A Study On High Energy Of Mg-based Hydro-reactive Metal Fuel Propellant

Water ramjet engine is cruise propulsion system as a new type of underwaterpropulsion in super high-speed torpedoes, uses high-energy hydro-reactive metal fuel asfuel and seawater as oxidant, gives high specific impulse and thrust and will be the bestpropulsion system for the ultra-high-speed underwater weapons in the future. The energy ofthe magnesium-based hydro-reactive metal fuel is released by two combustion process inthe water ramjet. The high energy property of the fuel is dependent on the metal content.However the high metal content is against to increase the processing technical feasibilityand the primary combustion properties. In this paper, high Mg or Mg-Al metal contenthydro-reactive metal fuel propellant was prepared by means of theoretical analysis,mechanics and combustion properties adjustment, the primary and secondary combustionprocess were studied, and the mechanisms of the two combustion processes were deducedrationally. The above mentioned results will supply theoretical and experimental data forthe performance modification of hydro-reactive metal fuel.In this paper, the best formula of Mg-based hydro-reactive metal fuel propellant wereobtainted as follows: Mg57%，AP28%, GFP4%, Binder11%, the burning rate reach21.3mm·s-1at3MPa. The action of Mg powders and other formulation parameters on thecondensed phase reaction were investigated by differential thermal analysis (DTA) andsimultaneous thermogravimetry (TG). A high-pressure combustor and a metal/steam reactorwere used to simulate two-stage combustion of fuel-rich propellant. Solid combustionproducts from the two stages were collected and characterized by scanning electronmicroscopy (SEM), X-ray diffraction (XRD) and chemical analysis. The results show thatthe solid products from the primary combustion mainly contain Mg, MgO, MgCl2, and C,the secondary combustion products is only MgO; Based the thermodynamic analysis, themainly the competition reactions are C, Mg and CH4oxidation reactions in primarycombustion; The process of secondary combustion mainly is the exothermic reaction of Mgwith water vapor.This paper discussed the energy calculation method of the hydro-reactive metal fuelpropellant, which can be divided into two processes, total propellant specific impulsedetermined by the two combustion process. The primary combustion was in the unequilibrium chemical state, therefore, the part involved in the combustion reaction wascalculated according to the chemical equilibrium calculation, the rest only absorbed the heatto keep the combustion temperature equal. The initial state calculation of secondarycombustion process contained the primary combustion products and the injected water. Theresults show that improving metal content or adding aluminum powder can improve theenergy performance of Mg based hydro-reactive metal fuel propellant effectively.In order to improve Mg based hydro-reactive metal fuel propellant energy level,atomized Al and Mg-Al alloy powders were added in the Mg based hydro-reactive metalfuel propellant under the casting technology, the combustion performance of which werestudied. The results show that the upper limit of Al powder adding in the system is only10%, so the energy performance improvement is very limited. The percent of coated Mg-Alalloy powder can reach50%, the energy performance increased obviously; On the otherhand, a new type of mould-casting process improves the solid content to be90%, the effecton mechanical properties of process parameters of the technology were studied. And thecombustion performance of the propellant with90%solid content were studied by means ofimproved the metal powder content, grain size distribution and adding alloy powder; Theresults show that the content of metal powder should not be beyond70%, the smallerparticle size of magnesium powder can improve the injection performance, and the contentof the coated alloy powder, replaced Mg powder, should be under50%.The combustion process of AM based hydro-reactive metal fuel propellant was studied.The primary combustion solid products mainly contain MgO、Al12Mg17、AlMg、Al4C3、MgCl2and C. And the priority response components are determined by the oxidationequilibrium constants, the primary combustion process is mainly the competition betweenC and Mg oxidation reaction, the carbonization of Al in the alloy is beneficial for primarycombustion heat release; The secondary combustion solid products mainly contain MgO,MgAl2O4and Al, after two combustion process, magnesium in the alloy powders reactcompletely, the reaction efficiency of aluminum is about71.1%; In the process of thesecondary combustion, thermodynamics analysis found that reaction of carbon and watervapor can occur spontaneously only above1000K, other primitive reaction can occurspontaneously in the range of800~3000K.Activated Mg and AM powders were prepared by high-energy milling, the morphologies,phases and the thermal oxidation performance of the powders were analysed by SEM, XRD, and TG techniques. The reaction characteristics in the heated steam and the morphology ofdifferent temperature products between the ball-milled metal powder and atomization werestudied, and the combustion performance of both them in the hydro-reactive metal fuelpropellant were studied. The results show that the original spherical metal powdermorphology is destructed by milling process, meanwhile the fresh metal surface and thelarger particle size distribution are increased; The ignition delay time of ball-milled metalpowder was short, and the reactivity and efficiency was higher than the atomised in heatedsteam. The combustion process of the AM powders at600°C is divided into three stages:the Mg in the alloy (Al12Mg17) first reacts with water to form magnesium hydroxide, andthe remainder of the Al and Mg in the alloy formed the new alloy phase; then themagnesium in the new alloy phase continued to react, forming magnesium oxide, andremaining elemental Al exists，and the aluminium in the AM powders reacts with the heatedsteam, forming MgAl2O4. The burning rate and combustion heat of propellant increasesignificantly by adding ball-milled metal powders, milling process with catalyst canimprove performance of propellant further, burning rate of milling AM with catalystpropellant system can be up to16.5mm·s-1, the combustion heat reaches6965.3kJ·kg-1, thereaction efficiency of aluminium in AM powder reaches88.6%.