An Experimental Study Of Physical And Chemical Factors' Effect On Clean And High Efficiency Diesel Combustion

Diesel low temperature combustion has been paid more and more attention in recent years for the shortage of energy and deterioration of environment. However, the physical characteristics of diesel fuel make it difficult to prepare the ignitable in-cylinder fuel/air mixture. How to promote the fuel/air mixing process and control the stratification of mixture temperature and concentration have been the key problems to realize diesel low temperature combustion. Based on the fuel injection strategy control and in-cylinder condition (temperature, pressure and oxygen concentration) control, and by the means of experiment and numerical simulation, this dissertation studied the effects of physical and chemical factors, including fuel injection strategy, intake pressure, EGR and VVT, on diesel combustion control mechanics.Based on the dwell time modulated multi-pulse injection strategy, the experimental results of diesel PCCI combustion give the following conclusions: pulse dwell time, pulse fuel mass and their proportion, pulse number and injection timing are the key parameters to control diesel PCCI combustion. Their optimization can obviously enhance the fuel/air mixing, lower the energy loss of unburned liquid fuel and control the stratification of mixture temperature and concentration, and then realize the ignition timing and heat release rate controllable PCCI combustion. Based on the PCCI combustion, the"molecular reforming"compound combustion concept can simultaneously obtain lower engine emissions and combustion noise, and at the same time can further complete combustion to get higher combustion efficiency and thermal efficiency.The optimization of multi-pulse injection mode, injection pressure, intake pressure, main injection timing and post injection strategy has great potential in improving of fuel/air mixing in"molecular reforming"compound combustion. Due to the improvement of mixture quality, diesel compound combustion with low NOx and Soot emissions,which have the potential to meet the emission standard of Chineseâ…¤, can be achieved at higher engine loads.Lower in-cylinder temperature and pressure, achieved with VVT have chain-like effect on the combustion characteristics of pilot, main and post injected fuel in the"molecular reforming"compound combustion. At the optimized intake valve close timing, use of VVT enables compound combustion to get lower NOx and Soot emissions while the IMEP and indicated thermal efficiency are keeping at high values.The optimized coupling of intake pressure, VVT, injection strategy and EGR can effectively change the in-cylinder temperature, pressure and oxygen concentration, and then has great influence on the fuel/air mixing and combustion process. The end result is that clean and high thermal efficiency diesel combustion at high load can be realized. At late intake valve close timing and optimized main injection timing, and under the pre-condition of higher intake pressure to guarantee sufficient oxygen in cylinder, use of small EGR rate can simultaneously reduce NOx and Soot emissions dramatically. At the same time the IMEP and indicated thermal efficiency are also keeping at high values.