[0001] This invention relates to apparatus for delivering charges of fuel to wording chambers
ot internal combustion engines.
[0002] More specifically, the invention is concerned with apparatus for delivering successive
charges of fuel to a working chamber of an internal combustion engine from a liquid
fuel supply line the flow rate to which is controlled in accordance with operating
conditions of the engine, comprising a nozzle mounted in tne side wall of an inlet
duct leading to the working chamber, the nozzle comprising a small bore fuel delivery
tube connected to the supply line and mounted in an air passage connected to receive
air from a supply by passing the engine throttle, the air passage being convergent
to an outlet for delivering fuel and air into the inlet duct.
[0003] Such apparatus is described in GB 1,286,851 and GB 1,330,181 in which the flow rate
from the supply line is controlled by the length of pulses fed to solenoid-operated
valves which periodically and simultaneously open and close the inlets to the fuel
delivery tubes, which in turn discharge fuel into the inlet manifold.
[0004] Apparatus according to the invention is characterised in that the delivery tube is
continuously connected to the supply line and in that the pressure maintained in the
supply line in relation to the dimensions of the delivery tube is insufficient to
discharge a charge of fuel from the delivery tube in the absence of air movement in
the air passage so that a charge of fuel is delivered by the delivery tube only during
induction of a charge of air into the combustion chamber.
[0005] Thus, preferably, for liquid fuel, the nozzle has a capillary fuel delivery tube
within an air passage connected to receive unthrottled air, the air passage being
convergent around the outlet end of the fuel delivery tube and leading to an outlet
in a wall of the inlet passage to the working chamber in a position where each successive
charge of air drawn into the combustion chamber will reduce the static pressure and
thus draw in air from the nozzle air passage. This in turn reduces the static pressure
at the fuel delivery tube outlet and draws off and atomises fuel from the tube. At
other stages in the engine cycle, the surface tension of the fuel prevents any substantial
flow of fuel Where the fuel is supplied under pressure, this should be insufficient
to overcome the surface tension , when air is not being drawn past the nozzle.
[0006] Preferably, the passage around the tube is gradually convergent over a sufficient
length to ensure that the velocity of the air drawn past the end of the tube is effectively
supersonic under all running conditions, thereby avoiding sudden charges and instabilities
in the operation of the nozzle.
[0007] Advantageously, the air inlet duct leading from the throttle towards the combustion
chamber is formed with a constriction to reduce the static pressure adjacent the nozzle.
This constriction should however not be so narrow as to cause sonic flow conditions
under maximum power or engine speed conditions. Accordingly, the constriction design
should ensure that the mean flow velocity during intake of a charge of air should
not appreciably exceed 125 metres/sec.
[0008] When the engine has a plurality of working chambers, the fuel delivery apparatus
will have a separate nozzle for each air inlet duct (which may serve one or more working
chambers), the remainder of the fuel delivery apparatus being common to all nozzles
which are effectively connected in parallel. With the usual phase differences between
the various working chambers, each nozzle in turn will be caused to deliver fuel as
a charge of air is drawn through its associated air inlet passage during the induction
phase, thereby helping to ensure that fuel cannot escape from the other nozzles.
[0009] Embodiments of the invention will now be described by way of example with reference
to the accompanying drawings, in which :-
Figure 1 shows diagrammatically the air and fuel delivery systems of a four stroke
spark-ignition internal combustion engine;
Figure 2 shows a fuel delivery nozzle of Figure 1 on an enlarged scale; and
Figures 3 and 4 are views corresponding to Figures 1 and 2 of a modified system.
[0010] Figure 1 shows a portion of the cylinder head 1 of an internal combustion engine.
During an induction stroke, air is drawn in from the atmosphere through a conventional
air filter assembly 2 into an induction pipe 3 past a butterfly throttle 4 and into
an inlet manifold 5. The air is drawn through the appropriate branch of the manifold
5 into an intake passage 6 in the cylinder head 1 and thence through a valve seat
7 (controlled by a poppet valve, not shown) into the combustion chamber 8. During
all other stages of the operating cycle, the valve seat 7 is closed by the poppet
valve and no air flow will occur in the passage 6.
[0011] Liquid fuel for the engine is stored in a tank 11. Fuel is drawn from the tank 11
by an electrically driven pump 12 and is delivered to a line 13 the pressure in which
is maintained at about eighteen pounds per square inch by a relief valve 14 which
spills excess fuel back into the tank 11 through a spill line 15.
