Aircraft hydrogen fuel systems and methods and systems of starting such systems are described. The aircraft hydrogen fuel systems include a hydrogen burning main engine, a main tank configured to contain liquid hydrogen to be supplied to the main engine during a normal operation, and a starter tank configured to contain gaseous hydrogen to be used during a startup operation of the main engine. Methods and processes for starting and/or restarting such systems are described.

A fuel system includes a fuel gathering system in fluid communication with a fuel storage container, and a fluid pump assembly in fluid communication with the fuel gathering system. The fluid pump assembly includes a main gear pump stage and a first flow attenuator. A main driven gear is meshed with a main drive gear in a main pump conduit, and a main pump bearing assembly rotatably supports the main drive gear and the main driven gear. The first flow attenuator is disposed around the main pump conduit, and includes a substantially polygonal fluid opening. Edges of the opening are substantially aligned with an undercut bearing portion on at least one of an inlet side and an outlet side of the main pump conduit to define a non-round fluid boundary.

A fuel system includes a fuel gathering system in fluid communication with a fuel storage container, and a fluid pump assembly in fluid communication with the fuel gathering system. The fluid pump assembly includes a main gear pump stage and a first flow attenuator. A main driven gear is meshed with a main drive gear in a main pump conduit, and a main pump bearing assembly rotatably supports the main drive gear and the main driven gear. The first flow attenuator is disposed around the main pump conduit, and includes a substantially polygonal fluid opening. Edges of the opening are substantially aligned with an undercut bearing portion on at least one of an inlet side and an outlet side of the main pump conduit to define a non-round fluid boundary.

A thermal management system includes at least one vapor control system (VCS) that is configured to cool portions of the vehicle. The VCS circulates a fluid therethrough to cool the portions of the vehicle through heat exchange. At least one reverse air control machine (RACM) couples to VCS through a first heat exchanger. The RACM is configured to receive ram air. The RACM expands the ram air. Heat from the fluid circulating through the VCS is transferred to the expanded ram air through the first heat exchanger.

A thermal management system includes at least one vapor control system (VCS) that is configured to cool portions of the vehicle. The VCS circulates a fluid therethrough to cool the portions of the vehicle through heat exchange. At least one reverse air control machine (RACM) couples to VCS through a first heat exchanger. The RACM is configured to receive ram air. The RACM expands the ram air. Heat from the fluid circulating through the VCS is transferred to the expanded ram air through the first heat exchanger.

A thermal management system includes at least one vapor compression system (VCS) that is configured to cool portions of the vehicle. The VCS circulates a fluid therethrough to cool the portions of the vehicle through heat exchange. At least one reverse air cycle machine (RACM) couples to VCS through a first heat exchanger. The RACM is configured to receive ram air. The RACM expands the ram air. Heat from the fluid circulating through the VCS is transferred to the expanded ram air through the first heat exchanger.

A hydrogen fuel including a safety marker and a method and apparatus for adding the safety marker to the hydrogen fuel. The hydrogen fuel may be stored in a tank in a liquid phase and then heated to at least one of a gaseous phase and a supercritical phase. The safety marker may be added to the hydrogen fuel when the hydrogen fuel is in the at least one of the gaseous phase and the supercritical phase after heating the hydrogen fuel. The hydrogen fuel may be delivered in the at least one of the gaseous phase and the supercritical phase to a power generator, such as a gas turbine engine. The safety marker may be a visual safety marker, such as a noble gas, or an odorant.

A hydrogen fuel including a safety marker and a method and apparatus for adding the safety marker to the hydrogen fuel. The hydrogen fuel may be stored in a tank in a liquid phase and then heated to at least one of a gaseous phase and a supercritical phase. The safety marker may be added to the hydrogen fuel when the hydrogen fuel is in the at least one of the gaseous phase and the supercritical phase after heating the hydrogen fuel. The hydrogen fuel may be delivered in the at least one of the gaseous phase and the supercritical phase to a power generator, such as a gas turbine engine. The safety marker may be a visual safety marker, such as a noble gas, or an odorant.

A fuel system for a power generator using hydrogen fuel and a method of recovering a safety marker added to the hydrogen fuel. The hydrogen fuel may be stored in a tank and delivered, in at least one of a gaseous phase and a supercritical phase, to a power generator. The hydrogen fuel is delivered with a fuel delivery assembly and contains at least one safety marker when the fuel is in the fuel delivery assembly. The at least one safety marker is separated from the hydrogen fuel, using, for example, a separator. The at least one safety marker separated from the hydrogen fuel is stored in a safety marker storage tank. The safety marker may be a visual safety marker, such as a noble gas, or an odorant.

A fuel system for a power generator using hydrogen fuel and a method of recovering a safety marker added to the hydrogen fuel. The hydrogen fuel may be stored in a tank and delivered, in at least one of a gaseous phase and a supercritical phase, to a power generator. The hydrogen fuel is delivered with a fuel delivery assembly and contains at least one safety marker when the fuel is in the fuel delivery assembly. The at least one safety marker is separated from the hydrogen fuel, using, for example, a separator. The at least one safety marker separated from the hydrogen fuel is stored in a safety marker storage tank. The safety marker may be a visual safety marker, such as a noble gas, or an odorant.