The effect of pilot injection on combustion in a turbocharged D. I. diesel engine

For reducing the exhaust emissions and improving the ignition characteristics, the effect of pilot injection was investigated experimentally in a turbocharged direct injection diesel engine. The pilot injection quantity was varied by changing the seat diameter of the Dodge plunger installed in the newly developed pilot injector while the separation period between the beginning of pilot injection and that of main injection was fixed at a short interval in the present experiment. The pilot injection effect on combustion was compared with the case of normal injection in two fuel oils with the cetane indexes of 55 and 40 respectively. The pilot injection showed some significant effects on improving the ignition characteristics and fuel consumption as follows; (1) The pilot ignition delay and the main ignition delay were about half of the ignition delay of the normal injection respectively. (2) The lower fuel consumption and NOx could be attained by the pilot injection at the retarded injection timing, especially under the lower load condition. (3) The trade-off relationship between the specific fuel consumption and NOx was significantly improved by the pilot injection, and a larger improvement was obtained in the lower load and in the fuel with a worse ignitability. (4) In the present short pilot-main interval, a small amount of pilot quantity was recommended to reduce NOx and fuel consumption without deteriorating smoke density.