Injection strategy to maximize efficiency in gaseous engine
A method is provided for an engine capable of burning gaseous fuel, the engine also including a combustion chamber, a fuel supply system with at least one fuel tank, at least one intake valve, and at least one exhaust valve, an injector to directly inject gaseous fuel into the combustion chamber, and an exhaust oxygen sensor. The method comprises directly injecting fuel from the injector into the chamber at a variable supply pressure which decreases as fuel tank pressure decreases; and adjusting at least one of an injection time and duration based at least on said variable pressure and information from the exhaust oxygen sensor.
1. A method for an engine capable of burning gaseous fuel, the engine also including a combustion chamber, a fuel supply system with at least one fuel tank, at least one intake valve, and at least one exhaust valve, an injector to directly inject gaseous fuel into the combustion chamber, and an exhaust oxygen sensor, the method comprising:
directly injecting fuel from the injector into the chamber at a variable supply pressure which decreases as fuel tank pressure decreases; and
adjusting at least one of an injection time and duration based at least on said variable pressure and information from the exhaust oxygen sensor, where the injection is performed with the intake valve closed and during a later half of a compression stroke, even as the supply pressure decreases to a low range where supply pressure energy is recovered in the combustion chamber.
2. The method of claim 1 , wherein the fuel injection starts near an end of a compression stroke.
3. The method of claim 2 , wherein the fuel injection time starts near a top dead center before the compression stroke is complete.
4. The method of claim 1 , wherein the pressure supplied to the injector is regulated by a pressure regulation device.
5. The method of claim 4 , wherein the pressure regulation device includes a variable pressure regulator or a second fuel tank.
6. The method of claim 1 wherein the fuel injector comprises a piezoelectric actuator.
7. The method of claim 6 , wherein the method further includes adjusting spark timing based at least on said variable pressure and information from the exhaust oxygen sensor.
8. The method of claim 6 , wherein the method further includes adjusting throttling based at least on said variable pressure and information from the exhaust oxygen sensor.
9. The method of claim 6 , wherein the method further includes adjusting at least one of an injection time and duration based on information from an in-cylinder pressure sensor.
10. A method for an engine capable of burning gaseous fuel, the engine also including a combustion chamber, a fuel supply system having fuel storage and at least one pressure regulation device, and a piezoelectrically actuated injector to directly inject gaseous fuel into the combustion chamber, the method comprising:
supplying fuel from the fuel storage to the piezoelectrically actuated injector under a first engine and tank condition with a higher tank pressure by substantially regulating down fuel tank pressure, the injector directly injecting the supplied fuel with regulation to the cylinder at least during a later half of a compression stroke;
supplying fuel from the fuel storage to the piezoelectrically actuated injector under a second engine and tank condition with a lower tank pressure and without substantially regulating down fuel tank pressure, the injector directly injecting the supplied fuel without regulation to the cylinder at least during a later half of a compression stroke with an intake valve closed;
varying an amount of regulation during the first tank and engine condition in response to the first engine and tank condition; and
adjusting at least one of an injection time and duration based at least on an injection pressure during at least said first and second engine and tank condition.
11. The method of claim 10 , wherein the first tank and engine condition includes a high fuel tank pressure and a low required fuel amount.
12. The method of claim 10 , wherein the second tank and engine condition includes a range of pressure that is within an operation range of the fuel injector.
13. The method of claim 10 , wherein the pressure regulation device includes one of a variable pressure regulator and a second fuel tank.
14. The method of claim 10 , wherein the method further includes adjusting spark timing based at least on said variable pressure and information from an exhaust oxygen sensor.
15. A system for an engine having a cylinder, comprising:
a first gaseous fuel tank;
a second gaseous fuel tank selectively coupled to the first fuel tank;
a direct injector coupled to the cylinder, the injector coupled at least to the first fuel tank;
a variable pressure regulator coupled between the first and second tank, where during at least one condition, the variable pressure regulator reducing fuel rail pressure by diverting gaseous fuel into the second tank; and
a control system operating the injector to delivery gaseous fuel directly to the cylinder during engine operation, and varying a fuel pressure delivery to the injector by selectively coupling the second gaseous fuel tank to the first gaseous fuel tank at least as a pressure in the first tank and a condition of the engine varies.
16. The system of claim 15 wherein the injector includes piezoelectric actuation.
17. The system of claim 16 wherein the second tank is coupled to the first tank through a selectively activatable check valve.
18. The system of claim 15 where the control system further operates to supply fuel from the second fuel tank to the engine during a low fuel rail pressure condition.