A system for assisting in the atomisation of liquid particles conveyed in a gas stream flowing along a flow path having a rigid boundary, said system involving the creation of one or more shock waves in the gas stream. In a preferred embodiment, the system comprises a fuel injection nozzle (10) comp
A system for assisting in the atomisation of liquid particles conveyed in a gas stream flowing along a flow path having a rigid boundary, said system involving the creation of one or more shock waves in the gas stream. In a preferred embodiment, the system comprises a fuel injection nozzle (10) comprising a fluid flow passage (43) terminating at a discharge orifice (15) and incorporating a delivery port (33) defined between a valve seat (31) and a valve member (23) movable with respect to the valve seat for opening and closing the delivery port. Fuel is delivered along the fluid flow passage (43) into a combustion chamber through the discharge orifice (15) upon opening of the delivery port (33). The valve member (23) devines an inner boundary surface (47) of the flow passage (43) and the valve seat (31) defines at least part of an outer boundary surface (45) of the flow passage (43). The inner and outer boundary surfaces (47, 45) are configured to generate one or more shock waves in an air-fuel mixture flowing at supersonic speed therebetween.
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1. An apparatus for atomising liquid particles conveyed in a gas flow, the apparatus comprising a fluid flow passage defined between first and second boundary surfaces and a movable element for controlling the flow of liquid through the passage, at least one of the first and second boundary surfaces
1. An apparatus for atomising liquid particles conveyed in a gas flow, the apparatus comprising a fluid flow passage defined between first and second boundary surfaces and a movable element for controlling the flow of liquid through the passage, at least one of the first and second boundary surfaces being configured to generate one or more oblique shockwaves and/or expansion shockwaves in the gas flow and within the fluid flow passage when the gas flow is moving at supersonic speed therethrough.2. Apparatus according to claim 1 wherein said at least one boundary surface is so configured to generate oblique shock waves by incorporation of a directional change or obstruction in a boundary surface converging towards the flow.3. Apparatus according to claim 2 wherein the or each directional change in the respective boundary surface is provided by a discontinuity in the boundary surface.4. Apparatus according to claim 2 wherein the or each directional change in the respective boundary surface is provided by a discontinuity in the boundary surface the discontinuity is selected from a group comprising an angular corner, a multitude of successive corners or a rounded corner.5. Apparatus according to claim 1 wherein said at least one boundary surface is so configured to generate expansion shock waves by incorporation of a directional change in the boundary surface involving a divergence from the flow.6. Apparatus according to claim 1 wherein the first and second boundary surfaces are each configured to provide a series of directional changes to produce a pattern of oblique shock waves in conjunction with expansion waves.7. Apparatus according to claim 1 wherein the fluid flow passage or at least a section thereof is configured as a convergent-divergent nozzle.8. Apparatus according to claim 7 wherein the shock waves are generated in the diverging section of the nozzle.9. Apparatus according to claim 1 wherein the flow passage is defined by a nozzle having a discharge orifice, with the liquid particles being subjected to the shock waves in the nozzle prior to issuing from the nozzle through the discharge orifice.10. Apparatus according to claim 9 wherein the nozzle comprises a first element defining the first boundary surface and a second element defining the second boundary surface.11. Apparatus according to claim 9 wherein the nozzle comprises a fuel injection nozzle in an air assist fuel injection system for an internal combustion engine.12. Apparatus according to claim 9 wherein the nozzle comprises a fuel injection nozzle in an air assist fuel injection system for an internal combustion engine the fuel injection nozzle comprises a fluid flow passage terminating at the discharge orifice and incorporating a delivery port, the movable element providing a valve member co-operating with a valve seat to define the delivery port therebetween, the valve member being movable with respect to the valve seat for opening and closing the delivery port, with fuel being delivered along the fluid flow passage into a combustion chamber of the engine through the discharge orifice upon opening of the delivery port.13. Apparatus