Effects of Momentum Ratio and Weber Number on Spray Half Angles of Liquid Controlled Pintle Injector

A pintle injector is advantageous for throttling a liquid rocket engine and reducing engine weight. This study ex- plores the effects of momentum ratio and Weber number at various injection conditions on spray characteristics of the pintle injector for liquid-gas propellants. A liquid sheet is injected from a center pintle nozzle and it is broken by a gas jet from an annular gap. The pressure drops of propellants, and the pintle opening distance were consi- dered as control variables; using 0.1 -1.0 as a bar for the pressure drop of the liquid injection, a 0.01-4）.2 bar for the pressure drop of gas jet and a 0.2 - 1.0 mm for the pintle opening distance. The discharge coefficient was de- creased linearly before the pintle opening distance of 0.75 mm and then, the coefficient was slightly increased. Spray images were captured by a CMOS camera with high resolution. Then, the shadow and reflected images were analyzed. Spray distributions were measured by a pattemator with an axial distance of 50 mm from a pintle tip. Finally, the spray half angles had an exponentially decreasing correlation as a momentum ratio divided by the Weber number. Also, the spray half angles from the spray distribution were underestimated compared to those measured from the captured images.

Numerical study on the morphology of a liquid-liquid pintle injector element primary breakup spray

Primary breakup in a liquid-liquid pintle injector element at different radial jet velocities is investigated to elucidate the impingement morphology,the formation of primary breakup spray half cone angle,the pressure distribution,the liquid diameter distribution,and the liquid velocity distribution.With a sufficient mesh resolution,the liquid morphology can be captured in a physically sound way.A mushroom tip is triggered by a larger radial jet velocity and breakup happens at the tip edge first.Different kinds of ligament breakup patterns due to aerodynamic force and surface tension are captured on the axial sheet.A high pressure core is spotted at the impinging point region.A larger radial jet velocity can feed more disturbances into the impinging point and the axial sheet,generate stronger vortices to promote the breakup process at a longer distance,and form a larger spray half cone angle.Because of the re-collision phenomenon the axial sheet diameter does not decrease monotonically.The inner rim on the axial sheet shows a larger diameter magnitude and a lower velocity magnitude due to surface tension.This paper is expected to provide a reference for the optimum design of a liquid-liquid pintle injector.

Verification on Spray Simulation of a Pintle Injector for Liquid Rocket Engine

The pintle injector used for a liquid rocket engine is a newly re-attracted injection system famous for its wide throttle ability with high efficiency. The pintle injector has many variations with complex inner structures due to its moving parts. In order to study the rotating flow near the injector tip, which was observed from the cold flow experiment using water and air, a numerical simulation was adopted and a verification of the numerical model was later conducted. For the verification process, three types of experimental data including velocity distributions of gas flows, spray angles and liquid distribution were all compared using simulated results. The numerical simulation was performed using a commercial simulation program with the Eulerian multiphase model and axisymmetric two dimensional grids. The maximum and minimum velocities of gas were within the acceptable range of agreement, however, the spray angles experienced up to 25% error when the momentum ratios were increased. The spray density distributions were quantitatively measured and had good agreement. As a result of this study, it was concluded that the simulation method was properly constructed to study specific flow characteristics of the pintle injector despite having the limitations of two dimensional and coarse grids.