Three-dimensional numerical analysis of diesel combustion under cold ambient conditions
CHALLENGE - A lower compression ratio has been demanded for diesel engines in recent years to improve fuel consumption, exhaust emissions and maximum power. However, low compression ratio may have combustion instability issues under cold temperature condition. As the first step in this study, cold temperature combustion was investigated on the basis of an in-cylinder pressure analysis.
SOLUTION - The test engine was a four-cylinder direct injection diesel engine with a compression ratio of 15.0:1. A modified time-scale interaction (TI) combustion model was used in this study to investigate in-cylinder combustion in detail under low-temperature conditions. Calculations were performed in this study with STARCD, a general-purpose CFD analysis code, in order to validate the modified TI combustion model. In order to predict ignition phenomena in a low temperature starting condition precisely, the constants of the shell model were optimized using a genetic algorithm in modeFRONTIER.
BENEFITS - By optimizing the constants of the shell model using modeFRONTIER, the simulated ignition delay below 900 K agreed well with the experimental results. Results revealed that ignition and combustion in low-temperature conditions started near the glow plug due to the temperature increase caused by chemical reactions. Indicated mean effective pressure and combustion stability can be improved by increasing the fuel mass and temperature surrounding the glow plug.