Research and Verification on the Solution of Bleed Air Temperature Deviation of Civil Aircraft Pneumatic System

The pneumatic system of civil aircraft is equipped with a precooler (PCE) to cool the high-temperature bleed air from the engine to meet the design requirement of a downstream user system. The PCE is usually a fork-flow heat exchanger. This heat exchange structure will make the outlet temperature difference especially large, which shall lead to the deviation of the inlet air temperature of the downstream wing anti-icing system and air conditioning system and cause the temperature of bleed air supplied to the wing anti-ice system unstable. During a flight test of a certain large passenger aircraft, it was found that the bleed temperature at the PCE outlet was lower than the piccolo inlet temperature of the wing anti-ice system when the wing anti-ice system was operated with two engine bleed systems on. This paper creatively proposes design ideas for the three kinds of mixers and determines the solution of adding a mixer downstream of the PCE to solve the temperature deviation problem. The mixer is installed at the hot side outlet of the PCE and used to mix the temperature field at the PCE outlet so that the air supplied to the downstream customer systems meets the design temperature requirements. According to the simulation calculation and laboratory test verification results, the design scheme of a certain large passenger aircraft is selected, which has successfully solved the problem of temperature stratification at the outlet of the PCE and supported the follow-up flight test.