The Experimental Study Of Effect Of Combustion Control Parameters On Combustion Of A Heavy Duty Diesel Engine

Under the pressures of energy, environment, regulations and shortage of precious metals, the strategy of diesel low temperature combustion has become a hot research at home and abroad. However, the physical characteristics of diesel fuel make it difficult to prepare the ignitable mixture of fuel and intake charge in cylinder. Therefore, how to reduce combustion temperature of the cylinder and promote mixing process of fuel and intake charge 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, this dissertation studied the effects of various parameters on premixed charge compression ignition combustion and lean diffusion combustion under low and middle load and obtained the best operation point by the optimization of parameters in the different injection modes.Based on the multi-pulse injection mode, the experimental results of diesel PCCI combustion give the following conclusions: With the increase of EGR rate and the decrease of oxygen concentration, NOx and Soot emissions show decreasing trend gradually, and indicated thermal efficiency rises at first and then declines. With the increase of EGR rate and the decrease of oxygen concentration, number concentrations of accumulation mode show the trend of decreasing at first and then increasing. The average particle size of accumulation mode is in the range of 40～65nm, while the average particle size of nucleation mode is in the range of 12～18nm. When the initial injection timing is the -80°CA ATDC, NOx and Soot emissions achieve ultra-low level simultaneously. The indicated thermal efficiency maintains very high, though there are higher HC and CO emissions to produce. With the increase of common-rail pressure, NOx, Soot, HC and CO emissions show decreasing trend, while indicated thermal efficiency increases slightly. It is of great significance to improve common rail pressure to reduce emissions of NOx and Soot, when the EGR rate is relatively small and oxygen concentration is relatively high.Based on single early spray injection mode, the experimental results of diesel PCCI combustion give the following conclusions: With the advancement of injection timing, NOx emissions decreases and Soot emissions increases, while the indicating thermal efficiency lowers. When the injection timing is -26°CA ATDC or -30°CA ATDC, NOx and Soot emissions achieve ultra-low level simultaneously, and indicating thermal efficiency maintains very high.Based on single late spray injection mode, the experimental results of diesel lean diffusion combustion give the following conclusions: The optimized coupling of intake pressure, intake valve closing timing (IVCT), injection timing and EGR can effectively change the in-cylinder temperature, pressure and oxygen concentration, and they have great influence on the mixing of fuel and intake charge and combustion process. Under the optimized injection timing, when the total intake flow keeps constant and intake valve closing timing is -60°CA ATDC, improving inlet pressure can simultaneously achieve ultra-low NOx and soot emissions with the introduction of the EGR rate of 20% to 35%. At the same time the IMEP and indicated thermal efficiency are also keeping at high values.