| Aluminum powder is a material of high energy and lightweight,while is rich in raw material and low in price.Aluminum powder is easy to store and transport because of its stable physical and chemical properties at room temperature.Under the same equivalence ratio,aluminum powder used as fuel can release more energy than that of hydrocarbon,so aluminum powder has been widely used as an additive in explosives and propellants.The pulse detonation engine(PDE)is one kind of efficient new engine.Compared with combustion,detonation is more efficient in energy utilization,resulting in greater thrust.The combination of aluminum powder and pulsed detonation engine fuel can give full play to both advantages,which is helpful to improve the performance of the propulsion system.However,there are significant differences in detonation characteristics and influencing factors between aluminum powder detonation and gas detonation and liquid detonation.It is of great significance to study the mechanism of aluminum powder/air detonation and the application of aluminum powder in pulsed detonation engine,which can enhance the further study on the mechanism of aluminum powder as fuel and can expand the field of application of pulse detonation engine.In this paper,the feasibility of alumin um powder as fuel on PDE through numerical calculations and experiments were analyzed.The main contents are as follows:(1)Based on the chemical reaction and the change of gas group component in the deflagration to detonation transition(DDT)process of aluminum powder,the governing equations of aluminum powder/air two-phase flow in tubes are established,including one-dimensional,two-dimensional,two-dimensional viscous,three-dimensional,and three-dimensional viscous.The calculation format of conservation element and solution element(CE/SE)method and the Jacob matrixes of the governing equations are deduced,including one-dimensional,two-dimensional,two-dimensional viscous,three-dimensional,three-dimensional viscous and nozzle thrust.The CE/SE method is adapted to discrete the control equations,to derive the relevant Jacobian matrix and compile numerical calculation programs.The aluminum/air two-phase detonation process in detonation tube is numerically studied to analyze the detonation characteristics of factors,such as pressure,temperature,velocity and gas-solid two-phase anisotropic aluminum dust particle size and gas phase components,the influence of initial particle size,gas viscosity and ignition position of detonation tube on detonation process is also investigated.The mechanism of gas solid two phase detonation is revealed.The mechanism of gas/solid two phase detonation wave formation is revealed.The results of one-dimensional gas/solid two phase numerical simulation show that:steady propagating detonation wave can form with the aluminum powder/air mixture under certain conditions.In the process of aluminum powder/air tube detonation,gas velocity and detonation wave pressure changes along the axial direction following the consistent law.The results of axisymmetric gas/solid two phase numerical simulations show that:there are obvious differences between pressure radial effect and axial effect in each period of combustion to detonation of aluminum powder.Based on the comprehensive analysis of the gas pressure and temperature in the detonation tube,aluminum powder/air in the detonation tube can form a self propagating detonation wave.With the burning of aluminum powder,the combustion product Al2O3 increases,and the energy generated by the combustion process can support the temperature in the tube reaching a certain height.The results of axisymmetric gas/solid two phase viscous numerical simulations show that:the initial particle size of aluminum powder can influence the detonation formation and propagation.The gas viscous action makes the peak velocity of detonation wave more stable,and the influence on the velocity at the inner surface of the detonation tube is more obvious than that of the axis.The results of gas/solid three phase numerical simulations show that:the stable detonation of the aluminum powder/air mixture in the tube can be realized with both the wall ignition method and the central ignition mode.The three-dimensional effect of the detonation pressure is significant in the stage before stable detonation has formed with the wall ignition method.When the center ignition is adopted,the temperature peaks appear earlier and the peak value is higher at the cross-section of the closed end,and the temperature difference is larger as the wave crest appears.(2)On the basis of the study of the two phase detonation of aluminum powder/air,the interaction between detonation wave and aluminum powder/air mixture is investigated,and the instantaneous thrust and total thrust of aluminum powder fuel PDE are studied,the Influence of particle size of aluminum powder and aluminum powder air ratio on thrust are also researched,which predict the thrust performance of pulsed detonation engine with aluminum powder as fuel.The numerical simulation results show that:under the actual exit condition of detonation tube by CE/SE method,the pressure of the gas phase decreases when the detonation wave propagates out of the tube,but it still maintains a certain speed.Comparing calculation and diagram,it is concluded that non gas phase characteristic of the aluminum powder/air chemical reaction product has little influence on the thrust performance of PDE,although it makes the thrust and total thrust of PDE decrease.(3)An aluminum powder fuel PDE experimental platform is set up,and the stable detonation of PDE with aluminum powder as fuel is realized by using pre-detonation ignition.The feasibility of using aluminum powder as fuel for PDE is verified by experiments.The experiment of aluminum powder/air tube detonation under different conditions is carried out to investigate the process of deflagration to detonation transition of aluminum powder fuel.The experimental results show that:the detonation of aluminum fuel in a short PDE tube can be realized by the method of pre-detonation,and the deflagration to detonation transition is obvious.The pre-detonation energy is only used as the initiating energy,while has no effect on the subsequent deflagration to detonation transition.Under the premise that the aluminum powder fuel is full of detonation tube,the steady detonation can be achieved when the oxygen content in the tube is close to the oxygen content in the air.,Through the research,the CE/SE method is developed,the detonation wave and the interaction process of aluminum/air mixture are explored,the thrust performance of aluminum fuel pulse detonation engine is predicted,the mechanism of gas-solid two-phase detonation wave causes is revealsed.In this paper,experiment platforms of aluminum fuel pulse detonation engine are set,adopting detonation ignition initiating mode.Through the experiment,the aluminum fuel pulse detonation engine can detonat steadily over short distances.Experiments validate the feasibility of aluminum powder as a pulse detonation engine fuel. |
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