Knock Prevention of Gas SI Engine by Adjunction of Inert Gases to the Fuel

This work focuses on the prevention from knock in the case of SI engines supplied by natural gas network. The effect of two inert gases (N₂ and CO₂) adjunction is experimentally studied. The added quantities are between 0% and 25% in volume for N₂ and between 0% and 15% for CO₂. A significant increase of the Knock Limited Spark Timing (KLST) is measured in all the cases. A twice-higher augmentation is noted when CO₂ is added compared to N₂ for an equivalent volumetric concentration. The overall augmentation varies between +1 to +6 °CA depending on the operation. Finally, a law for predicting the KLST augmentation implied by the adjunction of inert gases is deduced from all the measurements.