Experimental study on performance and emissions of a spark ignition engine fuelled with CNG-hydrogen mixtures

An experimental investigation was conducted on the influence of the different percent of hydrogen on the performance and emissions of a spark ignition engine fuelled with natural gas and hydrogen mixtures. Four different mixtures of hydrogen and natural gas were tested with hydrogen volumetric percent of 0%, 10%, 20% and 26%, respectively. An electronic control unit was developed to control the spark timing and mixture concentration. Compared with pure CNG operation, the engine fuelled with hydrogen and natural gas mixtures shows lower power output and effective thermal efficiency. With the same excess air ratio, the optimal spark timing retards and HC and CO₂ emissions decrease while NO_x emissions increases with the increase of hydrogen fraction. Adding hydrogen to natural gas can extend the lean burn limit of mixture. Moreover, low emissions of HC, CO, CO₂ and NO_x can be realized at lean mixture combustion for natural gas and hydrogen mixtures.