Patent Publication Number: US-2015083085-A1

Title: Fuel injection system for an internal combustion engine

Description:
The present invention relates to a fuel injection system for an internal combustion engine. The system is particularly suited for use with small capacity engines such as used in garden equipment, e.g. lawnmowers. 
     In GB 2421543 the applicant has described a “pulse count” injection system in which the quantity of fuel delivered to a combustion chamber in each engine cycle is controlled by controlling the number of operations of an injector which delivers in each operation a set quantity of fuel. Most commonly available systems operate with pulse width modulation (PWM) which controls the opening period of an injector to control the quantity of fuel delivered, with a need for a high pressure fuel supply to the injector and a pressure regulator to ensure that variations in pressure to the inlet manifold do not affect the quantity of fuel delivered. The apparatus of GB 2421543 avoided this by the injector itself operating as a pump and delivering a set quantity of fuel regardless of changes in pressure in the inlet manifold; then the total amount of fuel becomes a function of the number of times the injector is operated. 
     In UK application No. 0522068.6, a development of the system of GB 2421543 was described. In this a sonic nozzle was incorporated so that fuel delivered by the pulse count injector is entrained in air (or combusted gases) to be delivered to the inlet manifold via a sonic nozzle in which the gas flow reached or approached the speed of sound. This resulted in better atomisation of the delivered fuel. 
     The present invention in a first aspect provides an internal combustion engine as claimed in claim  1 . 
     The present invention in a second aspect provides an internal combustion engine as claimed in claim  3 . 
     The present invention provides an alternative method of atomisation of the fuel delivered by the fuel injector. The use of fuel and air mixing means has been found surprisingly to achieve better atomisation and fuel delivery than a sonic nozzle. Also, the new design allows the use of the arrangement to deliver fuel downwardly into an inlet manifold, rather than just upwardly. 
    
    
     
       Preferred embodiments of the present invention will now be described with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic illustration of an internal combustion engine having a first embodiment of fuel injection system according to the present invention; 
         FIG. 2  is an illustration of the throttle body of the fuel injection system of  FIG. 1 , showing in greater detail a mixing tube, pulse count injector and by-pass inlet passage; 
         FIG. 3  shows a variant of the  FIG. 2  embodiment, in which the by-pass inlet passage is connected to receive recirculated combusted gases rather than air; 
         FIGS. 4   a  to  4   d  show operation of the  FIG. 2  fuel injection system during a single engine cycle; 
         FIG. 5  is a view in greater detail of the mixing tube used in the fuel injection systems of  FIGS. 2 and 3 ; 
         FIG. 6  is a side elevation view of the mixing tube of  FIG. 5 ; 
         FIG. 7  is a cross-section through the mixing tube of  FIG. 6 ; 
         FIG. 8  is an isometric view of the mixing tube of  FIGS. 5 ,  6  and  7 ; 
         FIG. 9  is an end view of the mixing tube of  FIGS. 5 to 8 , 
         FIG. 10  shows a two-stroke internal combustion engine having a second embodiment of fuel injection system according to the present invention; 
         FIG. 11  is a schematic view of a second type of mixing tube suitable for use in fuel injection systems according to the present invention; 
         FIG. 12  is a cross-sectional view taken along a fuel delivery nozzle suitable for the fuel injector systems of  FIGS. 1 to 4   d;    
         FIG. 13  is a cross-sectional view across the  FIG. 14  fuel delivery nozzle; 
         FIG. 14  is an illustration of mixing apparatus comprising a perforated plate; 
         FIG. 15  is an illustration of mixing apparatus for a downwardly directing injector, comprising a plurality of perforated plates; 
         FIG. 16  shows a cross-section through a fuel injector suitable for use in the fuel injection system of  FIGS. 1 and 10 ; 
         FIG. 17  shows a cross-section through a fuel injector suitable for use with the mixing tube of  FIG. 12 ; 
         FIG. 18  is a perspective view of a mixing chamber formed from a first set of stacked discs; 
         FIGS. 19   a ,  19   b , and  19   c  show a disc of the type used for the top and bottom of the stack of  FIG. 18 ; 
         FIGS. 20   a ,  20   b  and  20   c  show a disc of the type used as an intermediate disc of the stack of  FIG. 18 ; 
         FIGS. 21   a ,  21   b  and  21   c  show a disc of the typed used as an intermediate disc of the stack of  FIG. 18 ; 
         FIG. 22  is a perspective view of a mixing chamber formed from a second set of stacked discs; 
         FIGS. 23   a ,  23   b  and  23   c  show a disc of the type used as an intermediate disc of the stack of  FIG. 22 ; and 
         FIGS. 24   a ,  24   b  and  24   c  show a disc of the type used for the top and bottom discs of the stack of  FIG. 22 . 
