Internal combustion engine and ignition system with a pre-chamber

Abstract

An ignition system for a vehicle internal combustion engine (12) has a capsule defining a pre-chamber (136), an ignition fuel supply system (500) configured to inject an ignition fuel to the pre-chamber to create an ignition fuel-air mix in the pre-chamber, an ignition surface (137) within the pre-chamber, the ignition surface being defined by an interior surface of the capsule and configured to be contacted by the ignition fuel in the pre-chamber to thereby ignite the ignition fuel by hot surface ignition, and at least one jet nozzle (152). The ignition fuel is characterised by having a carbon content by mass less than 65%, a hot surface ignition temperature less than 500 deg C., and a volumetric energy density (LHV) greater than 18 MJ/L. The at least one jet nozzle is configured such that ignition of the ignition fuel by contact with the ignition surface causes at least one of hot gases, partially combusted fuel and flames to leave the pre-chamber through the at least one jet nozzle.

Claims

1. A vehicle internal combustion engine comprising: at least one cylinder defining a combustion chamber; a piston disposed for movement within at least one cylinder to define a swept volume of at least one cylinder being less than or equal to 3.0 litres; a primary fuel supply system configured to supply a primary fuel to the combustion chamber to create a primary fuel-air mix in the combustion chamber; and an ignition system comprising: a capsule defining a pre-chamber having a volume less than the swept volume of the at least one cylinder and less than 5% of a compressed volume of the at least one cylinder; an ignition fuel supply system comprising an ignition fuel tank which is separate to the primary fuel tank and contains an ignition fuel which differs from the primary fuel, the ignition fuel supply system being configured to inject the ignition fuel the pre-chamber to create an ignition fuel-air mix in the pre-chamber; an ignition surface within the pre-chamber, the ignition surface being defined by an interior surface of the capsule and configured to be contacted by the ignition fuel in the pre-chamber to thereby ignite the ignition fuel by hot surface ignition such that ignition timing is determined by ignition fuel injection alone; and at least one jet nozzle in fluid communication with the combustion chamber of the cylinder; wherein the ignition fuel is characterised by all of the following characteristics: a liquid at ambient temperature and pressure; a carbon content by mass less than 65%; a hot surface ignition temperature less than 500 deg C; and, a volumetric energy density (LHV) greater than 18 MJ/L, wherein the ignition fuel supply system is configured to inject the ignition fuel into the pre-chamber in a quantity of less than 5% equivalent energy content of the primary fuel introduced into the combustion chamber; wherein the at least one jet nozzle is configured such that ignition of the ignition fuel by contact with the ignition surface causes at least one of hot gases, partially combusted fuel and flames to leave the pre-chamber and enter the combustion chamber through the at least one jet nozzle to thereby ignite the primary fuel.

2. The vehicle internal combustion engine according to claim 1, wherein the ignition fuel is an ether.

3. The vehicle internal combustion engine according to claim 2, wherein the ignition fuel is diethyl ether.

4. The vehicle internal combustion engine according to claim 1, wherein the ignition fuel supply system is configured to inject the ignition fuel into the pre-chamber at a pressure less than 200 bar.

5. The vehicle internal combustion engine according to claim 1, wherein the capsule is at least partially constructed from a material having one or more of the following characteristics: (a) a heat conductivity of below 10 W/mK; (b) a maximum service temperature of at least 750 degrees Celsius; and (c) a flexural strength of at least 500 MPa.

6. The vehicle internal combustion engine according to claim 1, wherein the capsule is at least partially constructed from a ceramic material.

7. The vehicle internal combustion engine according to claim 6, wherein the ceramic material defines the ignition surface.

8. The vehicle internal combustion engine according to claim 1, wherein the capsule is a ceramic capsule.

9. The vehicle internal combustion engine according to claim 1, wherein the capsule is a superalloy capsule.

10. The vehicle internal combustion engine according to claim 1, wherein the ignition system comprises a heater configured to heat the ignition surface upon cold start or cold operation.

11. The vehicle internal combustion engine according to claim 1, wherein the at least one cylinder defines a primary axis and the pre-chamber is intersected by the primary axis.

12. The vehicle internal combustion engine according to claim 1, wherein the pre-chamber is positioned proximate the perimeter of the at least one cylinder.

13. A vehicle internal combustion engine according to claim 12, wherein the at least one jet nozzle is directed towards the primary axis.

