The process of pressurized injection of ultra-fine powder extinguishing agents (UPEA) and the effect of injection from the nozzle directly affects the spatial dispersion characteristics and the effectiveness of fire extinguishing. Combining CFD simulations and experimental measurements, the UPEA pressurized injection process and injection effects were investigated. The transient process of injection is divided into three stages, initial injection stage, steady injection stage, and post-injection stage. The post-injection stage is divided into a slow decay process and a residual gas release process. Investigating the effect of different filling conditions on the effectiveness of particle injection. In the stable injection stage, the higher the filling ratio, the lower the mass flow of UPEA particles at the same filling pressure. At the same filling ratio, the higher the filling pressure, the higher the mass flow of UPEA particles. The maximum mass flow of the UPEA particles was 5.38 kg/s at a filling ratio of 20% and a filling pressure of 3.6 MPa. The steady injection time is mainly influenced by the particle filling ratio.
The flow and dispersion characteristics of the fire extinguishing agent in the pipings and the concentration distribution in the nacelle are essential for optimizing the aircraft fire extinguishing system. In the present work, we developed a three-dimensional CFD model to simulate the transport and dispersion of the agent in piping and nacelle. The results show that the length and structure of the pipings near the nozzles affect the concentration, pressure, flow rate, and flow distribution of the extinguishing agent. The smaller the bend of the pipings near the nozzles and the angle of connection with the main piping, the less time it takes for the agent to reach the nozzles and the more mass flow rate of the agent is injected, which is more conducive to extinguishing fire rapidly. External ventilation and the blockage of the nacelle’s ribs and other components impact the concentration distribution of the fire extinguishing agent in the nacelle. The agent is mainly concentrated in the middle and rear areas of the engine nacelle. Agent concentration tests were carried out in the simulated engine nacelle. The experimental result is similar to the simulation result, which verifies the feasibility of the simulation method. The simulation method can be used to increase the concentration of fire extinguishing agent to meet the safety requirements by changing the outside ventilation and increasing the filling amount of fire extinguishing agent, so as to achieve the optimization of the fire extinguishing system.
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