     
    
    
       FIG. 1  shows an internal combustion engine having a variable volume combustion chamber  10  defined by a piston  11  reciprocating in a cylinder  12 . 
     The piston  11  is connected by a connecting rod  13  to a crankshaft  14 . A poppet valve  15  is an exhaust valve controlling flow of combusted gases out of the combustion chamber  10  to an exhaust passage  16 . The valve  15  will be opened by a cam on a camshaft (not shown) which is connected to the crankshaft  14  to rotate with the crankshaft  14 . The valve  15  will be closed by a valve spring (not shown) which biases the valve into abutment with its valve seat. A poppet valve  17  is an inlet valve controlling flow of fuel/air charge into the combustion chamber  10  from an inlet passage  18 . The valve  17  will be opened by a cam on the aforementioned camshaft and closed by a valve spring (not shown). 
     The fuel injection system of the present invention comprises a fuel injector  20  of the type described in GB 2421543. The injector  20  is controlled by an engine control unit (ECU)  21  attached to a throttle body  22 . An inlet butterfly throttle  23  is pivotally mounted in the throttle body  22  to throttle flow of air through the inlet passage  18 . A sensor  24  will provide a signal indicative of throttle position to the ECU  21 , which will also receive other signals such as a crankshaft position signal and/or a signal from a pressure sensor measuring air pressure in the inlet passage  18 . The throttle body  22  incorporates a venturi  25 , a narrowing in cross-sectional area of the inlet passage, which will induce a localised increase in flow velocity of air flowing through the inlet passage  18  and a consequent localised reduction in pressure. The injector  20  delivers fuel to a mixing tube  26  from which fuel is delivered via a fuel delivery nozzle  27  into the venturi  25 , the fuel being entrained in air passing from a bypass passage  28  through the mixing tube  26  into the venturi  25 . This will be described in more detail below. 
       FIG. 2  shows that the fuel injector  20  delivers fuel to a mixing chamber and accumulation volume  30  of the mixing tube  26 . This is shown in greater detail in  FIG. 5 . The mixing tube  26  is located in a chamber  31  defined in the throttle body  22  and two rubber  0 -rings  32 , 33  are provided between the mixing tube  26  and the surrounding chamber  31  to provide a fluid seal, respectively preventing flow of fuel along the exterior of nozzle  27  to the venturi  25  and flow of fuel past the injector  20 . The inlet passage  28  opens on to the chamber  31  and delivers air to the chamber  31  from atmosphere, bypassing the throttle  23 . As an alternative and as illustrated in  FIG. 3 , the bypass passage  28  can be connected to an exhaust gas recirculation passage  40  so that combusted gases can be delivered to the chamber  41  via the bypass passage  28 . The hot combusted gases will aid fuel evaporation. A thermal barrier will be needed to prevent heat passing from the hot exhaust gases to the cool fuel supplied to the injector, but this can be achieved by careful positioning of passageways. 
     The mixing tube  26  is shown in detail in  FIGS. 5 ,  6 ,  7 ,  8  and  9 . The mixing tube  26  has four rows of four apertures; two rows  50 ,  51  are shown in  FIG. 8 . The apertures  60 ,  61 ,  62 ,  63  of row  40  are shown in  FIG. 6 . The apertures of the four rows allow flow of air from the chamber  31  into the mixing chamber  30 . The rows  60 ,  61 ,  62 ,  63  are disposed at  90 ° intervals around a lower cylindrical wall  55  of the mixing tube. Three spaced rows  50 ,  51 ,  52  are shown in the cross-sectional view of  FIG. 7  and all four rows  50 ,  51 ,  52 ,  53  in the cross-sectional view of  FIG. 9 . The fuel delivery nozzle  27  extends away from the lower part of the emulsion tube; the nozzle  27  is of a reduced diameter compared to wall  55  and an interior passage  59  in nozzle  27  is of a reduced diameter compared to chamber  30 . A delivery aperture in the form of slot  90  is provided at a distal end of the nozzle  27  (distanced from chamber  30 ) via which fuel and air is delivered to the venturi  25 . The slot  90  is elongate and aligned parallel with a central axis  91  of the nozzle  27 . 
