Investigation of Combustion Process and Emission Characteristics of CNG/Diesel Dual-Fuel PCCI Combustion in a 1.0 Liter Optical CI Engine

Abstract

Dual-fuel premixed charge compression ignition(PCCI) combustion is one of the advanced combustion concepts based on compression-ignition diesel engines. The use of natural gas as a low-reactivity fuel has been proven to be a promising solution for both improvement of thermal efficiency and reduction of pollutant emission, such as particulate matters and nitrogen oxides. In this study, the compressed natural gas(CNG)/diesel dual-fuel PCCI combustion was demonstrated in a heavy-duty optical engine. The diesel injection timing and natural gas substitution ratio were varied in order to implement the variation in mixture reactivity. Flame visualization results indicated that the mixture with a larger natural gas substitution revealed a considerable reduction in the soot-oriented luminous flame. Advanced injection of diesel resulted in a shift in the location and direction of early flame development, while the area of diffusion flame decreased significantly. The measurement of pollutant emission concentration in thermodynamic engine verified the reduction of particulate emissions with respect to the mixture formation parameters.