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An ignition and combustion model has been developed to predict the heat release rate in direct injection compression ignition engines employing very early injection timing. The model describes the chemical reactions, including low-temperature oxidation. The KIVA II computer code was modified with the present ignition and combustion model. The numerical results indicate that the model developed in this work reproduces major features of two-stage autoignition, as well as experimentally observed trends in NOx and unburned fuel emissions. The computational results show that fuel injection timing significantly influences NOx emissions. Results also indicate that fuel droplets that enter the squish region possibly become unburned fuel emissions. Some graphical results demonstrate the relationships among the in-cylinder fuel spray distributions, fuel-air equivalence ratio, temperature, and mass fractions of NO and unburned fuel.

Premixed diesel combustion was performed and various characteristics examined with fuel injection timing near top dead center (TDC). A lean and uniform fuel-air mixture was found to during 25° C.A. with a narrow injectionangle (27.5° with respect to horizontal), shallow dish combustion chamber, and low cetane number fuel (CN=19). These conditions enabled low NOx combustion in no exhaust gas re-circulation (EGR), despite fuel injection timing around 25° BTDC. Furthermore, HC emissions were lower than with premixed diesel combustion of the early injection type. Because fuel injection timing was near TDC, the volume of the mixture dispersed to a squish area was decreased. This combustion mode was also achieved with a high-cetane fuel (conventional diesel fuel) and high EGR rate conditions. However, in this case, it was difficult to adjust the ignition timing near top dead center. This combustion system also showed good performance in conventional diesel combustion mode. This system permits dual mode diesel combustion, as follows: Premixed diesel combustion mode, which results in low NOx and smoke at engine out, is useful for low load conditions, when exhaust temperatures are too low for effective use of aftertreatment catalysts. Conventional diesel combustion applies to high load condition when exhaust gas temperatures are suitable for aftertreatment system.