[0012] The line 13 leads to a solenoid operated valve 15 and a variable-orifice valve 16
which are connected in series in either order by a line 17. An electronic control
unit 18 receives signals from an engine driven tachometer 19 and delivers to the solenoid
20 of the valve 15 pulses of normally constant length, at a frequency proportional
to the engine speed registered by the tachometer 19. Typically, each pulse has a duration
in the range 3-10 milliseconds and the valve 15 is effectively fully opened during
this period.
[0013] The metering valve 16 defines a variable area constriction 22 which is defined conveniently
by the registering areas of a slot 23 and a triangular opening 24 in two adjacent
relatively movable members. In this embodiment, the member 25 formed with the triangular
slot 24 is interconnected through a linkage 26 with the throttle 4 in such a manner
that opening movement of the throttle 4 (hereby an accelerator Pedal 27 and linkage
28) causes the member 25 to move downwards relative to the slot 23 so that the width,
and thus flow area, of the orifice 22 is increased.
[0014] By suitable choice of the characteristics of the linkage 26 (which may for example
include a non-linear cam) and by appropriate shaping of the opening 24, the required
characteristics can be obtained. In general, the resistance to flow of the opening
22 should be similar to that of the appropriate jet or jets of a conventional carburettor
which would be used with the engine.
[0015] Fuel which has passed through the valves 15 and 16 is delivered through a line 29
to an accumulator and distributor valve assembly 30. The fuel from the line 29 is
supplied to the interior of a tubular valve seat 31 against which bears the underside
of a diaphragm 32 under the pressure of a compression spring 33, the tension of which
can be adjusted by means of a screw 34 with lock nut 35.
[0016] .The tension in the spring 33 is adjusted'so as to arrange that the pressure in an
annular outlet chamber 36 and in the line 29 is normally about eight pounds per square
inch.
[0017] The outlet chamber 36 is permanently connected by outlet ports 37 to lines 38 leading
to fuel delivery nozzles 39, there being one such nozzle 39 for each inlet passage
6.
[0018] As shown in Figure 2, each nozzle 39 has a hollow body 41 mounted in a bore 42 in
the inlet manifold 5by means of screw threads 43. At its discharge end, an O-ring
44 is located in a groove 45 to form a seal against the wall of the bore 42.
[0019] A ferrule 46 is engaged in the hollow body 41 and connected to the line 38. A long
capillary tube 47 is engaged in the ferrule 46 and has its outlet end 48 adjacent
an outlet orifice 50 in an orifice member 49 which is pressed into the interior of
the body 41 and has a frusto-conical surface 51 converging towards the orifice 50.
[0020] An annular air space 52 surrounds a reduced portion of the body 41 and communicates
with the interior of the body 41 through holes 53 and with an air supply duct 54 by
way of a short passage 55. The duct 54 is connected to receive air from the outlet
of the air filter 2 upstream of the throttle 4.
[0021] Adjacent the nozzle 39, the inlet manifold 5 is formed with a venturi-like constriction
56 the effect of which is to reduce the static component of pressure adjacent the
nozzle outlet orifice 50 when a charge of air is being drawn into the combustion chamber
8. This pressure reduction, coupled with the pressure reduction created by the throttle
4 and inlet manifold 5 draws air from the duct 54 into the interior of the nozzle
body 41 and through the space between the capillary tube tip 48 and the conical surface
51. As a result of the air flow in this region, the static pressure component is reduced
and the fuel pressure in the line 38 is able to overcome the surface tension at the
tube tip 48 with the result that fuel is drawn from the capillary tube 47 and atomized.
The resulting mixture of air and fuel travels adjacent the axis of the inlet passage
6 into the combustion chamber 8 with little risk of wetting the walls of the passage
8.
[0022] Towards the end of the induction stroke in the chamber 8, another chamber will be
undergoing its induction stroke under higher speed flow conditions than the first
combustion chambers. Accordingly, the nozzle associated with this second combustion
chamber will take over and will atomize all the fuel flow available from the accumulator
and distributor valve 30. As a result, the last part of the charge entering the first
combustion chamber may consist essentially of air alone with the result that a stratified
charge may be possible within the combustion chamber.
[0023] In order to supply enriched fuel for acceleration, a device 61 sensitive to rapid
movement of the throttle linkage 28 in the opening direction may feed a signal to
the electronic control unit 18 to cause the latter to operate the solenoid-operated
valve 20 continuously for a short time so as to greatly increase, temporarily, the
fuel supplied to the nozzle 39.
