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A computational fluid dynamics (CFD) guided design optimization was conducted for the piston bowl geometry for a heavy-duty diesel engine. The optimization goal was to minimize engine-out NOx emissions without sacrificing engine peak power and thermal efficiency. The CFD model was validated with experiments and the combustion system optimization was conducted under three selected operating conditions representing low speed, maximum torque, and rated power. A hundred piston bowl shapes were generated, of which 32 shapes with 3 spray angles for each shape were numerically analyzed and one optimized design of piston bowl geometry with spray angle was selected. On average, the optimized combustion system decreased nitrogen oxide (NOx) emissions by 17% and soot emissions by 41% without compromising maximum engine power and fuel economy.

This research investigates the combustion characteristics and engine performance of a conventional non-ethanol gasoline with a research octane number of 91(RON 91) and a higher reactivity RON80 gasoline under mixing-controlled combustion. The work was conducted in a model year 2013 Cummins ISX15 heavy-duty diesel engine. A split fuel injection strategy was developed to address the long ignition delay and high maximum pressure rise rate for the two gasoline fuels. Using the split fuel injection strategy, steady-state NOx sweeps were conducted at 1375 rpm with a load sweep from 5 to 15 bar BMEP. At 5 and 10 bar BMEP, both gasolines consistently exhibited lower soot levels than ULSD with the reduction more pronounced at 5 bar BMEP. 3-D CFD combustion simulation suggested that the higher volatility and lower viscosity of gasoline fuels can help improve the in-cylinder air utilization and therefore reduce the presence of fuel-rich regions in the combustion chamber.

Fuel stratification effects on the combustion and emissions behaviors for partially premixed compression ignition (PPCI) combustion of a high reactivity gasoline (research octane number of 80) was investigated using the third generation Gasoline Direct-Injection Compression Ignition (Gen3 GDCI) multi-cylinder engine. The PPCI combustion mode was achieved through a double injection strategy. The extent of in-cylinder fuel stratification was tailored by varying the start of second fuel injection timing (SOIsecond) while the first fuel injection event was held constant and occurred during the intake stroke. Based on the experimental results, three combustion characteristic zones were identified in terms of the SOIsecond - CA50 (crank angle at 50% cumulative heat release) relationship: (I) no response zone (HCCI-like combustion); (II) negative CA50 slope zone: (early PPCI mode); and (III) positive CA50 slope zone (late PPCI mode).

A detailed study of various air system configurations has been conducted for a prototype gasoline compression ignition (GCI) engine using a Cummins MY2013 ISX15 heavy-duty diesel engine as the base platform. The study evaluated the configurations with the assumption that RON80 gasoline would be used as the fuel and the combustion chamber would have a geometric compression ratio (CR) of 16.5. Using 3-D computational fluid dynamics (CFD) simulations, a high efficiency & low engine-out NOx GCI combustion recipe was developed across the five engine operating points from the heavy-duty Supplemental Emissions Test (SET) cycle: A100, B25, B50, B75, and C100. The CFD generated air-thermal boundary conditions and the combustion burn-rate & injector rate-of-injection profiles were imported into a calibrated 1-D engine model for the air-handling systems analysis.

A computational fluid dynamics (CFD) guided combustion system optimization was conducted for a heavy-duty diesel engine running with a gasoline fuel that has a research octane number (RON) of 80. The goal was to optimize the gasoline compression ignition (GCI) combustion recipe (piston bowl geometry, injector spray pattern, in-cylinder swirl motion, and thermal boundary conditions) for improved fuel efficiency while maintaining engine-out NOx within a 1-1.5 g/kW-hr window. The numerical model was developed using the multi-dimensional CFD software CONVERGE. A two-stage design of experiments (DoE) approach was employed with the first stage focusing on the piston bowl shape optimization and the second addressing refinement of the combustion recipe. For optimizing the piston bowl geometry, a software tool, CAESES, was utilized to automatically perturb key bowl design parameters. This led to the generation of 256 combustion chamber designs evaluated at several engine operating conditions.