14. A vehicle having a vehicle internal combustion engine comprising: at least one cylinder defining a combustion chamber; a piston disposed for movement within at least one cylinder to define a swept volume of at least one cylinder being less than or equal to 3.0 litres; a primary fuel supply system comprising a primary fuel tank configured to supply a primary fuel from the primary fuel tank to the combustion chamber to create a primary fuel-air mix in the combustion chamber; and an ignition system comprising: a capsule defining a pre-chamber having a volume less than the swept volume of the at least one cylinder and less than 5% of a compressed volume of the at least one cylinder; an ignition fuel supply system comprising an ignition fuel tank which is separate to the primary fuel tank and contains an ignition fuel which differs from the primary fuel, the ignition fuel supply system being configured to inject the ignition fuel to the pre-chamber to create an ignition fuel-air mix in the pre-chamber; an ignition surface within the pre-chamber, the ignition surface being defined by an interior surface of the capsule and configured to be contacted by the ignition fuel in the pre-chamber to thereby ignite the ignition fuel by hot surface ignition such that ignition timing is determined by ignition fuel injection alone; and at least one jet nozzle in fluid communication with the combustion chamber of the cylinder; wherein the ignition fuel is characterised by all of the following characteristics: a liquid at ambient temperature and pressure; a carbon content by mass less than 65%; a hot surface ignition temperature less than 500 deg C; and a volumetric energy density (LHV) greater than 18 MJ/L; wherein the ignition fuel supply system is configured to inject the ignition fuel into the pre-chamber in a quantity of less than 5% equivalent energy content of the primary fuel introduced into the combustion chamber, wherein the at least one jet nozzle is configured such that ignition of the ignition fuel by contact with the ignition surface causes at least one of hot gases, partially combusted fuel and flames to leave the pre-chamber and enter the combustion chamber through the at least one jet nozzle to thereby ignite the primary fuel.

15. The vehicle according to claim 14, wherein the ignition fuel tank is of variable volume and is configured to prevent contact between the ignition fuel in the ignition fuel tank and air.

16. The vehicle according to claim 15, wherein the ignition fuel tank comprises a tank shell and an airtight flexible bladder within the tank shell which is configured to be filled with the ignition fuel.

17. The vehicle according to claim 15, wherein the ignition fuel tank comprises a tank pressure control system configured to maintain the ignition fuel at a predetermined ignition fuel storage pressure which is greater than 1 bar by controlling an air pressure within the tank shell.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) An example IC engine according to the invention is described with reference to the accompanying Figures, in which:

(2) FIG. 1 is a schematic of an IC engine according to the present invention in a vehicle drivetrain;

(3) FIG. 2 is a section view of part of a first embodiment of a vehicle engine according to the present invention;

(4) FIG. 2a is a detail view of region A of FIG. 2;

(5) FIG. 3 is a section view of part of a second embodiment of a vehicle engine according to the present invention;

(6) FIG. 4 is a section view of part of a third embodiment of a vehicle engine according to the present invention;

(7) FIG. 5 is a schematic side section view through part of the engine of the third embodiment showing a jet spray pattern;

(8) FIG. 6 is a schematic plan section view through part of the engine of the third embodiment showing a jet spray pattern; and,

(9) FIG. 7 is a schematic drawing of a fuel system for an engine according to the present invention.

DETAILED DESCRIPTION

(10) Referring to FIG. 1, a vehicle 10, in this case and automobile comprises an internal combustion engine 12 having an output drivetrain 14 configured to drive wheels 16. The drivetrain 14 is shown schematically, but typically comprises a gearbox, differential etc. as known in the art. The engine 12 is also labelled as 12 and 12 to represent the second and third embodiments respectively.

(11) The engine 12 is an internal combustion engine comprising a plurality of cylinders. The general configuration of such reciprocating internal combustion engines are known in the art, and will not be described in detail here.

First Embodiment

(12) Referring to FIG. 2, a first embodiment of the present invention is shown. FIG. 2 shows a section through a part of the engine 12 according to the first embodiment. The engine 12 comprises an engine block 100, a piston 140, a cylinder head 106, a port primary fuel injector 130, a direct primary fuel injector 131 and an igniter 132.

(13) The engine block 100 defines an engine block cylinder cavity 102 extending from an abutment surface 104 thereof. The cylinder cavity has a main cylinder axis X. The engine block 100 is constructed from a unitary (e.g. cast) metal material.

(14) The cylinder head 106 is constructed from a unitary (e.g. cast) metal material and has an abutment surface 108 with a head cylinder cavity 110 extending therefrom. The head cylinder cavity 110 terminates at an end surface 112. The head cylinder cavity is centred on the main cylinder axis X. The cylinder head defines an intake port 114, an ignition system cavity 116 and an exhaust port 118 each of which is in communication with the head cylinder cavity via the end surface 112.

(15) The intake port 114 is defined as a conduit in the cylinder head 106 extending from a first end 120 to a second end 122. The first end 120 is in fluid communication with an intake manifold (as known in the art) and the second end is in fluid communication with the head cylinder cavity 110 via the end surface 112. Between the first and second ends 120, 122 there is provided a fuel injector cavity 124. The second end 112 of the intake port 114 joins the end surface 112 at a position offset from the axis X, and has an intake port axis I at a non-zero angle to, and directed towards, the axis X.

