Experimental Investigation on Flame Chemiluminescence and Flow Characteristics of a Reverse-Flow Combustor

Abstract

The reverse-flow combustor is extensively applied in small engines due to its compact structure. The cold-state flow characteristics, the ignition process, and flame chemiluminescence characteristics of the reserve-flow combustor were investigated experimentally. Using the particle imaging velocimeter, the cold-state time-averaged flow fields at three different total pressure loss coefficients $\left({\zeta }_B\right)$ are examined. The ignition processes of the combustor, as well as flame characteristics during stable combustion at different equivalent ratios $\left(\phi \right)$ , are analyzed based on flame chemiluminescence imaging when ${\zeta }_B$ is 3%. As ${\zeta }_B$ increases from 1% to 5%, the flow field of the combustor remains almost unchanged while the flow velocity increases. For ${\zeta }_B$ =3%, the ignition time $T$ drops from 26 ms to 16 ms with an increase of $\phi$ . In addition, the ignition performance is enhanced. Proportions of the T2 phase (quasi-stable phase) are 73%, 68%, and 66%, respectively, suggesting that the quasi-stable phase is the key to successful ignition. As $\phi$ increases, the flame becomes thinner and shorter. Furthermore, standard deviations of continuous image areas of $\text{CH}\ast$ and $\text{OH}\ast$ drop from 0.0143 and 0.0132 to 0.0115 and 0.0109, respectively, which indicates the enhancement of combustion stability. According to the brightness distributions of $\text{CH}\ast$ and $\text{OH}\ast$ along the axial direction of the combustor at different equivalent ratios, the production of $\text{OH}\ast$ is significantly affected by the temperature. It can be adopted as an important sign of heat release during combustion.