Engine system and method of operating the same

A method of operating an engine system in which mechanical power is generated by combustion or oxidation of a fuel in an engine, wherein the fuel includes a first fuel and a second fuel different from the first fuel, the method comprising:

• providing the first fuel from a first fuel store to the engine at a first mass flow rate;
• providing the second fuel from a second fuel store to the engine at a second mass flow rate, and
• wherein the first mass flow rate and the second mass flow rate contribute to a total mass flow rate of fuel to the engine,
• during a period of acceleration of the engine, increasing the relative fraction of the total mass flow rate of fuel represented by the second mass flow rate in order to control a surge margin of one or more compressors of the engine;
• and
• controlling the relative fractions of the total mass flow rate of fuel provided by the first mass flow rate and the second mass flow rate such that:
• the surge margin during at least a portion of the period of acceleration is the same as operating on only the first fuel during the at least a portion of the period of acceleration;
• and
• the rate of acceleration is increased during the at least a portion of the period of acceleration compared to operation using only the first fuel during the at least a portion of the period of acceleration,
• wherein the second fuel is selected to have a higher specific energy than the first fuel and to release a greater mass of water per unit mass of fuel than the first fuel,
• wherein the second fuel is a non-hydrocarbon fuel.

An engine system comprising:

• a first fuel store of a first fuel;
• a second fuel store of a second fuel different from the first fuel;
• an engine arranged to produce mechanical power by combustion or oxidation of a fuel in the engine, the fuel including the first fuel and the second fuel;
• a fuel distribution system arranged to deliver the fuel from the first and second fuel stores to the engine,
• the first fuel delivered at a first mass flow rate,
• the second fuel delivered at a second mass flow rate,
• the first and second mass flow rates contributing to a total mass flow rate of fuel to the engine;
• and
• a control system arranged to increase the relative fraction of the total mass flow rate of fuel represented by the second mass flow rate during a period of acceleration of the engine, in order to control a surge margin of the engine,
• wherein the second fuel is selected to have a higher specific energy than the first fuel and to release a greater mass of water per unit mass of fuel than the first fuel,
• wherein the second fuel is a non-hydrocarbon fuel,
• wherein the control system is arranged to:
• control the relative fractions of the total mass flow rate of fuel provided by the first mass flow rate and the second mass flow rate such that:
• the surge margin during at least a portion of the period of acceleration is the same as operating on only the first fuel during the at least a portion of the period of acceleration;
• and
• the rate of acceleration during the at least a portion of the period of acceleration is increased compared to operation using only the first fuel during the at least a portion of the period of acceleration.

An engine system comprising:

• a first fuel store of a first fuel;
• a second fuel store of a second fuel different from the first fuel;
• an engine arranged to produce mechanical power by combustion or oxidation of a fuel in the engine, the fuel including the first fuel and the second fuel different from the first fuel;
• a fuel distribution system arranged to deliver the fuel from the first and second fuel stores to the engine,
• the first fuel delivered at a first mass flow rate,
• the second fuel delivered at a second mass flow rate,
• the first and second mass flow rates contributing to a total mass flow rate of fuel to the engine;
• and
• a control system arranged to increase the relative fraction of the total mass flow rate of fuel represented by the second mass flow rate during a period of acceleration of the engine, in order to control a surge margin of the engine,
• wherein the second fuel is selected to have a higher specific energy than the first fuel and to release a greater mass of water per unit mass of fuel than the first fuel,
• wherein the second fuel is a non-hydrocarbon fuel,
• wherein the control system is arranged to:
• control the relative fractions of the total mass flow rate of fuel provided by the first mass flow rate and the second mass flow rate to increase the surge margin during at least a portion of the period of acceleration compared to operation using only the first fuel during the at least a portion of the period of acceleration,
• wherein all handling bleeds are closed during the at least a portion of the period of acceleration.