Fuel injector

Abstract: A fuel injector for supplying liquid fuel to an air inlet manifold of a spark ignition engine has an outlet (15) defined in a tubular component (31) The fuel enters the outlet through an orifice (30) formed in a valve seat member (27). The tubular component is mounted in a tubular part (32) of the injector body and the tubular component is spaced from the valve seat member. An air circulation duct (34) is defined between the component and part and the spray of fuel flowing through the outlet draws air through the duct to minimise dribble of fuel from the injector.

Description: This invention relates to a fuel injector for supplying liquid fuel spray to an air inlet duct of a spark ignition engine, the injector comprising a valve seat member defining an annular seating for engagement by a solenoid actuated valve member, an orifice through which liquid fuel alone and under pressure can flow when the valve member is lifted from the seating, the fuel due to the pressure at which it is supplied, forming a spray which passes along a tubular outlet extending from adjacent the orifice to the end of the injector which in use is disposed in the air inlet duct and an air circulation duct which opens at one end into the tubular outlet at a position adjacent the valve seat member. An example of such an injector is seen in GB-A-2147949. The fuel flowing through the orifice or orifices forms a fuel spray which exits from the outlet to mix with the air flowing in the air inlet duct. In the case where the seat member has more than one orifice the jets of fuel leaving the orifices may impinge on each other to provide a special spray pattern. Care is taken to ensure that the fuel spray leaving the orifice or orifices does not impinge on the side wall of the outlet unless a special spray pattern is required. However, since a precise spray pattern is not produced some droplets of fuel do impinge on the wall of the outlet and the tendency is for the droplets of fuel to coalesce to form a larger drop which eventually falls into the air inlet duct. The tendency for this to happen increases as the inclination of the longitudinal axis of the nozzle from the vertical increases. The large drops of fuel do not mix properly with the air flowing to the engine cylinders and simply wet the surface of the air inlet duct thereby causing combustion problems. Moreover, in injectors in which the diameter of the outlet is small, fuel can accumulate within the outlet thereby impairing and in some cases inhibiting the formation of a fuel spray. GB-A-2058914 discloses an injector for a spark ignition engine in which atomisation of the liquid fuel is achieved using air or exhaust gas which is admitted into the body of the injector. The atomised fuel along with the air or exhaust gas flows into the air inlet manifold of the engine through a mixture guide duct formed in a mixture guide pipe which is a part of the injector. In each of the examples illustrated preliminary preparation of the fuel to be injected takes place in a tubular nozzle body which is positioned within the injector at a position to direct the air fuel mixture into the mixture guide duct. FR-A-563174 also discloses an injector in this case for delivering fuel directly into a combustion chamber of an engine. The injector utilises compressed air to assist the delivery of fuel into the combustion chamber. The injector incorporates a heated block in which is formed a convergent/divergent nozzle the purpose of the heated block being to cause ignition of the air/fuel mixture. A further example of an injector is seen in GB-A-2155693 in which the fuel spray leaving the spray orifice is directed into the adjacent end of a tubular outlet or mixing tube. An air duct is defined about the mixing tube and in use is connected to a source of hot atomisation air. The air which flows through the air duct enters the mixing tube through an annular opening which is adjacent the point of entry of the fuel spray into the mixing tube. The atomisation air is derived from a source external of the injector. The object of the present invention is to provide an injector of the kind specified in a simple and convenient form. According to the invention in an injector of the kind specified the other end of the air circulation duct opens into the air inlet duct at a position adjacent the end of the tubular outlet at said end of the injector, the fuel spray flowing along the tubular outlet inducing a flow of air along the air circulation duct from said one end of the injector. An example of a fuel injector in accordance with the invention will now be described with reference to the accompanying drawings in which:- Figure 1 is a sectional side elevation of a known form of injector, Figure 2 is a view to an enlarges scale of part of the injector shown in Figure 1 and modified in accordance with the invention, and Figure 3 is an inverted plan view of the portion of the injector seen in Figure 2. Referring to Figure 1 of the drawings the injector comprises a hollow generally cylindrical outer body 11 formed from magnetic material and within the body there extends a magnetic hollow flanged core 13. Extending within the core is a passage 14 which connects an inlet 12 with an outlet 15 of the body. Surrounding the core 13 is a former 16 which is formed from synthetic resin material and upon which is wound a solenoid winding 17. The outlet which in the example of Figure 1, is in the form of a sleeve retained within the body 11, projects in use into the air inlet duct of a spark ignition engine. Adjacent the outlet 15 the body 11 defines an integral radially inwardly extending annular shoulder 18 against which a non-magnetic annulus 19 is trapped by a non-magnetic valve seat member 21. The seat member is in the form of a disc the diameter of which is equal to the internal diameter of the body 11 and the disc has a central outlet orifice 22 formed therein. The orifice extends from the surface of the valve seat member remote from the outlet and it is surrounded by a pair of annular spaced seat elements which project above the general level of the aforesaid surface. Located within the non-magnetic annulus 19 is a valve member 24 which is formed from magnetic material. The valve member is in the form of a disc slidably received within the annulus 19. Formed in the valve member is a plurality of circumferentially spaced apertures 25 which are disposed outside the inner seat element. The valve member is biased into contact with the seat elements by means of a coiled compression spring 26 which is housed within the passage 14. The shoulder 18 and the end face of the core 13 form the pole pieces of a solenoid which includes the winding 17 and when the winding is energised the pole pieces assume opposite magnetic polarity. The internal diameter of the shoulder 18 is less than the diameter of the annulus 19 and the shoulder therefore overlies the outer peripheral portion of the valve member. Upon energising the winding the valve member is attracted towards the shoulder and the end of the core to allow fuel flow through the orifice 22. When the solenoid winding is de-energised the spring 26 returns the valve member into contact with the seating elements to interrupt the flow of fuel through the orifice 22. Referring now to Figure 2 the seat member 27 is formed with a central cylindrical recess 28 in its face remote from the valve member and opening into the recess from within the inner seat element 29, are six orifices 30 which are angularly spaced, as shown in Figure 3, about the axis of the nozzle. Moreover, as will be seen from Figure 2, the axes of the orifices are inclined. In addition, the outlet 15 is defined by a tubular component or member 31 which is secured within a tubular part 32 of the body. The tubular component is spaced from the seat member 27 and furthermore, as shown in Figure 3, is provided with four equiangularly spaced flats 33 which define air circulation ducts 34 extending between the ends of the tubular component. The bore at the inner end of the tubular component is provided with a flared entrance portion 35 and at the outer end of the component the material forming the outer surface of the component is machined away to form an annular sharp edge 37. Moreover, the angle of the orifices 30 and the length of the component 31 are so chosen that the spray pattern produced by the jets of fuel flowing through the orifices in the main just clears the outer end of the tubular component. As previously explained the spray produced by the orifices does not have a precise pattern and droplets of the spray will impinge upon the inner surface of the component and will coalesce to produce larger drops of fuel. However, the spray which is formed in the bore in the tubular component will entrain air and will therefore cause an air flow through the ducts 34 in the direction opposite to the flow of fuel. Any drops of fuel which do tend to form at or near the sharp edge will be entrained in the air flowing towards the ducts and will therefore tend to be drawn upwardly through the ducts and returned to the inner end of the bore within the tubular component. As a result there will be a reduced tendency for large drops of fuel to fall into the air inlet duct of the engine. Moreover, since air can flow along the ducts the risk of excess liquid fuel collecting within the bore in the tubular component and thereby impairing or inhibiting the formation of a fuel spray, is minimised. As a result of the air flow through the bore in the tubular component, it is anticipated that the atomisation of the fuel will be improved. Moreover, tests have shown that a satisfactory spray pattern can be obtained even when the longitudinal axis of the nozzle is substantially horizontal. Although in the example the ducts are defined by flats formed on the tubular member, they can be defined between ribs angularly spaced about the tubular member, and which support the tubular member within the part 32. The ribs may be defined on the tubular member within the bore in the part. Moreover, the bore in the tubular member particularly when a single orifice is formed in the orifice plate may taper inwardly almost to the outer end of the tubular member.

