Experimental and numerical investigation of confined laminar diffusion flames

Abstract

A laminar methane-air diffusion flame has been extensively probed for its temperature, velocity, and stable species' concentration profiles. The data obtained were used to validate a theoretical model capable of characterizing flame macrostructure and useful in predicting the effects of flow rate, equivalence ratio, fuel and air preheat, and nozzle size on the thermal and aerodynamic fields established in confined, axisymmetric, laminar diffusion flames. The model utilizes the Burke and Schumann flame sheet concept to locate the stoichiometric fuel-oxygen interface and, hence, the points of heat release. The model eliminates the restrictions of the classical Burke-Schumann model in that allowances are made for natural convection effects and variable thermodynamic and transport properties. The stoichiometric fuel-oxygen interface was found to coincide with the outer edge of the primary reaction zone and represented a surface through which an amount of oxygen in stoichiometric proportion to the amount of fuel fired diffuses. The inner edge of the reaction zone was defined by the profile of the luminous flame core and was found to be well fitted by the theoretical predictions when the ratio of oxygen and fuel diffusing to the flame front was assigned a value 0.88 times the stoichiometric coefficient. The concentration and temperature profiles could be generalized by plotting the results as a function of the local-equivalence ratio.