EP3201462A1

EP3201462A1 - Fuel injector

Info

Publication number: EP3201462A1
Application number: EP15763851.1A
Authority: EP
Inventors: Frederic BICHON; Cyrille Lesieur
Original assignee: Delphi International Operations Luxembourg SARL
Current assignee: Delphi International Operations Luxembourg SARL
Priority date: 2014-10-01
Filing date: 2015-09-03
Publication date: 2017-08-09
Also published as: GB201417310D0; WO2016050444A1

Abstract

The present disclosure relates to a fuel injector (101, 201, 301, 401) comprising a fuel supply line, a fuel return line (111, 211, 311, 411), a control chamber (107, 207, 307, 407), a control valve (104, 204, 304, 404) for controlling fuel pressure in the control chamber (107, 207, 307, 407), the control valve (104, 204, 304, 404) comprising a valve member (105, 205, 305, 405) and a cooperating valve seat (106, 206, 306, 406),and a fuel flow restriction (149, 249, 349, 449) for maintaining a positive pressure in the fuel return line (111, 211, 311, 411). The fuel flow restriction (149, 249, 349, 449) comprises a first aperture having a restriction width (W _R ).A particle trap (152, 252, 352, 452) is disposed between the valve seat (106, 206, 306, 406) and the fuel flow restriction (149, 249, 349, 449). The particle trap (152, 252, 352, 452) comprises at least one second aperture having a clearance width (W _c ). The clearance width (W _c )is less than or equal to the restriction width (W _R ).

Description

FUEL INJECTOR

TECHNICAL FIELD

The present disclosure relates to a fuel injector for an internal combustion engine. BACKGROUND

One type of known fuel injection system for a compression-ignition internal combustion engine (e.g. a diesel engine) comprises a high pressure pump, a common rail accumulator volume and a plurality of fuel injectors, each of which is associated with a respective combustion chamber of the engine.

The high pressure pump is arranged to receive fuel at low pressure from a fuel supply, such as a vehicle fuel tank, and to pump fuel at high pressure, e.g. at least 1450 bar, into the common rail. The common rail feeds each of the plurality of fuel injectors with fuel at high pressure.

Each of the plurality of fuel injectors typically comprises a needle valve which is moveable relative to a valve seat to control the injection of fuel through one or more injection ports. The position of the needle valve is controlled in dependence on the fuel pressure in a control chamber. The control chamber has an inlet for receiving fuel at high pressure from the common rail, and an outlet via which fuel may flow out of the control chamber into a low pressure return path or fuel return line through a control valve. The fuel return line comprises a fuel return outlet which is typically connected to a fuel return conduit used as a connector for connecting the fuel injector to a fuel reservoir where fuel is directed for re-use in a subsequent injection cycle.

It is known from the Applicant's earlier patent application GB141 1 162.9, the content of which is incorporated herein in its entirety by reference, to provide a fuel flow restriction in the fuel return line to increase the upstream fuel pressure of fuel to help reduce or inhibit cavitation. In particular, the fuel pressure upstream of the fuel flow restriction is maintained above a return pressure of the fuel downstream of the fuel flow restriction. In other words, the fuel flow restriction creates a positive pressure in the return (back leak) circuit. The fuel flow restriction could be provided in the fuel return conduit, as illustrated in Figure 1 . In the example shown in Figure 1 , the fuel return conduit 1 comprises a fuel passage 3, a first connector 5 configured to be connected to the fuel return outlet, and a second connector 7 configured to be connected to a connection member for connecting the fuel injector to the reservoir. The second connector 7 is provided with a fuel flow restriction 9 formed by a portion of restricted diameter of the fuel passage 3. It has been recognised that a potential problem associated with this type of fuel injector is that particles present in the fuel could flow through the fuel return line and clog the fuel flow restriction.

At least in certain embodiments, the present invention sets out to overcome or ameliorate at least some of the problems associated with known fuel injectors. In particular, at least in certain embodiments, the present invention sets out to provide a fuel injector in which clogging of the fuel flow restriction is avoided.

