Diffusion flame of a GU_4/H_2 jet in hot low-oxygen coflow

摘要

This paper reports an investigation by RANS modeling on diffusion flames of a methane-hydrogen (CHVH2) jet issuing into a hot and low-oxygen ([O_2] = 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 (T_(cof)~*), ranging from 1250 K to 1700 K, is investigated. Besides, the effect of the hydrogen fraction (f_(H2)~*, by mass) in the mixture of CH4/H2 is examined at f_(H2)~*= 11%, 15%, 20% and 30%. It is found that, as T_(cof)~*is increased, the mean temperature is distributed more uniformly whereas the concentrations of radical species (e.g., OH, HCO, H_2CO) become less homogeneous. Interestingly, also, the overall effect of f_(H2)~* 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 f_(H2)~* does not change the JHC flame structure significantly. Hence, f_(H2)~* has a significant influence on the JHC flame while the impact of varyinf_(H2)~* is much weaker.