoline or higher-octane liquid fuels. However, natural gas is an inherently knock-resistant fuel and small natural gas engines and generators could see increased market penetration. Power generators typically operate at a fixed frequency with varied load, which can take advantage of intake and exhaust system tuning. In addition, stationary engines may not be subject to size restrictions of optimal intake and exhaust systems.

This paper examines methods to improve combustion stability, efficiency, and power density of a 29cc air-cooled two-stroke engine converted to operate on natural gas. Initial conversion showed significant penalties on delivery ratio, which lowered power density and efficiency. To overcome these issues a tuned intake pipe, two exhaust resonators, and a combustion dome were designed and tested. The engine was operated at 5400 RPM and fueling was adjusted to yield maximum brake-torque (MBT). All tests were conducted under wide-open throttle conditions. The intake and exhaust systems were designed based on Helmholtz resonance theory and empirical data. The engine utilized a two-piece cylinder head with removable combustion dome. The combustion dome was modified for optimal compression ratio while decreasing squish area and volume. With all designs incorporated, power increased from 0.22 kW to 1.07 kW — a factor of 4.86. Efficiency also increased from 7% to 12%. In addition to these performance gains, the coefficient of variation (COV) of indicated mean effective pressure (IMEP) decreased from just above 11% to less than 4%.

Commentary by Dr. Valentin Fuster
2017;():V002T07A009. doi:10.1115/ICEF2017-3559.

Chromium nitride (CrN) is the main protecting coating applied to top rings for gasoline and diesel engines, due to its excellent wear resistance, low friction and minor environmental impacts, especially in modern engines operating with low viscosity oils. Recently, diamond like carbon (DLC) coatings reported improved tribological performance, but at a higher cost. Therefore, in the present work, wear and friction of CrN and DLC coated rings were evaluated on reciprocating and floating liner engine tests running on 0W-20 and 0W-16 lubricant formulations, which additives tailored for different markets (Japanese, European and Emerging). DLC outperformed CrN for both friction and wear when running on lubricant formulations without molybdenum additives. On opposite, with high molybdenum content additives, CrN presented synergic effects that significantly reduced friction and wear, whilst DLC did not. Same comparison on floating liner engine tests demonstrated again superior performance of CrN by 9% reduction on friction losses, running on oils containing molybdenum additives, whilst DLC lowered 6%. From that, it can be estimated 0.4% fuel saving at urban conditions by combining Japanese lubricant oil formulation and CrN top rings.

Commentary by Dr. Valentin Fuster
2017;():V002T07A010. doi:10.1115/ICEF2017-3562.

The effect of diffuser on compressor performance and noise emission is studied in this paper. Firstly, on the basis of the mature compressor model, the airflow geometry from impeller inlet to volute exit has been simulated numerically. Then, the number of diffuser blade is changed and the impeller blade number remains unchanged. The effects of different diffuser blade number on compressor performance at three different compressor operating lines were analyzed and noise emission has been investigated at selected compressor operating point. It is found that flow range narrows down with blade number increase but there are pressure and efficiency enhancement at maximum efficiency working range with specific blade number. The noise simulation results show that there has the best stator blade number when the impeller blade unchanged. Moreover, a special kind of technique that called pinched diffuser is investigated in this paper. The results of four different pinch constructions indicate that the pinched diffuser can shift the surge line to low flow rates but the pressure passing through centrifugal compressor has decreased at the same time, small pinch is conducive to noise reduction which means there is also an optional structure that can obtain minimum noise, which means a more reasonable pinched construction design should be studied to improve the compressor performance and control the radiated noise.

Commentary by Dr. Valentin Fuster
2017;():V002T07A011. doi:10.1115/ICEF2017-3624.

