Study On Reaction Characteristics Of Magnesium-based Hydro-reactive Metal Fuel With Water

Water ramjet, an advanced type of propulsion system, uses fuel-rich metal-based hydro-reactive fuel and the outside water as main oxidizer. In water ramjet, the magnesium-based hydro-reactive metal fuel occur self-sustaining combustion firstly and generates high temperature fuel-rich gas, which includes liquid Mg, gaseous Mg, C, CH4 etc. The water from outside comes into the combustion chamber and reacts with magnesium, carbon and hydrocarbons. The reactions convert the chemical energy of the fuel into the thermal energy in the combustion chamber of the ramjet. The reaction characteristics between metal-based hydro-reactive fuel and water is one of the key technologies of water ramjet. On the other hand, the reaction characteristics are the basic and core of efficient combustion and efficient energy transform. Therefore, it is very important to study the reaction between the magnesium and water and that between fuel and water to reach high reaction rate and extent of the two reactions.It is investigated that the relationship between energy properties and formulation of magnesium-based hydro-reactive metal fuel by means of thermodynamic numerical analysis. The reaction characteristic of the fuel is studied on the basis of the operation process of water ramjet. Therefore,the main reactions of magnesium-based hydro-reactive metal fuel has been determined by thermodynamic analysis. It is studied systematically that the reaction and dynamic characteristics of the Mg/H₂O reaction under the low temperature environment. It is investigated that action of temperature, particle size of Mg powder and additives on the properties of the Mg/H₂O reaction. It is also investigated that action of formulation parameters of the fuel on the properties of the fuel/water reaction. The article also analyzed the reaction characteristics of fuel/water and analyses the influence on the properties of the reaction of fuel/water. Two kinds of high-efficient catalysts for the two reactions have been found. The catalytic mechanism of the two kinds of catalysts has been discussed. A model for the reaction characteristics of magnesium-based hydro-reactive metal fuel and water, which considers the different control factors in the different temperature range, and the reactions of Mg/H₂O and C/H₂O, has been established. Then, numerical analysis has been made based on the model.The higher the content of magnesium in the fuel, the higher the content of active Mg in the self-sustaining combustion products is. The specific impulse increased with the content of active Mg. The mass flow of water should be divided into two parts to inject into the ramjet to ensure efficient and fast combustion and high performance of ramjet. One of the water is to react with self-sustaining combustion products. And the other changes into vapor to absorb the heat of the reactions. The combustion of magnesium-based hydro-reactive metal fuel includes three zones in the water ramjet: self-sustaining combustion zone, the first water-reaction zone and the second water-reaction zone. The products of self-sustaining combustion zone are consisted of hydrogen, magnesium oxide, unreacted gaseous and liquid active magnesium, carbon and hydrocarbons. In the first water-reaction zone, the reaction of Mg/H₂O releases large amount of heat to increase the temperature rapidly, which is benefit for the reaction of C/H₂O, hydrocarbon/H₂O. In the second water-reaction zone, only a little water react with the uncompletely-reacted Mg, and the remains water absorbs heat to vaporize to increase the flow of the gas medium and improve the heat utilization efficiency to increase the specific impulse. Therefore the reactions of Mg/H₂O and C/H₂O must be pay attention.Under the low temperature range (30 to 85℃), both the rate and the extent of Mg/H₂O reaction are low. The high temperature and existence of high efficient catalyst is good for improving the rate and extent of reaction about Mg/H₂O. The activation energy of the reaction is 77.99kJ·mol-1. The reaction is controlled by diffusional factor. The dynamics equation of reaction has been established. It is found that some ammonium salts are the high-efficient catalysts for the reaction of Mg/H₂O at low temperature. The catalyst changes the reaction mechanism and accelerates the reaction by removing Mg(OH)2 from the surface of magnesium powder. The reaction of Mg/H₂O is a twice-order dynamic controlled reaction.Under the high temperature range (600 to 900℃), the rate and extent of the Mg/H₂O reaction are much higher than those at the low temperature. The activation energy of the reaction is 18.86kJ·mol-1. The reaction is a first-order chemical dynamic controlled reaction. The Mg/H₂O dynamics equation of reaction is established under the high temperature range. The cobalt compounds are the high-efficient catalysts for the reaction of Mg/H₂O at high temperature. Some ways, such as, fine magnesium powder and cobalt carbonate or perovskite oxides, can increase the reaction rate and efficiency.The results show that the Mg/H₂O reaction is different in the condition of low and high temperature because of the different reaction mechanism. Additionally, the kinds of catalysts and catalysis mechanism are also different in the high and the low temperature range.Vapor environment over the range of pressures from 0.30 to 0.95MPa, the higher the vapor pressure, the lower the reaction rate of fuel/H₂O. The reaction rate decreases with the high extent of the reaction. The rate and extent of the reaction between fuel and vapor decrease with the increase of the magnesium content. The reaction rate can be increased by higher mass ratio of oxidizer and binder or increase of fine magnesium content. The existence of some catalysts, such as, LSCF, Co compound and Fe compound can increase the reaction rate of fuel/H₂O. The most effective catalyst is the Fe compound.A model for the reaction characteristics of magnesium-based hydro-reactive metal fuel and water, which considers the different control factors in the different temperature range, and the reactions of Mg/H₂O and C/H₂O, has been established. In the model, the reaction between the fuel and vapor is controlled by the chemical factor at low temperature range. However, the reaction is controlled by diffusional factor at high temperature range. The model also considers the action of condensation of part of gasous magnesium oxide. The reaction between carbon and vapor is also included in the model. The calculated results are consistent to the experimental results, which demonstrate the rationality of the model. The model can be used in wide formulation range and wide temperature range. The function of the model is to analyze the action of various formulations and operating parameters on the reaction characteristics of the fuel and vapor. On the basis of the model, the effect of some parameters, such as, the mass ratio of oxidizer and binder, the mass ratio of water and the fuel, and the content of magnesium powder, on the reaction of magnesium-based hydro-reactive metal fuel with vapor has been analyzed numerically.