Achievement of Diesel Low Temperature Combustion through Higher Boost and EGR Control Coupled with Miller Cycle

Diesel engines generally tend to produce a very low level of NO_x and soot through the application of Miller Cycle, which is mainly due to the low temperature combustion (LTC) atmosphere resulting from the Miller Cycle utilization. A CFD model was established and calibrated against the experimental data for a part load operation at 3000 r/min. A designed set of Miller-LTC combustion modes were analyzed. It is found that a higher boost pressure coupled with EGR can further tap the potential of Miller-LTC cycle, improving and expanding the Miller-LTC operation condition. The simulated results indicated that the variation of Miller timings can decrease the regions of high temperatures and then improve the levels and trade-off relationship of NO_x and soot. The in-cylinder peak pressure and NO_x emissions were increased dramatically though the problem of insufficient intake charge was resolved by the enhanced intake pressure that is equivalent to dual-stage turbo-charging. In addition, the positive effect of EGR can overwhelm the side effect of a high intake pressure on the in-cylinder peak pressures and NO_x emissions, mitigating the mechanical load of diesel engines and improving the emission levels. Therefore the operation range of Miller-LTC cycle diesel engines was expanded to high load conditions, and the adaptability to variable operating conditions was enhanced through the optimization of Miller timings, high intake pressures and EGR ratios. However, the amount of BSFC in these cases couldn't be involved in this paper.