     Two pairs of aligned apertures are provided in the wall  55 , spaced axially apart. One aperture  110  of a first pair and one aperture  111  of the second pair are shown in FIG.  7 . These allow two bars  120 ,  121  to be located extending across the chamber  30  as can be seen in  FIG. 9 ; the bars  120 , 121  extend at right angles to each other when viewed as seen in  FIG. 9 . The two bars  120 ,  121  are also seen in part in  FIG. 5 . When fuel is delivered by the injector  20  into the chamber  30  then the two bars  120 ,  121  prevent the fuel flowing immediately through the mixing chamber  30  and out of the nozzle  90  and instead ensure that the fuel accumulates in mixing chamber  30  for subsequent entrainment by air flowing through the bypass passage  28 . 
     Operation of the fuel injection system is shown in  FIGS. 4   a  to  4   d .  FIGS. 4   a  and  4   b  show operation at part throttle; the throttle  23  is rotated to partially close the inlet passage  18 .  FIG. 4   a  shows the condition when the inlet valve  17  is closed. While the valve is closed the injector  20  is used to deliver fuel into the mixing chamber  30 , which fills up as illustrated (if desired the injector  20  could continue to inject fuel when the inlet valve  17  is open). The apertures of the four rows  50 ,  51 ,  52 ,  53  are sized such that surface tension of the fuel will prevent fuel flowing out of the mixing chamber  30  via the apertures. In  FIG. 4   b  the intake valve  17  has been opened and air is drawn into the combustion chamber by downward motion of piston  11 . The air is drawn through inlet passage  18  past throttle  23 . A depression will be occasioned downstream of the throttle  23  by the air flow past the throttle  23 . This will cause air to be drawn from the bypass passage  28  through the chamber  31  and via the emulsion tube  22  and out of the nozzle  27 . The air drawn from the bypass passage  28  will entrain the fuel in the mixing chamber  30  as it flows through the emulsion tube  30 . This will give rise to a mixture of fuel and air which is then delivered into the charge air in venturi  25  and is atomised in the air and the fuel/air charge is then delivered into the combustion chamber  10  for combustion. 
       FIGS. 4   c  and  4 D show operation at full load: the throttle  23  is rotated to a wide open condition.  FIG. 4   c  shows the condition when the inlet valve  17  is closed. Whilst the valve  17  is closed, the injector  20  delivers fuel to the chamber  30  of the emulsion tube, which fills as illustrated (the injector could continue to deliver fuel when the inlet valve  17  is open). Then at  4 d the inlet valve  17  has opened and the piston  11  draws air into the combustion chamber  10  via the intake passage  17 . Since the throttle  23  is wide open it offers little resistance to air flow and so does not itself give rise to a depression in pressure downstream of the throttle  23 . Instead a fast flow of air through the intake passage  18  at high engine speeds/loads gives rise to a drop in pressure in the venturi  25 . This drop in pressure draws air from the bypass passage  28  into the intake passage  18  via the mixing tube  26  and delivery nozzle  27 . The air passing through the mixing tube  26  entrains the fuel in the mixing chamber  30  and delivers the fuel to the intake passage  18 . The air passing through mixing chamber  30  forms an emulsion and gives rise to good atomisation of the fuel delivered to the intake passage  18  and hence to the combustion chamber  16 . 
     The embodiment described, particularly with reference to  FIG. 1 , delivers gasoline fuel to a mixing chamber for mixing with air, e.g. in a four stroke engine. In a two-stroke engine it is necessary to mix both fuel and two-stroke lubricating oil with air, the mixture then typically being delivered to a crankcase and thereform via a transfer passage to a combustion chamber.  FIG. 10  shows an arrangement of two injectors  9000  and  9001  which both deliver liquid into a mixing tube  9002  of the type already described prior to delivery via a nozzle  9003  into an intake passage  9004  downstream of a throttle valve  9005 . A first injector  9000  delivers gasoline fuel to a mixing chamber  9005  in the mixing tube  9002 . A second injector  9001  delivers two-stroke lubricating oil into the mixing chamber  9005 . As can be seen in  FIG. 10 , the injector  9000  is immersed in gasoline  9006  provided in a gasoline reservoir  9007  which is connected via a pipe  9008  to a fuel supply line (not shown) connected to a fuel tank (again not shown)—fuel will flow from the fuel tank to the gasoline reservoir by gravity feed or pumped by a small fuel pump, e.g. a diaphragm pump driven by the vacuum cyclically induced downstream of the throttle  9005 . It will also be seen that the second injector  9001  is immersed in two-stroke lubricating oil  9008  in a lubricating oil reservoir  9009 , which is connected by a pipe  9010  to a lubricating oil supply line (not shown) connected to an oil tank (again not shown)—oil will flow from the fuel tank to the lubricating oil reservoir  9009  by gravity feed or pumped by a small oil pump, e.g. a diaphragm pump driven by the vacuum cyclically induced downstream of the throttle  9005 . 
