Experimental detection of two-dimensional temperature distribution in Rocket-Based Combined Cycle combustion chamber using multispectral imaging processing

•A new method was proposed to measure flame temperature in RBCC combustion chamber.•Effects of equivalence ratio on flame temperature were investigated.•The position of peak flame temperature oscillated with time sequence.•Effects of laser-induced plasma and plasma jet torch on combustion were analyzed. The extremely harsh environment and highly unsteady and transient nature during supersonic combustion bring great challenges for quantitative diagnostics. In the present work, for the first time, we report measurements of two-dimensional distributions of flame temperatures in a Rocket-Based Combined Cycle (RBCC) combustion chamber using a multispectral imaging technique with both spatial and spectral resolutions. The relation between the multispectral radiation intensity images and the flame 2-D temperature distributions was established by combing the Lvevenberg-Marquardt algorithm and the Hottel and Broughton emissivity models. The experimental results revealed that both laser-induced plasma (LIP) and plasma jet (PJ) torches had positive effects on combustion stabilization, and LIP had better effect on combustion enhancement. In the ignition stage of a fuel/air mixture with an equivalence ratio of 1.0, the average temperature of a flame initiated by LIP combustion enhancement was 100 K higher than that by PJ torch combustion enhancement. A recirculation zone was formed inside a cavity, which improved the combustion stability. The injected fuel and inflow were most fully mixed on the slope at the rear of the cavity, where 70 % and 65 % of the peak flame temperature points of LIP and JP were located, respectively. The combustion in the RBCC chamber showed an oscillation phenomenon that peak flame temperature and the flame structure oscillated continuously around the central axis with a horizontal extent of 162 mm. Due to the insufficient fuel blending, the oscillation amplitude was minimal when the equivalence ratio was 1.0. Overall, the results of flame temperature distributions demonstrated that the proposed multispectral thermometry was suitable for measuring temperatures of supersonic combustion flames.