* Bond discussed the complexities involved in manufacturing the very fine tubes required for the pre coolers, and assembling them into the finished modules. The tubes are checked by automated electromagnetic sensors, with any anomalies passed to human inspectors.
* The thermodynamic cycle of the SABRE-3 engine was outlined.
We have constructed a cryogenic wind tunnel facility at our laboratories at Culham Science Centre. This facility has been used to develop a frost control system for the ‘air pre-cooler’ heat exchanger of the SABRE engine. The pre-cooler is designed to cool the engine airflow (about 400kg/s) from intake recovered conditions (up to 1000°C at Mach 5) down to about -140°C prior to compression. At low altitudes atmospheric moisture will clog the matrix with frost within a few seconds unless preventive measures are taken.
The heat exchanger matrix is cooled by cold gaseous nitogen whose thermal capacity matches the helium flow employed in the real engine. Although the test matrix is much smaller than the real pre-cooler, it is built with the correct tube diameter, wall thickness and material. Therefore no ‘scaling’ problems can arise since it is tested at identical flow mass fluxes and Reynolds numbers to the real engine.
Heat Exchangers – Manufacturing
Current research is mainly focused on the design and manufacture of the novel pre-coolers required for the SABRE engine.
These heat exchangers have a mass of 1250 kg and are designed to transfer about 400 MW of heat at Mach 5. Their lightweight design is able to cope with thermal expansions and withstand the inertial and aerodynamic loads experienced during flight.
The construction of these heat exchangers pushes manufacturing technology in a number of areas such as:
The drawing of matrix tubes in heat-resisting nickel based alloys ensuring correct wall thickness and diameter.
Brazing heat exchanger tubes to headers.
Machining of heat exchanger tubes to give a profiled (non-constant) wall thickness to ensure good heat exchange properties without compromising physical strength.
Tube forming without ovalisation or wall thinning/buckling.
The assembly of large heat exchanger modules incorporating thousands of tubes.
More from the Rocketeer Presentation coverage
* He showed preliminary photos and videos from the STRICT altitude-compensating nozzle test firings undertaken by Airborne Engineering at Westcott. The use of altitude compensation would cut the typical Skylon takeoff run by 600 meters.
* Low-NOx combustor development work for the EU-funded LAPCAT programme was described.
* Cryogen plumbing is in place in the B9 test area at Culham in preparation for precooler flow tests
* Bond described objectives of the Phase 3 development programme.
– raise SABRE engine technology to TRL 6 through ground testing
– complete the design of the SABRE 4 to manufacturing drawings
– ensure that the vehicle requirements and SABRE 4 engine design are compatible
– Flight test the nacelle design
It is likely that Phase 3 will grow from the specified 30 months to at least 39 months.
* First images of the proposed Nacelle Test Vehicle were shown. The NTVs are ‘one-shot’ expendable flight test vehicles, propelled by LOX-methane biprops, and intended for aerodynamic verification of the nacelle geometry. The NTVs appear as ‘scaled-down’ Skylons, and are 9m long, with a 3.5m wingspan, massing approx 1 tonne each.
* Tests with LOX film cooling of combustion chambers was conducted in conjunction with DLR at Lampoldhausen. The results were very promising.
STRICT (Static Test Rocket Incorporating Cooled Thrust-chamber)
The STRICT engine is a follow on to the STERN (Static Test of Expansion/Deflection Nozzle) project and involves the same team. It has the more ambitious goal of running the engine for longer by water cooling the combustion chamber. By cooling bits of the engine separately and monitoring the heat absorbed by the water, the temperature distribution in the engine can be established and compared with the theoretical modelling.
The STRICT project has only just started and the basic parameters like thrust have still to be established. The project will start with a series of small test nozzles to establish the exact design; this might be an Expansion/Deflection Nozzle like STERN or a dual bell where one nozzle shape using a low altitude with high atmospheric pressure becomes a second nozzle when in low pressure and vacuum environments.