     The lubricating oil and fuel delivered to the mixing chamber  9005  by injectors  9000  and  9001  is entrained by bypass air flowing through a bypass passage  9011 , in the manner described above. The mixture of fuel, oil and air delivered by the nozzle  9003  is mixed with the charge air flowing in intake passage  9004  and delivered to a crankcase  9012 , from where it is delivered to a combustion chamber  9013  via a transfer passage  9014  (reciprocation of piston  9015  cyclically draws a fresh charge of fuel, air and oil into the crankcase  9012  and then expels the mixture from the crankcase  9012 ). A valve  9016  prevents the mixture of fuel, air and oil in crankcase  9012  flowing back to the throttle  9005  rather than through the transfer passage  9014 . 
     The delivery of both oil and fuel into the mixing chamber gives a better efficiency of lubrication than existing systems which inject lubricating oil directly into an intake air passage to be picked up from the walls thereof by the fuel/air charge downstream of the carburettor. The atomisation and mixing of the oil ensures that it is more evenly dispersed in the charge air and better wets the parts requiring less lubricating oil, which results in cleaner emissions from the engine. The amount of oil dispensed can be carefully controlled by controlling the number of operations of the injector  9001  per engine cycle (or over a number of engine cycles) in response to engine demand. Thus the oil consumption and emissions of the engine are improved in comparison to a standard two-stroke engine which has oil injected directly into the intake passage downstream of the carburettor, to be picked up from the walls by the air intake. The present invention pre-mixes the oil with air prior to delivery into the charge air. 
     Whilst vaporisation of gasoline is a problem and the injector  9000  is ideally cooled or shielded from heat sources in the engine, vaporisation of two-stroke lubrication oil is not a problem and indeed some heating of the oil can be of benefit. No vapour control mechanism is needed to the two-stroke lubricating oil. 
     The embodiments described above have injectors  20 ,  9000  arranged to deliver gasoline fuel vertically upwardly into a venturi  25 . However, it may be desired to arrange a gasoline injector to deliver fuel vertically downwardly or laterally into the venturi  25 . The designs previously described must be modified to prevent fuel flowing under gravity out of the mixing chamber of the mixing tube. One possible modification is shown in  FIG. 11 , in which the injector  1020  is oriented to deliver fuel vertically downwardly into a chamber  1030  of a mixing tube  2026 ; the fuel is shown at  1031 . The mixing tube  1026  comprises an inner tube  1010  and an outer tube  1011 . The fuel  1031  fills an annular cavity defined between the tubes  1010  and  1011 . Rows of apertures are provided in both tubes  1010  and  1011 . The apertures are sized (as described above) such that surface tension of the fuel will prevent the fuel flowing through the apertures until entrained by air flowing through the bypass passage. The inner and outer tubes  1010 ,  1011  are co-axial. The inner tube  1010  extends vertically downwardly through an aperture in the outer tube  1011 . The inner tube  1010  provides a delivery nozzle  1027  which extends vertically downwardly into a venturi  25  and has an orifice  1090  via which fuel is dispensed when entrained in air. For a two-stroke engine an injector of two-stroke lubricating oil could also be provided to inject lubricating oil into the mixing chamber  1030 . 
     Recent work on fuel atomisation has indicated to the applicant that use of a mixing tube gives better results than sonic atomisation. Although the introduction of a mixing tube means that the air flow does not reach sonic velocities, the less restricted airflow has been found to better entrain the delivered fuel. 
     Instead of using two bars in a mixing tube as described above, a perforated plate or other baffle could be used. 
     The mixing tube could be made of brass or stainless steel both of which are corrosion resistant and are easy to machine. It is also possible that the mixing tube could be injection moulded in plastic, but the heat of EGR may cause problems for this. 