SUMMARY OF THE INVENTION

Aspects of the present invention relate to a fuel injector and to a fuel return conduit for use with a fuel injector.

According to a further aspect of the present invention there is provided a fuel injector comprising:

a fuel supply line;

a fuel return line;

a control chamber;

a control valve for controlling fuel pressure in the control chamber, the control valve comprising a valve member and a cooperating valve seat; and

a fuel flow restriction for maintaining a positive pressure in the fuel return line, the fuel flow restriction comprising a first aperture having a restriction width;

wherein a particle trap is disposed between the valve seat and the fuel flow restriction, the particle trap comprising at least one second aperture having a clearance width, the clearance width being less than or equal to the restriction width. Any particles present in the fuel having a dimension which is greater than or equal to the clearance width can be trapped in the particle trap. Since the clearance width is less than or equal to the restriction width, the particle trap traps particles which might otherwise cause a blockage in the fuel flow restriction.

The first aperture can be a circular aperture, for example formed by a bore. The restriction width can be a diameter of said circular aperture. The restriction width is the same as or larger than the clearance width. The restriction width can, for example, be in the range of 0.3mm to 1.5mm (inclusive). More particularly, the restriction width can be in the range of 0.4mm to 0.6mm (inclusive). The restriction width can be approximately 0.5mm. The first aperture can have a length of between 0.3mm and 1.5mm (inclusive). The fuel injector can comprise an outlet port. The particle trap can be disposed between the outlet port and the fuel flow restriction.

The fuel injector can comprise a fuel injector body. The fuel return line can comprise a fuel return conduit (also known as a back leak pipe). The fuel return conduit can be at least partially received in the fuel injector body.

The at least one second aperture can be defined between the fuel injector body and the fuel return conduit. The outlet port can be formed in the fuel injector body. The fuel return conduit can comprise a cylindrical portion disposed in the outlet port, and the at least one second aperture can be an annular aperture defined between the fuel injector body and the cylindrical portion. The clearance width can be a radial width of the annular aperture (i.e. a difference between an outer radius and an inner radius of the annular aperture). Alternatively, the at least one second aperture can be formed in the fuel return conduit. The at least one second aperture can be formed in a sidewall of the fuel return conduit. For example, the at least one second aperture can extend transversely or radially through a sidewall of the fuel return conduit. The clearance width can be a width of the at least one second aperture. In arrangements in which the at least one second aperture extends radially, the clearance width can be measured in a tangential direction. Each said second aperture can comprise a transverse bore and the clearance width can be a diameter of the transverse bore. The fuel return conduit can comprise a cylindrical portion disposed in an outlet port formed in the fuel injector body, and the at least one second aperture can be formed in said cylindrical portion. The particle trap can comprise a plurality of said second apertures formed in said fuel return conduit. A plurality of said second apertures can be distributed about the circumference of the fuel return conduit.

The fuel return conduit can comprise a return passage having an insert disposed therein. The at least one second aperture can be a defined between a sidewall of the return passage and the insert. The clearance width can be a width of said clearance, for example measured in a radial direction from a longitudinal axis of the return passage. The clearance width can be a radial clearance between the sidewall of the return passage and the insert. The insert can be fixedly mounted in the return passage. The at least one second aperture can be in the shape of a segment. The particle trap can comprise two second apertures. The insert can be truncated by two parallel planes to form two of said second apertures. The two second apertures can be disposed on opposing sides of the insert. The insert can be configured to form more than two of said second apertures. For example, the particle trap can comprise three of said second apertures. The insert can be truncated by three planar surfaces. The three planes can be arranged so that the insert has a triangular cross-section, for example an equilateral triangular. More than one insert could be provided, for example to form a series of said second apertures having decreasing clearance widths.

