Influence of injection conditions and exhaust gas recirculation in a high-speed direct-injection diesel engine operating with a late split injection

Abstract

This paper describes an investigation on low-temperature combustion in a small single-cylinder high-speed direct-injection diesel engine. This engine is representative of turbocharged passenger car diesel engines equipped with a particulate trap and an oxidation catalyst. A medium-load engine operation condition was evaluated using two fuel injection events near top dead centre and high levels of exhaust gas recirculation. The combustion was characterized by extremely low emission of nitrogen oxides (of the order of 10—15ppm) and low combustion noise. The study was carried out by means of a design of experiments, consisting of four factors varied on three levels according to a Box—Behnken design. This Box—Behnken design was extended with validation points, allowing all factors to be studied independently in a parametric approach. Additionally, some relevant two-factor interactions have been studied. The investigated factors were the exhaust gas recirculation rate, the combustion phasing, the injection pressure, and the dwell between the split injections. The results show how it is possible to achieve very low levels of nitrogen oxides and low combustion noise with reasonable fuel consumption, smoke emissions, hydrocarbons, and carbon monoxide emissions, with injection and combustion just after top dead centre.