Sealing structure for gaseous fuel

1. A sealing structure for forming a gaseous fuel seal between a first conduit and a second conduit in an internal combustion engine comprising:

an inwardly tapering section in the first conduit, the inwardly tapering section including a surface shape that is one of a frustoconical surface, a spherical surface, a parabolic surface or a hyperbolic surface;

a fitting extending around the inwardly tapering section and secured to the first conduit;

a nut;

an end-form at one end of the second conduit, the end-form including a surface shape that is one of a frustoconical surface, a spherical surface, a parabolic surface or a hyperbolic surface and is different from the surface shape of the inwardly tapering section, the second conduit extending through the nut;

wherein the nut threadedly engages the fitting to secure the end-form to the inwardly tapering section thereby forming a contact band;

wherein a width of the contact band is at least equal to the larger of:

a minimum contact pressure width predetermined by determining the minimum contact pressure width where contact pressure is at least equal to a contact pressure sufficient to form a gas tight seal in the contact band; and

a minimum yield zone width predetermined by determining a minimum yield zone width where at least one of a surface of the end-form and a surface of the inwardly tapering section have plastically deformed.

2. The sealing structure of claim 1 , wherein at least one of the minimum contact pressure width is within a range of 0.5 millimeters to 1 millimeter and the minimum yield zone width is within a range of 0.5 millimeters to 1 millimeter.

3. The sealing structure of claim 1 , wherein at least one of the inwardly tapering section is a low to medium strength carbon steel and the end-form is a low to medium strength carbon steel.

4. The sealing structure of claim 1 , wherein the first conduit is one of a gaseous fuel rail and a conduit in a gaseous fuel injector.

5. The sealing structure of claim 1 , wherein the first conduit is one of an elongated tube, a forged component having a fuel passageway, and a molded component having a fuel passageway.

6. The sealing structure of claim 1 , wherein the second conduit is a fuel line.

7. The sealing structure of claim 1 , wherein the second conduit is an elongated tube comprising an outer diameter and an inner diameter, wherein the outer diameter is less than two times the inner diameter.

8. The sealing structure of claim 1 , wherein the predetermined minimum contact pressure width is greater than then the predetermined minimum yield zone width.

9. The sealing structure of claim 1 , wherein the contact pressure is at least equal to four times the gaseous fuel pressure.

10. The sealing structure of claim 1 , wherein the inwardly tapering section includes a surface shape that is the frustoconical shape and the end form includes a surface shape that is the spherical shape.

11. A method for sealing a gaseous fuel at fluid connections between gaseous fuel conduits in an internal combustion engine comprising:

forming a contact band between two surfaces of a sealing structure between a first conduit and a second conduit, one of the two surfaces including a surface shape that is one of a frustoconical surface, a spherical surface, a parabolic surface or a hyperbolic surface and the other of the two surfaces having a surface shape that is different from the surface shape of the one of the two surfaces and is one of a frustoconical surface, a spherical surface, a parabolic surface or a hyperbolic surface;

determining a minimum contact pressure width where contact pressure is at least equal to a contact pressure sufficient to form a gas tight seal between the two surfaces of the sealing structure; and

determining a minimum yield zone width where at least one of the two surfaces have plastically deformed;

wherein a width of the contact band is at least equal to the larger of:

the determined minimum contact pressure width; and

the determined minimum yield zone width.

12. The method of claim 1 , wherein the width of the contact band is between the larger of the determined minimum contact pressure width and the determined minimum yield zone width.

13. The method of claim 1 , further comprising selecting the contact pressure as a function of at least one of:

gaseous fuel pressure;

at least one of the material of the first conduit and the material of the second conduit; and

surface finish of at least one of the first conduit and the second conduit around the contact band.

14. The method of claim 1 , further comprising selecting the contact pressure as at least equal to four times the gaseous fuel pressure.

15. The method of claim 1 , wherein determining the minimum yield zone width comprises determining the minimum yield zone width as a function of at least one of:

gaseous fuel pressure;

at least one of the material of the first conduit and the material of the second conduit; and

surface finish of at least one of the first conduit and the second conduit around the contact band.

16. The method of claim 11 , further comprising selecting a softer material for the second conduit compared to the first conduit.

17. The method of claim 16 , further comprising selecting the softer material such that only the second conduit plastically deforms.

18. The method of claim 11 , wherein the second conduit is a fuel line, further comprising selecting a wall thickness of the second conduit less than a wall thickness for a liquid fuel line.

19. The method of claim 11 , further comprising finishing the surfaces such that a surface roughness is within a range of 0.06 root mean square and 1.6 root mean square.

20. The method of claim 11 , wherein the one of the two surfaces includes a surface shape that is the frustoconical shape and the other of the two surfaces includes a surface shape that is the spherical shape.