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A method and apparatus pump fuel to a fuel injection system in an internal combustion engine. The method comprises steps of pumping a liquid fuel to a first pressure, using the liquid fuel at the first pressure as a hydraulic fluid for driving a gaseous fuel pump, and pumping a gaseous fuel to a sec

A method and apparatus pump fuel to a fuel injection system in an internal combustion engine. The method comprises steps of pumping a liquid fuel to a first pressure, using the liquid fuel at the first pressure as a hydraulic fluid for driving a gaseous fuel pump, and pumping a gaseous fuel to a second pressure with the gaseous fuel pump.

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1. A method of pumping fuel to a fuel injection system in an internal combustion engine comprising: (a) pumping a liquid fuel to a first pressure;(b) using the liquid fuel at the first pressure as a hydraulic fluid for driving a gaseous fuel pump; and(c) pumping a gaseous fuel to a second pressure w

1. A method of pumping fuel to a fuel injection system in an internal combustion engine comprising: (a) pumping a liquid fuel to a first pressure;(b) using the liquid fuel at the first pressure as a hydraulic fluid for driving a gaseous fuel pump; and(c) pumping a gaseous fuel to a second pressure with the gaseous fuel pump. 2. The method of claim 1, wherein the liquid fuel is diesel fuel, and said first pressure is a common rail pressure. 3. The method of claim 1, wherein the gaseous fuel is natural gas. 4. The method of claim 1, further comprising: (d) controlling the second pressure by varying the first pressure. 5. The method of claim 1, wherein the step of driving the gaseous fuel pump comprises a sub-step of hydraulically driving the gaseous fuel pump using the liquid fuel at the first pressure. 6. The method of claim 1, wherein the step of driving the gaseous fuel pump comprises a sub-step of mechanically driving the gaseous fuel pump using the liquid fuel at the first pressure. 7. The method of claim 1, wherein the step of driving the gaseous fuel pump comprises a sub-step of electrically driving the gaseous fuel pump using the liquid fuel at the first pressure. 8. The method of claim 1, further comprising: (d) delivering said gaseous fuel from said gaseous fuel pump to a plurality of fuel injectors. 9. The method of claim 1, further comprising: (d) delivering the liquid fuel at the first pressure to a fuel injection system; and(e) injecting said liquid fuel into a combustion chamber of the internal combustion engine. 10. The method of claim 9, wherein the liquid fuel is diesel fuel, and the step of injecting comprises using the diesel fuel as a pilot fuel in the combustion chamber. 11. The method of claim 1, further comprising: (d) delivering the liquid fuel at the first pressure to a fuel injection system; and(e) injecting said liquid fuel into an intake charge upstream of a cylinder in the internal combustion engine. 12. The method of claim 1, further comprising: (d) delivering the gaseous fuel at the second pressure to a fuel injection system; and(e) injecting said gaseous fuel into a combustion chamber of the internal combustion engine. 13. The method of claim 1, comprising further steps of: (d) delivering the gaseous fuel at the second pressure to a fuel injection system; and(e) injecting said gaseous fuel into an intake charge upstream of a cylinder in the internal combustion engine. 14. The method of claim 1, wherein the step of pumping the gaseous fuel comprises a sub-step of returning the liquid fuel upstream of the first pressure wherein said liquid fuel can be pumped to the first pressure again. 15. The method of claim 1, wherein the gaseous fuel is in a liquefied state when being pumped by said gaseous fuel pump. 16. The method of claim 1, wherein the second pressure is equal to or greater than a pressure suitable for injecting said gaseous fuel into a combustion chamber of the internal combustion engine. 17. The method of claim 1, further comprising: (d) taking said gaseous fuel at said second pressure and then regulating to a third pressure. 18. The method of claim 1, wherein the step of pumping comprises a step of controlling flow of the liquid fuel for a compression stroke and for an intake stroke of the gaseous fuel pump. 19. The method of claim 18, wherein the step of controlling comprises a step of switching the flow of the liquid fuel between the compression stroke and the intake stroke. 20. The method of claim 1, wherein the step of driving the gaseous fuel pump comprises a sub-step of converting energy available in the liquid fuel at the first pressure to a form suitable for driving the gaseous fuel pump. 21. A fuel apparatus for an internal combustion engine comprising: (a) a liquid-fuel supply being a source of a liquid fuel;(b) a liquid-fuel pump receiving said liquid fuel from the liquid-fuel supply and being operable to pressurize the liquid fuel to a first pressure;(c) a gaseous-fuel supply being a source of a gaseous fuel;(d) a gaseous-fuel pumping system receiving said gaseous fuel from the gaseous-fuel supply and being responsive to said liquid fuel at the first pressure to pressurize the gaseous fuel to a second pressure, the liquid fuel at the first pressure acting as hydraulic fluid for said gaseous-fuel pumping system;(e) a fuel injection system receiving the gaseous fuel at the second pressure and being operable to introduce said gaseous fuel into the internal combustion engine; and(f) an electronic controller programmed to selectively actuate the gaseous-fuel pumping system to pressurize said gaseous fuel to the second pressure. 