The first aperture can be formed in the fuel return conduit. The first aperture can extend transversely through a sidewall of the fuel return conduit. The first aperture can extend radially or axially. The restriction width can be measured perpendicular to a central axis of the first aperture. The first aperture can comprise a restriction bore. The restriction width can correspond to a diameter of the restriction bore.

The first aperture can be in the form of a restrictor formed in the fuel return conduit. For example, a restriction bore can be formed in the fuel return conduit. Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the present invention will now be described, by way of example only, with reference to the accompanying Figures, in which:

Figure 1 shows a longitudinal cross-sectional view of a fuel return conduit incorporating a fuel flow restriction;

Figure 2 shows a perspective view of a fuel injector in accordance with a first embodiment of the present invention;

Figure 3 shows a sectional view of a detail of the fuel injector shown in Figure 2; Figure 4A shows a longitudinal cross-sectional view of a fuel return conduit for use with the fuel injector of Figure 2 according to a first embodiment of the present invention;

Figure 4B shows an end view of the fuel return conduit in an outlet port of the fuel injector shown in Figure 4A; Figure 5A shows a longitudinal cross-sectional view of a fuel return conduit according to a second embodiment of the present invention;

Figure 5B shows an end view of the fuel return conduit in an outlet port of the fuel injector shown in Figure 5A;

Figure 6A shows a longitudinal cross-sectional view of a fuel return conduit according to a third embodiment of the present invention;

Figure 6B shows an end view of the fuel return conduit in an outlet port of the fuel injector shown in Figure 6A;

Figure 7A shows a longitudinal cross-sectional view of a fuel return conduit according to a fourth embodiment of the present invention; and

Figure 7B shows a transverse cross-sectional view of the fuel return conduit along lines VIM-VIM in Figure 7A.

DETAILED DESCRIPTION

A fuel injector 101 in accordance with a first embodiment of the present invention will now be described with reference to Figures 2 to 4.

The fuel injector 101 is configured to deliver fuel into a combustion chamber (not shown) of an associated internal combustion engine. The fuel injector 101 has particular application in a compression-ignition engine (i.e. a diesel engine), but the present invention could be implemented in a fuel injector 101 for a spark-ignition engine (i.e. a gasoline engine). The terms "downstream" and "upstream" are herein used in relation to the normal direction of the flow of fuel in the fuel injector 101. As illustrated in Figures 2 and 3, the fuel injector 101 comprises a fuel injector body 103 in which a control valve 104 is provided. The control valve 104 comprises a valve member 105 which is movable relative to a cooperating valve seat 106 to control fuel pressure in a control chamber 107. A needle valve 108 is movably mounted in an injection nozzle 109 to control the injection of fuel into the combustion chamber of the internal combustion engine through one or more injection ports. The position of the needle valve 108 is controlled in dependence on the fuel pressure in the control chamber 107. The control chamber 107 is maintained in fluid communication with a high pressure fuel supply line (not shown). The operation of the control valve 104 selectively places the control chamber 107 in fluid communication with a low pressure fuel return line 1 1 1 in a return circuit (also known as a back leak circuit). The fuel supply line is configured to receive fuel at high pressure via a fuel supply inlet 1 12. The fuel return line 1 1 1 is configured to return fuel expelled from the control chamber 107 (and fuel coming from static leaks and leaks due to grinding surfaces of the fuel injector 101 ) to a fuel reservoir (not shown) for re-use in a subsequent injection cycle.

The fuel injector 101 comprises an outlet port 1 13 (also known as a spill orifice) and a fuel return conduit 1 15 (also known as a back leak pipe). As illustrated in Figure 4A, the outlet port 1 13 comprises an outlet bore 1 19 and a female flared section 121. The outlet bore 1 19 is cylindrical and has an outlet radius R₀. The female flared section 121 forms a tapered seat having a constant taper angle for receiving the fuel return conduit 1 15, as described herein. The fuel return conduit 1 15 has a longitudinal axis X and comprises a sidewall 125 defining a return passage 127; a first connector 129 having an outlet 131 ; and a second connector 133 having an inlet 135. The return passage 127 has an internal diameter of approximately 2mm. The first connector 129 is configured to be connected to a return conduit (not shown) to return fuel to the fuel reservoir. The second connector 133 is in the form of a nipple configured to locate within the outlet port 1 13 to connect the inlet 135 to the fuel return circuit. The longitudinal axis X of the fuel return conduit 1 15 is arranged coaxially with a central axis of the outlet bore 1 19 in the assembled fuel injector 101.