(16) The ignition system cavity 116 is in communication with the head cylinder cavity 110 and is intersected by the axis X.

(17) The exhaust port 118 is defined as a conduit in the cylinder head 106 extending from a first end 126 to a second end 128. The first end 126 is in fluid communication with the head cylinder cavity 110 via the end surface 112 and the second end is in fluid communication with an exhaust manifold (as known in the art). The first end 126 of the exhaust port 118 joins the end surface 112 at a position offset from the axis X, and has an exhaust port axis E at a non-zero angle to, and directed away from, the axis X.

(18) The engine block 100 and cylinder head 106 are assembled such that the engine block cylinder cavity 102 and the head cylinder cavity 110 align, thus cooperating to define a cylinder 142.

(19) The piston 140 is disposed within the cylinder 142 for sliding movement along the cylinder axis X. The piston 140 is attached via a con rod (not shown) to a crankshaft (not shown) that provides the mechanical power output from the engine, as known in the art. The piston 140 comprises a plurality of sealing ring grooves that receive sealing rings to seal the piston 140 against the engine block cylinder cavity 102. Movement of the piston creates a variable working volume 144 within the cylinder 142.

(20) The port primary fuel injector 130 is generally known in the art, and is positioned in the fuel injector cavity 124 of the intake port 114. Therefore it is an indirect injection (IDI) injector. The port primary fuel injector is connected to a primary fuel supply system and is configured to create a primary fuel-air mix in the intake port 114 upstream of the head cylinder cavity 110. In this embodiment the primary fuel is a fuel which lends itself to atomisation in the inlet port at low injection pressure, for example gasoline, although other fuels could be used in both liquid or gaseous form.

(21) The direct primary fuel injector 131 is generally known in the art, and is positioned downstream of the intake port 114. It is a direct injection (DI) injector. The direct primary fuel injector is connected to a primary fuel supply system (supplied with the same primary fuel as the port injector) and is configured to create a primary fuel-air mix in the head cylinder cavity 110i.e. in the working volume 144 of the cylinder 142. As such this embodiment has combined IDI and DI fuel injection, although it will be understood the present invention works with IDI and/or DI.

(22) The igniter 132 is part of an ignition system (to be described below). The igniter is shown in more detail in FIG. 2a. The igniter 132 comprises an ignition fuel injector 134, an ignition capsule 136 and a glow plug 138.

(23) The ignition fuel injector 134 is configured to inject an ignition fuel, different to the primary fuel, in this embodiment diethyl ether, into the ignition capsule 136. The ignition fuel injector comprises a nozzle 146 configured to meter, atomise and disperse the ignition fuel into the pre-chamber. The exact geometry of the injector spray plume will be optimized for the pre-chamber geometry used. As such it will ensure that the correct fuel and air mixture (as a function of the injection process) reaches the hot surfaces to initiate ignition.

(24) The ignition capsule 136 is constructed from a ceramic material, in this embodiment Yttria partially stabilized Zirconia Oxide (YTZP) The capsule has an inlet port 148 for receiving the fuel injector 134. The capsule 136 defines a pre-chamber 150 with the inlet port 148 defined at a first end 154, and a plurality of exhaust nozzles 152 defined at a second end 156. The nozzles 152 are directed into the cylinder 142 and also radially outwardly from the axis X. The pre-chamber is tapered from the first end 154 to the second end 156. Although not shown in the drawing the ignition capsule will typically be held in place by some form of clamping device which places the ceramic capsule in compression. Appropriate sealing will be incorporated to withstand maximum firing cylinder pressures. The detailed design of the capsule will be optimized for thermal loading during operation. It will be noted that the capsule 136 defines an entirely ceramic interior surface 137 in direct contact with the chamber 150.

(25) In this embodiment the pre-chamber volume is approximately 3% of the volume of the cylinder at piston top dead centre (i.e. the fully compressed working volume 144).

(26) The glow plug 138 is a conventional high speed metal diesel glow plug. It is capable of reaching temperatures of around 1000 degrees C., and as such capable of heating the interior walls of the capsule in which it is embedded, to above the temperature required. Such devices are compact, with the end penetrating the capsule being in the order of 4 mm in diameter tapering to 3.3 mm. The threaded section is only an M8 thread. The glow plug 138 is positioned such that it lies in the path of the fuel spray plume from the injector 134.

(27) Referring to FIG. 7, an ignition fuel system 500 according to the invention is shown. The system 500 comprises an ignition fuel tank 502, a tank pressure control system 504, and an ignition fuel delivery system 506. In general, fluid lines are shown in solid line, and data/power is shown in dashed (hidden) line.

