Transient Model of a Pneumatic Ejector: Application to the Simulation of Aircraft Bleed Air Temperature Control Systems

A transient pneumatic ejector model suitable for use in simulation of aircraft environmental control systems is presented. The ejector model is formulated to accommodate modulation of both primary and secondary ejector flows using butterfly modulating valves. The two-state variable ejector model is employed in the simulation of an actual aircraft bleed air temperature control system, which utilizes ejector secondary air as the heat sink for a heat exchanger. The thermo-fluid system simulation equations and a qualitative description of control system operation are presented. Additionally, comparisons of the closed loop transient math model performance characteristics relative to actual ground and flight test results are presented.