Surface heat loss and chemical kinetic response in deflagration-to-detonation transition in microchannels

The effects of cold, hot, and adiabatic walls on flame propagation and deflagration-to-detonation transition (DDT) in a microscale channel are investigated by high-resolution numerical simulation. Results show that the conducting, cold, and hot walls lower the flame acceleration rate, while DDT can occur and originate from local explosion near the flame tip for both the hot and adiabatic walls. Furthermore, for the adiabatic wall, autoignition near the wall produces fast flames in the boundary layer, inducing two shocks propagating and colliding at the center, inducing a local explosion near the flame tip. However, for the hot wall, fast flames do not appear in the boundary layer due to heat loss at the wall; DDT occurs due to coupling of the compression waves with the stretched flame, and needs strong local explosion due to the absence of autoignition in the boundary layer. Nevertheless, compared with the adiabatic wall, occurrence of DDT is delayed while the run-up distance is reduced because of heat input from the hot wall to the fresh gas. For the cold wall, a flame propagates oscillatorily and fails to develop to detonation. It is identified that the flame retreat is caused by thermal contraction due to heat loss at the cold wall. It is further demonstrated that realistic chemistry is needed for an accurate description of the occurrence of autoignition within the boundary layer and DDT.