Observations and predictions of jet diffusion flame behaviour

Abstract

A simple model has been developed for jet diffusion flames to estimate flame height ( h f ) and angle of the flame to the vertical ( α B ). The model is based upon the assumption that flame behaviour is dominated by momentum effects. Buoyancy influences on behaviour are assumed to be negligible. Predictions of the model were assessed against flame parameters as observed in a wind tunnel and during field tests with an industrial flare. The wind tunnel studies involved experiments with hydrocarbon (methane, propane, ethylene, butane) diffusion flames. Field experiments involved measuring h f and α B of flames resulting from the combustion of acid gas-fuel gas mixtures possessing molecular weights of about 37 g mol −1. The one-to-one correlation coefficient between predicted and observed behaviour resulting from combustion of all hydrocarbon fuels, except methane, was about 0.85. The model significantly underestimated flame heights for methane. This seems to have been due to the neglect of buoyancy effects which could be appreciable for this relatively light gas. Evaluation of results from the tests conducted with the industrial flare showed a one-to-one correlation coefficient between observed and predicted values of h f to be 0.92. The corresponding magnitude for the correlation coefficient between observed and predicted values of α B was only 0.71. A partial explanation for this relatively low correlation coefficient lies in the small range of α B values contained in the population sample.