Experimental investigations on the temperature equilibrium process inside a detonation tube operating in a valveless scheme

As the previous studies have clarified that the temperature of detonation combustor wall will increase with the increase of operating frequency, but the mechanisms are still not clarified. An experimental work has been conducted to investigate the temperature equilibrium process of the internal wall in a pulse detonation tube, which was operated in a valveless scheme without the purge process. Ethylene and oxygen-enriched air with an oxygen volume fraction of 50% were used as fuel and oxidizer, respectively. The injections of fuel and oxidizer were both controlled by pressure oscillations in the detonation tube. The heat transfer process inside the detonation tube was studied by employing a fast response thermocouple installed near the internal wall. The results indicate that the heat transfer process in an individual detonation cycle in multi-cycle operation contains a heating up process and a cooling down process. Heat transferred from the burned gases to the tube wall in the heating process, while it reversed into the fresh mixture in the cooling down process. The equilibrium temperature was determined by the competition of the two processes. The cooling duration decreased when the operating frequency increased. The heating up duration was influenced by the expansion waves and the wall temperature, and it decreased with the increase of the wall-temperature. In addition, the temperature differences, among the burned gases, the fresh mixture, and the tube wall, were the main factors that influenced the heat load and the equilibrium process of the wall-temperature.