Effect of excess air ratio on natural gas engine fueled by diesel fuel

To study the application of Compressed Natural Gas (CNG) for diesel engines, a turbocharged diesel engine has been converted into a dual-fuel natural gas engine fueled by diesel fuel. CNG was injected into the intake pipe via a gas injector. The engine, which is operating in dual-fuel mode, has been tested at the speed of 1400 r/min, 1600 r/min and 1800 r/min. The pilot injection of diesel fuel is about 20% of maximum fuel delivery per cycle. This paper analyzed the effect of excess air ratio on the engine performance and exhaust emissions in all tested operating conditions. Experimental results show that, with decrease of the excess air ratio, brake power increases at different speeds, brake specific fuel consumption decreases, NO_x emissions increase, HC and CO increase at λ>1.6 while they decrease sharply at λ < 1.6.