Effects of charge temperature and exhaust gas re-circulation on combustion and emission characteristics of an acetylene fuelled HCCI engine

In this work, experiments were conducted on a homogeneous charge compression ignition (HCCI) engine with acetylene as the sole fuel at different power outputs. Initially, the intake air was heated to different temperatures in order to determine the optimum level at every output. Charge temperatures needed were in the range of 40–110 °C from no load to a BMEP (Brake Mean Effective Pressure) of 4 bar. Subsequently, exhaust gas re-circulation (EGR) was done at the identified charge temperatures and brake thermal efficiency was found to improve. At high BMEPs, use of EGR led to knocking. Thus, fine control over charge temperature and EGR quantity is needed at these conditions. Nitric oxide and smoke levels were very low. However, HC levels were high at about 1700–2700 ppm. Brake thermal efficiencies were comparable to or even better than the compression ignition mode of operation.