Mixing in a plane free-turbulent-jet diffusion flame

Abstract

This paper deals with a study of plane free-turbulent-jet diffusion flames. The theoretical analysis is based on Reichardt's similarity hypothesis which is extended to the plane case. Using solutions for the spread of momentum and nozzle gas-mass fluxes, expressions for the location of the flame front were derived. These results can be used to calculate density, velocity, temperature, and concentration fields in the flame. Experimental results obtained for plane, isothermal turbulent air jets and a vertically burning, plane turbulent city-gas flame are reported. The measurements include momentum and nozzle gas-mass-flux distributions with air and flame jets. The results served to evaluate momentum and mass transfer coefficients appearing in the theory. Comparing the results with earlier investigations of round jets and diffusion flames it was similarly found that-though generally having higher values-the transfer coefficients of plane jets decrease with growing ratio of nozzle and ambient gas density. The different behavior of isothermal and burning gas jets seems to be caused by the fact that the nozzle fluid of the latter almost spreads in combustion products at flame temperature. If one introduces the density, when plotting the measured transfer coefficients versus the ratios of nozzle and ambient gas densities, it is observed that the empirical curve connecting the transfer coefficients continually declines towards greater density ratios. From the experiments the validity region of the theory was determined, and a comparison of calculated and measured flame contours was made.