A theoretical investigation of thermodynamic performance for a ramjet based on a magnesium—water reaction

Abstract

A preliminary study on the operating performance of a certain kind of water ramjet engine was implemented theoretically. With regard to this proposed powerplant operating in an available water environment, inspiration drawn from a supercavitation phenomenon coupled with a hydroreactive characteristic of several metals was the inducement for its attractive development. In terms of the requirement to provide the highest possible performance, a multiple water-injection mechanism was employed; i.e. the introduction of sufficient ambient water was suggested in order to maintain a successful combustion, while in the meantime not being too large to avoid a potential condensation phenomenon at the nozzle exit. Then against a ramjet carrying a metal fuel grain with a 50 per cent magnesium mass fraction, a performance analysis proceeded on the basis of a proposed thermodynamic calculation theory. The upper limit of the primary water—fuel ratio was predicted as 2.4 when considering the conditional temperature of the main magnesium—water reaction. Peak values of both specific impulse and thrust exist on the order of 4695.86 N s/kg and 2.57kN respectively, while the water—fuel ratio approached 4.2. Furthermore, rules governing the characteristic velocity along with the water—fuel ratio were also examined. Then, altering physical conditions such as metal fuel formation and chamber pressure, a conclusion was drawn that a higher performance was related to a relatively higher chamber pressure and a higher magnesium mass fraction as long as normal working conditions were guaranteed.