Flame structure of GCH4/GOX pintle model combustor with wall confinement

The pintle injector is a representative option for designing a throttleable rocket engine that can be applied for various applications, including the vertical soft landing of reusable launch vehicles. Although the most direct research method to investigate the characteristics of pintle injectors experimentally is the high-pressure combustion test, it is often limited due to its cost and operational hazards. Consequently, atmospheric combustion or cold flow tests are frequently applied in the rocket injector field to simulate and study the fundamental combustion or spray characteristics. However, previous works, including such simulated experiments under atmospheric conditions, involved an unrealistically wide combustor or open condition. Since only a single pintle injector is typically used per engine, the combustor wall may significantly influence the fundamental characteristics. Thus, in this study, a pintle injector combustor with adequate wall confinement is designed, and its flame structure is investigated across a wide range of total volume flow rates and mixture ratio conditions, incorporating several geometries with varying gaseous oxygen injection areas. This research primarily focuses on the flame structure and its angle. Under specific experimental conditions, the unreported unstable flame was newly observed. The overall experimental results, supported by numerical methods, indicate that wall confinement has substantial importance in simulating a realistic flame structure and internal flow field within the combustor.