Combustion improvement and exhaust emissions characteristics in a direct injection natural gas engine by throttling and EGR

Abstract

A natural gas direct injection test engine equipped with a newly developed natural gas injector was built. The high THC emission at part-load condition and the high NOx emission at high-load condition are left as the problems for a direct injection natural gas engine. The THC reduction and combustion improvement by throttling and the NOx reduction by EGR were investigated. The following results were obtained: (1) The combustion at light- and medium-load conditions is improved by throttling. It is possible to improve the thermal efficiency at light-load condition in spite of pumping loss by throttling. The concentration of THC emission is greatly decreased in this condition; (2) The great NOx reduction can be obtained without combustion deterioration by appropriate EGR at high-load condition; and (3) It is possible to decrease both THC and NOx emissions by both throttling and EGR at part-load condition.