     When the engine is idling or on start-up the air flow is slow and the mixing tube can give very good atomisation in these circumstances, e.g. from when the engine is first cranked over. In most conventional engines, fuel is delivered onto the back of the intake valve(s) and then as the intake valve(s) open(s) the initially small annular clearance provides a restricted path for fuel/air flow which aids atomisation (the heat of the intake valve also aiding atomisation). However, in small engines (e.g. started by a hand pull mechanism) then there is not a high starting speed and there will be no heat on start up and so injecting fuel in such a conventional manner gives very poor mixing of fuel and air. The present invention permits use of a special regime on start up. In the start-up regime, all the airflow will be through the bypass passage  28  (the throttle valve  23  will be closed) and there will thus be maximum atomisation of the fuel and also the atomised fuel is delivered straight to the combustion chamber  10  without residence time in the cold intake passage. 
     In an alternative start-up strategy, a second start up valve is provided in the air intake passage in addition to the throttle. The start up valve will either completely close the air intake passage or will open the passage fully. On starting of the engine the start up valve will be closed so that all the intake air is drawn through the bypass passage. The start up valve will be opened once the engine has started. 
     The air intake passage need not be completely closed on start up; the passage could be mostly closed instead, by either or both of the throttle valve or the start up valve. The majority of the air supplied to the combustion chamber would still be supplied via the bypass passage, but a minority would flow past the throttle. This can be advantageous for larger capacity engines and also can be advantageous when the bypass passage is connected to the exhaust system to receive recycled combusted gases. 
     Above the fuel delivery nozzle  27  has been illustrated with a single delivery aperture  90 . However, the performance of the apparatus could be improved by configuring the nozzle with a plurality of apertures—this is shown in  FIGS. 12 and 13 .  FIG. 11  shows a row of vertically spaced apart apertures  6000 ,  6001 ,  6002 ,  6003  and  6004  provided on the downstream facing side of the fuel delivery nozzle  27 .  FIG. 13  shows that a plurality of such rows, numbered  6010 ,  6011 ,  6012  and  6013  are provided in the downstream side of the nozzle  27 . The arrows in the  FIGS. 11 and 12  indicate the direction of the airflow past the nozzle  27 . 
     Above the embodiments have used a mixing tube as emulsion apparatus, but the applicant envisages that alternative apparatus could be used and examples are given in  FIGS. 14 and 15 . 
     In  FIG. 14  a fuel injector  7000  of the type described previously delivers fuel upwardly into a mixing chamber  7001  defined between two plates  7002  and  7003  provided in a chamber  7004  defined in a throttle body  7005 . The plates each have a plurality of apertures which allow a flow of air from a bypass passage  7006  into the mixing chamber  7001  and then a flow of fuel and air mixture out of the mixing chamber  7001  via a delivery nozzle  7007  into a venturi  7008  in the air flow passage. The nozzle  7007  is an aperture in the throttle body wall rather than a tube extending into the venturi  7008 . The apertures in the plates  7002  and  7003  are sized such that liquid fuel delivered to and then resident in the mixing chamber  7001  will not flow out of the mixing chamber in the absence of a bypass air flow, due to surface tension. The plate  7003  does not have any apertures aligned with an outlet of injector  7000 , in order that fuel delivered to the chamber  7001  under pressure by the injector  7000  does not flow directly out of nozzle  7007 . Instead plate  7003  ensures that the injected fuel remains in the mixing chamber  7001  until entrained in a flow of bypass air. 
       FIG. 15  shows an arrangement similar to  FIG. 14 , except in the  FIG. 15  embodiment only one apertured plate  8000  is used, rather than two plates, and in  FIG. 15  fuel in injected downwardly into a mixing chamber  8001  by an injector  8002  and then delivered downwardly via nozzle  8003  into venturi  8004 . Gravity will hold liquid fuel on the upstream surface plate  8000  until there is a flow of bypass air through passage  8005 . Like in  FIG. 13 , the plate  8000  does not have apertures aligned with the outlet of injector  8002 . 
     The present invention could use any fuel and air mixing apparatus which comprises a mixing chamber into which fuel is delivered by a fuel injector for subsequent mixing with bypass gas flow to form a mixture of fuel and gas for subsequent delivery to a combustion chamber. 