(28) The ignition fuel tank 502 comprises a stiff tank shell 508 which is airtight (except for the inlet and outlet mentioned below). Within the shell 508 there is provided a non-permeable, flexible airtight bladder 510. The tank has a fuel filling conduit 512 that passes through the shell to be in fluid communication with the bladder 510. The fuel filling conduit 512 is connected to a fuel filling point 514 at a first end, to enable the bladder 510 to be filled with ignition fuel.

(29) The tank pressure control system 504 comprises an air compressor 516 having an inlet 518 and an outlet 520, the outlet being in fluid communication with the shell 508. The tank pressure control system also comprises an air pressure sensor 522 configured to determine the pressure within the shell 508, a vent valve 524 in communication with the shell 508 and a tank pressure controller 526. The tank pressure controller 526 is electronic and configured to control the air compressor 516, to receive data signals from the sensor 522 indicative of the pressure within the shell 508 and to control the tank vent valve 524. The controller 526 is therefore able to control the pressure within the shell 508 (and therefore the pressure of the ignition fuel within the bladder 510) by using the sensor to determine whether the pressure is under or over a predetermined ignition fuel tank pressure and adjusting using the compressor 516 to increase the pressure or the valve 524 to decrease pressure.

(30) The ignition fuel delivery system 506 comprises a tank outlet conduit 528 in communication with the bladder 510 at a first end, and with an electric fuel pump 530 at a second end. The system 506 further comprises a fuel accumulator 532, fuel pressure sensor 534 and the fuel injector 134. An engine controller 536 is also shown. The engine controller is configured to control the fuel pump 530 to raise the ignition fuel pressure from the predetermined ignition fuel tank pressure (which in this embodiment is 5 bar) to a delivery pressure (in this embodiment 100 bar). This charges the fuel accumulator 532. The pressure at the accumulator is sensed by the sensor 534 and the pressure reading from the sensor 534 enables the controller to raise the pressure by activating the pump 530 as and when required. The engine controller also controls the fuel injector 134, which contains an actuable valve to selectively release fuel into the chamber of the capsule 136.

Operation of the First Embodiment

(31) Of importance to the invention (as will be clear below) is maintenance of the temperature of the interior surface 137 of the capsule 136 (TC) at a value greater than the predetermined hot surface temperature (HST) of the primary ignition fuel. This temperature is generally maintained by compressed gases of the main cylinder compression stroke. The gas temperature in the vicinity of the capsule will easily be raised to over 600 degrees C. for compression ratios of 12:1 and ambient air temperatures of 20 degrees C. Since the capsule is constructed from a ceramic with a low thermal conductivity, the inside surface will be heated to a high temperature without heat being conducted away.

(32) For cold start, the glow plug 138 is activated (by the engine controller) to provide the hot surface for ignition of the ignition fuel, and furthermore pre-heat the surfaces 137 of the capsule 136 to TC>HST (the surfaces will be heated by a combination of heat from the glow plug 138 and combustion of the ignition fuel). Once TC>HST then the glow plug 138 can be deactivated. It is envisaged that once the engine is running continuously, the glow plug 138 will not be required.

(33) The primary fuel injectors 130, 131 are controlled by an engine controller 536 to introduce gasoline fuel into the intake port 114 thus creating an ultra-lean premix in the cylinder 142. Specifically, the injectors 130, 131 are controlled to create an air-fuel mix with typically ?=1.6 to 2.0 on the intake stroke (for the purposes of this embodiment).

(34) Following the compression stroke whereby the ultra-lean air-fuel mix is compressed in the working volume 144, the igniter is controlled to ignite the mix for the expansion stroke. A predetermined volume of ignition fuel is injected into the capsule 136 by the injector 134 as follows.

(35) The ignition fuel (diethyl ether) is stored within the bladder 510 at the predetermined ignition fuel tank pressure (5 bar in this embodiment). The ignition fuel high pressure (in this embodiment 100 bar) delivery system from the electric fuel pump to the injector will be maintained at all times by the fuel accumulator 532. When fuel needs to be injected, the ECU controls the injector 134 to release ignition fuel for combustion into the capsule 136. This will naturally reduce the volume of the fuel delivery system 506. While the accumulator 532 is discharging to a predetermined volume, the electric high pressure pump 530 need not be operating. Once the fuel accumulator 532 has reached the threshold discharge volume, the electric high pressure pump 530 will be activated to supply 100 bar pressure to the system and re-charge the accumulator to a predetermined full capacity. As the fuel level is depleted in the tank 502, the fuel is maintained at a constant pressure of 5 bar (in this embodiment) by the tank pressure controller 526.