according to claim 12 wherein the fuel is delivered directly into the combustion chamber of the engine by the fuel injection nozzle.14. Apparatus according to claim 12 wherein the fuel is delivered along the fluid flow passage and through the discharge orifice by a quantity of air which entrains the fuel and promotes the atomisation thereof.15. Apparatus according to claim 14 wherein the fluid flow passage is defined between the valve member and a body which surrounds the valve member and which incorporates the valve seat, the valve member defining an inner boundary surface of the flow passage and the body including the valve seat defining an outer boundary surface of the flow passage.16. Apparatus according to claim 15 wherein the inner and outer boundary surfaces are each configured to provide a series of directional changes to produce a pattern of oblique shock waves in conjunction with expansion waves.17. Apparatus according to claim 15 wherein shock waves reflect from the inner and outer boundary surfaces.18. Apparatus according to claim 17 wherein the nozzle is configured such that there is interaction between the shock waves, as well as their reflected waves, to provide a criss-cross array of shock waves through which the liquid fuel particles must traverse.19. Apparatus according to claim 12 wherein the valve seat is located at or upstream of the discharge orifice.20. Apparatus according to claim 12 wherein the profile of the valve seat, and the corresponding section of the valve member adapted to sealingly engage the valve seat, form part of the configuration of the boundary surfaces.21. Apparatus according to claim 12 wherein the fuel injection nozzle comprises an outwardly opening poppet valve, and wherein oblique shock waves generate from the valve seat and expansion waves propagate from the poppet valve.22. Apparatus according to claim 12 wherein the fuel injection nozzle comprises a projection extending downwardly from the valve member which is configured to promote a desired shaping of a fluid spray issuing from the discharge orifice.23. Apparatus according to claim 9 further comprising a surface disposed outwardly of the discharge orifice in the direction of liquid-gas flow, the surface being configured to generate expansion waves in the liquid-gas flow issuing from the discharge orifice, the expansion waves propagating in a direction which traverses the liquid-gas flow.24. Apparatus according to claim 1 wherein the boundary surfaces are configured to promote reflection of shockwaves generated in the fluid flow passage.25. Apparatus according to claim 1 wherein the boundary surfaces are configured to promote the reflection and/or interference of shockwaves generated in the flow passage to promote pressure disturbances therein for assisting the atomisation of the liquid particles.26. Apparatus according to claim 1 wherein the boundary surfaces are configured in the direction of fluid flow to promote exposure of the liquid particles to shockwaves within the flow passage.27. Apparatus according to claim 26 wherein the boundary surfaces are configured to promote separation of the liquid particles therefrom thereby to promote exposure of the liquid particles to the shockwaves.28. An apparatus for atomising liquid particles conveyed in a gas flow, the apparatus comprising a fluid flow passage defined between first and second boundary surfaces and a movable element for controlling the flow of liquid through the passage, at least one of the first or second boundary surfaces being configured to provide one or more directional changes to produce one or more shockwaves in the gas flow and within the fluid flow passage when the gas flow is moving at supersonic speed therethrough.29. Apparatus according to claim 28 wherein the shock waves comprise oblique shock waves, normal shock waves, or expansion shock waves, or any combination thereof.30. Apparatus according to claim 29 wherein the shock waves comprise oblique shock waves and expansion shock waves.31. Apparatus according to claim 28 wherein the shock waves interact to create a low pressure region along the fluid flow passage through which the liquid particles must traverse.32. Apparatus according to claim 28 wherein the first and second boundary surfaces are each configured to provide a series of directional changes to produce a pattern of oblique shock waves in conjunction with expansion waves.33. A fuel injection nozzle comprising a fluid flow passage terminating at a discharge orifice and incorporating a delivery port defined between a valve seat and a valve member movable with respect to the valve seat for opening and closing the delivery port, with fuel being delivered along the fluid flow passage into a combustion chamber through the discharge orifice upon opening of the delivery port, wherein the valve member