Hydrogen fuelled gas turbine engine

A fuel system for a gas turbine engine configured to combust hydrogen fuel, the fuel system comprising:

• a main fuel conduit;
• a fuel pump configured to operate on hydrogen within the fuel conduit to provide pressurised fuel to a core combustor of the gas turbine engine;
• an auxiliary combustor downstream in fuel flow of the fuel pump, and configured to combust a portion of fuel diverted from the main fuel conduit and to heat a remainder of fuel in the main fuel conduit;
• and
• a fuel turbine downstream in fuel flow of the auxiliary combustor, the fuel turbine being configured to be driven by the heated fuel from the auxiliary combustor and configured to power the fuel pump;
• wherein
• the fuel system comprises a fuel turbine inlet valve provided upstream in hydrogen fuel flow of the fuel turbine configured to control mass flow rate and/or pressure of fuel flowing into the fuel turbine, and
• the fuel system further comprises one or more sensors for providing information on pressure, temperature and flow of fuel downstream of the fuel turbine to a controller, the controller configured to control at least the auxiliary combustor and the fuel turbine inlet valve and provide desired pressure, temperature and flow rate of fuel downstream of the fuel turbine.