Thermal Environment Analysis And Thermal Protection Of A Pintle Injector For GOX/GCH₄ Rocket Engines

Taking a GOX/GCH₄ pintle engine as the research object,this thesis makes asystematic investigation on the influences of pintle injector's length,injection holesshape and head shape on its characteristics of combustion and heat transfer numerically,supporting optimized geometry designs with a better thermal protection for the pintle injector.Besides,the law that temperature of pintle tip changes with varied working conditions is obtained by conducting a series of firing experiments based on a self-designed 500N GOX/GCH₄ pintle engine.The evaluation indexes of pintle injectors'thermal environment include maximumtemperature and heat flux on the pintle tip and global combustion efficiency,while the specific parameters studied consists of a skip distance,L_s,an interval between double rows of injection holes,L_i,a head shape parameter,b/a,a ratio of circular holes'diameters,D_f/D_s,and a ratio of rectangular holes'height and width,l/w.Firstly,as a typical feature of the pintle engine,in general there are two pairs of recirculation zones in the flow field of the combustion chamber,one in the head-dome region,another one in the center of the chamber.These two recirculation zones play a key role of propelling mixing and combustion,simultaneously keeping a stable combustion.Secondly,for methane centered pintle injectors with double rows of injection holes,the cooling of the pintle head is mainly realized by the small recirculation zone under the pintle tip,which is formed by oxygen film of high concentration escaping from the interspace of the double rows of holes.There is a negative relationship between tip temperature and oxygen concentration in the small recirculation zone.When the oxygen concentration is identical,the cooling effect is mainly dominated by the distance between the tip and cool methane inside the pintle body,the distance shorter,the cooling better.While it is intensively influenced by the geometry parameters that whether the small recirculation zone exists or not and how large its dimension is.Additionally,global combustion efficiency decreases significantly when l/w is increasing from 0.5 to 4 and maximum reduction amplitude is over 10%.However,it is not much sensitive for the varying of other geometry parameters.Finally,for working conditions with low O/F ratio and low chamber pressure,both of experimental and numerical result indicate that under the same chamber pressure level,the tip temperature declines firstly and then rises with O/F increasing.The quantitative comparison shows that the maximum difference between the two results of the tip temperatures is no more than 30%of the experimental one.While under the designed working condition,the true tip temperature derived from microstructure analysis on ablated region is at least over 1000?,smaller than the numerical one 20%.Therefore,the present simulation model could give a trend of pintle tip temperature change consistent with the actual situations,which is of applied value for guiding the primary design of the pintle injectors.