A Spectroscopic Investigation into the Structure of Diffusion Flames

Ammonia-oxygen, ethylene-oxygen and other diffusion flames were examined spectroscopically using the flat flame technique described in a previous paper. Each flame is shown to consist of a main reaction zone where the temperature is a maximum. The emission from this zone is thermal, and the component gases are in chemical equilibrium. On either side of the main reaction zone there is a region with a steep temperature gradient which constitutes a pre-heating zone Fuels such as hydrocarbons or ammonia and oxidizers such as nitric oxide undergo chemical change in these pre-heating zones. On the fuel side the change is principally a thermal decomposition because the main reaction zone presents a barrier to oxygen penetration Thus carbon formation in hydrocarbon diffusion flames is essentially a pyrolytic process. The application and value of absorption spectroscopy are discussed and quantitative measurements of the concentrations of molecular oxygen and OH radicals are recorded which could not have been otherwise obtained. These results and a number of qualitative observations clearly show that diffusion flames with oxygen at atmospheric pressure have the structure predicted for a flame in which diffusion is the rate determining process A number of differences are described between the characteristics of diffusion and pre-mixed gas or Bunsen flames