     The good atomisation provided by use of mixing chambers also allows the use of alternative fuels such as kerosene and diesel and also blended fuels (e.g. with ethanol). Two different injectors could be used to inject two different fuels with a common mixing chamber, e.g. gasoline and ethanol, for pre mixing together and with air prior to delivery into charge air in an intake passage. 
     In the embodiments described the fuel injection system is conveniently provided in the form of a unit detachable from the engine, the unit comprising: the throttle body  22  having the throttle  23  mounted therein and the bypass passage  28  and bypass chamber  31  integrally formed therein; the mixing tube  26  located in the bypass chamber  31 ; and the fuel injector  20  and associated electronics  21  provided as a unit attached to the throttle body  22 . This eases repair/replacement and also facilitates incorporation of the fuel injection system in existing engine designs. 
       FIG. 16  shows a fuel injector  1600  suitable for use in the fuel injector system of  FIGS. 1 ,  2  to  5  and  10 , as any or all of the injectors  20 ,  9000  or  9001 . The injector  1600  comprises a fuel inlet  1601  with a one-way inlet valve  1602  controlling flow of fuel from the fuel inlet  1601  into a variable volume pumping chamber  1603 . The fuel injector also comprises a fuel outlet  1610  via which fuel is dispensed from the injector with a one-way outlet valve  1611  provided in the outlet. A piston  1604  is slidable in a housing  1605  to define with the housing  1605  the variable volume pumping chamber  1603 . A spring  1606  biases the piston  1604  to a position in which the chamber  1603  has its smallest volume. An electrical coil  1607  surrounds the piston  1604  and can generate a field acting to draw the piston downwardly, as shown in the Figure, to a position on which the chamber  1607  has its greatest volume. The piston  1604  is movable between two end stops  1608  and  1609  which define a fixed travel distance Xd for the piston and thus a fixed swept volume. In each and every operation of the injector  1600  the set distance Xd is transversed so that a set constant unvarying volume is dispensed from the chamber  1603 . The total volume of fuel delivered to an engine in each operating cycle is not altered by a changing the volume dispersed in each operation of the injector, but by solely controlling the number of operations of the injector per engine cycle. 
     In each operation of the injector the piston  1604  moves under action of the field generated by the coil  1601  to draw fuel (or lubricating oil) into the pumping chamber  1603  from the inlet  1601  via the one-way inlet valve  1602 . The piston  1604  eventually hits the end stop  1609  and the induction of fuel (or lubricant) is completed. Then the applied field is switched off and the piston  1608  under action of spring  1606  moves to expel fuel (or lubricant) from the pumping chamber  1603  out of the outlet  1610  via the one-way outlet valve  1611 . The one-way inlet valve  1602  prevents expulsion of fuel (or lubricant) from the pumping chamber  1603  to inlet  1601  and similarly the one-way outlet valve  1611  prevents fuel or lubricant being drawn into the chamber  1603  from the outlet  1610 . 
       FIG. 17  shows the injector of  FIG. 16  inverted for operation in the arrangement of  FIG. 12 . In  FIG. 17  there can be seen: a fuel inlet  1701 ; a one-way inlet valve  1702 ; a pumping chamber  1703 ; a fuel outlet  1704 ; a one-way outlet valve  1705 ; a piston  1706  reciprocating in a cylinder  1707 ; a biasing spring  1708 ; and an electrical coil  1709  with an associated back iron  1710 . The injector works in the same way as the  FIG. 16  injector, but delivers liquid downwardly rather than upwardly. 
     The pumping chambers  1607  and  1703  are both frusto-conical in shape to improve flow of fluid therefrom to the outlet  1610 ,  1704 . 
       FIGS. 18 to 21   c  show a further variant of mixing chamber  1800 , usable in place of the mixing tube  26  of any of  FIGS. 1 to 5 , formed from a plurality of stacked discs. An end view of a completed stack  1800  is shown in  FIG. 18 , formed from a plurality of stacked discs comprising two end plates  1801  and  1802  sandwiching a plurality of intermediate discs  1803 - 1807  of a first type and  1808 - 1811  of a second type. Each disc  1803 - 1806  is sandwiched between either two discs  1808 - 1811  of the second type or between one disc  1808 - 1811  of the second type and an end plate  1801 ,  1802 . 
       FIGS. 19   a ,  19   b  and  19   c  show one of the end plates  1801 ,  1802  (both are identical to each other). The plate  1802  shown is a circular disc having an aperture  1812  which functions either as a fuel inlet or fuel outlet and a pair of locating holes  1813 ,  1814  which allow the plate to be stacked on posts or secured by bolts. 
