The advanced hydrogen preburner is a lean-burning hydrogen combustor. In SABRE it provides heat energy to the engine cycle at take-off and early flight. The HX3 is a microtube heat exchanger that connects to the preburner and exchanges heat between combustion gas and helium.
The advanced hydrogen preburner and HX3 together provide the heat source to the core engine to enable flight from sea level. As the aircraft accelerates, the heat energy converted in the engine intake and extracted through the precooler gradually takes over the energy provided by the preburner extracted through the HX3 heat exchanger.
The objectives of both campaigns were to manufacture full size test rigs to validate performance modelling and de-risk high temperature operation in advance of further integration. The preburner test campaign further aimed to show that our novel fuel injection system would function at full scale, that we are able to control the heat output precisely and provide even temperature to the HX3.
The HX3 campaign was commissioned with Airborne Engineering at their test facility in Buckinghamshire. Airborne has been a close collaboration partner of Reaction Engines for many years over a number of rocket engine, combustion and heat exchanger test campaigns with complex instrumentation and control challenges. Airborne designed and built the custom hot gas source for the HX3 tests, which was capable of providing partially combusted air with variable massflow and temperatures controlled from 428℃ to well in excess of 928℃. The test rig also required closed-loop feedback control of the mass flow of hydrogen and air for combustion, the mass flow of helium coolant and the pressure of the hot coolant exhausted from the heat exchanger.
James Macfarlane, Managing Director of Airborne Engineering, had this to say regarding the test campaign:
“This programme continued the close working relationship that we have with Reaction Engines. Together we have successfully delivered another cutting-edge test campaign to further the evolution of SABRE technology. Despite the complex nature of the testing requirements, and the high accuracy required for the hot-gas uniformity and flow control, we are pleased to have developed a custom solution for them that was not only efficient to test but worked first time.”
The preburner test campaign was conducted in collaboration with S&C Thermofluid at Kemble Airfield in Gloucestershire. Their air delivery system using Gnome gas turbines was able to provide the temperature pressure and mass flows required to test the preburner at full conditions needed for a SABRE engine. In addition S&C already had a hydrogen delivery rig available that was suitable for this campaign. The partnership has worked really well and despite the challenges facing everyone, the test campaign itself was completed in under a month.
The HX3 achieved a top temperature 1126℃, making it our hottest test to date, even higher than the precooler’s validation at speeds representative of Mach 5 in 2019. Performance exceeded model predictions with slightly more heat exchange and less pressure loss than expected. Similarly, the preburner exceeded expectations and actually provided a larger performance envelope. The preburner campaign involved testing a lot of new technology at the same time and significant redesigns were expected, however only relatively minor issues ensued.
Shaun Driscoll, Programmes Director at Reaction Engines had this to say about the test campaigns:
“These test campaigns have been a huge success and we are very pleased with the results. With excellent teamwork and the help of our close partners we have been able to verify model predictions on real hardware, gain useful insight into performance and limitations and move onto the next phase of the development of our technology.”
The fact that both campaigns not only proved but exceeded model predictions is testament to Reaction Engines’ modelling capabilities. Ultimately all objectives were achieved and a huge amount of expertise has been gained that will benefit our wider technology programmes and will underpin the innovation and advances already made being across a variety of commercial sectors.
HX3 test article
Preburner control room at Kemble Airfield
Preburner test article
Custom hot-gas source for HX3 designed by Airborne Engineering Ltd.