Thrust Throttling of Large Liquid Propellant Rocket Engines

Summary

The paper concerns rocket engines of the type currently employed in ballistic missiles and satellite booster vehicles, outlining some advantages to be gained from a reduction in thrust towards the end of the burning period. Several methods of throttling a rocket engine are then examined.

Low frequency combustion instability which can arise when an engine is operated below its normal thrust level is considered in some detail, including the effect of such instability on engine performance. Means of ensuring stable operation both in the main thrust chamber and the turbine gas generator are described and compared.

The mechanism of heat transfer to the main injector has been studied and the modifications to the injection pattern necessary to maintain this at a safe level are described. Also, changes in the overall heat transfer rate to the thrust chamber walls are discussed with special reference to the formation of an insulating layer which occurs with carbon-bearing propellants.

The discrepancy between the inlet heads of the propellants at high vehicle accelerations is noted and the relative effect of this on engine operating conditions for the throttled and unthrottled cases described.

Finally, the effect of pressure change on the thrust chamber performance is considered with reference to studies made on the Rolls-Royce RZ.2 engine.