22. The apparatus of claim 21, wherein the liquid fuel is diesel and the liquid-fuel pump is a common rail pump. 23. The apparatus of claim 21, wherein the gaseous fuel is natural gas. 24. The apparatus of claim 21, wherein the gaseous fuel is in a liquefied state when being pressurized by said gaseous-fuel pumping system. 25. The apparatus of claim 21, wherein the gaseous fuel is in a gaseous phase when being pressurized by said gaseous-fuel pumping system. 26. The apparatus of claim 21, wherein the electronic controller is further programmed to control the second pressure by varying the first pressure of the liquid-fuel. 27. The apparatus of claim 21, wherein the fuel injection system comprises a gaseous fuel injector being disposed to introduce said gaseous fuel directly into a combustion chamber of the internal combustion engine. 28. The apparatus of claim 21, wherein the fuel injection system comprises a gaseous fuel injector being disposed to introduce said gaseous fuel upstream of a cylinder in the internal combustion engine. 29. The apparatus of claim 21, further comprising: (g) a liquid-fuel pressure regulator receiving the liquid fuel from the liquid-fuel pump and providing pressure regulated liquid-fuel to the fuel injection system. 30. The apparatus of claim 21, further comprising: (g) a liquid-fuel pressure regulator receiving the liquid fuel from the liquid-fuel pump and providing pressure regulated liquid-fuel to the gaseous-fuel pumping system. 31. The apparatus of claim 21, further comprising: (g) a return conduit connected with the gaseous-fuel pumping system and the liquid-fuel supply and being operable to return the liquid fuel from said gaseous-fuel pumping system to the liquid-fuel supply. 32. The apparatus of claim 21, further comprising: (g) a return conduit connected with the gaseous-fuel pumping system and an upstream side of the liquid-fuel pump, the return conduit being operable to return the liquid fuel from said gaseous-fuel pumping system to said upstream side. 33. The apparatus of claim 21, wherein the liquid-fuel pump is driven by the internal combustion engine. 34. The apparatus of claim 21, wherein the fuel injection system further receives the liquid fuel at the first pressure. 35. The apparatus of claim 34, wherein the fuel injection system further comprises an injector operable to receive the liquid fuel and the gaseous fuel and to inject said liquid fuel and said gaseous fuel independently and separately into the combustion chamber. 36. The apparatus of claim 21, wherein the gaseous-fuel pumping system comprises a gaseous-fuel pump and a driving mechanism, said gaseous-fuel pump receiving said gaseous fuel from the gaseous fuel supply and said driving mechanism being responsive to said liquid fuel at the first pressure to drive the gaseous-fuel pump to pressurize the gaseous fuel to the second pressure. 37. The apparatus of claim 36, wherein the computer is further programmed to control the driving mechanism to actuate said gaseous-fuel pump. 38. The apparatus of claim 36, wherein said driving mechanism comprises a hydraulic drive to drive said gaseous fuel pump. 39. The apparatus of claim 36, wherein said driving mechanism comprises a mechanical drive to drive said gaseous fuel pump. 40. The apparatus of claim 36, wherein said driving mechanism comprises an electric drive to drive said gaseous fuel pump. 41. The apparatus of claim 36, wherein said driving mechanism comprises a flow control device operable to switch the flow of the liquid fuel at the first pressure. 42. The apparatus of claim 36, wherein the gaseous-fuel pump is one of two gaseous-fuel pumps that operate in parallel and 180° out of phase with each other. 43. The apparatus of claim 36, wherein the gaseous-fuel pumping system further comprises a gaseous-fuel booster pump operating in series with the gaseous-fuel pump in a multi-stage arrangement. 44. The apparatus of claim 36, wherein said gaseous-fuel pump is a reciprocating piston-type pump. 45. The apparatus of claim 44, wherein the reciprocating piston-type pump comprises a piston selected from the group consisting of a single-acting piston and a double-acting piston. 46. The apparatus of claim 44, wherein the gaseous-fuel pump comprises a driving chamber, a compression chamber and a piston therebetween, the piston comprising a driving chamber face adjacent the driving chamber and a compression chamber face adjacent the compression chamber, a ratio of an area of the driving chamber face to an area of the compression chamber face being less than one. 47. The apparatus of claim 44, wherein the gaseous-fuel pump comprises a driving chamber, a compression chamber and a piston therebetween, the piston comprising a driving chamber face adjacent the driving chamber and a compression chamber face adjacent the compression chamber, a ratio of an area of the driving chamber face to an area of the compression chamber face being greater than one.