Research On The Characteristics Of Pyrotechnic Cartridge Start For Micro Turbojet Engine

Micro turbojet engine turbojets have become the preferred power unit of miniature air weaponplatform such as small unmanned aerial vehicles (UAVs), decoys, and loitering munitions, because oftheir extremely-high thrust-to-weight ratio. For fast reaction of aircraft, pyrotechnic cartridge start isthe fastest and the most reliable of starting methods in general use. Based on characteristics of start,the research presented in this paper accomplished the way to choose the starter matching with engine,and used the prediction model for driving moment from starter with performance parameters of starterand the relation between resistant torque and rpm to predict the parameters and curve of starting.According to the characteristics of the micro turbojet engine’s structure and industrial art, it waschosen that starting is accomplished through direct impingement onto the turbine blades by pyrotechnicgas, and the start system was design. In order to simplify the analysis, the real process, the highpressure gas impinges the turbine blades, is replaced by a thought process, the jet impinges a singleblade, to model the relation between driving moment from starter with the performance parameters ofstarter or the parameters at the exit of the spray nozzle.To study the effect of the total pressure, the total temperature, the shaft speed, the relative positionof blade with the spray nozzle and the intake air flow, the flow in a small axial turbine driven by thehigh energy gas was calculated by CFD. Statistical results of the effect of the total pressure, the totaltemperature and the shaft speed were fitted by the prediction model to determine the undeterminedcoefficients in the model. The effect of the relative position of blade was considered in the model.Based on the theory of pyrotechnic cartridge start, a simulation test was conducted, in which thepower source used the high pressure air tank. According to the results of test and model, the differencebetween them was less than10%. The relation between total-pressure for monitoring and the totalpressure was demarcated by a free jet flow test. Based on a test data gathered, torque for accelerationwas calculated as a function of rpm during acceleration, and resistant torque was calculated as afunction of rpm during deceleration when the air was cut off to derive driving moment from starter.To predict the parameters and curve of starting with high pressure air impact, the predictionmodel for the driving moment from starter and the relation between resistant torque and rpm wereapplied. It was proven that the prediction method is feasible.