Precooler Technology Could Bring Advantages To Fighter Engines

By Tony Osborne

Technology developed by Britain's Reaction Engines for its SABRE (Synergistic Air-Breathing Rocket Engine) hypersonic powerplant is to be fitted on the Eurojet EJ200 engine from a Eurofighter Typhoon to understand if the technology can help transform the powerplant's operating envelope.

The £10 million ($12 million) project announced by the Royal Air Force (RAF) Rapid Capability Office (RCO) in July will see BAE Systems, Reaction Engines and Rolls-Royce engineers work to better comprehend Reaction's precooler technology and how it could be integrated for use on a jet engine—perhaps even the powerplant for Britain's future combat aircraft, the Tempest.

Two-year project will scope integration to better understand precooler potential benefits

Heat exchanger is an enabler for Reaction Engines' SABRE technology

The trials represent the first acknowledged application of the precooler technology

At high speed, jet engines struggle with a thermal challenge as air entering the intake becomes too hot, reducing thrust and limiting the ability to reach speeds beyond Mach 3. Reaction's precooler, essentially a highly efficient heat exchanger, already has proven its ability to quench megawatts of heat energy from the incoming air. Trials in the U.S. have shown the precooler technology to cool intake airflow from more than 800F (426C) to around 212F in just 1/20th of a second, helping to maximize performance.

Applied to a fighter engine, the precooler could allow it to work more efficiently at high speeds but also enable manufacturers to be less reliant on exotic, expensive and heat-resistant materials such as titanium. This could lead to lower costs in terms of purchase and maintenance, which are both key focuses of Britain's Future Combat Air System Technology Initiative (FCAS TI). The goal of the FCAS TI is to research and develop new technologies that can be spiraled into Britain's Eurofighter Typhoons and Lockheed Martin F-35s, but also potentially featured in a combat aircraft to replace the Typhoon in the 2030s.

“This is Phase 1 of something more,” Air Vice Marshal, Simon “Rocky” Rochelle, chief of staff for capability and the brainchild behind the RAF's RCO, said at the Royal International Air Tattoo, where the contract was signed. “There is something here that needs to be explored, investigated, tested and tried.”

Over the next two years, engineers will study how the precooler can be integrated onto the EJ200. Once this is established, the engine and precooler will be ground-tested together.

“This isn't about a new market for EJ200. We are using existing assets to try and address that heat challenge,” Conrad Banks, Rolls-Royce's chief engineer for future defense programs, tells Aviation Week.

“If you can cool the intake air down, suddenly you can expand the flight envelope of your gas turbine and it introduces some exciting supersonic and hypersonic applications.”

There is no suggestion the UK is looking for a hypersonic fighter, especially with the high costs associated with the airframe alone. Nonetheless, the technology could enable higher supercruise performance—sustained supersonic flight without the use of afterburner, or more simply better fuel economy.

“What we will do on the testbed is assess the drop in temperature and then see how that affects the core of the engine, that then validates our model. . . . This is not about massively changing the engine,” Banks explains.

How the precooler could be fitted to the engine is also part of the scope of the study. One option could be a donut-like configuration around the intake, Banks suggests. The work also will consider how the introduction of a precooler affects the rest of the airframe and whether such an installation is affordable. The precooler fitted to the EJ200 will be “designed and scaled to the engine to match its performance,” says Banks.

As Banks describes it, the technology will not change the low-observability aspects of the platform such as the engine's infrared signature, pointing out that will depend on what is done on the back end of the engine. However, officials note such a heat exchanger also could be mounted to the rear of the engine.

For Reaction Engines, the trials build on its lightweight heat exchanger (HTX) experiments, which were conducted in Colorado and used a J79 engine from an F-4 Phantom to feed the precooler. The technology is key to the company's SABRE concept, which is targeted at air-breathing hypersonic and space access vehicles. In this role, the engine is designed to efficiently extract oxygen from the atmosphere for rocket combustion. In the fully integrated SABRE, the chilled air will be passed from the HTX to a turbo-compressor and into the rocket thrust chamber, where it will be burned with sub-cooled liquid hydrogen fuel.

Reaction Engines has raised over £100 million in the last three years from public and private sources. In addition, the UK government in 2013 announced a £60 million commitment to assist with the demonstrator engines. Strategic investments also have been made at BAE Systems in 2015 and more recently in 2018 by Rolls-Royce and by Boeing's capital venture arm, HorizonX.

https://aviationweek.com/defense/precooler-technology-could-bring-advantages-fighter-engines