Local momentum ratio-dominated stability control in a throttleable liquid oxygen/methane pintle combustor

This study examines how local momentum ratio (LMR) governs combustion stability in a pintle combustor through liquid oxygen (LOX) flow throttling experiments. Rough combustion occurs and its severity is governed by operational conditions. When the LMR decreases from 0.85 to 0.25 during the regulation stage, the chamber pressure amplitude decreases by 52%, and its standard deviation decreases by 50%. Based on the topology of spray and flame acquired by the spray–flame synchronous observation method, it is found that the spatial decoupling of the heat release zone and the oscillation zone is the key to improving combustion status. A reconstruction mechanism from “wall-impacting combustion” to “gas-confined combustion” is proposed. At high LMR, the momentum of the LOX spray dominates, causing the strong heat release zone near the wall to overlap with the strong oscillation zone. At low LMR conditions, the gas film encapsulation effect promotes the movement of the heat release core, realizing the spatial decoupling of the two zones. The dual-threshold criteria of flame area/brightness precisely locate the critical interval of the combustion status transition at LMR = 0.60–0.65, characterized by the disappearance of the liquid spray wall-impingement phenomenon and the reconstruction of the heat release rate distribution. The regulation process can be divided into three substages. Mode1 dominates both rapid- and slow subphases, accounting for 34.9% and 28.2% of the energy distribution, respectively. That suggests the regulation process avoided triggering notable coherent structures and the robust flame stabilization within the recirculation zone effectively suppresses combustion instability.