空气节流对超燃发动机燃烧性能的影响

为优化隔离段及燃烧室内的流场结构,减小流动速度,提高流道压力,在凹槽稳焰器下游布置空气节流装置,向燃烧室内喷入高压空气,目的是在隔离段建立合适的激波串,以利于点火和火焰稳定.采用CFD方法,对比了无/有空气节流时的冷流流场、燃烧流场,结果表明:节流激波串扩大了低动量区域,激波引起的流动扭曲和较长的驻留时间使得分离流内的空气/燃料混合程度得到显著增强,混合效率由无节流时的40％提高到85％,燃烧效率由无节流时的10％提高到60％.对节流位置和节流量进行了参数化研究,以隔离段入口为坐标原点,分别考察了785,1 000,l 100 mm三个流向节流位置,以及10％,15％,30％三种节流量的影响,结果表明:距离凹槽较近的节流位置对燃烧的影响更为显著,所需节流量更少.30％的节流量将使燃烧室背压急剧提高,引起流动壅塞.研究表明在785mm的流向节流位置采用15％的节流量可获得最好的燃烧性能.

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.