Impact of nozzles on the wall-temperature in a valveless pulse detonation engine

As the increase of wall-temperature during the long-duration operation, pre-ignition of the fresh mixture in the filling process often occur in the detonation tube, resulting in the failure of operation. An experimental work has been conducted to investigate the impact of nozzle on the wall-temperature of the detonation tube. In the present study, kerosene and oxygen enriched air were employed in the experiments, and an internally grooved semi-circle spiral, instead of traditional Shchelkin spiral was utilized to facilitate the deflagration to detonation transition (DDT) process. The theoretical results showed that the temperature of fresh mixture increase along the detonation tube during the filling process, and it is likely to be ignited near the open end. It was observed from the experimental results that the convergent section and the divergent section of the exit nozzle has different influence on the wall-temperature. The convergent nozzle will not prevent the wrapping flame near the open end of the detonation tube, and lead to the increase of equilibrium wall-temperature. The nozzle with a diverging section will eliminate the occurrence of wrapping flame during the operation, and the wall temperature near the open end are dramatically decreased. In addition, smaller expansion ratio of the nozzle will lead to lower equilibrium wall-temperature.