A preliminary design of a magnesium fueled martian ramjet engine

This paper presents a preliminary design study for a solid fuel ramjet containing a super-stoichiometric loading of magnesium for operation in the Martian atmosphere. The methods and theory used for analysis are derived from first principles. A feasible ramjet design was obtained which has an operational speed of Mach 4 to 5, requires nine times the mass intake of atmosphere relative to the mass flow rate of solid grain, and a chamber pressure of approximately 250 kPa. The length of the combustion chamber is approximately 0.1 meters for the case of 100-micron diameter magnesium particles, and 3 to 10 meters for the case of 500-micron particles. The ratio of grain burn area to throat area is approximately 17. A suitable inlet design was made which would have nine 8-degree ramps. The inlet height and length would be 0.35 and 1.0 meter, respectively. An end-burning grain design was selected with a burn area of 0.45 m². Hypothetical ballistic values of the magnesium/ sodium nitrate mixture of n=0.15 and a=0.002125 m/s^-1 Pa^-0.15 (where the regression rate is b_r=aP_ch ⁿ), produce a thrust of 2900 N and a specific impulse (adjusted for gas augmentation) of 400 seconds. Thrust predictions obtained by varying the ballistic pressure exponent indicate an upper limit above which the thrust curve falls below the drag curve and operation is not possible.