Auto-ignition of homogeneous hydrogen/air mixture subjected to unsteady temperature fluctuations

The effect of unsteady temperature oscillation on the ignition of homogeneous constant-volume hydro-gen/air mixture is studied both computationally with detailed chemical kinetics and theoretically using asymptotic analysis. The study is of practical importance in the recent development of low temperature combustion engines (such as homogeneous charge compression ignition engines) in which control of igni-tion timing and burn duration in the presence of temporal and spatial temperature variations becomes a technical challenge. Both low temperature and high temperature regimes of hydrogen ignition are stud-ied. It is found that ignition delay shows a harmonic response to the frequency of imposed temperature oscillation and the response monotonically attenuates as frequency increases. For both ignition regimes, it is found that the ignition delay results at various pressures scale well when both ignition delay and frequency are non-dimensionalized with corresponding steady ignition delay. Asymptotic analysis is also conducted to derive a closed form solution for the ignition delay in the two different temperature regimes. Theoretical results compare well with the computational results.