Mathematical model for describing the influence of initial pressure on the flammability limits of light hydrocarbons at subatmospheric pressures

Abstract

Fuel in aircraft fuel tanks, as well as some industrial processes, are under conditions of reduced pressure. However, few models have been proposed for estimating the influence of the initial pressure on flammability limits at subatmospheric pressures. A model to describe this influence was derived in this study according to the assumption that the heat release rate is equal to the heat loss rate. Several assumptions used in the model simplification process were verified to accord with real situations. The experimental data on seven gaseous fuels, namely methane, ethane, ethylene, propane, propylene, n-butane, and n-butylene, were analysed to validate the proposed model. In general, the simulation results accord well with the data on flammability limits measured at subatmospheric pressures. In its extension to systems functioning at elevated pressures, the proposed model accurately estimated the lower flammability limit data for atmospheric pressures up to 30 MPa and the upper flammability limit (UFL) for atmospheric pressures from 0.1 to 0.9 MPa. However, large deviations were noted between the estimated and actual UFLs for atmospheric pressures from 0.1 to 24.9 MPa. Nevertheless, the proposed model accurately describes the variation trends of flammability limits over a wide pressure range.