Flow Choking by Drag and Combustion in Supersonic Engine Testing

condition was calculated by incorporating results of a chemical equilibrium numerical code. The fuel rates causing the flow choking were successfully reproduced and matched with the limit of fuel rates observed in our tests. Inlet unstart of the engine caused the loss of the ejector-pumping effect in the diffuser system, which triggered flow choking. Choking was also promoted by the drag of the gas sampling rakes. The choking in diffuser flow and the engine unstart may be coupled, resulting in hysteresis in the diffuser breakdown, which was also experienced in our tests. As the rocket-based, combined-cycle engine is scheduled to be tested under the Mach 4 condition in 2007, the safety of the experiment is now a primary issue. The current analysis showed that the new engine would easily cause choking of diffuser because of the larger propellant supply rates and the relatively low specific impulse. Reasonable operation of the wind tunnel to control the flow choking in future tests was examined.