GB2311327A

GB2311327A - Combined fuel injector and spark plug arrangement in an engine cylinder

Info

Publication number: GB2311327A
Application number: GB9605789A
Authority: GB
Inventors: Constantine Arcoumanis; Shinji Kono
Original assignee: FLUIDS RES Ltd; Aisin Seiki Co Ltd
Current assignee: FLUIDS RES Ltd; Aisin Corp
Priority date: 1996-03-19
Filing date: 1996-03-19
Publication date: 1997-09-24
Anticipated expiration: 2016-03-19
Also published as: GB9605789D0; GB2311327B; JPH1037836A; JP3900210B2

Abstract

The injector 15 directs fuel towards the spark gap 35 which is downstream of the earth electrode axial portion 34 or a plate (85, Fig.7) in the direction of tumble weak mixture flow from an intake port (12, Fig.1) which receives fuel from an injector (14). The portion 34 or the plate provides for a spark-ignitable mixture at the gap 35. The injector 15 is supplied with fuel by a pump (50, Fig.5) including a pressure amplifying piston (56, 58) subject to the pressure in the engine cylinder.

Description

TITLE Ignition Apparatus DESCRIPTION The present invention relates to an ignition system for use in future ultra-lean-burn engines and for extending the lean limit of present production lean-burn spark ignition engines.

The internal combustion engine is required to operate and to burn the fuel efficiently over a wide range of speed and load conditions. This is normally achieved by using a stoichiometric mixture which burns evenly during the power cycle. Although a stoichiometric rich mixture gives the engine high performance characteristics, it is a waste of fuel and produces high levels of gaseous pollutants.

Lean-burn engines driven under increasingly higher air-fuel ratios have been proposed around the world. The air-fuel ratio of such lean-burn engines is around 25 but recently a direct-injection engine was developed which can operate at ratios as high as 40. To achieve this ultra -lean-combustion a stratified charge mixture is required.

That is, a rich mixture must be present around the spark plug at the time of ignition, while the rest is lean. The spark plug ignites the rich mixture and the developing flame spreads towards the unburnt gas allowing the overall lean mixture to burn efficiently.

The following three prior art proposals disclose combined spark plug and fuel injectors which offer promise for extending the lean limit of production lean-burn spark-ignition engines without any major modification to the engine itself.

UK Patent No. 1519514 proposes a system that enhances vaporization of liquid fuel (gasoline) in the rich mixture region. The spark plug of the UK Patent has a fuel injector centrally positioned. The injector injects fuel into a region around the gap of the spark plug through a vaporizing tube formed longitudinally in the spark plug.

When fuel flows through the vaporizing tube, the fuel is vaporized by the heat from the spark plug. The spark plug faces towards the combustion chamber so that the temperature of the spark plug gets very high. However, deposits from the fuel may adhere to the vaporizing tube after the engine has been driven for a long time, and the durability of the fuel vaporizer system is therefore questionable.

UK Patent No. 1561017 proposes a system whereby a spray hole of a fuel injector is positioned close to the spark gap of a spark plug. The spray hole of the injector opens in a 360 degree direction and forms a wide mixture region and thus the capacity for stratification of charge ignition is limited. The system is based on a lean mixture provided by a carburettor and does not consider the interaction between the flow and the localized mixture near the spark plug.

US Patent No. 4546740 proposes a system whereby a hole of a gaseous fuel injector is located opposite to the spark gap and injects into the secondary chamber required to cause satisfactory ignition and flame initiation. If the system is used for a liquid fuel, the injector must inject significant amount of liquid fuel so as to fill the chamber and supply fuel to the spark gap. As a result, a lot of fuel may exist around the spark gap thus causing misfiring and reducing the capability of the engine to run very lean.

