On the structure of nonsooting counterflow ethylene and acetylene diffusion flames

The structures of ethylene/oxygen/nitrogen and acetylene/oxygen/nitrogen diffusion flames in the counterflow configuration were investigated experimentally and computationally. The temperature and major species concentration profiles were measured with spontaneous Raman scattering. The experimental situations were computationally simulated with detailed reaction mechanisms and transport properties. The kinetic mechanism was based on GRI- Mech, with modifications to predict more closely the adiabatic flame speeds of ethylene/air and acetylene/air mixtures, and with additional description of higher hydrocarbon formation and oxidation up to C₆ species. The numerical predictions were found to be in reasonably good agreement with the experiment. Both experimental and computational results indicate that acetylene is the major intermediate species in the ethylene flame, having a significant influence on the heat release, overall fuel destruction, and molecular mass growth. The reaction pathways leading to benzene formation in these flames were examined computationally, with the goal of achieving a better understanding of soot nucleation in diffusion flames.