Visualizations of combustion and emissions characteristics in a light-duty diesel engine with achieved premixed low temperature combustion

Abstract

This paper presents a study on the feasibility of premixed low temperature combustion (PLTC) in a light-duty engine, employing moderate early injection (MEI) and high level exhaust-gas recirculation (EGR). Tests were carried out under constant speed and low load. In-cylinder pressure was measured for heat release rate analysis and exhaust emissions were measured in the exhaust pipe. To capture spray and combustion images, an optical diesel engine equipped with an endoscope and a color CCD camera was used. In addition, the AVL-Thermo Vision software was applied into the measurement of temperature and soot distribution of diffusion flame. The influence of injection timing and oxygen concentration on combustion and emissions characteristics were studied. With moderate advanced injection, premixed combustion was observed from the heat release rate and combustion images. Diffusion flame and soot emissions reduced evidently while NOx emissions increased and combustion phase occurred earlier. The introduction of EGR delayed combustion phasing to approach TDC, thus enhancing combustion thermal efficiency. The NOx decreased monotonically with increasing level of EGR and Soot emissions decreased under the condition of very low oxygen concentration. MEI coupled with high level EGR have high potential to decrease Soot and NOx simultaneously.