Claims: A fuel injector for supplying a liquid fuel spray to an air inlet duct of a spark ignition engine comprising a valve seat member (27) defining an annular seating (29) for engagement by a solenoid actuated valve member (24), an orifice (30) through which liquid fuel alone and under pressure can flow when the valve member (24) is lifted from the seating, the fuel due to the pressure at which it is supplied, forming a spray which passes along a tubular outlet (15) extending from adjacent the orifice to the end of the injector which in use is disposed in the air inlet duct, and an air circulation duct (34) which opens at one end into the tubular outlet (15) at a position adjacent the valve seat member (27), characterised in that the other end of the air circulation duct opens into the air inlet duct at a position adjacent the end of the tubular outlet (15) at said end of the injector, the fuel spray flowing along the tubular outlet (15) inducing a flow of air along the air circulation duct from the air inlet duct at said one end of the injector whereby droplets of fuel which collect at said one end of the injector will be entrained in the air flowing along the air circulation duct from the air inlet duct. A fuel injector according to Claim 1 characterised in that the outlet (15) is defined by a tubular component (31) located in a tubular part (32) of the housing of the injector, the end of said tubular component (31) being spaced from said valve seat member (27), said air circulation duct (34) being defined between said tubular component (31) and the tubular part (32). A fuel injector according to Claim 2 characterised in that the outer surface of the end of said tubular component (31) remote from the valve seat member (27) is machined to define a sharp edge (37). A fuel injector according to Claim 3 characterised in that said air circulation duct (34) is defined by a flat (33) formed on the exterior surface of said tubular component (31). A fuel injector according to Claim 4 characterised in that the injector is provided with a plurality of air circulation ducts (34). A fuel injector according to Claim 2 characterised in that the outlet (15) has a flared entrance (35) at its end adjacent the valve seat member (27). A fuel injector according to Claim 6 characterised in that the face of the valve seat member (27) presented to the outlet is formed with a recess (28), the injector having a plurality of orifices (30) formed in the base wall of the recess, said orifices being positioned so that a generally conical fuel spray issues from the outlet (15).

Inventors: BAXTER RANDY C, KIRACOFE JOHN W, BAXTER, RANDY C., KIRACOFE, JOHN W.
Applicants: LUCAS IND PLC, LUCAS INDUSTRIES PUBLIC LIMITED COMPANY
Application year: 1988
Main classification: F02M51
IPC codes: F02M51, F02M61, F02M69