Research Of Starting Characteristics In Windmill State For Micro Turbine Engine

As a new propulsion device, Micro-turbine engine (MTE) can be widely used inmicro and small aircraft. Based on the emission characteristics of micro and smallaircraft, study of windmill starting process of MTE is significant for engineeringapplications. In this paper, by method of numerical simulation and experiment, windmillfeatures, propane and oil ignition characteristics are studied. Based on this, the process ofwindmill starting the engine was optimized, in order to get the best starting process. Thestudy obtained the following conclusions:(1) In this paper, based on resource of laboratory,design of MTE test bed, vacuum pumpair system, engine condition monitoring system, engine control systems, fuel supplysystem, propane gas supply system, temperature measurement and collection system,pressure measurement and collection, seven modules in all, MTE windmill starting testbed was designed.(2) Study of the MTE windmill characteristics as a whole, we found that the windmillbalanced speed and air flow are approximately linear to the free flow speed.the higherfree flow speed,the higher windmill balance rotation speed and the more engine air flow.When the stream velocity changes from10to65m/s, the engine windmill balance speedranged from5000RPM to45000RPM, while engine air flow ranged from20to170g/s.On this basis, low-speed numerical simulation of compressor and turbine characteristicswere carried on, to obtain a low-speed turbine and compressor characteristic line.Combined with tests of windmill starting, the compressor and turbine windmill statework together line were calculated, in order to estimate the characteristics of its powerand obtain the mechanical loss and mechanical efficiency of the engine, under differentwindmill rotor speed conditions.(3) Under different free flow speed and propane gas flow rate conditions, the enginepropane ignition test was carried on, to determine the success of ignition, and acquiredreliable propane ignition envelope range. The reliable free flow speed for propaneignition ranges from5to10.33m/s, while propane concentrations ranges from0.502%to1.343%.After the success of the propane ignition, we increase the flow speed to study theproperties of propane extinguish characteristics, to obtain the extinguish boundary. The engine does not turn off when flow speed ranges from5to25m/s, while the lowestpropane concentration is0.12%and the largest propane concentration is14.4%.Underdifferent flow conditions and different concentrations of propane, we study thecharacteristics and effects of the start, and acquired that the combustion chamber preheattemperature available ranges from450K to700K, while propane start balancing speedranges from3200~11200RPM and propane burning has much more effect on enhancingthe engine speed than windmill-driven.(4) Under the condition of different free flow speed, different mass flow of propane anddifferent initial fuel supply, the windmill starting experiment was carried on, to obtain therequirement of fuel ignition and engine characteristics during the start process. Thereliability for fuel ignition speed ranges7440~9360RPM, the amount of propane gasranges0.08~0.2g/s, and the initial fuel supply ranges0.67~1g/s. On the basis of a largeamount of fuel ignition experiment, the reliable fuel ignition envelope range wasachieved with the flow speed range of3.6~10.33m/s and fuel concentrations range of2.38%~7.78%.(5) Based on above study, the process of windmill starting the engine was optimized.Firstly a series of optimum parameters was achieved through the optimization processwith the optimum flow6.51m/s, the optimum engine speed for propane ignition3360RPM, the optimum mass flow of propane0.125g/s, the optimum fuel ignition flow11.3m/s, and the optimum mass flow of the initial fuel0.56g/s. Secondly, afteroptimizing the process from fuel ignition to idle, the optimum fuel control law is that thesupply of fuel is first big after small; from idle to80%full speed, the slope of fuel supplyshould be divided into two with one0.79and the other0.14in optimum state. Finally, theacceleration time of the engine was also optimized, and it greatly shorts the accelerationtime. The acceleration process of windmill was shorten by42%and the accelerationprocess of propane start was shorten by53%. From fuel start to idle, the accelerationtime was also cut down by36%and the acceleration time during idle to80%full speedcan be mostly shorten by93%in the experiment condition of this paper. Based on thecomprehensive optimization process of the windmill start from0to80%full speed, thewhole time of engine start and acceleration was27s.