An object of this invention is to provide an ignition system for ultra-lean-burn engines running with liquid fuel, which can supply a rich mixture around the spark gap with a very low probability for misfiring. According to the invention, the ignition system comprises: a main injector for injecting fuel into an intake port of the engine and creating a tumble flow of an ultra-lean fuel-air mixture past a spark plug in a combustion chamber of the engine; an obstructor in the flow path of the ultra-lean fuel-air mixture, creating a wake in the flow path; and a pilot injector incorporated into the spark plug and having an injection nozzle near the spark gap for injection fuel towards the spark gap and into the wake; whereby the obstructor is located immediately upstream of the spark gap and the spark gap is located immediately upstream of the injection nozzle of the pilot injector, with respect to the direction of the tumble flow of the ultra-lean fuel-air mixture in the combustion chamber.

The invention is illustrated with reference to Figures 1 to 7 of the accompanying drawings. In the drawings: Figure 1 is a schematic view of the ignition system positioned in the engine according to the invention; Figure 2 is an enlarged sectional view of the plug-injector shown in Figure 1; Figure 3 is a partially enlarged view of Figure 2; Figure 4 is a partially enlarged view of Figure 2, but showing another configuration of the second electrode; Figure 5 is a cross-sectional view of a pressure amplifier that may be used in the invention; Figure 6 is similar to Figure 3, but showing the case when the ignition system is operating and fuel is injected towards the spark gap; Figure 7 is an under view of Figure 2, but showing another configuration of the plug-injector; and Figure 8 is a stylized indicator diagram for four stroke engine.

Referring first to Figure 1, an ignition system according to the invention comprises a combustion chamber 11, an intake port 12, an exhaust port 13, a main injector 14, the pilot injector 15 and the spark plug 16. The pilot injector 15 and the spark plug 16 are integrated in one body 17, as shown in Figure 2.

A cylinder block 21 and a cylinder head 22 of the engine form the combustion chamber 11. The intake port 12 is connected to the chamber 11. The main injector 14 injects fuel into the intake port 12 and mixture is formed in the intake port 12. This mixture is ultra-lean and is introduced into the chamber 11 when an intake valve 23 is open. The quantity of fuel injected by the main injector 14 is quite small in comparison with that injected by a conventional port/manifold injector. According to the invention, the air-fuel ratio of the ultra-lean-mixture can be as high as 50, at its maximum. This is possible because the pilot injector 15 allows a flame kernel to be initiated which can burn all of the ultra-lean-mixture in the combustion chamber 11 provided the cylinder charge is highly turbulent and the ultra-lean-mixture in the combustion chamber 11 is in the form of a tumble flow 24, which is known to generate high levels of mean flow and turbulence. As shown in Figure 1, the ultra lean-mixture tumbles in a certain direction determined by the geometry of the port. Near the pilot injector 15 and the spark plug 16, the tumble flow 24 of the ultra lean-mixture flows horizontally, as shown in Figure 2.

The exhaust port 13 is also connected to the chamber 11 to allow the combustion gases to leave the chamber 11. An exhaust valve 25 is located between the combustion chamber 11 and the exhaust port 13.

Referring to Figure 3, the spark plug-injector 30 is now going to be explained. The body 17 of the combined spark plug and injector 30 houses both the pilot injector 15 and the spark plug 16. An off-centre (first) electrode 31 of the spark plug 16 extends longitudinally from the body 17.

A side (second) electrode 32 of the plug 16 has a longitudinal portion 34 and transverse portion 33. The transverse portion 33 makes a spark gap 35 with the off-centre first electrode 31. The longitudinal portion 34 is fixed to the body 17 and acts as an obstruction to the tumble flow, being positioned upstream to the flow.

The pilot injector 15 has a hole 40 that is positioned directly adjacent to the spark gap 35 downstream of the spark gap 35 in the direction of tumble flow 24. That is, the fuel injected from the hole 40 is introduced into the spark gap region 35. The longitudinal portion 34 of the side electrode 32 is located upstream of the spark gap 35 and the spark gap 35 is located upstream of the hole 40 of the pilot injector 15, both with respect to the direction of the tumble flow 24 in the combustion chamber 11. The spark gap 35, the hole 40 of the pilot injector 15 and the longitudinal portion 34 of the side electrode 32 acting as the obstructor are well within the diameter of the housing 17. Further, as shown in Figure 4, the transverse portion 33 of the side electrode 32 may have a reflector end 41, so that even if the hole 40 of the pilot injector 15 is not strictly opposite to the spark gap 35, the reflector end 41 may direct the fuel injected from the hole 40 towards the spark gap 35.