An increase in lubricating oil consumption in an engine causes an increase in particulate matters in exhaust gases, poisoning the catalyst of after treatment devices, abnormal combustion in a turbo-changed gasoline engine and so on. Recent trend of low friction of a piston and piston ring tends to increase in lubricating oil consumption. Therefore reducing oil consumption is required strongly. It is known that oil pressure generated under the oil ring affects lubricating oil consumption. It is also known that the position of oil drain holes affects lubricating oil consumption. In this study, the effect of the position of oil drain holes on oil pressure under the oil ring and lubricating oil consumption was investigated. The oil pressure under the oil ring is measured using fiber optic pressure sensors and pressure generation mechanisms were investigated. Lubricating oil consumption was also measured using sulfur tracer method and the effects of oil drain holes against the oil pressure under the oil ring were evaluated. Four types of arrangement of oil drain holes were tested. The oil pressure variations under the oil ring in the circumferential direction was measured using a gasoline engine. An increase in oil pressure was found during down-stroke of the piston. The lowest oil pressure was found for the piston with four oil drain holes. Two holes nearby the front / rear end of the piston skirt showed relatively lower pressure. The measured results of oil consumption showed good agreement to measured oil pressure under the oil ring. It was found that oil pressure under the oil ring affected oil consumption, and oil drain holes set near the front / rear end of the piston skirt were effective for reducing oil consumption.

Commentary by Dr. Valentin Fuster
2017;():V002T07A012. doi:10.1115/ICEF2017-3645.

Two-stroke engines are capable of providing very high power density levels in a cost effective, easy-to-maintain package. They are, however, typically susceptible to higher levels of hydrocarbon emissions, lower durability, and a shorter lifecycle when compared to four-stroke engines. These detriments are easily overlooked in some military applications where power density is paramount, but most commercial two-stroke engines require specialized consumable lubricant. Typical military applications strive to minimize their logistics “trails,” which includes minimizing the variety of fluids they require. As a result, there has been very limited success in fielding small two-stroke engines for military use.

As a preliminary study, MIL-PRF-2104K Single Common Powertrain Lubricant (SCPL, a four-stroke heavy diesel engine oil) was utilized as the consumable lubricant (in place of conventional two-stroke oil) in a liquid-cooled, semi-direct fuel injected, spark-ignition, two-stroke engine. Empirical data was collected to study the impact of the oil on deposit build-up, power, wear, combustion stability, and fuel conversion efficiency. Over 147 hours of operation were logged and analyzed.

The performance of the engine on SCPL was consistent with conventional two-stroke oil and showed no degradation over the test duration. Brake specific fuel consumption was not negatively impacted with SCPL. Increased deposit build-up in the exhaust ports and on the spark plugs were the primary negative impacts of the SCPL oil. Spark plugs with hotter classifications and modification of the oiling rate resulted in a reduction of soot accumulation and spark plug fouling.

Commentary by Dr. Valentin Fuster
2017;():V002T07A013. doi:10.1115/ICEF2017-3670.

This study discusses the motion of the articulated connecting rod of an integral-engine compressor and the effect of the kinematics on in-cylinder pressure and port timings. A piston position modeling technique based on kinematics and engine geometry is proposed in order to improve the accuracy of simulated in-cylinder compression pressures.

Many integral-engine compressors operate with an articulated connecting rod. For this type of engine-driven compressor, two power pistons share a crank throw with the compressor. The hinge pins that attach the power piston connecting rods to the crank are offset, causing the piston locations for each cylinder to be out of phase with each other. This causes top dead center to occur at different crank angles, alters the geometric compression ratio, and also changes the port timings for each cylinder.

In this study, the equations of motion for the pistons of the four possible compressor/piston configurations of a Cooper-Bessemer GMW are developed. With the piston profiles, the intake and exhaust port timings were determined and compared to those of a slider-crank mechanism. The piston profile was then inputted into GT-POWER, an engine modeling software developed by Gamma Technologies, in order to obtain an accurate simulation match to the experimental in-cylinder pressure data collected from a Cooper-Bessemer GMWH-10C.

Assuming the piston motion of an engine with an articulated connecting rod is similar to a slider-crank mechanism can create a difference in port timings. The hinge pin offset creates asymmetrical motion about 180°aTDC, causing the port timings to also be asymmetrical about this location. The largest differences are shown in the intake port opening of about 10° and a difference in exhaust port opening of about 7° when comparing the motion of the correct configuration to the motion of a slider-crank mechanism.

It is shown that properly calculating the piston motion profiles according to the crank articulation and engine geometry provides a good method of simulating in-cylinder pressure data during the compression stroke.

Commentary by Dr. Valentin Fuster

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