(36) As the ignition fuel enters the pre-chamber, it is atomised in the compressed air and fuel present (from the prior intake stroke). As soon as the atomised ignition fuel/air mix contacts the interior surface 137 of the capsule 136, it ignites. As the flame propagates and the pressure rises inside the capsule, the flames and/or hot gases are forced through the nozzles 152 into the working volume 144 containing the ultra-lean premix. The nozzles 152 are so-shaped as to provide multiple jets of burning mixture to penetrate the working volume 144 to provide a distributed source of ignition throughout the primary fuel mix. Further, the speed of the gases from the capsule tends to cause turbulence within the compression chamber, further enhancing combustion.

(37) This acts to ignite the lean air-fuel mix present in the volume 144 to start the expansion stroke.

Second Embodiment

(38) Referring to FIG. 3, a second embodiment of the present invention is shown. FIG. 3 shows a section through a part of the engine 12 according to the second embodiment. The engine 12 comprises an engine block 100, a piston 140, a cylinder head 106, a port primary fuel injector 130, a direct primary fuel injector 131 and an igniter 132.

(39) The engine block 100 defines an engine block cylinder cavity 102 extending from an abutment surface 104 thereof. The cylinder cavity has a main cylinder axis X. The engine block 100 is constructed from a unitary (e.g. cast) metal material.

(40) The cylinder head 106 is constructed from a unitary (e.g. cast) metal material and has an abutment surface 108. The cylinder head defines an intake port 114, a primary fuel injector cavity 116 and an exhaust port 118 each of which is open to the abutment surface 108.

(41) The intake port 114 is defined as a conduit in the cylinder head 106 extending from a first end 120 to a second end 122. Between the first and second ends 120, 122 there is provided a fuel injector cavity 124. The first end 120 is in fluid communication with an intake manifold (as known in the art) and the second end is in fluid communication with the abutment surface 108. The second end 122 of the intake port 114 joins the abutment surface 108 at a position offset from the axis X, and has an intake port axis I at a non-zero angle to, and directed towards, the axis X.

(42) The ignition system cavity 116 is in communication with the abutment surface 108 and it intersected by the axis X.

(43) The exhaust port 118 is defined as a conduit in the cylinder head 106 extending from a first end 126 to a second end 128. The first end 126 is in fluid communication with the abutment surface 108 and the second end is in fluid communication with an exhaust manifold (as known in the art). The first end 126 of the exhaust port 118 joins the abutment surface 108 at a position offset from the axis X, and has an exhaust port axis E at a non-zero angle to, and directed away from, the axis X.

(44) The engine block 100 and cylinder head 106 are assembled such that the engine block cylinder cavity 102 and the intake and exhaust ports align, thus cooperating to define a cylinder 142.

(45) The piston 140 is disposed within the cylinder 142 for sliding movement along the cylinder axis X. The piston 140 is attached via a con rod (not shown) to a crankshaft (not shown) that provides the mechanical power output from the engine, as known in the art. The piston 140 defines a cavity 141 on a surface thereof forming part of a working volume 144 with the part of the cylinder 142 about the piston 140. The piston comprises a plurality of sealing ring grooves that receive sealing rings to seal the piston 140 against the engine block cylinder cavity 102. Movement of the piston varies the working volume 144 within the cylinder 142.

(46) The port primary fuel injector 130 is generally known in the art, and is positioned in the fuel injector cavity 124 of the intake port 114. Therefore it is an indirect injection (IDI) injector. The port primary fuel injector is connected to a primary fuel supply system and is configured to create a primary fuel-air mix in the intake port 114 upstream of the cylinder. In this embodiment the primary fuel is a fuel which lends itself to atomisation in the inlet port at low injection pressure, for example gasoline, although other fuels could be used in both liquid or gaseous form.

(47) The primary fuel injector 131 is generally known in the art, and is positioned in the fuel injector cavity 116. The primary fuel injector is connected to a primary fuel supply system 536 and is configured to create a primary fuel-air mix in the working volume 144 via direct injection (DI). In this embodiment the primary fuel is a hydrocarbon fuel, specifically gasoline, although it will be understood that other primary fuels may be used with the invention.

(48) The igniter 132 is part of an ignition system (to be described below). The igniter 132 comprises an ignition fuel injector 134, an ignition capsule 136 and a glow plug 138.

(49) The ignition fuel injector 134 is configured to inject an ignition fuel, different to the primary fuel, in this embodiment diethyl ether, into the ignition capsule 136. The ignition fuel injector comprises a nozzle configured to atomise and disperse the ignition fuel as it exits.

(50) The ignition capsule 136 is constructed from a ceramic material, in this embodiment Yttria partially stabilized Zirconia Oxide (YTZP). The capsule has an inlet port for receiving the fuel injector 134. The capsule 136 defines a pre-chamber 150 with the inlet port defined at a first end, and a plurality of exhaust nozzles 152 defined at a second end. The nozzles 152 are directed into the cylinder 142 and also radially towards the axis X. The chamber is tapered from the first end to the second end. It will be noted that the capsule 136 defines an entirely ceramic interior surface 137 in direct contact with the chamber 150.

