M.Sc Thesis

M.Sc StudentTsin-Shwartz Irit
SubjectExperimental Investigation of a Boron Loaded Gel Fuel Ramjet
DepartmentDepartment of Aerospace Engineering
Supervisor PROF. Benveniste Natan
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


The ramjet is a supersonic air breathing engine, which contains no moving parts. Its main advantage lies in the fact that it does not need to carry the oxidizer and can still provide the same thrust as a rocket engine due to higher  However, it cannot accelerate from zero velocity and requires a rocket booster to reach the working point.

A gel is defined as a liquid substance whose rheological properties are modified by adding a gelling agent, resembling the behavior of a solid. Since the gel state is a combination of solid and liquid, it enjoys the advantages of both, which makes gel fuels attractive.

In order to improve the energetic performance of hydrocarbon fuel, metal powders can be added. The use of boron as an addition to the fuel seems to be the most promising. However, despite its significant chemical potential, it is very hard to utilize it in air breathing platforms. Generally, combustion of boron in an air breathing results in low combustion efficiency due to multiple reasons, such as particle agglomeration and inadequate burning conditions.

More than 150 valid tests were conducted for various boron loadings. The parametric investigation included the effect of pressure, boron content, fuel/air ratio, bypass ratio and more. In order to experimentally verify the feasibility of gel fuel boron loaded ramjet combustor, a lab-scale ramjet combustor was designed and built and a parametric investigation was conducted.

The experimental results indicate that the concept of the Gel Fuel Ramjet combustor with boron is feasible. For the different types of fuels, the mean combustion efficiency was 0.8-0.92. The 30% boron loaded fuel was found to be the optimal boron percentage in the fuel. The highest combustion efficiency is obtained when the bypass ratio equals 4.

It was found that the highest combustion efficiency was obtained for the longest combustor configuration. In addition, it was found that the combustion chamber pressure had limited influence on the combustion efficiency. Another conclusion was that the ramjet combustor cannot reach its operation point at sea level altitude for the low combustion pressure.

Theoretical heat loss calculations were also performed and showed an increase of 9%-25% of the experimental combustion chamber temperatures and 3%-7% increase in combustion efficiency.

The influence of ramjet combustor configuration on the combustion efficiency was tested as well. For the short configuration the heat losses are limited, however boron combustion was not completed and/or boron oxide did not totally condense. In the long configurations there were significant differences between experimental combustion temperature and efficiency to the theoretical (no heat losses) combustion temperature and efficiency. The reason is that in long combustors, the residence time of boron particles in the engine allows complete burning and boron oxide condensation; however, there are significant heat losses to the environment.