Design and Implementation of a Fuel System for a Supersonic Solid Fuel Ramjet

Zander, Fabian (2004). Design and Implementation of a Fuel System for a Supersonic Solid Fuel Ramjet Honours Thesis, School of Engineering, The University of Queensland.

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Author Zander, Fabian
Thesis Title Design and Implementation of a Fuel System for a Supersonic Solid Fuel Ramjet
School, Centre or Institute School of Engineering
Institution The University of Queensland
Publication date 2004
Thesis type Honours Thesis
Total pages 141
Language eng
Subjects 0913 Mechanical Engineering
Formatted abstract
This thesis covers the design and development of the fuel system for a solid fuel ramjet. The fuel system design encompassed the selection and casting of a fuel and the design of the combustion chamber. This system was then integrated with three other thesis students systems and formed a full supersonic solid fuel ramjet that was flight tested in Woomera in October.

The ramjet was launched on a Zuni rocket motor. The Zuni motor has a burn time of approximately 1.5 seconds and will propel the ramjet up to mach two. Once mach 2 is reached and the Zuni burns out the testing time for the ramjet has begun. As the ramjet can not maintain combustion during launch a two stage fuel was proposed. A layer of rocket fuel would burn for the same time as the Zuni and after this the actual ramjet testing will occur.

The ramjet fuel was chosen based on availability, safety and performance parameters. From these considerations a carboxyl terminated polybutadiene (CTPB) fuel with aluminium additive was selected. The exact composition of the fuel was determined by analysing previous experimental work and conducting some basic fuel tests. The fuel tests were also used to give an estimate for the regression rate of the fuel to determine how much to use. This estimate was also checked by theoretical analysis. The rocket fuel used was taken from another University of Queensland (UQ) project and composed of a ammonium perchlorate , aluminium and CTPB mixture.
The amount of fuel used was dependent of the regression rate and the burn time required. The rocket fuel was found to have a regression rate of approximately 1mm/s at atmospheric pressure and was required to burn for 1.5 seconds. This gave a layer thickness of 1.5mm which equated to a fuel mass of approximately 500g. The ramjet fuel was found to have a regression rate of 1mm/s during flight conditions and had a required burn time of 3 to 5 seconds. From this a fuel thickness of 4mm was determined. This resulted in a mass of ramjet fuel of approximately 1kg.

The casting of the fuel was a complex process that required numerous trials to get a sufficiently accurate method to get the correct geometry of the casting. The final casting was done on a sheet of Mylar and later glued to the EDPM rubber which was insertedinto the outer casing. The casting also required a vacuuming process to remove the voids in the fuel. This was initial attempted using vacuuming bagging however after this failed the fuel was placed into a dump tank and put under a vacuum there.

The design of the combustion chamber was critical to ensure that stable combustion could occur. The correct air mass flux was required to ensure the desired equivalence ratio was established, a rearward step was introduced to develop a recirculation zone to ensure combustion stability and an allowance was made for a modified aft mixing chamber to increase the efficiency of the combustion.

The ramjet was constructed and assembled in preparation for a launch in the Australian Space Research Institute’s (ASRI’s) October launch campaign. The launch was undertaken on October 3rd 2004. Video evidence and inspection of the engine revealed that the rocket fuel had combusted however ramjet combustion did not occur. Analysing the data showed that approximately 3g’s of thrust had been developed by the rocket fuel.

Ramjet combustion did not occur during the flight test and this was attributed to numerous different reasons. The ramjet never reached the design speed of mach two which meant the air mass flow and pressures were lower. The data recovered showed that the pressure in the combustion chamber only reached approximately half what was expected and this would not have maintained ramjet combustion. Another problem that was thought to occur was that due to the lower pressures the regression rate of the rocket fuel would have been slower, increasing the burn time meaning that the ramjet fuel would not have begun combustion until much lower speeds were reached that may not have supported the combustion.

Recommendations for future development of the project include extensive ground testing of the fuels to determine the specific flammability limits, designing for mach 1.8 and the incorporation of an aft mixing plate at the entrance to the aft mixing chamber.
Keyword Solid Fuel Ramjet

Document type: Thesis
Collection: UQ Theses (non-RHD) - UQ staff and students only
Citation counts: Google Scholar Search Google Scholar
Created: Fri, 21 Nov 2014, 15:50:13 EST by Asma Asrar Qureshi on behalf of Scholarly Communication and Digitisation Service