Analysis Of The Influence Of Engine Firewall On The Dynamic Parameters Of Ring Cavity Fire

The nacelle of aero-engine is a typically cylindric structure and contains some assemblies such as delivered fuel pipeline,accessory gearbox and electronic controller.Due to the pipeline vibration and wears,the fuel could leak from the loosen or damaged pipeline joints.Once the leaked fuel encounters with the high temperature zone or heat source,the potential fire scenarios occur probably.Thus,the firewall with thin ring plate is placed inside the nacelle to separate the high temperature areas from the combustible aviation fuel to reduce the occurrence of fire accidents.Therefore it is important to examine effects of firewall on fire dynamic characteristics of the leaked fuel fire in the firewall structural design and arrangement optimization.The numerical study on the non-premixed flame diffusion characteristics of aviation fuel was carried out in present paper in one typical turbofan nacelle.Firstly,one turbofan Trent 800 numerical model was established by software FDS.Three kinds of grid sizes were considered in calculations.Then the oil flame diffusion features were analyzed.The fact that the calculated oil flame velocities agree well with experiment ones from the literature verifies the accuracies and validation of the numerical method,model and chosen grid sizes adopted in the present study.Secondly,the nacelle models containing ventilation,obstacle types(accessory gearbox and electronic controller)and firewall were constructed,some initial parameters such as boundary conditions and fire source power were also provided prior to calculations.Finally,the effects of ventilation,obstacle types and firewalls on the fire characteristic parameters in the nacelle were analyzed by a series of the calculation nephograms.The numerical results show that:(1)the changes of all the characteristic parameters such as temperature,velocity,oxygen and soot concentration undergo two stages in the nacelle filled with different ventilation,obstacles and firewall location.In the transient stage,the parameters increase or decrease in a few seconds,then oscillate around one constant in the steady stage.(2)The ventilation increases the amplitude of oscillated flame temperature and the high temperature distribution area.The diffused flame has a higher velocity near the top vent,but the oxygen and soot concentration distribution areas decrease.The flame has a typically asymmetric structure due to effects of gearbox and EEC.The flame shape oscillates with time.Meanwhile the flame diffusion speed and soot concentration at the top of the engine nacelle are increased,but the oxygen concentration are reduced at proximity of the gearbox and EEC.(3)The firewall location along the nacelle axial direction changes the volume of the fuel and oxygen mixtures in combustion.When the firewall is located in the middle of the nacelle,the temperature has one highest value,the flame reaches a highest velocity and the soot concentration is at the maximum,but the oxygen concentration is the lowest.Note that the pressure keeps at one constant.With the firewall locations moving backward,the diffused flame peak temperature and soot concentration in the nacelle decrease,but the oxygen concentration increases slightly.