(51) In this embodiment the chamber volume is 3% of the volume of the cylinder at piston top dead centre (i.e. the fully compressed working volume 144).

(52) The glow plug 138 is a conventional high speed metal diesel glow plug. It is capable of reaching temperatures of around 1000 degrees C., and as such capable of heating the interior walls of the capsule in which it is embedded to above the temperature required. Such devices are compact, with the end penetrating the capsule being in the order of 4 mm in diameter tapering to 3.3 mm. The threaded section is only an M8 thread. The glow plug 138 is positioned such that it lies in the path of the fuel spray plume from the injector 134.

(53) As with the first embodiment, the ignition fuel system 500 is used to deliver fuel to the injector 134,

(54) The primary difference between the first and second embodiments is the position and orientation of the igniter 132. In the first embodiment, the igniter 132 is intersected by the cylinder axis X, and furthermore is configured to direct the ignition plume into the axial centre of the cylinder between the intake and exhaust ports. By contrast, in the second embodiment, the igniter is positioned away from the axis X, near the periphery of the cylinder 142. The entry point for the plumes (i.e. the nozzles 152) is closer to the cylinder periphery than to the axis X. The injector 134 is directed towards the cylinder 142 towards the piston cavity 141, and indeed towards the axis X. The glow plug 138 is engaged with the capsule in a direction normal to the axis X.

(55) This embodiment has certain advantagesin particular it allows for a primary fuel injector to be positioned between the intake and exhaust ports (i.e. on the axis of the cylinder), which facilitates direct primary fuel injection. Further, because it is positioned to the side, there is more space to package the igniter 132.

Third Embodiment

(56) Referring to FIG. 4, a third embodiment of the present invention is shown. FIG. 4 shows a section through a part of the engine 12 according to the third embodiment. The engine 12 comprises an engine block 100, a piston 140, a cylinder head 106, a primary fuel injector 130 and an igniter 132.

(57) The engine block 100 defines an engine block cylinder cavity 102 extending from an abutment surface 104 thereof. The cylinder cavity has a main cylinder axis X. The engine block 100 is constructed from a unitary (e.g. cast) metal material.

(58) The cylinder head 106 is constructed from a unitary (e.g. cast) metal material and has an abutment surface 108. The cylinder head defines an intake port 114, a primary fuel injector cavity 116 and an exhaust port 118 each of which is in communication with the abutment surface 108.

(59) The intake port 114 is defined as a conduit in the cylinder head 106 extending from a first end 120 to a second end 122. Between the first and second ends 120, 122 there is provided a fuel injector cavity 124. The first end 120 is in fluid communication with an intake manifold (as known in the art) and the second end is in fluid communication with the abutment surface 108. The second end 112 of the intake port 114 joins the end surface 122 at a position offset from the axis X, and has an intake port axis I at a non-zero angle to, and directed towards, the axis X.

(60) The ignition system cavity 116 is in communication with the abutment surface 108 and lies on the axis X.

(61) The exhaust port 118 is defined as a conduit in the cylinder head 106 extending from a first end 126 to a second end 128. The first end 126 is in fluid communication with abutment surface 108 and the second end is in fluid communication with an exhaust manifold (as known in the art). The first end 126 of the exhaust port 118 joins the abutment surface 108 at a position offset from the axis X, and has an exhaust port axis E at a non-zero angle to, and directed away from, the axis X.

(62) The engine block 100 and cylinder head 106 are assembled such that the engine block cylinder cavity 102 defines a cylinder 142.

(63) The piston 140 is disposed within the cylinder 142 for sliding movement along the cylinder axis X. The piston 140 is attached via a con rod (not shown) to a crankshaft (not shown) that provides the mechanical power output from the engine, as known in the art. The piston 140 defines a cavity 141 on a surface thereof forming part of a working volume 144 with the part of the cylinder 142 about the piston 140. The piston comprises a plurality of sealing ring grooves that receive sealing rings to seal the piston 140 against the engine block cylinder cavity 102. Movement of the piston creates a variable working volume 144 within the cylinder 142.

(64) The port primary fuel injector 130 is generally known in the art, and is positioned in the fuel injector cavity 124 of the intake port 114. Therefore it is an indirect injection (IDI) injector. The port primary fuel injector is connected to a primary fuel supply system and is configured to create a primary fuel-air mix in the intake port 114 upstream of the cylinder. In this embodiment the primary fuel is a fuel which lends itself to atomisation in the inlet port at low injection pressure, for example gasoline, although other fuels could be used in both liquid or gaseous form.

