Theoretical Performance Evaluation of a Marine Solid Propellant Water-Breathing Ramjet Propulsor

Abstract

This work analyzes and presents theoretical performance of a marine water-breathing ramjet propulsor. A conceptual scheme of the motor is shown, the equation of thrust is presented, and the dependence on cruise velocity and depth are discussed. Different propellant compositions, representing a wide variety of formulations suitable for propelling a water-breathing ramjet, are investigated. The theoretical results reveal that the specific impulse of a water-breathing ramjet can increase by as much as 30% compared to a standard rocket, when using a conventional hydroxyl terminated polybutadiene (HTPB)-ammonium perchlorate (AP) propellant, which does not react chemically with the water. When employing a water-reactive propellant containing metal particles such as magnesium or aluminum, the specific impulse may be more than doubled. The thrust coefficient of the propulsor was computed at different cruise velocities and depths and was found to be greater than the predictable drag even at significant depth.

Examining Metal Additives in a Marine Hybrid-Propellant, Water-Breathing Ramjet

“…The influence of external underwater forces on the performance of a hybrid propulsor has not been taken into account in this work but have been investigated by [10,19] in regard to the ratio between the drag to the thrust produced by the motor.…”

“…Aluminum has a higher heat of reaction with water, whereas magnesium is more reactive with water, which, in practice, may lead to a better reaction efficiency, compensating for its lower heat of reaction. Works performed in the field have mainly focused on different aspects of solidpropellant, water-breathing ramjets, such as evaluating optimal operating conditions and maximal theoretical performance [7][8][9][10][11], combustion properties of different propellants and fuels tailored for a water-breathing operation [1][2][3][4][5], and static firing tests [12,13] as well as other aspects [14]. Previous research conducted by these authors [15,16] suggested considering the use of a ducted, hybrid, ram-rocket-based water-breathing ramjet.…”

Open-Sea Testing of Two-Phase Marine Ramjet Propulsion

“…Some of those works have been related to pump-operated waterjets. The ram rocket, a rocket-based water-breathing ramjet concept, has been investigated by Eisen and Gany [24][25][26]. Unlike the bubbly jet, where the gas mass fraction in the two-phase flow is a fraction of the percent of the water amount, the ram rocket concept aims at augmenting the thrust and energetic performance compared to that of a rocket at very high underwater cruise velocities.…”

Feasibility Study of a Hybrid Thruster using Wire-Shaped Magnesium and Water for Application to Small Spacecraft

“…Nevertheless, at high temperatures, it has a high reactivity with water when compared to other metals such as aluminum or boron. 19) Huang et al concluded from experimental results that the ignition temperature of magnesium in water vapor is 1178 K. 20) Yuasa reported that the ignition temperature decreased in a moistened atmosphere compared to that in air or carbon dioxide. 21) There are several studies using water and magnesium for the propulsion system of launch vehicles or spacecraft, underwater propulsion, and hydrogen generation, and there are fundamental studies on the combustion characteristics.…”

“…21) There are several studies using water and magnesium for the propulsion system of launch vehicles or spacecraft, underwater propulsion, and hydrogen generation, and there are fundamental studies on the combustion characteristics. 19,20,[22][23][24][25][26][27][28][29][30][31][32][33] Due to the higher reactivity, most of them basically used micro-or nano-size magnesium powder, which is not suitable for small spacecraft for three reasons. First, powder needs a carrier gas to be transported into a combustor.…”