The role of third-body collision efficiency in autoignition of hydrogen–air mixtures

Numerical simulations of autoignition of lean (6% H2), stoichiometric, and rich (90% H2) hydrogen–air mixtures have been performed to examine the influence of third-body efficiency (chaperon efficiency, CE) on the value of ignition delay, τ. The temperature ranges explored in the computations are 850–1000 K for P0 = 1 bar and 1000–1200 K for P0 = 6 bar. By using a detailed kinetic mechanism, it has been found that the sensitivity of ignition delay to CE is the highest for the reaction step H + O2 + M = HO2 + M, which can lead to a variation in τ by a factor of 2 to 3. A pressure increase or deviation from stoichiometry reduces the sensitivity. The influence of CE is qualitatively different and weaker for the reaction step OH + OH + M = H2O2 + M.