Performance Analysis Of Power Turbine In Air Cycle Environmental Control System

Traditional aircraft environmental control system(ECS) needs a great deal of engine compressor bleed air to achieve cabin pressurization and take away heat load, it has an impact on the performance of the engine. To get limited flow and appropriate temperature of the cabin air supply, ECS uses pre cooler, absolute pressure regulating device and other components for cooling and reducing pressure of engine compressor bleed air, causing greatly energy wasting and the effective power of the engine doesn’t get fully used. Under the condition of cabin requirement, the current research focus is to reduce the engine compressor bleed air flow. In this paper, a new type of ECS driven by power turbine for MA700 civil aircraft is proposed. High temperature and high pressure engine compressor bleed air entraining directly into the power turbine to expand, the energy of the engine compressor bleed air can be used to the maximum extent. In the same time, the pre cooler, absolute pressure regulating devices and other components can be cancelled to reduce the quality of the system. In this paper, the structure characteristics of power turbine is with adjustable nozzle ring blades, it can change the nozzle ring opening according to ECS compressor power demand to control bleed air flow. This paper mainly includes the following contents:1) According to the MA700 aircraft engine compressor bleed air parameters to calculate the bleed air flow needed in power turbine driven ECS in flight profile. In the ground state, the environment temperature is high, the cabin heat load is large; ram air temperature is high, so heat exchanger efficiency is low; power turbine expansion ratio is small, the amount of bleed air needed is large. So aircraft ground state engine compressor bleed air parameters are chosen to design the power turbine. Cursing time is the longest in flight profile, choosing this state to optimize the power turbine can achieve the best result. The speed of the power turbine, the number of impeller blades and impeller blades shape are optimized at cruising altitude. The optimization goal is to improve the overall performance of the power turbine in the nozzle ring opening degree +3, 0,-3,-6.2) Power turbine performance analysis under the same working conditions: the turbine flow field is compared before and after optimization, and at different nozzle ring openings to explain the reasons for the change of turbine efficiency.3) Power turbine numerical simulation in the flight profile to obtain output power curves, thus determining the opening of nozzle ring blades at any time during the flight.The engine compressor bleed air flow is significantly reduced compared with the original system. The efficiency of the power turbine is between 0.851~0.885 in the flight profile, so it can keep high efficiency under variable working condition.