Over the last century, propulsion technology has advanced steadily, moving from piston engines through to the modern era of turbofan jet engines. Yet innovation continues behind the scenes, and the industry may now be on the verge of introducing a new form of propulsion that uses hydrogen as its primary fuel. Although hydrogen engines have been under development for years, they remain a long way from being ready for widespread commercial use.
Leading engine maker Rolls-Royce is pursuing its own hydrogen engine designs and has recently patented a fuel system for a gas turbine engine configured to burn hydrogen fuel. This novel approach could help solve one of the major challenges of using liquid hydrogen as a fuel source: its extremely low temperature. Rolls-Royce’s idea is to use a fuel turbine to warm the hydrogen before it reaches the engine, creating a more stable combustion process.
According to the patent filing, the new fuel system includes a main fuel line equipped with a pump designed to handle hydrogen and deliver pressurised fuel to the engine’s core combustor. It also features an auxiliary combustor, which will burn a small portion of the hydrogen to warm up the rest of the fuel. In effect, this creates a self-sustaining loop: a small amount of hydrogen is diverted from the main line to pre-heat the overall fuel supply.
Although hydrogen is theoretically one of the cleanest fuels available, putting it into practice on an aircraft is extremely challenging. Compared to conventional jet fuel, hydrogen takes up much more space when stored, creating major headaches for both aircraft design and ground infrastructure at airports. In addition, liquid hydrogen must be kept at extremely low temperatures and has a less stable combustion process than traditional fuels.
Rolls-Royce’s proposed system would help tackle both of these problems by offering a controlled and efficient way to deliver fuel. While hydrogen fuel cells have shown greater practical promise so far, hydrogen combustion remains a tougher nut to crack. Liquid hydrogen needs to be stored at -253°C, meaning aircraft would require specially insulated tanks for safe storage. However, because hydrogen is less dense than jet fuel, those tanks would need to be larger than conventional ones — a persistent challenge for aircraft designers.