Design and CFD-Based Optimization of Multi-Slit Pintle Injector for High Pressure LOx-Methane Rocket Engine

Increase in demand for sustainable technologies has accelerated the use of environmentally friendly propellants in rocket propulsion. Liquid oxygen (LOx) and methane (CH₄) have gained attention as a green alternative to hypergolic propellants due to their high performance, non-toxic nature, and in-situ resource utilization potential. Injector plays a key role in governing mixing, combustion efficiency, and stability. Throttling capability is essential for reusable launch vehicles and planetary landers, where precise thrust control is required. Pintle injectors address these needs by offering smooth throttling, reduced combustion instabilities, and reliable operation. This study presents design and analysis of an oxidizer centred pintle injector for a high-pressure LOx-methane engine, with the objective of optimizing the pintle design through CFD simulations. An analytical procedure to design multi-slit pintle injector is presented and combustion modelling at supercritical conditions is carried out to study the influence of key geometric parameters. Flamelet Generated Manifold (FGM) combustion model with the Soave Redlich Kwong (SRK) real fluid EoS is used in a RANS framework. Results show that injector geometry strongly influences mixing behaviour. Variations in annular gap and skip ratio have no substantial impact on mixing performance, whereas pintle geometric parameters play a dominant role in mixing. Decrease in the number of slits leads to improved mixing efficiency. Further, the single row slit configuration enhances mixing even at higher slit numbers as the interaction area between the LOx and methane significantly increases. This work offers systematic insight into pintle injector design optimization for LOx-methane propulsion systems and supports the development of efficient and sustainable rocket engines.