       FIGS. 20   a ,  20   b  and  20   c  show one of the intermediate plates of the plurality  1803 - 1807 . This has a first slot  1815  which connects a first circular aperture  1816  to the exterior of the disc and a second slot  1817  which connects the first aperture  1817  with a second larger circular aperture  1818 . The slot  1815  provides an air inlet for the stack, as can be seen in  FIG. 18 . It is sized so that surface tension of the fuel (or lubricant) prevents the fuel flowing out of the slot  1815 . The plate also has a pair of locating holes  1819 ,  1820  which allow the plate to be stacked on posts or secured by bolts. 
       FIGS. 21   a ,  21   b  and  21   c  show one of the intermediate plates of the plurality  1808 - 1811 . This has two circular apertures  1821 ,  1822  of equal size which in use will align with the apertures  1816  and  1818  of an abutting adjacent plate of the plurality  1803 - 1807 . Also two locating holes  1823  and  1824  are provided which allow the plate to be stacked on posts or secured by bolts. 
     When the plates are all assembled then two channels are formed. One is formed by aligned apertures  1816  of the plates  1803 - 1807  and the apertures  1821  of plates  1808 - 1811  aligned therewith; this is open at the bottom of the stack to receive fuel from an injector via an aperture  1812  in an end plate at the bottom of the stack. The other is formed by aligned apertures  1818  of the plates  1803 - 1807  and the apertures  1822  of plates  1808 - 1811  aligned therewith. This passage is open to the exterior of the stack via an aperture  1812  in an end plate at the top of the stack and a mixture of fuel and air can be delivered via this passage to the outside of the stack. 
     In use the stack will receive fuel in the passage formed in part by the apertures  1816 . This will initially be prevented from flowing through the slots  1815  and  1817  by surface tension. Then bypass air will flow through the slots  1815 , entrain fuel in the passage defined in part by apertures  1811  and the fuel/air mixture will be delivered via slots  1817  to the passage formed in part by apertures  1818 , from where it will be delivered e.g. through a nozzle into the charge air in the intake passage. 
     The choice of diameters for apertures  1821  and  1822  which differ from those of apertures  1816  and  1818  is deliberate to promote mixing of the fuel with the air by encouraging a turbulent flow. Also a greater surface area is presented to the flow of fuel and air which means that there is a greater heat transfer. The stack of plates is advantageously thermally coupled to the injector associated therewith so that the heat is transferred from the injector to flow of fuel and air, advantageously heating the fuel/air mixture to encourage vaporisation and advantageously cooling the injector to limit unwanted vaporisation of the fuel in the injector. In this regard the stack of plates will be mounted close to the injector to maximise heat transfer. 
       FIGS. 22 ,  23   a  to  23   c  and  24   a  to  24   c  show a variant on the idea of stacked plates. The stack  2200  of  FIG. 22  is formed with plates  2300  as shown in  FIGS. 23   a  to  23   c , sandwiched between two end plates  2400  as shown in  FIGS. 24   a  to  24   c . The plates  2300  are stacked one on top of the other without interposition of the plates  2400 , with the orientation of one plate  2300  reversed in relation to the plate  2300  below and/or above, so that an aperture  2309  of one plate is aligned with an aperture  2303  in a plate immediately above or below. Two passages for receiving fuel or lubricant are thus formed, both of which communicate with a central passage for delivering of a mixture of air with fuel and/or lubricant—for instance one passage could receive fuel and the other lubricant, or one passage receive gasoline and the other ethanol. Slits  2303  allow bypass air to flow from outside the stack to each passage and slits  2304  then allow fuel or lubricant mixed with air to flow onwards to the central passage defined by apertures  2302 . The slits  2303  and  2304  are sized to prevent flow of fuel or lubricant out of a passage in the absence of flow of air—the surface tension of the fuel or lubricant preventing this. 
     The discs  2300  are also provided with flow apertures  2305 - 2308  which align with flow apertures  2405 - 2408  in the discs  2400  and provide flow passages for fuel. Fuel can flow through these passages to the fuel injector and be cooled by heat transfer with the fuel and air mixture flowing from the stack—the fuel evaporating in the fuel/air mixture will have a cooling effect. The fuel supplied to the fuel injector is advantageously cooled in order to limit vaporisation.