Spray characteristics of a multi-slit type throttleable pintle injector with different slit heights

A pintle injector is a type of variable-area injector that has been effectively applied in throttleable rocket engines. Among the several types of pintle injectors, multi-slit type pintle injectors are advantageous in terms of combustion efficiency and suitability for continuous throttling. However, the spray characteristics of multi-slit type pintle injectors have been rarely investigated. Therefore, spray characteristics such as pressure drop, spray angle, and droplet size for a multi-slit type pintle injector were analyzed in this study based on slit height and throttling level. Cold flow experiments and numerical simulations using two types of pintle tips with different slit heights were conducted under a wide throttling range of 20-100 %. The experimental and numerical results indicated that adopting a vertically heightened slit significantly reduces the pressure drop, spray angle, and droplet size at high throttling levels, which can be beneficial in terms of combustion performance and combustion chamber durability. Moreover, changes in spray characteristics over a wide range of throttling levels can be alleviated by applying a vertically heightened slit. The numerical simulation models used in this study were validated such that these could be applied to predict the spray characteristics of multi-slit type pintle injectors.