The variation of volumetric isentropic exponent and temperature isentropic exponent of the gas mixture of nitrogen (N2) and fire extinguishing agent vapor with pressurized pressure and temperature are a key influential factor to the fire extinguishing agent discharge progress for the aircraft fire extinguishing system. Based on the PR(PengRobinson) equation associated with the classical van der Waals mixing rule

a program was developed to estimate volumetric isentropic exponent and temperature isentropic exponent for the mixture of N2 and fire extinguishing agent vapor. The curves of volumetric isentropic exponent and temperature isentropic exponent varying with temperature were calculated with the pressurized pressure of 42MPa and 25MPa and initial temperature of 293K for the binary system of N2/HFC227ea

N2/CF3I and N2/CF3Br. The results showed that volumetric isentropic exponent and temperature isentropic exponent decreased as temperature increased and the relation was nearly linear. The volumetric isentropic exponent and temperature isentropic exponent of all the three binary systems had a higher value with pressurized pressure of 42MPa than with 25MPa at the same temperature. When pressurized to an equal pressure at same temperature

isentropic exponent of N2/CF3I had a largest value followed by the results of N2/HFC227ea and N2/CF3Br.