The second connector 133 comprises a first cylindrical portion 137; a second cylindrical portion 139 disposed at the distal end of the fuel return conduit 1 15; and an annular sealing flange 141 . The first cylindrical portion 137 has a first radius R_Ci which is substantially equal to the outlet radius R₀ of the outlet bore 1 19, so that the first cylindrical portion 137 is sealingly located in the outlet port 1 13. The second cylindrical portion 139 has a second radius R_C2 which is less than the outlet radius R₀ of the outlet bore 1 19. A tapered section is formed in the sidewall of the fuel return conduit 1 15 between the first cylindrical portion 137 and the second cylindrical portion 139. The male flared section 142 comprises first and second tapered sections 143, 144 which form a compound-angle annular seal for seating in the female flared section 121 to form a metal-on-metal seal. An end wall 145 is provided to close the end of the return passage 127.

The fuel return conduit 1 15 comprises a fuel flow restriction 149 for restricting the flow of fuel into the return passage 127. In the present embodiment, the fuel flow restriction 149 is in the form of a restrictor disposed in the second cylindrical portion 139. The fuel flow restriction 149 comprises a restriction bore 151 extending radially through the sidewall 125. The diameter of the restriction bore 151 (approximately 0.5mm in the present embodiment) is referred to herein as a restriction width W_R. In use, the fuel flow restriction 149 maintains a positive pressure in the fuel return line 1 1 1 . In other words, the fuel in the region between the valve seat and the fuel flow restriction 149 is maintained above a return pressure of the fuel in the fuel return line 1 1 1 downstream of the fuel flow restriction 149.

The fuel injector 101 comprises a particle trap 152 between the valve seat 106 and the fuel flow restriction 149 to prevent particles in the fuel clogging the fuel flow restriction 149. In the present embodiment the particle trap 152 is in the form of an annular aperture 153 formed between the second cylindrical portion 139 of the fuel return conduit 1 15 and the outlet bore 1 19 of the outlet port 1 13, as illustrated in Figure 4B. As outlined above, the second radius Rc2 of the second cylindrical portion 139 is less than the outlet radius R₀ of the outlet bore 1 19, thereby forming the annular aperture 153. The annular aperture 153 has a radial clearance between the second cylindrical portion 139 and the outlet bore 1 19 (i.e. the difference between the outlet radius R₀ and the second radius R_C2)- The radial clearance of the annular aperture 153 is referred to herein as a clearance width W_c. The clearance width W_c is less than the restriction width W_R. In the present embodiment, the clearance width W_c is within the range 0.3mm to 0.4mm (inclusive) and is smaller than the restriction width W_R defined by the restriction bore 151 .

The operation of the fuel injector 101 according to the first embodiment will now be described. When the valve member 105 lifts from the valve seat 106, fuel flows from the control chamber 107 through the fuel return line 1 1 1 to the fuel reservoir. Fuel flows through the particle trap 152 and then through the fuel flow restriction 149. Any particles suspended in the fuel having a dimension which is greater than or equal to the clearance width W_c can be trapped in the annular aperture 153. As the clearance width W_c is less than the restriction width WR, particles which may otherwise clog the fuel flow restriction 149 are trapped by the particle trap 152. The fuel flow restriction 149 restricts the flow of fuel through the fuel return line 1 1 1 , thereby increasing the fuel pressure upstream of the fuel flow restriction 149. The fuel flows through the fuel flow restriction 149 and through the outlet 131 to the fuel reservoir. It will be appreciated that the cross sectional area of the annular aperture 153 of the particle trap 152 is larger than the cross sectional area of the restriction bore 151 of the fuel flow restriction 149. This configuration can help to prevent the particle trap 152 becoming clogged or blocked. Also, in use, the particle trap 152 does not restrict fuel flow through the fuel return line 1 1 1 , or is less effective in restricting fuel flow than the fuel flow restriction 149.

