Bloodhound
test, a great deal of electrochemical work was done to produce an improved silver deposit on the catalyst disk. The Mk 2 catalyst disks were tested on the second firing and provided a decomposition efficiency of around 98%. The target specific impulse (ISP) of 200 sec was also achieved on the second firing.
The following firings examined different fuel grain arrangements and higher HTP delivery pressures, the ISP was increased with each firing. The oxidiser:fuel (O:F) ratio moved closer to the target and a specific impulse of 220 sec was achieved on firing number five. We then began to push the chamber towards the higher HTP delivery pressure and flow rates we would need for the large hybrid. The first problem occurred on firing number six, when a leak occurred from one of the extractable dowels used to retain the catalyst pack outlet plate. A jet of hot decomposition products cut through the phenolic liner and ruptured the combustion chamber.
The removable outlet plate was intended to permit the testing of various types of catalyst material. With this research completed, the next catalyst pack outlet plate was welded in place. The next problem was the insulation material which protects the combustion chamber casing from the extremely high temperatures in the combustion chamber (which can reach 2800°C). The two key areas are the interface between the catalyst pack and the fuel grain and the post fuel grain combustion chamber. On firing number eight, the insulation failed around the catalyst pack/ fuel grain interface. New materials were required to withstand the high temperature, oxygen rich environment in this area and the improvements were tested successfully on firings nine and ten.
Richard Noble, project director
Continued improvements to the fuel grain have resulted in more even regression and the use of silica phenolic insulation around the post fuel grain combustion chamber has allowed the burn times to be extended to over 12 seconds. On firing number ten we also experimented with throttling the chamber and were very pleased to find that combustion was smooth over a 6:1 throttle range; three full throttle cycles were completed during the test.
While the 6-inch test programme continued, on the other side of the test site the massive reinforced concrete test stand for the full size tests was starting to take shape. In order to withstand the huge force exerted by the 18-inch hybrid chamber and to support the chamber at the same height as it will be installed on the vehicle, the large horizontal test stand required eight 0.91 metre (3 foot) diameter by 3.66 metre (12 foot) deep holes to be drilled into the ground. These were filled with reinforced concrete and onto these foundations a base was constructed, which carries the 0.61 metre (2 foot) thick blast wall.
This will carry the thrust from the chamber and also serves to protect the HTP tank, Cosworth V8 and pump from any unexpected occurrences! Other infrastructure to support the tests was also put in place including a water deluge system and trenches to carry high pressure gas and electrical cables.
Early in 2009 the project decided that the early runs of the car would be conducted with a monopropellant chamber. This would use the catalyst pack from the hybrid chamber to produce around 44.5 kN (10,000 lbs) of
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