(65) The direct primary fuel injector 131 is generally known in the art, and is positioned in the fuel injector cavity 116. The port primary fuel injector is connected to a primary fuel supply system 536 and is configured to create a primary fuel-air mix in the working volume 144 of the cylinder 142 via direct injection (DI). In this embodiment the primary fuel is a hydrocarbon fuel, specifically gasoline, although it will be understood that other primary fuels may be used with the invention.

(66) The igniter 132 is part of an ignition system (to be described below). The igniter 132 comprises an ignition fuel injector 134, an ignition capsule 136 and a glow plug 138.

(67) The ignition fuel injector 134 is configured to inject an ignition fuel, different to the primary fuel, in this embodiment diethyl ether, into the ignition capsule 136. The ignition fuel injector comprises a nozzle configured to atomise and disperse the ignition fuel as it exits.

(68) The ignition capsule 136 is constructed from a ceramic material, in this embodiment Yttria partially stabilized Zirconia Oxide (YTZP). The capsule has an inlet port for receiving the fuel injector 134. The capsule 136 defines a pre-chamber 150 with the inlet port defined at a first end, and a plurality of exhaust nozzles 152 defined at a second end. The nozzles 152 are directed into the cylinder 142, in particular the piston cavity 141 and also radially towards the axis X. The chamber 150 is tapered from the first end to the second end. It will be noted that the capsule 136 defines an entirely ceramic interior surface 137 in direct contact with the chamber 150.

(69) In this embodiment the chamber volume is 3% of the volume of the cylinder at piston top dead centre (i.e. the fully compressed working volume 144).

(70) The glow plug 138 is a conventional high speed metal diesel glow plug. It is capable of reaching temperatures of around 1000 degrees C., and as such capable of heating the interior walls of the capsule in which it is embedded to above the temperature required. Such devices are compact, with the end penetrating the capsule being in the order of 4 mm in diameter tapering to 3.3 mm. The threaded section is only an M8 thread. The glow plug 138 is positioned such that it lies in the path of the fuel spray plume from the injector 134.

(71) As with the first embodiment, the ignition fuel system 500 is used to delivery fuel to the injector 134,

(72) The primary difference between the second and third embodiments is the configuration of the igniter 132. Like the second embodiment, the igniter is positioned away from the axis X, near the periphery of the cylinder 142. The entry point for the plumes (i.e. the nozzles 152) is closer to the cylinder periphery than to the axis X. The injector 134 is oriented perpendicular to the axis X, directed straight towards the axis X. The glow plug 138 is engaged with the capsule in a direction at an angle to the axis X and to the axis of the injector 134.

(73) Referring to FIGS. 5 and 6, jet spray patterns for the third embodiment are shown. The piston 140 has a cavity 141 on a surface thereof forming part of the working volume 144. The cavity covers most of the area of the inlet ports 114 The piston 140 is shown at TDCi.e. with the working volume 144 at full compression. At this point most of the working volume is formed of the cavity 141. As ignition fuel is injected into the capsule 136, it ignites on the hot surface and jet plumes JP are emitted from the nozzles 152 into the working volume 144. This ignites the present air-fuel mixture to start the expansion stroke. It will be noted that the shape of the cavity 141 means that the jet plumes JP fill the working volume 144, and thus provide diffuse and turbulent ignition, ideal for lean fuel mixtures.

Variations

(74) Referring to FIG. 1, a system is shown in which the IC engine drives the vehicle wheels via a mechanical drivetrain. The present invention may also be used in IC engines where motive power is supplied indirectlyfor example in electric hybrid vehicles where the engine may be used to generate electricity wholly or partly which can then be used to drive the wheels via electric motor(s).

(75) The above embodiments mention specific primary fuels. Other primary fuels are possible, including (but not limited to): liquid fuels including gasoline, ethanol, methanol, Diesel, gaseous fuels including Liquified Petroleum Gas (LPG), natural gas, methane and hydrogen

(76) The ignition capsule in the above embodiments is described as being constructed from Yttria partially stabilized Zirconia Oxide (YTZP) The capsule may be constructed from other ceramics such as sintered Silicon Nitride (Si.sub.3N.sub.4) or any ceramic with similar thermal conductivity, coefficient of thermal expansion, fracture toughness, bending strength and maximum service temperature properties. Superalloy metals with high temperature capability could also potentially be used.

(77) The above embodiment specifies an ignition pre-chamber size of 3% of the cylinder volume at top dead centre. It will be noted that sized from 3 to 5% are also possible.

(78) Although a glow plug is described for cold start, other means of generating heat are possible.

(79) A pressure sensing device may be provided within the capsule to monitor the gas pressure throughout the above-described cycle.