defines an inner boundary surface of the flow passage and the valve seat defines at least part of an outer boundary surface of the flow passage, the inner and outer boundary surfaces being configured to generate one or more shock waves in an air-fuel mixture flowing at supersonic speed therebetween.34. A fuel injection nozzle according to claim 33 wherein the inner and outer boundary surfaces are each configured to provide a series of directional changes to produce a pattern of oblique shock waves in conjunction with expansion waves.35. A fuel injection nozzle according to claim 34 wherein the surfaces at the delivery port are configured such that the expansion shock waves occur internally to the delivery port.36. A fuel injection nozzle according to claim 33 wherein the valve member is provided with an extension portion extending beyond the discharge orifice of the fuel injection nozzle and presenting a flow directing surface to which the air-fuel mixture issuing through the orifice is exposed.37. A fuel injection nozzle according to claim 36 wherein the flow directing surface comprises a curved surface and is positioned so as to be in the flight path of any fuel droplets or liquid particles issuing through the discharge orifice.38. A fuel injection nozzle according to claim 37 wherein the curved surface is convex.39. A fuel injection nozzle according to claim 36 wherein the flow directing surface provides a solid boundary on the inner side of the air-fuel mixture issuing from the discharge orifice as a spray plume, and wherein the curved surface is adapted to influence the flow direction of the plume involving a change of direction to consequently generate expansion waves which propagate outwardly as a Prandtl Meyer expansion fan from the curved surface to traverse the flow path of the plume.40. A fuel injection nozzle according to claim 33 wherein the inner and outer boundary surfaces of the fuel injection nozzle, and/or the extension portion, are configured so as to reduce the formation of any carbon deposits at or adjacent the delivery port.41. A fuel injection nozzle according to claim 33 wherein the outermost extremities of the inner and outer boundary surfaces are configured to correspond at an exit point of the delivery port.42. A fuel injection nozzle according to claim 33 wherein no surfaces extend downstream of the discharge orifice.43. A fuel injection nozzle according to claim 33 further comprising a surface disposed outwardly of the discharge orifice in the direction of air-fuel flow, the surface being configured to generate expansion waves in the air-fuel charge issuing from the discharge orifice, the expansion waves propagating in a direction which traverses the air-fuel charge.44. A method of atomising liquid particles entrained in a gas flow comprising the steps of passing the gas flow at a supersonic flow rate along a flow passage defined between first and second boundary surfaces one of which is movable for controlling the flow of liquid through the flow passage, and causing the supersonic gas flow to change direction within the flow passage and generate one or more shockwaves in the gas as it passes along the flow passage.45. A method according to claim 44 wherein oblique shock waves are generated where the supersonic flow is caused to change direction by incorporating a directional change or obstruction in a boundary surface converging towards the flow.46. A method according to claim 44 wherein expansion shock waves are generated by causing a directional change in the supersonic flow involving a divergence from the flow.47. A method according to claim 44 wherein the shock waves generated comprise oblique shock waves and expansion shock waves providing a combination of interacting shock waves.48. A method of injecting fuel into an internal combustion engine having a combustion chamber, comprising the steps of delivering a flow comprising a metered quantity of fuel entrained in a gas to the combustion chamber through a selectively openable delivery port to provide a fuel spray issuing from the port when opened, and subjecting the flow to one or more directional changes in the delivery port to generate one or more shock waves in the gas flow when the gas flow is moving at a supersonic flow rate through the delivery port to assist atomisation of liquid fuel droplets in the flow.49. A method according to claim 48 wherein the liquid fuel droplets are subjected to the shock waves prior to, during and/or after passing through the delivery port.50. A method according to claim 48 wherein the delivery port when opened defines a flow passage configured to generate one or more shockwaves in the gas flow.51. A method according to claim 50 wherein the delivery port when opened defines a convergent-divergent nozzle.
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