The investigation of the effects of using CNG on engine performance emissions and combustion in an HCCI engine

In this study, the conversion of a single-cylinder four-stroke direct injection diesel engine to partial HCCI combustion mode and the use of premixed CNG fuel were investigated in terms of engine performance, emissions and combustion characteristics. A CNG fuel system placed on the intake manifold and an intake air heating system were used for the conversion to partial HCCI combustion mode. The experiments were carried out at 2200 rpm and at four different engine loads of 16 Nm, 12 Nm, 8 Nm and 4 Nm. In the experiments, the performance, emission and combustion characteristics of the engine were investigated depending on the torque change rate at 3 different intake air inlet temperatures, 40 ºC and 60 ºC and without preheating. Specific fuel consumption, thermal efficiency, exhaust gas temperature, CO, HC, NO and soot emissions, in-cylinder pressure, heat release rate, pressure increase rate, COVimep and cumulative heat release rate were investigated at 0-90% torque change rate, four different engine loads and different preheat preheating temperatures, and the stable operating range of the engine was determined. Minimum specific fuel consumption was obtained as 240.84 g/kWh with D90+CNG10 fuel at 3/4 load. Maximum thermal efficiency was obtained as 34,43% with D90+CNG10 torque change rate at 3/4 engine load. CO emissions decreased depending on the torque change rate at full load and an improvement of up to 93.12% was achieved. HC emissions decreased by 2.59% at full load up to the D60+CNG40 torque change rate and an increasing trend was obtained after this torque change rate. Minimum NO emissions were obtained at 1/4 load. At full load, a 97.96% reduction at smoke emissions was achieved compared to diesel operating conditions with D10+CNG90 fuel. Maximum in-cylinder pressure was obtained as 60.98 bar at full load and D50+CNG50 torque change ratio. The start of combustion shifted somewhat ahead of the experiments without preheating with the increase in the preheating temperature. The cylinder pressure rise rate values were below the knock limit at all engine loads and heating temperatures. According to the COVimep values, the engine remained in the stable operating range up to the D50+CNG50 torque change rate in the experiments without preheating, and this rate expands to the D40+CNG60 with preheating.