Performance and emission characteristics of a direct-injection spark-ignition hydrogen enriched natural gas engine diluted with EGR

An experimental study was conducted on a direct-injection spark-ignition (DISI) engine fuelled with hydrogen-natural gas blends with the introduction of EGR (exhaust gas recirculation). The effects of the EGR rate, the hydrogen fraction and the injection timing on the engine performance and emission characteristics were investigated. The results show that the hydrogen addition reduced the brake mean effective pressure (BMEP) and the brake thermal efficiency at the lower EGR rate but increased the BMEP and the brake thermal efficiency at the higher EGR rate. The BMEP decreased with an increase in the EGR rate, and the brake thermal efficiency increased at first and then decreased with an increase in the EGR rate. The NO_x concentration decreased with an increase in the EGR rate and increased with the hydrogen fraction. The HC emission increased with the EGR rate and decreased with an increase in the hydrogen fraction. The CO emission changed slightly with the EGR rate and decreased with an increase in the hydrogen fraction. In addition, the variation coefficient of indicated mean effective pressure C_imep increased with the EGR rate, and the hydrogen addition could reduce the C_imep more effectively for late injection.