预喷对柴油燃烧碳烟生成特性的影响

Influences of pilot injection on soot formation characteristics in heavy duty DI diesel engine

针对一台直喷式涡轮增压重型柴油机,建立了基于内窥镜技术的缸内燃烧过程光学测量系统,研究了采用不同的燃油预喷策略对柴油机缸内燃烧和排放物生成的影响作用,通过不同的预喷燃油量和预喷正时,实现柴油机的预混合低温燃烧.基于内窥镜技术的双色法对柴油机缸内温度场分布、碳烟生成和氧化分布进行测量和分析.结果表明:随着预喷燃油量的增加和预喷正时的提前,碳烟颗粒排放量逐渐下降,NOx排放量逐渐增加,而CO和未燃碳氢的排放量先增加后下降;在燃烧过程中碳烟高浓度区主要出现在喷束下游的中心区域,并向燃烧室边缘发展;不同的预喷正时主要影响主喷燃烧峰值或燃烧剧烈程度,但对其燃烧相位影响较小.

To investigate the effects of pilot injection strategies on the engine＇s combustion process in inter-cooled turbocharged heavy-duty DI （direct injection） diesel engines, an optical measurement sys- tem of the combustion process in the cylinder was proposed based on the endoscope technology. The pilot injection strategies included different pilot injection fuel mass and pilot injection timing, to a- chieve low-temperature combustion （LTC） in the diesel engines. The two-color method based on the endoscope technology was applied to 2-D flame images and area-averaged soot radiation signals to ob- tain the in-cylinder temperature field and soot concentration distribution. The results show that with the advance of the pilot injection timing and the increase of the pilot injected fuel mass, the engine-out soot emissions decrease significantly, NO~ emissions increase, while CO and HC emissions increase firstly and then decrease. The soot particles with higher concentration are concentrated in the fuel-rich core of the spray plumes near its leading edge, and develop along the bottom and the wall of the piston bowl. The pilot injection timing manly affects the peak pressure and intensity of main combustion, and has a relatively small impact on the ignition timing.