A fuel injector 201 comprising a fuel return conduit 215 according to a second embodiment of the present invention is represented in Figures 5A and 5B. The second embodiment corresponds closely to the first embodiment and like reference numerals have been used for like components, albeit incremented by 100 for clarity. The fuel return conduit 215 comprises a fuel flow restriction 249 and a particle trap 252. Only the differences in relation to the fuel return conduit 1 15 according to the first embodiment are described below.

The fuel flow restriction 249 is in the form of a restrictor disposed in the first connector 229 of the fuel return conduit 215. The fuel flow restriction 249 comprises a restriction bore 251 extending axially along the longitudinal axis X of the fuel return conduit 215. The diameter of the restriction bore 251 (approximately 0.5mm in the present embodiment) is referred to herein as a restriction width WR.

The particle trap 252 comprises an annular aperture 253 defined between the second cylindrical portion 239 and the outlet bore 219. As illustrated in Figure 5B, the annular aperture 253 has a radial clearance between the second cylindrical portion 239 and the outlet bore 219 (i.e. the difference between the outlet radius R₀ and the second radius R_C2)- The radial clearance of the annular aperture 253 is referred to herein as a clearance width W_c. The clearance width W_c is less than the restriction width W_R. A central recess 255 is formed in the second connector 231 to receive a spherical ball 257 to close the end of the return passage 227. The inlet 235 comprises first and second transverse openings 259 formed by a radial bore through the sidewall 225. The dimensions of the first and second transverse openings 259 are chosen so as not significantly to restrict the flow of fuel into the return passage 227.

The operation of the fuel injector 201 according to the second embodiment will now be described. When the valve member lifts from the valve seat, fuel flows from the outlet port 213 through the particle trap 252 and then through the fuel flow restriction 249. In particular, the fuel flows through the annular aperture 253 and any particles suspended therein having a dimension greater than the clearance width W_c can be trapped therein. The fuel flows through the two transverse openings 259 into the return passage 227 and then through the fuel flow restriction 249. As outlined above, the clearance width W_c is less than the restriction width WR, such that any particles present in the fuel having a dimension which is greater than or equal to the restriction width W_R can be trapped by the particle trap 252. Therefore, any such particles in the fuel can be prevented from reaching the fuel flow restriction 249. A fuel injector 301 comprising a fuel return conduit 315 according to a third embodiment of the present invention is partially represented in Figures 6A and 6B. The third embodiment corresponds closely to the first embodiment and like reference numerals have been used for like components, albeit incremented by 200 for clarity. The fuel return conduit 315 comprises a fuel flow restriction 349 and a particle trap 352. Only the differences in relation to the fuel return conduit 1 15 according to the first embodiment are described below. The fuel flow restriction 349 is in the form of a restrictor disposed in the first connector 329 of the fuel return conduit 315. The fuel flow restriction 349 comprises a restriction bore 351 extending axially along the longitudinal axis X of the fuel return conduit 315. The diameter of the restriction bore 351 (approximately 0.5mm in the present embodiment) is referred to herein as a restriction width W_R.

A central recess 355 is formed in the second connector 331 to receive a spherical ball 357 to close the return passage 327. As illustrated in Figure 6B, the particle trap 352 is formed by first, second, third and fourth slots 359 formed in the second connector 331 of the fuel return conduit 315. The slots 359 extend radially outwardly from the longitudinal axis X and are angularly offset from each other by 90°. Each slot 359 has a width measured in a tangential direction and this width is referred to herein as a clearance width W_c. The clearance width W_c is less that the restriction width W_R. The second cylindrical portion 339 has a second radius R_C2 which is less than the outlet radius R₀ of the outlet bore 319 to facilitate manufacturing of the fuel injector 301 .

