Experimental study on heat release distribution during supersonic combustion

Abstract

The operation performance of scramjets is largely dependent on heat release distribution in combustor. An experiment on supersonic combustion is conducted using a direct-connected facility. The CH* chemiluminescence and schlieren images are captured synchronously to identify the heat release characteristic and quantify its intensity. With the increase in fuel injection strength and equivalence ratio, three distinct heat release modes are sequentially observed: boundary-layer (BL) mode, long-distance-distributed (LDD) mode, and short-distance-concentrated (SDC) mode. Heat release under BL mode is characterized by a stable region, weak intensity, and low-frequency oscillation. SDC mode exhibits an intense heat release with significant oscillation. LDD mode can be considered as a transition between BL and SDC modes. A regime diagram is developed based on chemical kinetics and flow separation theory. This allows for a quantificational distinction between different modes. Furthermore, a one-dimensional heat release rate distribution model is proposed based on a quasi-Gaussian function. This model integrates both heat release intensity and its spatial range, providing a comprehensive and accurate representation of heat release rate distribution. The verification results indicate that the current model can accurately replicate the heat release rate distribution observed in both experimental and numerical studies. When coupled with the quasi-one-dimensional flow equations, the current model exhibits significant potential for evaluating operation performance and optimizing design of scramjets.