Investigations On The Supercritical Injection,Evaporation,and Detonation Characteristics Of The RP-3 Aviation Kerosene

With the development of hypersonic aircrafts,both the working parameters and cooling requirements would significantly increase for high-performance engines in the future,and the supercritical condition will gradually appear in the engine combustor.Generally,as the combustor environment and injecting fuel reach supercritical condition,the fuel injection,evaporation,and combustion process are quite different from that under normal condition.When approaching the supercritical condition,the properties of liquid hydrocarbon fuels would undergo changes and the original liquid fuel then becomes the quasi-gaseous substance of high density with almost the same heat value.As a result,the supercritical fuel could be directly burned in the combustor without experiencing the atomization and evaporation process required by liquid fuels.This kind of rapid combustion could well and exactly meet the very requirement of fast evaporation and rapid combustion by high-performance engine.Therefore,under the scenario of developing supercritical combustors for future high-performance engines,it would be very significant to study and reveal the supercritical characteristics of popularly used hydrocarbon fuels for the future effective application of supercritical combustion.For this end,the present study focuses on systematically investigating the supercritical injection,evaporation,and combustion of the RP-3 aviation kerosene both experimentally and numerically.1)For the RP-3 aviation kerosene,its composition and quite a few of physical properties under different initial conditions,including the density,bubbling point,dew point,and critical point,were measured through a series of experiments.By analyzing the great amount of these significant data systematically,a method was developed for calculating the density of the RP-3 aviation kerosene on the basis of PR state equation.Also,an empirical formula was established for computing bubbling points and dew points by fitting the experimental data using the Clausius-Clapeyron equation.In addition,the choked mass flow rate of the supercritical RP-3 aviation kerosene was experimentally measured,and the variation of supercritical flow quantity with temperature and pressure was analyzed.2)By suspending a single RP-3 aviation kerosene droplet on a quartz fiber in the supercritical chamber,the evaporation characteristics of the droplet under supercritical conditions were studied.The differences between supercritical and subcritical evaporation processes were analyzed.The variations of the squared non-dimensional diameters,transient evaporation constant,droplet life,thermal expansion ratio,and phase transition at the droplet boundary with environment parameters and initial temperatures of the droplet were obtained in detail.Critical phase transition at the droplet boundary was considered to be the main reason for deviation of the supercritical evaporation process from the conventional D2 vaporization law.3)Coaxial injection and mixing of the supercritical RP-3 aviation kerosene with nitrogen was experimentally investigated.The jet structure,condensation characteristics,and temperature field of the mixing flow affected by the mixing structure and injection parameters were studied.The rules of how to accelerate or decelerate the condensation were achieved,and that how the near-field shock structure of the mixing flow was influenced by the injection pressure ratio,mass flow rate,mixing structure,critical phase transition,and condensation was also analyzed.4)Injection characteristics of the supercritical RP-3 into a quiescent supercritical nitrogen chamber were numerically investigated.The influence of the ambient and injection parameters on the jet length and jet spreading angle was analyzed.The supercritical injection process was found to be affected by many factors,such as injection velocity,fluid viscosity,density ratio,momentum ratio,etc.Among all these factors,the injection momentum ratio was considered to be the dominant one.5)The stand test of pulse detonation rocket engine supplied with supercritical RP-3 aviation kerosene was conducted to verify the superior combustion performance of the supercritical fuel.As the fuel being heated to supercritical state under the constant fuel supply pressure of 3.0 MPa,the mixture specific impulse of the engine increased by 15.14 %,and the fuel specific impulse increased by 169.67 %,while the DDT distance was shortened by 52.6 %.In addition,the specific impulse of the engine was almost doubled with supercritical fuel compared to the one with liquid fuel,under the constant fuel flux of 1.524 g/s.