Prediction of the extent of diluents concentrations in flammability limited gaseous fuel–diluent mixtures in air

A method is described for estimating the maximum diluent concentration in a gaseous fuel–diluent mixture in air that would just render flame propagation from an ignition source possible at different initial temperature conditions. This would also correspond to the threshold of diluent concentration needed to prevent fire spread within the mixture. Only knowledge of the flammability limit values of the pure fuel on its own in air at atmospheric pressure and temperature conditions are needed. The common gaseous fuel–diluent mixtures considered included methane, ethylene, propane, butane, carbon monoxide and hydrogen with the diluents nitrogen, carbon dioxide, helium and argon. It is shown that there is a satisfactory agreement between predicted and corresponding experimental values.