Analytical prediction of syngas induction times

Computations indicate that, under all possible conditions of practical interest, including temperatures both above and below the crossover temperature at which the rates of the H2 + O2 branching and termination steps are equal, twelve irreversible elementary steps suffice to provide accurate values of induction times in autoignition processes of fuels consisting of mixtures of H2, CO, and inerts. At high temperatures, this time is controlled by the time required for the radical pool to reach a steady state, with heat release being negligible during that time. This time is approximated well by the time that it would take for HO2 to reach a steady state if its consumption rate were dominated by formation of H2O2 at all temperatures, as it is at low temperatures. Below the crossover temperature, the time to reach an HO2 steady state becomes shorter than the induction time, and the heat release becomes non-negligible once HO2 has reached a steady state, resulting in the induction time progressively approaching that of a thermal explosion, which includes an effectively autocatalytic production of H2O2. On the basis of these observations, analytical approximations are introduced here that enable induction times to be calculated accurately under all conditions.