Ignition probabilities in turbulent mixing flows

Abstract

The paper describes experiments on ignitability carried out in a turbulent jet of natural gas. The turbulence properties of this jet, in terms of its mean and fluctuating velocity and concentration parameters have been extensively measured using laser Raman spectroscopy, and in the 17th Combustion Symposium the authors presented a theory in which the turbulent concentration parameters were used to derive a flammability factor and predict ignition probability. By using a single spark source this theory has been tested and results are presented which demonstrate the validity of the theory and define the flammable boundary of the jet. The results confirm that in a turbulent flow it is not meaningful to consider just the mean concentration in order to define the flammability or probability of ignition. However, in the absence of intermittency, this probability will approach zero when the mean falls below about half the lower flammable limit.