Predicting filling mass of nitrogen in fire agent bottle based on Peng-Robinson equation of state with Wong-Sandler mixing rule

Nitrogen supplies driving force for the rapid discharge of fire agent in the fire extinguisher of the helicopter. Calculating the filling nitrogen and its mole fraction is one of the key issues to be solved in the design of fire extinguishing system of the engine nacelle in helicopter. Based on Peng-Robinson (PR) equation of state and Wong-Sandler (W-S) mixing rule, a prediction method to calculate the filling mass of nitrogen is proposed. To different filling cases of Halon1301 and HFC-227ea, the mass of filling nitrogen is obtained after three layers iteration relation and compared with the experimental and literature data. Also the change of pressure and mole fraction of nitrogen with temperature in the fire agent bottle is analyzed. The results show that, for the one-half and two-thirds filling conditions of Halon1301, the calculation errors of nitrogen are about 4.7% for one-half condition and 1.1% for two-thirds condition, and the calculation results are better than those of the PROFISSY and HFLOW software. For the one-half and two-thirds filling conditions of HFC-227ea, the calculation errors of nitrogen are about 4.3% and 2.3%, respectively. This method can be used in the design of aircraft fire extinguishing system.