Experimental study on the characteristics and mechanism of flame stabilization in liquid oxygen/methane pintle injector

This experimental study investigates the dynamic characteristics and stabilization mechanisms in the liquid oxygen/gas methane (LOX/GCH4) pintle-type combustor. Utilizing high-speed flame spontaneous emission imaging (FSEI), spray-flame synchronous imaging (SFSI), and particle image velocimetry (PIV), four distinct combustion stages were identified without high-frequency instability. The flame exhibits low-frequency shape oscillations (28.88 Hz), inducing corresponding chamber pressure oscillations (28.82 Hz), while intermittent pressure spikes arise from flow field interactions. Based on FSEI, the flame anchors on the leeward side of the liquid jet near the pintle head during ignition. Subsequently, the flame's center of mass moves downstream while its lower boundary expands outward. Key findings based on SFSI and PIV reveal dual flame anchoring mechanisms: (1) Below the pintle head, aerodynamic deformation of the LOX column into a cape-shaped film creates a low-speed recirculation zone where droplet-gas mixing sustains stabilization. (2) Within bilateral spray boundary bands, intense shear layers (leeward flow blockage and windward flow diversion) enhance mixing, forcing flame anchoring toward low-strain zones. Remarkably, flame stability persists across drastic mixture ratio shifts (oxygen-rich to fuel-rich regimes) due to adaptive flow field structures. The study provides experimental evidence of flame stabilization in pintle injector and elucidates how liquid column dynamics govern the characteristics of flow field. These insights advance the design of LOX/GCH4 engines for reusable applications, offering fundamental data for validating three-dimensional reactive flow models. This study presents the direct experimental investigation of flame stabilization mechanisms in a LOX/GCH4 pintle-type combustor. By employing novel synchronous spray-flame imaging combined with high-speed flame visualization and particle image velocimetry, it reveals previously unreported flame anchoring characteristics, including a distinct low-frequency flame oscillation mode (∼29 Hz) governing chamber pressure dynamics and dual stabilization sites. Critically, the work elucidates the fundamental roles of liquid column-induced flow separation creating low-speed recirculation zones and intense shear layers at spray boundaries in dictating flame topology. These mechanistic insights advance the understanding of spray combustion dynamics in variable-thrust rocket engines using LOX/CH4 propellants.