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(11) | EP 0 370 659 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Fuel injection nozzle |
| (57) A fuel injection nozzle has a fuel pressure actuated valve member 13 shaped to co-operate
with a seating 12 to control fuel flow through an outlet orifice 14 extending from
a space 11 downstream of the seating 12. The orifice 14 at its inner end is radiused
the radius lying between 0.3 and 0.75 of the diameter of the orifice at the region
of greatest separation of the fuel as it flows into the orifice and between .05 and
0.2 of the diameter of the orifice in the region of least separation of the fuel.
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[0001] This invention relates to fuel injection nozzles for supplying fuel to compression ignition engines and comprising a valve member slidable within a bore formed in a nozzle body, a seating defined at one end of the bore, the valve member being shaped for cooperation with the seating to prevent fuel flow through an outlet orifice, the valve member when lifted from the seating allowing fuel flow through the outlet orifice from a fuel inlet.
[0002] Fuel injection nozzles of the aforesaid type are well known in the art and in most cases the outlet orifice extends from a small cavity known as the "sac" volume which is downstream of the seating. The "sac" volume is usually formed in an integral projection or tip of the body of the nozzle and the axis of the orifice is often inclined to the axis of the nozzle body. In other designs the orifice extends from the seating so that when the valve member is in the closed position the inner end of the orifice is covered by the valve member.
[0003] The nature of the fuel spray which develops as the fuel leaves the orifice has a bearing on the combustion of fuel in the engine combustion chamber and therefore the engine performance and the level of smoke in the engine exhaust. In some engines enhanced performance and smoke reduction may be obtained by having a more penetrating spray.
[0004] The object of the invention is to provide in a fuel injection nozzle of the kind specified, a convenient way of modifying the form of spray which issues from the orifice.
[0005] In the accompanying drawings:-
Figure 1 is a sectional side elevation of part of a known form of fuel injection nozzle,
Figure 2 is a view to an enlarged scale of part of the nozzle seen in Figure 1 and
Figure 3-5 show modifications to the shape of the outlet orifice and in some cases different types of nozzle.
[0006] With reference to Figures 1 and 2 of the drawings there is shown the tip 10 of a conventional inwardly opening fuel injection nozzle, the tip defining a "sac" volume 11 located downstream of a frusto conical seating 12 with which can cooperate the end of a valve member 13. The valve member is slidable in a bore 9 formed in a nozzle body 8 and it defines an annular area 7 against which fuel under pressure can act to lift the valve member away from the seating against the action of resilient means 6. When the valve member is lifted from the seating fuel under pressure can flow from a nozzle inlet 5 into the "sac" volume 11 and then through one or more orifices 14 extending through the wall of the tip 10. In the example the diameter of the orifice is constant throughout its length.
[0007] The fuel spray which issues from the orifice will tend to diverge but will have moderate penetration. The flow of fuel as it flows through the orifice tends to contract to a smaller diameter, the contraction being termed the "vena contracta" and this contraction is shown in Figure 2 at 15. The inevitable separation of the fuel from the wall of the orifice causes cavities to form in the fuel which assist the atomization of the fuel.
[0008] In order to increase the penetration of the fuel spray it is proposed to relax the "vena contracta" and this can be achieved by modifying the cross-section of the orifice at the entrance end thereof. As shown in Figure 3 the edge defined at the junction of the orifice and the surface of the wall which defines the "sac" volume is rounded off. The effect of this is to produce a less pronounced "vena contracta" and a more penetrative spray.
[0009] The entrance conditions for the fuel flowing into the orifice are not the same all the way around the orifice and the greatest separation will occur where there is a combination of high fuel velocity and the most acute angle between the surface of the orifice and the surface of the wall which defines the "sac" volume.
[0010] It is known from United States specification 4578164 to round off the edge or junction defined between the surface of the wall which defines the "sac" volume and the orifice and it is disclosed in the aforesaid specification that the rounding off influences the combustion of fuel in the engine and therefore the level of smoke in the engine exhaust. The aforesaid specification also discloses in one form of nozzle, the fact that different radii can be applied around the orifice to suit the entrance conditions. We have discovered that the actual radii applied around the entrance to the orifice are important so far as the formation of smoke is concerned and for an orifice which is inclined at 60° to the axis of the valve member as is shown in Figure 3, it is found that the radius RA in the region of greatest separation should lie between 0.15 and 0.75, preferably between 0.3 and 0.75 of the diameter of the orifice and ideally 0.5 of the diameter of the orifice. The radius RB in the region of least separation should be up to 0.75, preferably between 0.05 and 0.2 and ideally 0.1 of the diameter of the orifice.
[0011] As will be seen from Figure 3 the "vena contracta" 16 is less pronounced than in the case of the known injection nozzle seen in Figures 1 and 2. In the case of a nozzle having a single orifice 14 it is to be expected that as the axis of the orifice approaches the axis of the nozzle the difference in radii will become smaller. However since most injection nozzles will have a number of orifices the difference in the entrance conditions will tend to remain.
[0012] Figure 4 illustrates a nozzle in which the orifice 17 extends from the seating 18 below the seatline so that in the closed position of the valve member the entrance to the orifice is closed by the valve member. The same shaping of the entrance to the orifice is effected as is the case with the example shown in Figure 3. In the example of Figure 4 it will be observed that the axis of the axis is so arranged that it is at right angles to the seating then the entrance conditions will be substantially the same all the way around the seating. Again however the nozzle will tend to have a number of orifices so that whatever the angle of the orifice relative to the seating the differences in the entrance conditions will remain.
[0013] The nozzle shown in Figure 5 has a valve member 19 which includes an obturator 20 which is partly located within the "sac" volume. The obturator has a clearance with the surface of the wall defining the "sac" volume so as to provide an annular area through which fuel can flow, the area providing a restriction to the flow of fuel at least during the initial stage of lift of the valve member.
[0014] The invention is also applicable to fuel injection nozzles of the so called two stage lift type as seen in Figure 4 in which at the end of the first stage of lift the annular area 21 of the flow passage within the nozzle e.g. as formed between the valve member and the seating, is less than the flow area of the orifice or orifices.
1. A fuel injection nozzle for supplying fuel to a compression ignition engine comprising
a valve member (13) slidable in a bore (9) formed in a nozzle body (8), a seating
(12) defined at one end of the bore (9), the valve member (13) being shaped for co-operation
with the seating to prevent flow of fuel through an outlet orifice (14, 17), the valve
member (13) when lifted from the seating (12) allowing fuel flow through the outlet
orifice (14,17) from a fuel inlet (5), said outlet orifice (14,17) extending from
an enclosed space (11) defined downstream of the seating line between the seating
(12) and the valve member (13), the orifice (14, 17) extending at an angle from the
wall of the space (11) so that the fuel flow entrance conditions into the orifice
(14, 17) from the space (11) are not the same around the orifice, characterised in
that the radius (RA) in the region of the greatest separation of the fuel as it flows
into the orifice (14,17) should lie between 0.3 and 0.75 of the diameter of the orifice
and in the region of least separation of the fuel the radius (RB) should lie between
0.05 and 0.2 of the diameter of the orifice.
2. A nozzle according to Claim 1 characterised in that the radius (RA) is 0.5 and
the radius (RB) is 0.1 of the diameter of the orifice.