M.Sc Thesis

M.Sc StudentHaddad Arza
SubjectTheoretical Evaluation of the Performance of a Boron
Containing Gel Fuel Ramjet
DepartmentDepartment of Aerospace Engineering
Supervisors PROF. Benveniste Natan
Full Thesis textFull thesis text - English Version


The ramjet engine is an air-breathing engine that operates without any moving parts. Consequently, the ramjet is a simple and effective means of propulsion. The engine operates at high Mach numbers, at a range unsuitable for turbojet engines. Moreover, the ramjet engine is characterized by a very high specific impulse in comparison to chemical rockets.

Boron is a metal element with remarkably high energy content and enjoys great gravimetric and volumetric energy densities. Thus, adding boron to hydrocarbon fuels can improve performance significantly. With boron, it is possible to increase the range attainable, in a reasonable time by a relatively small vehicle. This work focuses on the possibility of combining the advantages of a ramjet engine with the energetic potential of boron.

By using a gelled fuel, it is possible, due to the unique structure and properties of the gel state, to obtain a good dispersion of boron particles within the fuel without risking sedimentation under the effect of acceleration. Nonetheless, there is a great difficulty in realizing the full energetic potential of boron because much of the energy stored in boron is trapped in the gaseous boron oxide released during boron combustion. Boron oxide is usually expelled from the engine at a hot temperature in gaseous form, and as a result, the latent heat of vaporization of boron oxide is not exploited. This obstacle can be overcome by dividing the combustion process into two stages: first the fuel burns with air at high fuel to air ratio and then in the second stage, bypass air is added to cool the products of the first combustion stage. This makes the condensation of boron oxide within the engine possible and enables the extraction of most of the energy of boron.

This work investigates the feasibility of a system powered by a boron enriched gel fuel ramjet engine. This is done through the analysis of the performance of a missile capable of delivering a 500 kg payload to over 1000 km range, with a launch weight of less than 1500 kg. The missile is launched at an altitude of 12 km and a Mach number of 0.88 and reaches at its cruise flight a Mach of 3.5. The work includes a comparison of the ramjet missile in question to a missile powered by a solid rocket motor launched at the same altitude and speed and carrying the same payload.