高压燃油喷雾诱导激波产生机理及频率特性

Generated Mechanism and Frequency Characteristics of Shock Waves Induced by High Fuel Injection Pressure

基于纹影法对不同工况下的燃油喷雾诱导激波产生机理及频率特性进行了试验,结果表明:喷雾周围的激波主要分为前导激波和伴生膨胀波,其产生原因以及对喷雾的影响均不同.喷射初期喷孔出口处喷雾前锋面马赫数大于1直接导致了前导激波的产生,根据喷雾前锋面马赫数的大小不同,前导激波又分为斜激波和弓形激波两种形态.喷雾体的周围是伴生膨胀波的产生位置之一,且喷雾周围的伴生膨胀波为膨胀马赫波,伴生膨胀波强度与喷雾锥角相互联系,在低背压下不明显;喷孔出口处喷雾剪切层也可能是激波产生位置之一,且为弱激波.另外,对激波的频率特性进行了研究,结果表明:低频激波频率平均值约为111.11,kHz,当背压相同时,激波的平均频率大小与喷射压力呈正相关关系;当喷射压力相同时,激波平均频率大小与背压呈正相关关系.激波频率的增加促进了缸内的混合气扩散,喷雾的雾化效果更好.

Generated mechanism and frequency characteristics of shock waves induced by high injection pressure under different kinds of working conditions were studied using a schlieren imaging visualization.Experimental results show that there are leading shock wave and expansion waves around the high pressure spray,which has different generated mechanisms and effects on spray.Early spray tip near the orifice has Mach number higher than 1,leading to the leading shock wave generation.Based on the difference of spray tip Mach number,leading shock waves have two types:the oblique shock wave and the bow shock wave.One of the expansion wave generated places is on the side of the spray.Furthermore,the expansion waves are inflation Mach waves.Their strength has a correlation with spray angle,so they are not obvious under low ambient pressure.Another shock wave generated place may be within the shear layer of the spray near the orifice,but the shock waves are weak.Besides,shock waves frequency characteristics were studied.Experimental results show that the low average frequency of the shock waves is 111.11,kHz approximately.It has a positive correlation with the injection pressure at the same ambient pressure and a negative correlation with the ambient pressure at the same injection pressure.The increase of the shock wave frequency promotes mixture diffusion and makes atomization better.