A method of operating a gas turbine engine is provided. The method includes: providing a flow of a primary fuel to a combustor of a turbomachine, the turbomachine including a compressor, a turbine, and a spool rotatable with the compressor and the turbine; receiving data indicative of a spool parameter of the spool; and modifying a flow of a secondary fuel to the combustor in response to the received data indicative of the spool parameter of the spool.