The operation of the fuel injector 301 according to the third embodiment will now be described. When the valve member lifts from the valve seat, fuel flows from the outlet port 313 through the particle trap 352 and then through the fuel flow restriction 349. In particular, the fuel flows through the slots 359 and any particles suspended therein having a dimension greater than the clearance width W_c can be trapped therein. The fuel flows through the return passage 327 and then through the fuel flow restriction 349. As outlined above, the clearance width W_c is less than the restriction width W_R, such that any particles present in the fuel having a dimension which is greater than or equal to the restriction width W_R can be trapped by the particle trap 352. Therefore, any such particles in the fuel can be prevented from reaching the fuel flow restriction 349.

A fuel injector 401 comprising a fuel return conduit 415 according to a fourth embodiment of the present invention is partially illustrated in Figures 7A and 7B. The fourth embodiment corresponds closely to the first embodiment and like reference numerals have been used for like components, albeit incremented by 300 for clarity. The fuel injector 401 comprises a fuel flow restriction 449 and a particle trap 452. Only the differences in relation to the fuel return conduit 1 15 according to the first embodiment are described below. The fuel flow restriction 449 is in the form of a restrictor located in the first connector 429 of the fuel return conduit 415. The fuel flow restriction 449 comprises a restriction bore 451 extending axially along the longitudinal axis X of the fuel return conduit 415. The diameter of the restriction bore 451 (approximately 0.5mm in the present embodiment) is referred to herein as a restriction width W_R.

An enlarged bore 461 is formed in the second connector 431 of the fuel return conduit 415. An insert 463 is fixedly mounted within the enlarged bore 461 , as shown in Figure 7A. The insert 463 is a cylinder having a longitudinal axis arranged coincident with the longitudinal axis X of the fuel return conduit 415. The cylinder is truncated by two planes extending parallel to and symmetrical about a diametral plane of the cylinder. Thus, as shown in Figure 7B, the insert 463 comprises first and second curved sealing surfaces 465 for sealingly engaging a sidewall 467 of the enlarged bore 461 ; and first and second planar surfaces 469, each defined by one of the parallel planes. The particle trap 452 comprises first and second segment-shaped apertures 459 formed between the respective first and second planar surfaces 469 and the sidewall 467 of the enlarged bore 461 . Each segment-shaped aperture 459 has a radial clearance which is referred to herein as a clearance width W_c. The clearance width W_c is the difference between the diameter of the enlarged bore 461 and the radial position of the first and second planar surfaces 469. The clearance width W_c is less than the restriction width W_R.

The operation of the fuel injector 401 according to the fourth embodiment will now be described. When the valve member lifts from the valve seat, fuel flows from the outlet port 413 through the particle trap 452 and then through the fuel flow restriction 449. In particular, the fuel flows through the first and second segment-shaped apertures 459 and any particles suspended therein having a dimension greater than the clearance width W_c can be trapped therein. The fuel flows through the first and second segment-shaped apertures 459 into the return passage 427 and then through the fuel flow restriction 449. As outlined above, the clearance width W_c is less than the restriction width W_R, such that any particles present in the fuel having a dimension which is greater than or equal to the restriction width W_R can be trapped by the particle trap 452. Therefore, any such particles can be prevented from reaching and clogging the fuel flow restriction 449. It will be appreciated that the particle trap 452 could be modified to define more than two apertures 459. For example, the insert 463 could comprise three or more planar surfaces 469 arranged to define a polygonal cross-section. The insert 463 could have a triangular cross-section (for example in the form of an equilateral triangle); or a rectangular cross- section (for example in the form of a square).

