Study On Combustion Characteristics Of An LNG/diesel Dual-fuel Engine

This paper is based on the high pressure diesel engine YC6G270-30 with electronically controlled common rail system, which is added a set of LNG supply system and dual-fuel engine control system, and converted to LNG/diesel dual-fuel engine. The combustion process of internal combustion engine has a decisive effect on the performance of its power, thermal efficiency, mechanical load, thermal load, noise, vibration, smoke and exhaust, etc. So, this paper decides to study on the combustion characteristics of dual-fuel engine. The LNG/diesel dual-fuel engine combustion characteristics are compared and analyzed by bench tests of the dual-fuel engine.1) When the speed is at 1400 r/min, the load rate is 60%(the original machine output power is 79.5 kW), and the diesel fuel injection timing is the maximum torque timing, the influence of blending ratio on combustion characteristics of dual-fuel engine is studied. The results show that with the increase of blending ratio, in-cylinder pressure, in-cylinder pressure rise rate, instantaneous heat release rate in dual-fuel mode increase first and then decrease, in-cylinder temperature increases all the time; Maximum cylinder pressure cyclic variation coefficient in dual-fuel mode increases first and then decreases and then increases again, maximum rate of pressure rise cycle variation coefficient decreases first and then increases; Ignition timing in dual-fuel mode advance first and then delay and then advance again, combustion duration increases first and then decreases, injection timing and indicated thermal efficiency increases first and then decreases and then increases again.2) When the speed is at 1000 r/min, the load rate is 60%(the original machine output power is 53.1 kW), and the blending ratio is the maximum mixing ratio of 90%, the influence of the pilot fuel injection timing on combustion characteristics of dual-fuel engine is studied. The results show that with the increase of fuel injection timing, the cylinder pressure, in-cylinder pressure rise rate, in-cylinder temperature, instantaneous heat release rate in dual-fuel mode increase; Maximum cylinder pressure cyclic variation coefficient in dual-fuel mode increases first and then decreases, maximum rate of pressure rise cycle variation coefficient decreases all the time; Ignition timing in dual-fuel mode keeps advancing, combustion duration, effective power and indicated thermal efficiency increase first and then decrease.3) When the speed is at 1400 r/min, the load rates are 15%, 20%, 30%, 60%, and the blending ratio is the maximum mixing ratio, the influence of the load on combustion characteristics of dual-fuel engine is studied. The results show that with the increase of load, in-cylinder pressure, in-cylinder temperature rise rate, instantaneous heat release rate in the original machine mode and dual-fuel increase; Maximum cylinder pressure cyclic variation coefficient and maximum rate of pressure rise cycle variation coefficient in original machine mode and dual-fuel mode decrease first and then increase; Ignition timing in original machine mode and dual-fuel mode advances first and then delays, combustion duration and injection timing in dual-fuel mode increase first and then decrease, blending ratio in dual-fuel mode keep increasing, indicated thermal efficiency in original machine mode and dual-fuel mode keep increasing.