Effects of Dimensionless Numbers on the Pintle Injector Performance

Variable-area injectors are suitable for developing throttleable rocket engines because it is difficult to efficiently control thrust when fixed-area injectors are used. A pintle injector is a variable-area injector that can be used to control the mass flow rate of propellants. In practice, an injector plate containing several fixed-area injectors is replaced with a single pintle injector. In this research, a two-stage pintle injector is designed, manufactured, and tested for the effects of dimensionless numbers (Momentum ratio, Weber number, and discharge coefficient) on the injector’s performance, including the spray angle change, which is an important characteristic of the spray. The tests were done at ambient temperature and pressure conditions. The Weber number ranged from 19 to 1830, and the ratio of the fuel to the oxidizer momentum was varied from 0.2 to 13. Water is used instead of the oxidizer as a central propellant, and the air is used instead of the fuel as an external propellant. Shadowgraph and photography were used to measure the spray angle and study the desired parameters. Empirical relationships between functional parameters and dimensionless numbers were obtained that can be used in the design process.