Buoyancy-controlled laminar diffusuion slot flame heights: A comparison of theoretical predictions and microgravity results

The results of an investigation into the premise that, in the buoyancy-controlled regime, the flame height of a laminar diffusion flame produced using a slot burner is inversely proportional to the buoyant acceleration raised to the one-third power are presented. The validity of this premise is examined by considering the behavior of a laminar diffusion flame at different gravitational levels. Variation in the gravitational level was produced by conducting a series of experiments aboard the KC-135a at the NASA Johnson Space Center. Stoichiometric flame heights and shapes for laminar diffusion slot flames burning propane in quiescent air at gravitational levels in the range of 0.1g to 1.7g for two burner ports with different burner port widths were measured. Reduced gravity slot flames exhibited behavior qualitatively similar to reduced gravity flames produced using circular burner ports. Roper’s classical expression for the flame height of a buoyancy-controlled flame was able to predict the trend in the experimentally observed flame height. The diffusion to buoyancy parameter is shown to provide insight into which regime a flame exists i.e., buoyancy-controlled, momentum-controlled, or diffusion-controlled.