  The deflagration-to-detonation transition (DDT) process is of great
importance to both combustion theory and industry safety. In this study, the
propagating mechanism of Chapman-Jouguet (C-J) deflagration is studied.
Firstly, three models are put forth to decouple the C-J detonation front. These
three models are (a) to introduce an expansion parameter into the
one-dimensional energy equation, (b) to increase the activation energy of the
chemical reaction model and (c) to decouple the shock wave from the flame front
by artificial method. The C-J deflagration is obtained after the C-J detonation
is decoupled by one-dimensional numerical simulations with different models,
chemical reaction kinetics and numerical schemes. Secondly, the propagating
mechanism of C-J deflagration is discussed. For the C-J deflagration with a
propagating velocity of about 1/2 C-J detonation, the static temperature behind
the leading shock wave is too low to ignite the combustion. But, the total
temperature of the flow induced by the leading shock wave is high enough to
ignite the mixture. The induced flow is slowed down by the rarefaction waves
form the wall and its static temperature increases. The flame and the leading
shock wave propagate with almost the same velocity and the double-discontinuity
structure of the flow field keeps stable. The propagating velocity equals to
the sound speed of the combustion products, which is about 1/2 C-J detonation
velocity.
