Air-throttling effect of scramjet combustion characteristics

Compressed air was introduced into the combustor to establish pre-combustion shock train.The main purpose of air throttling is to optimize flow structure of isolator and combustor to reduce the local flow velocity,increase the pressure and make ignition and combustion easier.Using CFD method,the cold and reactive flow fields with/without air throttling were compared.The results show that the throttling shock enlarges low momentum regions and slows down the air/fuel mixture.The flow distortion caused by the throttling shock and extended residence time enhance air/fuel mixing remarkably.The mixing efficiency increases from 40% to 85%.Also the combustion efficiency increases from 10% to 60%.A parametric research was conducted to investigate the effect of throttling location and throttling mass flow rate on the combustion characteristics.Three throttling locations,x=785mm,x=1000mm and x=1100mm,and three throttling mass flow rates with 10%,15%,30% were studied respectively.The results show that the effect of the nearest throttling location is most notable,where the least throttling mass is required.30% throttling mass flow rate increases back pressure sharply and makes the flow choked.In the given condition,throttling with 15% air flow mass at x=785 mm obtains the best combustion efficiency.