Research On The Dynamic Spray Characteristics Of The Gas-centered Swirl Coaxial Injector

Unstable combustion is one of the most difficult problems in the field of the liquid rocket engine.The dynamic spray characteristics of injector have a big influence on the unstable combustion.It’s important to conduct extensive research on the dynamic characteristics of the gas-centered swirl coaxial injector for its wide application in the LOX/kerosene engine.To investigate the dynamic characteristics of a swirl gas-centered swirl coaxial injector,experiments are operated with high-speed photography and Malvern laser particle size analyzer under different injection conditions and injector geometries.Firstly,the five different modes of spray breakup are obtained through the photographic study.They are segmented sheet breakup,perforated sheet breakup,bubble breakup,pulsating breakup and air-blasting breakup.And the disintegration modes of an annular liquid sheet mainly result from interaction among aerodynamic force,surface tension and viscous force.A tentative map on the disintegration modes of liquid sheets in the terms of liquid Reynolds number and the aerodynamic Weber number representing those effects is illustrated.The varying regularities of spray angle,breakup length and(SMD)Sauter mean diameter along with GLR(the ratio of the mass flow rate of gas to liquid)and recess ratio are studied through data processing,and the mechanisms of the central gas and liquid annular sheet inducing varying regularities is explained.Secondly,the self-pulsation phenomenon of the gas-centered swirl coaxial injector is observed in the experiments,and self-pulsation boundary with injection conditions and recess length is obtained.The frequency data got by image processing shows that the frequency of self-pulsation is mainly affected by the central gas,and increases with the gas Reynolds number.The self-pulsation occurs when kinetic energy of the central gas overcomes inertia potential energy of liquid sheet and induces shrinkage and expansion of liquid sheet periodically.Self-pulsation expands distribution of spray,however,increase the amount of large droplet.So this phenomenon deteriorates atomization of spray.Finally,the hydro-dynamic pulsator is used to investigate the spray characteristics of the gas-centered injector under oscillation of liquid mass flow rate.When the liquid swirl injector operates alone under oscillating condition,Klystron effect of spray is observed and mechanism of Klystron effect is discussed.Dynamic respond of spray angle to mass flow rate is also researched by image processing.As the central gas injector and swirl injector are operated together,self-pulsation and klystron effect both appear in the spray pattern,and the interaction between self-pulsation and Klystron effect is analyzed.The varying regularities of spray angle are obtained with oscillation frequency of liquid mass flow rate.