1IntroductionWater is an abundantly present oxidizer,w hich can be used for underwater propulsion, assuming that there are fuels, which are capable of splitting water molecules, reacting with oxygen,a nd releasing hydrogen.T he same reaction occurringi nadifferent configuration can be used to generate enhancedu nderwater blast in advanced undersea munitions. The same water splitting reaction, forming ac hemically bound oxygen and free hydrogen but occurring at lower temperatures and at the respectively lower rate, can be used to controllably generate heat and simultaneously produce hydrogenf or fuel cells. Oxidation in water is favored thermodynamically for such metals as Al, Mg,B ,T i, Zr,a nd some others;r espectively such metals have long been considered as potential fuels capable of combusting in water [1,2].I np articular,r eactionsw ith Al, Mg, and Ba re most attractive because of their high theoreticalh eating values and the relatively low cost of Al, Mg, and Bpowders. It was recently shown that replacing battery-basedu nderwater propulsion and power systemsw ith those based on aluminum combustion could increase range/endurance by factors of four to ten [3].O ther metals, i.e.,M g, are also actively evaluated for underwater propulsion systems [ 4].D evelopment of aluminum-water underwater propulsion systems has beena no ngoing effort during several decades [5,6],w ith focus on the mechanism of aluminum-water combustion,d esign of both ramjets and powerp lants, in which am etal powder is fed in the combustionc hamber, and dealing with the generated condensed products. Despite thermodynamic predisposition to react with water,i gnition of aluminum and other practically important reactive metals in water vapor occurs with substantial delays;c ombustion is typically not self-sustained,a nd the reaction may terminate well before it is completed. The difficulties of burning metal powders in water are associated with the reaction kinetics bottlenecks, specifically,c aused by the generated metal oxides and/or hydroxides, whichs eparate metal surface from water.B ecause of the naturally present oxide films, it is difficult to ignite metal particles;f urther, molten oxide layers and inclusions formed duringc ombustion cause agglomeration of burning particles, resulting in their quenching.Recently,n ano-powders of aluminum were widely explored as an alternative to conventional micron-sized powders used as fuel additives to various energeticf ormulations, including those with water as an oxidizer [7][8][9].Abstract:M echanicallya lloyed Al·Mg powders with the mole fraction of Al varied from 0.47 to 0.9 were burned at atmospheric pressure in water vapor.T he powders were carried by nitrogen through the center of ah ydrogenoxygen diffusion flame. The particles ignited in the steam at approximately 2500 K, generated as the hydrogenoxygen flamep roduct.F ilteredp hotomultiplier tubes were used to capture the opticale mission traces of individual particles as they burned. It was assumed that the measured durations of indivi...
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