The Effect of Fuel Rail Pressure on the Performance of a CNG-Direct Injection Engine

The effects of fuel rail pressure variations on the performance of a compressed natural gas (CNG) direct injection (DI) engine is presented. In order to maximize the performance, the engine was designed with a compression ratio of 14 and equipped with central DI system. The results presented focused on the effect of lowering the injection pressure from the designed injection pressure of 18 bar. The result shows that an 18-bar injection pressure gives a better engine performance at lower engine speed while a 12-bar injection pressure gives a better performance at higher engine speed. In the former case, the combustion is strongly affected by the volumetric efficiency while in the latter case it is strongly affected by rate of air-fuel mixing.