Spark knock suppression in spark ignition engines with hydrogen addition under low and high engine speeds

The influence of hydrogen addition on spark knock characteristics is investigated under two engine speeds (2000 rpm and 4800 rpm) with experiments and chemical analyses to describe the effect of hydrogen addition on the high-speed knock as well as on the low-speed knock. The experimental results showed that the hydrogen addition of 15 HV% advances the knock limit by 3°CA at 2000 rpm, while by 1°CA at 4800 rpm, indicating that the knocking suppression effect weakens at higher engine speeds. The chemical kinetic analyses showed that hydrogen addition reduces the heat release rate under 900 K where the low temperature oxidation (LTO) appears, while it promotes the heat release rate above 900 K. These results suggest that the smaller effect of hydrogen addition at the higher engine speed is due to the smaller dependence of the LTO on the ignition process, with the shorter residence time below 900 K.