Experimental investigation of NOx impact on ignition delay times for lean H2/air mixtures using a rapid compression machine under internal combustion engine conditions

This study investigates the effects of nitric oxides addition on ignition delay times of lean hydrogen/air mixtures (9 = 0.4), in the 890 K - 1000 K temperature range and for medium-to-high compression pressures (pC = 30, 40, 50, and 60 bar). Results show that ignition delay times decrease with the addition of nitric oxide and nitrogen dioxide, regardless of the compression pressure. These datasets provide new insights to assess the validity of kinetic mechanisms under such conditions and predict autoignition phenomena. As such, a comparison with recent kinetic mechanisms is conducted. A sensitivity analysis on OH radical is performed and highlights the role of the HO2/H2O2 and NO/NO2 recycling sequences in OH production, yielding an increase in the mixture reactivity. Finally, this work highlighted the importance weight of (R17) in reactivity enhancement and gave a perspective to optimize NOx sub-mechanisms for hydrogen ignition under internal combustion engine conditions.