Patent Application
20250027457
A hydrogen-fueled internal combustion engine vehicle uses an internal combustion engine with hydrogen as fuel, and is to be distinguished from hydrogen fuel cell vehicles that use hydrogen electrochemically rather than combustion. The absence of carbon in hydrogen fuel means that no carbon dioxide is produced during combustion, which eliminates the main greenhouse gas emission of conventional petroleum engines. As used herein “hydrogen-fueled engine” refers to a hydrogen-fueled internal combustion engine, whether fueled entirely with hydrogen or using multi-mode fuels.
One challenge for vehicles with hydrogen-fueled engines is on-board fuel storage. A hydrogen-fueled vehicle can store its hydrogen as either a gas or a liquid. Gas storage is typically the method used, with high-pressure tanks of 350-700 bar (5,000-10,000 psi) tank pressure. Hydrogen-fueled vehicles require the fuel to be stored at high pressure to store enough fuel mass in a reasonable tank volume to have acceptable fuel range. 700 bar is a commonly discussed maximum pressure for hydrogen fuel storage on board a vehicle.
As fuel is consumed by the vehicle, fuel pressure in the fuel tank will decrease down to some minimum value. At this fuel level, a fuel tank is considered functionally empty and will have to be refueled.
Depending on how the hydrogen fuel is introduced into the engine, the minimum pressure required for fuel delivery can vary. Fuel delivery by port fuel injection may operate at a relatively low fuel pressure, 20 bar for example. Direct injection systems, which introduce the fuel directly into the cylinder for increased engine efficiency and performance, may require higher pressure, especially if the fuel is to be injected at or near top-dead-center firing, 300 bar for example. If the minimum fuel tank pressure is required to be 300 bar instead of 20 bar to supply fuel to the injectors at the required pressure, the usable amount of fuel stored in 700 bar fuel tanks is reduced by approximately half.
In the embodiment of
Hydrogen fuel is stored as a gas in hydrogen tank 12. As indicated in the Background, the engine's fuel delivery system may have a desired fuel delivery pressure that varies from the storage pressure in tank 12.
In the example of
Because hydrogen fuel is gaseous and low density, the amount of energy required to deliver fuel from low pressure storage in tank 12 to high pressure injection is high compared to traditional liquid fuels. For example, an engine that nominally operates at 42 percent brake thermal efficiency would suffer a fuel economy penalty of greater than 7 percent if it needed to compress hydrogen fuel from a nearly-depleted fuel tank at 20 bar up to a required fuel delivery pressure of 300 bar. Conversely, if the fuel pressure from a nearly full tank of 700 bar is reduced to the delivery pressure of 300 bar through a conventional regulator, expansion energy is lost to irreversible throttling losses.
A feature of the invention is the use of compressor/expander 13 to receive hydrogen from fuel tank 12 and to deliver hydrogen to injector(s) 15 (via a fuel rail) at the desired injection pressure. Compressor/expander 13 is installed in fluid communication with and between the fuel tank 12 and the engine's fuel delivery system (typically a fuel rail).
Compressor/expander 13 operates in either of two modes: compression mode or expansion mode. It operates as a compressor if the fuel tank pressure is below the desired fuel delivery pressure. It operates as an expander if the fuel tank pressure is higher than the desired fuel delivery pressure. As explained below, the mode in which compressor/expander operates is controlled by metering valves at the inlet(s) and outlet(s) of the cylinder(s).
Compressor/expander 13 may be implemented with various positive displacement devices. In the embodiment of this description, compressor/expander 13 is implemented with a piston-type device. Other positive displacement devices could be used, rotary or piston type. In general, any device that cyclically increases and decreases its internal volume and is controlled by valves could be used. “Controlled by valves” means that inlet and outlet flow are controlled by valves rather than covering and uncovering ports.
Expansion work is captured by compressor/expander 13 when it is operating in expansion mode. The recovered energy from the fuel tank pressure during the time the tank is nearly full can offset fuel economy penalties during the time the tank is nearly empty. In the example of
Further range could be gained by pumping from even lower pressures, assuming sufficient pump displacement and drive power, at a tank fuel economy penalty significantly reduced compared to the pump-only case. The lower the required fuel delivery pressure the lower the tank mileage breakeven fuel tank pressure. If only 120 bar fuel delivery pressure is required, then the tank mileage breakeven fuel tank pressure is 20 bar for a 700-bar-rated fuel tank.
The inlet and outlet (exhaust) valves of the compressor/expander's cylinder are actively controlled inlet and outlet metering valves 31 and 32, respectively. In other embodiments, compressor/expander 13 may have more than one cylinder. It may have more than one inlet and/or more than one outlet valve per cylinder. In general terms, compressor/expander 13 will have at least one metered inlet valve and one metered outlet valve per cylinder.
Inlet metering valve 31 connects the fuel tank 12 to the cylinder of compressor/expander 13. Outlet metering valve 32 connects the cylinder to the engine's fuel delivery system, such as its fuel rail.
Controller 14 receives measured fuel input pressure and temperature from sensors 36 and 37, respectively. Controller 14 also stores desired injection pressure and fuel flow. From this data, controller 14 determines whether compressor/expander 13 will operate in compressor mode or expander mode. It ensures that the fuel delivered to the engine's injector(s) is maintained at the desired pressure at the point of delivery. Typically, this delivery will be via an engine fuel rail. Controller 14 further calculates the opening and closing timing for valves 31 and 32 to maintain the desired fuel flow.
More specifically, during the piston travel, controller 14 controls the timing of the inlet and outlet metering valve opening and duration to minimize pressure drop and thus throttling losses across valves 31 and 32 during the filling and discharge strokes. The metering valves are controlled to control the fuel input and output to ensure that the engine is only fed the amount of fuel required at the desired pressure.
