  Understanding the mechanisms of explosions is important for minimizing
devastating hazards. Due to the complexity of real chemistry, a single-step
reaction mechanism is usually used for theoretical and numerical studies. The
purpose of this study is to look more deeply into the influence of chemistry on
detonation initiated by a spontaneous wave. Results of high resolution
simulations performed for one-step models are compared with simulations for
detailed chemical models for highly reactive and low reactive mixtures. The
calculated induction times for H2/air and for CH4/air are validated against
experimental measurements for a wide range of temperatures and pressures. It is
found that the requirements in terms of temperature and size of the hot spots,
which produce a spontaneous wave capable to initiate detonation, are
quantitatively and qualitatively different for one-step models compared to the
detailed chemical models. The impact of detailed chemical model is particularly
pronounced for the methane-air mixture. In this case, not only the hot spot
size is much greater than that predicted by a one-step model, but even at
elevated pressure the initiation of detonation by a temperature gradient is
possible only if the temperature outside the gradient is so high, that can
ignite thermal explosion. The obtained results suggest that the one-step models
do not reproduce correctly the transient and ignition processes, so that
interpretation of the simulations performed using a one-step model for
understanding mechanisms of flame acceleration, DDT and the origin of
explosions must be considered with great caution.