[0024] In the system shown in Figures 3 and 4, elements corresponding to the system shown
in Figures 1 and 2 are indicated by the same reference numerials increased by 100.
In this system, the variable constriction 116 is upstream, in the direction of fuel
flow, of pulser valve 115. Fuel filters F are advantageously included in the fuel
supply lines.
[0025] The nozzle construction shown in Figure 4 may also be used in the system of Figures
1 and 2. In the arrangements shown in.Figure 4, the nozzle 139 is retained in position
by a clamping plate 161 secured by a screw 162. An additional sealing O-ring 163 is
located in a groove 164 in the non-screw threaded shank 165 of the nozzle.
[0026] The orifice member 149 has its frusto-conical surface 151 extending for substantially
the whole length of the orifice member at a semi-vertical angle of
15°. If A is the diameter of the outlet orifice, B is the internal diameter of the portion
of the orifice member .surrounding the end of the capillary tube 147 and C is the
spacing between the end of the capillary tube 147 and the end of the cylindrical portion
of diameter B, the following tests results were obtained using a capillary tube of
internal diameter
0.6 mm and external diameter 0.89 mm, the flow rates corresponding to continuous operation
of the nozzle;
1. Aφ = 0.381 mm φ and Bφ = 1.2 mm C = 0.381 mm.
[0027] Very good atomisation at low flows, (30-80cc/ min) but at flows over 80cc/min start
to form a jet and at 100cc/min it becomes a pure jet.
2. Aφ = 0.381 mm φ and Bφ = 1.1 mm C = 0.381 mm.
[0028] Just as good atomisation as above but can flow up to 100cc/min before we can see
the jet start, it becomes a pure jet at around 120/130cc/min.
3. Aφ = 0.381 mm Bφ = 1.2 and C = 2.54 mm.
[0029] A very narrow cone with good atomisation and shut-off point but starts to form a
jet at around lOOcc/min and forms a pure jet at 150 cc/min.
[0030] A
φ = 0.381 mm B
φ = 1.2 and C = 1.524 mm.
[0031] Not such a narrow cone as above and around the same shut-off-point as well as flows
with producs a jet.
4. Aφ = 0.381 mm Bφ = 1.3 and C. = 0.381 mm.
[0032] Good atomisation to around 200 cc/min then starts to become a jet. Shut-off-point
is around (70/80 cc/min).
[0033] Further details of the fuel delivery system and its electronic control unit are disclosed
in our parent application no. 82901977.7 - 0083348.
1. Apparatus for delivering successive charges ot fuel to a worKing chamber of an internal combustion engine from a liquid fuel supply line (38,138)
the flow rate to which is controlled in accordance with operating conditions of the
engine, comprising a nozzle (39, 139) mounted in the side wall of an inlet duct (5,
105) leading to the worKing chamber (8), tne nozzle comprising a small bore fuel delivery
tube (47,147) connected to the supply line and mounted in an air passage (52,152)
connected to received air from a supply (54,154) by passing the engine throttle, the
air passage being convergent to an outlet (50, 150) for delivering fuel and air into
the inlet duct (5, 105), characterised in that tne delivery tube (47,147) is continuously
connected to the supply line (38, 138) and in that tne pressure maintained in the
supply line (38, 138) in relation to the dimensions of the delivery tube is insufficient
to discharge a charge of fuel from the delivery tube in the absence of air movement
in the air passage so that a charge of fuel is delivered by the delivery tube only
during induction of a charge of air into the combustion chamber.
2. Apparatus according to claim 1, characterised in that the air passage (52,152)
is convergent around the end of the delivery tube (48, 148).
3. Apparatus according to claim 1 or 2, characterised in that the inlet end of the
small bore delivery tube (47) is oblique.
4. Apparatus according to claim 1 or 2, characterised in that the convergent portion
(151) of the air passage is sufficiently gradually convergent over a sufficient length
to ensure acceleration of the airflow therethrough during an induction stroke to a
supersonic velocity.
5. Apparatus according to any of the preceding claims, characterised in that the air
inlet duct (5) is formed with a venturi-like constriction (56, 156) adjacent the nozzle.
6. Apparatus according to claim 5, characterised in that the constriction (56, 156)
is insufficient to cause supersonic air velocities therein.
7. Apparatus according to any of the preceding claims for a multicylinder engine naving
an iniet manilold defining a plurality of inlet ducts and a said nozzle (39, 139)
in each said duct characterised in that the supply lines (38,138) for all the nozzles
are continously connected to the same said source (30,130) of fuel.