NUMERICAL MODELING OF BUOYANT ETHANOL-AIR WICK DIFFUSION FLAMES

A numerical model based on a conserved-scalar approach is presented for buoyant ethanol-air wick diffusion flames at atmospheric and subatmospheric conditions. The model incorporates an equation that describes the interface condition of wick combustion. The prediction yields similarity solutions for flat-plate ethanol-air wick diffusion flames, but not for cylindrical wick diffusion flames. The flat-plate solution yields a mass burning rate per unit surface area following the x-1/4 dependence of the classical similarity solution, where x is the streamwise distance. A pressure dependence of P0.644 is predicted for the flat-plate overall mass burning rate, in agreement with the P2/3 dependence reported in the literature. The cylindrical wicks have a mass burning rate per unit surface area that deviates from the x-1/4 dependence. The predicted mass burning rate, however, does not substantially deviate from the flat-plate solution for cylinders with a moderate aspect ratio (of the order one). The deviation in mass burning rate is most pronounced when needle-like cylinders are considered. The variable-property effects are also examined. The results show that the Chapman gas and constant-Prandtl-number assumptions are not adequate for wick diffusion flames, even at the subatmospheric-pressure condition studied.