It will be appreciated that various changes and modifications can be made to the fuel injectors 101 ; 201 ; 301 ; 401 described herein without departing from the scope of the present invention. The particle trap 152; 252; 352; 452 can comprise one or more clearance apertures each having a clearance width W_c which is less than or equal to a restriction width WR of the fuel flow restriction 449. It will be appreciated that the clearance apertures can extend axially or transversely and can have different profiles. For example, the clearance apertures can be circular, annular, elliptical, oval, polygonal, elongated etc.

Claims

CLAIMS:

1 . A fuel injector (101 , 201 , 301 , 401 ) comprising:

a fuel supply line;

a fuel return line (1 1 1 , 21 1 , 31 1 , 41 1 );

a control chamber (107, 207, 307, 407);

a control valve (104, 204, 304, 404) for controlling fuel pressure in the control chamber (107, 207, 307, 407), the control valve (104, 204, 304, 404) comprising a valve member (105, 205, 305, 405) and a cooperating valve seat (106, 206, 306, 406); and

a fuel flow restriction (149, 249, 349, 449) for maintaining a positive pressure in the fuel return line (1 1 1 , 21 1 , 31 1 , 41 1 ), the fuel flow restriction (149, 249, 349, 449) comprising a first aperture (151 , 251 , 351 , 451 ) having a restriction width (W_R);

wherein a particle trap (152, 252, 352, 452) is disposed between the valve seat (106, 206, 306, 406) and the fuel flow restriction (149, 249, 349, 449), the particle trap (152, 252, 352, 452) comprising at least one second aperture having a clearance width (W_c), the clearance width (W_c) being less than or equal to the restriction width (W_R).

2. A fuel injector (101 , 201 , 301 , 401 ) as claimed in claim 1 comprising an outlet port (1 13, 213, 313, 413), wherein the particle trap (152, 252, 352, 452) is disposed between the outlet port (1 13, 213, 313, 413) and the fuel flow restriction (149, 249, 349, 449).

3. A fuel injector (101 , 201 ) as claimed in claim 1 or claim 2 comprising a fuel injector body (103, 203) and a fuel return conduit (1 15, 215) at least partially received in the fuel injector body (103, 203), wherein the at least one second aperture is defined between the fuel injector body (103, 203) and the fuel return conduit (1 15, 215).

4. A fuel injector (101 , 201 ) as claimed in claim 2 and claim 3, the outlet port (1 13, 213) being formed in the fuel injector body (103, 203), the fuel return conduit (1 15, 215) comprising a cylindrical portion (139, 239) disposed in the outlet port (1 13, 213), wherein the at least one second aperture is an annular aperture (153, 253) defined between the fuel injector body (103, 203) and the cylindrical portion (139, 239), the clearance width (W_c) being a radial width of the annular aperture (153, 253).

5. A fuel injector (301 , 401 ) as claimed in claim 1 comprising a fuel return conduit (315, 415), the at least one second aperture being formed in the fuel return conduit (315,

415).

6. A fuel injector (301 ) as claimed in claim 5, wherein the at least one second aperture extends transversely through a sidewall of the fuel return conduit (315).

7. A fuel injector (301 ) as claimed in claim 5 or claim 6, wherein the clearance width (W_c) is a width of the at least one second aperture.

8. A fuel injector (401 ) as claimed in claim 1 comprising a fuel return conduit (415) having a return passage (427) and an insert (463) disposed therein, wherein the at least one second aperture is defined between a sidewall (467) of the return passage (427) and the insert (463).

9. A fuel injector (401 ) as claimed in claim 8, wherein the clearance width (W_c) is a radial clearance between the sidewall (467) of the return passage (427) and the insert (463).

10. A fuel injector (401 ) as claimed in claim 8 or claim 9, wherein the at least one second aperture is in the shape of a segment.

1 1 . A fuel injector (101 , 201 , 301 , 401 ) as claimed in any one of claims 3 to 10, wherein the first aperture (151 , 251 , 351 , 451 ) is formed in the fuel return conduit (1 15, 215, 315, 415), the first aperture (151 , 251 , 351 , 451 ) extending radially or axially.