Research on Low Temperature Combustion of Homogeneous Charge Induced Ignition (HCII) in a Light-Duty Diesel Engine

Homogeneous Charge Induced Ignition (HCII) is an innovative combustion mode that has the potential to achieve high-efficiency and low-emission combustion. The effects of cooled Exhaust Gas Recirculation (EGR) and hot EGR on the combustion characteristics, emissions characteristics and thermal efficiency are studied contrastively in a light-duty diesel engine. The results show that as EGR rate increased, NOx emissions reduced significantly. Cooled EGR resulted in lower NOx emissions than hot EGR. At low load, Hot EGR can decrease the THC emissions in HCII mode and improve the combustion, with a biggest indicated thermal efficiency increase of 2 %. As EGR rate increased, the NOx emissions decreased and smoke emissions increased in diesel Compression Ignition (CI) combustion at high load, exhibiting the classical NO-soot trade-off. However, in HCII mode, the NOx emissions decreased and smoke emissions were maintained at a low level, which demonstrated that low temperature was achieved apparently. EGR is an effective technology to reduce the combustion noise in HCII mode at high load. As EGR ratio increased, the ignition delay increased in general. Comparing to diesel CI combustion, the ignition delay in HCII mode increased more significantly, which was beneficial to the fuel–air mixing. At high load, the combustion duration in HCII mode was shorter than diesel CI combustion, and the combustion was closer to constant volume combustion, which was conductive to improving thermal efficiency.