EXPERIMENTAL AND COMPUTATIONAL STUDY OF TEMPERATURE, SPECIES, AND SOOT IN BUOYANT AND NON-BUOYANT COFLOW LAMINAR DIFFUSION FLAMES

In this study, we extended previous numerical and experimental investigations of an axisymmetric lam-inar diffusion flame to assess the role of buoyancy and dilution in flame properties such as temperature, fuel and oxygen concentration, and soot volume fraction. Measurements were made both in normal gravity and on the NASA KC-135 reduced-gravity aircraft. Computations of temperature and major species were performed with a two-dimensional, axisymmetric flame model using a 26-species C2 hydrocarbon mech-anism. This set of temperature and major species measurements affords the most extensive set of com-parisons with flame computations to date. Results indicate that the predicted temperature profiles are in excellent agreement with measurement in both normal gravity and microgravity flames at low dilution levels. In these well-predicted flames, however, subtle differences existed in fuel/air mixing between mea-surement and computation, in which the contrast was most visible in normal gravity. As the fuel stream was diluted, the computations began to lose their predictive ability, again most markedly in normal gravity. Additionally, relative soot volume fraction was measured with laser-induced incandescence (LII) in both normal gravity and in the time-varying gravitational field provided by the KC-135. Results indicate that the soot concentration and distribution are extremely sensitive to the “g-jitter ” present, and that the peak soot volume fraction can increase by as much as a factor of 15 in the absence of gravity