Effect of Fuel Properties on the Specific Thrust of a Ramjet Engine

Alon Gany

doi:10.14429/dsj.56.1895

Alon Gany Technion-Israel Institute of Technology, Haifa 32000, Israel

DOI: https://doi.org/10.14429/dsj.56.1895

Keywords: Ramjet engine, specific thrust, specific impulse, ramjet propulsion, fuel-air ratio, specific heat release, fuels, fuel efficiency, fuel rich propellant

Abstract

Various aspects of specific thrust in ramjet propulsion have been considered. It is shown
that while the peak specific impulse of ideal ramjet is theoretically obtained for fuel/air ratio
f 0, the specific thrust which determines the thrust level of a given engine at certain operating
conditions, increases with increasing fuel/air ratio up to (approximately) the stoichiometric ratio.
Furthermore, in general, the specific thrust is related to the heat release per unit mass of air
fqR, where the theoretical maximum is approximately proportional to its square root in stoichiometric
conditions, fstqR. This can be the basis for selecting an appropriate fuel according to its potential
specific thrust. It should be noted that certain metals such as magnesium, aluminum, and zirconium
can provide about three-times higher specific heat release than hydrocarbons or hydrogen.
Thus, these may be the better candidates for missions requiring high specific thrusts.