(80) The geometry of the capsule may be varied depending on production and packaging requirements. Some areas of the capsule may be designed such that the operating temperature is either increased or lowered compared to the rest of the capsule. Likewise the detail design will optimize the geometry of the capsule where the fuel injector is located to reduce heat transfer into the nozzle of the injector from the pre-chamber.

(81) The second and third embodiments are similar to the first embodiment and reflect two different ignition capsule configurations. All three embodiments show combined direct (DI) and indirect (IDI) injection. Where the ignition capsule is placed at the edge of the combustion chamber (as with the second and third embodiments) it opens the possibility to use either direct injection or port injection or a combination of both. Preferably port injection is used because for premixed fuel preparation that is all that is needed. However, there may be cases where an engine designer insists on direction injection. Reasons might include (for example) direct injection of hydrogen or compressed natural gas; DI is considered the most effective way of getting the gas into an engine. It is important to recognise that in all three embodiments it is possible to use either port injection or direct injection or a combination of both (which some engine manufacturers are doing).

(82) The invention may also be described or defined in accordance with the following clauses: 1. A vehicle internal combustion engine comprising: at least one cylinder defining a combustion chamber; a piston disposed for movement within at least one cylinder to define a swept volume of at least one cylinder being less than or equal to 3.0 litres; a primary fuel supply system configured to create a primary fuel-air mix in the combustion chamber; an ignition system comprising: a pre-chamber having a volume less than the swept volume of the cylinder; an ignition fuel supply system configured to create an ignition fuel-air mix in the pre-chamber; an ignition surface within the pre-chamber, the ignition surface being configured to be contacted by the ignition fuel in the pre-chamber to thereby ignite the ignition fuel by hot surface ignition; at least one jet nozzle in fluid communication with the combustion chamber of the cylinder; wherein: the primary fuel and the ignition fuel are different fuels, and wherein ignition of the ignition fuel by contact with the ignition surface causes at least one of hot gases, partially combusted fuel and flames to enter the combustion chamber through the at least one jet nozzle to thereby ignite the primary fuel. 2. A vehicle internal combustion engine according to clause 1, wherein the ignition fuel is a fuel which is characterised by all of the following characteristics: a carbon content by mass less than 65%; a hot surface ignition temperature less than 500 deg C.; and, a volumetric energy density (LHV) greater than 18 MJ/L. 3. A vehicle internal combustion engine according to clause 1 or 2, wherein the ignition fuel is an ether 4. A vehicle internal combustion engine according to clause 3, wherein the ignition fuel is diethyl ether. 5. A vehicle internal combustion engine according to any preceding clause, wherein the ignition fuel supply system is configured to inject the ignition fuel into the pre-chamber at a pressure less than 200 bar. 6. A vehicle internal combustion engine according to any preceding clause, wherein the ignition fuel supply system is configured to inject the ignition fuel into the pre-chamber of quantity less than 5% equivalent energy content of the main chamber fuel introduced into the main cylinder. 7. A vehicle internal combustion engine according to any preceding clause, wherein the primary fuel supply system is configured to premix primary fuel-air mixture prior to combustion. 8. A vehicle internal combustion engine according to clause 7, wherein the primary fuel supply system is an indirect injection system. 9. A vehicle internal combustion engine according to clause 8, wherein the primary fuel supply system comprises a port fuel injector. 10. A vehicle internal combustion engine according to clause 7, wherein the primary fuel supply system is a direct injection system. 10. A vehicle internal combustion engine according to any preceding clause, wherein the pre-chamber is at least partially constructed from a ceramic material. 11. A vehicle internal combustion engine according to clause 10, wherein the ceramic material defines part of the ignition surface. 12. A vehicle internal combustion engine according to any preceding clause, wherein the ignition system comprises a heater for providing the ignition surface upon cold start. 13. A vehicle internal combustion engine according to clause 12, wherein the heater is a glow plug. 14. A vehicle internal combustion engine according to any preceding clause, wherein the volume of the pre-chamber is less than 5.0% of the compressed volume of the working cylinder. 15. A vehicle internal combustion engine according to any preceding clause, wherein the primary fuel supply system configured to create a primary premixed fuel-air mixture in the combustion chamber. 16. A vehicle internal combustion engine according to clause 15, wherein the primary premixed fuel-air mixture has 1.6???2.0. 17. A vehicle internal combustion engine according to any preceding clause, wherein the primary fuel is any fuel (liquid, gaseous or solid) capable of being premixed. 18. A vehicle internal combustion engine according to any preceding clause, wherein the cylinder defines a primary axis and the pre-chamber is intersected by the primary axis. 19. A vehicle internal combustion engine according to clause 18, wherein the pre-chamber is positioned proximate the perimeter of the cylinder. 20. A vehicle internal combustion engine according to clause 19, wherein the at least one jet nozzle is directed towards the primary axis.