Effects of wall heat loss on deflagration-to-detonation transition in micro-scale tubes studied via chemiluminescence imaging

Detonation in the micro-scale tubes represents one of the promising propulsion systems that can be applied in various engines. One key issue is that the wall heat-loss of the tube plays a significant role in the detonation modes in the tubes. To address this issue, this work reports an experimental study on the effects of the wall heat-loss on the deflagration-to-detonation transition (DDT) modes inside the micro tubes. For this purpose, DDT was triggered in the micro-scale tubes, and the tubes were placed in a sub-sonic wind tunnel operated under different flow rates. The wall heat-loss coefficient (represented by Biot number, Bi) varies with different flow rates of wind tunnel. A high-speed camera with a temporal resolution of 90 kHz captured the chemiluminescence signal generated in the detonation tube. Based on the measurements, the flame tip velocity and the DDT distance are calculated. The results shows that the influence of wall heat-loss is more remarkable in the lean and rich fuel cases compared to the stoichiometric cases.