Numerical Simulation On Ignition Of Hybrid Rocket Motor

Hybrid rocket motor(HRM)is a new kind of propulsion system which combines the characteristics of solid rocket motor and liquid rocket motor.With the advantages of safety,low cost,restart-ability and adjustable thrust,HRM has gradually become an important chemical propulsion device.The ignition process of HRM involves multi-field and multiphase coupling flow,heat transfer and turbulent combustion,which makes the unsteady process extremely complex.The experiment study about the HRM ignition is difficult and costly.The N2O/HTPB HRM is selected as the research object in this article,and,combining theoretical analysis and numerical simulation,the characteristics of flow field,ignition,misfire and re-ignition of the motor is studied which will provide an important theoretical reference for the design of HRM system.The theoretical analysis about the flow,heat transfer,evaporation,ignition and combustion processes in the combustor during ignition of HRM is carried out,and the numerical model and a calculation method of ignition process of N2O/HTPB HRM is established.Based on the model established,the numerical simulation is conducted.The comparison between the simulation results and the experimental results shows that the calculation method is reliable.The evaluation index system of ignition performance of HRM is established.The effects of ignition charge,ignition timing and oxidizer mass flow rate on the ignition performance of the engine are calculated and analyzed.The results show that the delay time of ignition start compared to oxidant injection should be as short as possible;the increase of ignition charge can raise the rate of pressure rising,reduce the ignition delay time,and will significantly increase the ignition pressure peak and pressure oscillation amplitude.Oxidant flow rate effects both the engine working condition and the ignition process,when the oxidant flow rate is too small,the engine cannot work normally and the hypothesis that the fuel will burn instantly when the temperature around the fuel boundary comes to the pyrolyzation point of the solid fuel becomes untenable.With the oxidizer mass flow rate increasing,the stable working pressure will increase,the ignition pressure peak will gradually increase,and the initial ignition point on solid fuel surface will move forward,while the ignition delay time varies slowly.The numerical analysis on misfire and re-ignition process of HRM is carried out.The results show that the closedown process of engine response rapidly,the pressure of the combustion chamber decreases to the circumstance pressure in a very short time,and the thrust of the engine drops to zero at the same time.After a relatively short period of time,the combustion temperature keeps high,and there is still a lot of fuel gas existence,and the engine can be restarted automatically from a re-injection of oxidant.After a longer period of time,the engine cannot restart automatically,and an additional ignition energy input is needed to assist ignition,and the ignition delay time decreases slightly when combustion chamber temperature is relatively high.