Diffusion flame of a CH4/H2 jet in hot low-oxygen coflow

This paper reports an investigation by RANS modeling on diffusion flames of a methane-hydrogen (CH4/H2) jet issuing into a hot and low-oxygen ([O2] = 3%, 6% and 9%) coflow from a burner system similar to that of Dally et al. [Proc. Combust. Inst. 29 (2002) 1147–1154]. The experimental conditions of Dally et al. are used for validation of the modeling. The Eddy Dissipation Concept (EDC) model is used with three detailed reaction mechanisms, i.e. DRM-22, GRI-Mech 2.11 and GRI-Mech 3.0. The influence of the coflow temperature (Tcof∗), ranging from 1250 K to 1700 K, is investigated. Besides, the effect of the hydrogen fraction (fH2∗, by mass) in the mixture of CH4/H2 is examined at fH2∗=11%,15%,20%and30%.It is found that, as Tcof∗ is increased, the mean temperature is distributed more uniformly whereas the concentrations of radical species (e.g., OH, HCO, H2CO) become less homogeneous. Interestingly, also, the overall effect of fH2∗ is mixed by two individual effects from the jet entrainment ratio (decelerating chemical reaction) and jet strain rate (accelerating chemical reaction). As a result, a variation of fH2∗ does not change the JHC flame structure significantly. Hence, Tcof∗has a significant influence on the JHC flame while the impact of varying fH2∗ is much weaker.

► The present RANS modelling predicts well for diffusion flame of a CH4/H2 jet into a hot coflow (JHC). ► The JHC flame depend more on the coflow temperature than on the hydrogen addition. ► As the coflow temperature is increased, the jet entrainment decreases but the strain rate changes little. ► As the hydrogen addition is increased, both the jet entrainment and strain rate increase.