Liquid hydrogen engines for aircraft propulsion

It essential that we act to reduce CO2 emissions across all sectors of industry to minimise our contribution to climate change.
For aviation the technical challenges of decarbonising are especially problematic. Electric and hybrid technology offer only partial solutions: batteries cannot achieve the energy density for transatlantic flight, and fuel cells lack the necessary power density. For medium and long-haul flight, gas turbines will therefore remain the primary power plants for the foreseeable future.
In the near-term, the industry will reduce emissions by improving engine efficiency and switching to non-fossil hydrocarbon fuels. Synthetic Aviation Fuel generated with renewable electricity (eSAF) can reduce net CO2 emissions by around 60% and could be used in existing aircraft. Though significant, these reductions will not be enough in the long term.
We must therefore look to other fuels to achieve decarbonised flight. Liquid Hydrogen is a promising contender and has support across industry, including Airbus and Rolls-Royce. The switch from Kerosene presents many challenges for the engine and fuel-management, notably how to thermally manage liquid hydrogen at 20K, bring it to combustible temperatures and optimising the engine cycle to reduce fuel burn. This project will examine aspects of these challenges, in particular the fundamentals of thermal management and cryogenic heat exchanger design. The technology landscape is rapidly developing and therefore the key target areas are hard to define at the project outset, but will include, for example, condenser heat exchangers for hydrogen steam re-injection cycles, recuperator design and hydrogen bottoming cycles. Such components not only need to function from a thermal viewpoint, but they also need to be aerodynamically integrated into the engine to achieve optimal system performance.
The key research questions that the project will address are:
(1) How can we model the fundamental behaviour of cryogenic liquids in heat exchanger design?
(2) How can we exploit this behaviour to design and integrate the novel heat exchangers required for advanced hydrogen engine cycles?
(3) What are the implications of icing on the air/gas side of the heat exchanger and how do we assess this ?
The project will combine novel research methods to provide a detailed understanding of the heat transfer and flow processes. We will use numerical simulations of heat exchangers and develop low-order models of cryogenic fluid behaviour and perform detailed design studies for integration into novel cycles. We expect that these simulations will be supported with experimental measurements on cryogenic heat exchangers. The understanding that we build from these studies will be used to guide the design of cryogenic heat exchangers across multiple applications, enabling rapid assessment of designs for different engine cycles. This work builds on much of the wider work in Oxford studying heat exchangers design and installation.
This project falls within the EPSRC Fluid dynamics and aerodynamics research area.
The project is in collaboration with Rolls-Royce plc.