Modeling Early Injection Processes in HSDI Diesel Engines

Numerical simulations were performed to investigate the combustion process in the Premixed Compression Ignition (PCI) regime in a light-duty diesel engine. The CHEMKIN code was implemented into an updated KIVA-3V release 2 code to simulate combustion and emission characteristics using reduced chemistry. The test engine used for validation data was a single cylinder version of a production 1.9L four-cylinder HSDI diesel engine. The engine operating condition considered was 2,000 rev/min and 5 bar BMEP load. Because high EGR levels are required for combustion retardation to make PCI combustion possible, the EGR rate was set at a relatively high level (40%) and injection timing sweeps were considered. Since injection timings were very advanced, impingement of the fuel spray on the piston bowl wall was unavoidable. To model the effects of fuel films on exhaust emissions, a drop and wall interaction model was implemented in the present code. The simulation results showed good levels of agreement with the measured in-cylinder pressure, heat release rate and exhaust emissions. Also, optimum injection timings were revealed using both simulation and experimental methods. As the injection timing was advanced from 15o BTDC to 51 o BTDC, distinct regions of emission characteristics controlled by mixing and the combustion bowl geometry were found and explained by the simulation results. The calculation results also showed that the prediction of carbon monoxide emissions and the pressure history for early injections depend critically on key oxidation reaction rates in the chemical mechanism.