Experiments on flame holding position of the fin-less projectile in ram accelerator

Abstract

Supersonic combustion flow around a projectile in a ram accelerator has been visualized and investigated by using the rectangular bore ram accelerator in Hiroshima University. The velocity range of the experiment is 1100 to 1350m/s, that is 0.77 to 0.93 of the velocity ratio to the C-J detonation velocity of the CH4-O?-CO2 mixture. In the present paper, the effects of the projectile velocity on the supersonic combustion flow around the projectile are discussed. In the present study, it becomes clear that the flame propagates quickly forward up to the front of the projectile when the projectile comes into the ignition tube, where easily ignitable gas mixture is filled. If the projectile velocity is enough high, the remained flame in boundary layer on the leading wedge of the projectile will be blew out and goes back to the rear part of the projectile. On the other hand, the flame front remains at the leading wedge, if the velocity is not so high. In the present experimental conditions, we can divide into three cases. When the projectile velocity is smaller than 1200m/s, ram acceleration occurs even through the leading flame front exists at the leading wedge. But the stronger leading shock wave, caused by the leading flame front, reduces the thrust. When the projectile velocity is 1200-1300m/s, the leading flame exits around the projectile shoulder. But because the thermal choking point is a little bit far from the projectile, the