Design Procedure of a Movable Pintle Injector for Liquid Rocket Engines

摘要

When developing a throttleable rocket engine, variable area injectors are a suitable choice because when using fixed shape injectors, it is difficult to efficiently control thrust A pintle injector, a type of variable area injector, can control the mass flow rate of propellants, thereby replacing a large injector plate with its many injector elements with a single injector unit. To achieve high performance at all throttling conditions, we established an optimal design procedure for a pintle injector based on spray characteristics. Critical performance parameters were considered to be the spray half-angle and droplet diameter. In spray experiments using water and air as simulants at atmospheric conditions, backlight imaging and laser diffraction methods were used to measure the spray half-angle and droplet diameter. The momentum ratio and Reynolds number were considered to be major non-dimensional numbers. In addition, a new characteristic number was defined using these non-dimensional numbers. Correlations were estimated between performance parameters and characteristic numbers and these correlations were applied to our design procedure. In consequence, using this procedure, a pintle injector for a 500 N combustor was desined at specific performance conditions and maintained performance at both full- and half-throttling levels.