Numerical Simulation of the Effect of Additives on Autoignition of Lean Hydrogen-Air Mixtures

Simulations of the effect of addition of atoms, molecules, and radicals on autoignition of lean (14%) and ultra-lean (6%) hydrogen-air mixtures are performed in the temperature range of 800 to 1700 K at initial pressures of 1 and 6 bar. Computed results demonstrate that adding H, O, OH, HO2, and H2O2 reduces ignition delay time tau. Common tendencies are revealed in the temperature-dependent effects of the added species. For each additive, the corresponding effect is found to be the strongest at temperatures near 900 and 1100 K at pressures of 1 and 6 bar, respectively. It is shown that the effects of addition of O and H are similar in magnitude. The effect of HO2 is much weaker compared to other additives, and its temperature dependence is qualitatively analogous to that of H2O2. While the extent of ignition-delay reduction decreases towards the endpoints of the temperature interval explored for all additives, significant effects persist in its high-temperature part for OH and in the low-temperature one for HO2 and H2O2. Addition of water up to 1% does not affect the value of tau.