Returning to Figure 3, a fuel chamber 42 is able to communicate fluidically with the hole 40 through an annular pipe. A needle valve 43 located in the chamber 42 allows the fuel communication between the chamber 42 and the hole 40 when the fuel pressure in the chamber 42 is higher than the resisting pressure of the spring 44. The resisting pressure is controlled by a pre-load set screw 45. The needle valve 43 is sliding and supported on a needle guide 46. The fuel pressure in the chamber 42 is amplified by a mechanical pressure amplifier 50 shown in Figure 5. The amplifier 50 amplifies the fuel pressure supplied from a fuel tank 51 through a fuel pump 52 and then supplies the amplified fuel pressure to the chamber 42.

The pressure in the combustion chamber 11 is always fed via a narrow passage 53 into an entry region 54 of the amplifier 50. One end of the passage 53 is exposed through an annular chamber 55 around the spark plug 16, as shown in Figure 3. A first driving piston 56 of the amplifier 50 reciprocates inside larger cylinder 57. A second driven piston 58 slides in a smaller cylinder 59. A small rod 60 connects the first and second pistons 56,57 so that the pistons 56,57 move simultaneously. A return spring 61 located in a compression chamber 62 at the end of the smaller cylinder 59 causes return movement of the pistons 56,58, while an adjustable stop 63 limits the extent of return movement of the pistons 56,58. The stop 63 may also be used to adjust the load of the spring 62. A space 64 is located between the pistons 56,58 and communicates with the atmosphere through a vent passage 65. A fuel inlet 66 is fixed to the body 70 of the amplifier 50 and establishes fluid communication between the fuel tank 51 and the compression chamber 62 through a check valve 67.

The check valve 67 has a spring 68 which prevents the back flow of fuel from the compression chamber 62 to the fuel tank 51. A fuel outlet 69 is also fixed to the body 70 and allows fluid communication between the compression chamber 62 and the fuel chamber 42 of the pilot injector 15.

The function of the ignition system is described as follows: After the engine is started, the main injector 14 injects liquid fuel such as gasoline to the intake port 12. When the intake valve 23 is opened, fuel and air are drawn into the combustion chamber as an ultra-lean mixture. The air-fuel ratio could be as high as 50.

As the engine turns over, the pressurized air in the combustion chamber 11 is introduced into the entry region 54 of the fuel pressure amplifier 50. Figure 8 is a stylized indicator diagram (Pressure-Volume) for four -stroke engine. When the engine is in the compression stroke, the pressure in the entry region 54 increases driving the first and second pistons 56,58 against the resisting force of the spring 61. According to the diameter difference of the pistons 56,58 the pressure in the entry region 54 is amplified and pressurizes the fuel in the second space 62 via the pistons 56,58. At this time, the check valve 67 is closed and the needle valve 43 of the pilot injector 15 is also closed. Because the pressure in the fuel chamber 42 of the pilot injector 15 is the same as the pressure in the compression chamber 62, it is lower than the force of the spring 44 of the pilot injector 15. As the compression stroke however proceeds, the fuel pressure in the compression chamber 62 and the fuel pressure in the fuel chamber 42 become higher than the resisting force of the spring 44 of the pilot injector so that the needle valve 43 moves downstream against the resisting force of the spring 44 and a highly pressurized small amount of fuel is injected through the hole 40 towards the spark gap. The pressure at that time is about 3 to 4 times higher than the pressure in the combustion chamber before TDC (Top Dead Centre). The quantity of fuel injected from the pilot injector can be controlled to be about 5-10 percent of the quantity of fuel injected from the main injector 14. There is no additional control for injecting liquid fuel from the pilot injector 15. The set load of the spring 44 decides the injection timing of the pilot injector 15.

Referring to Figure 6, a wake 80 of the tumble flow 24 is formed in the spark gap 35, as the tumble flow 24 of the ultra-lean-mixture flows around the portion 34 of the spark plug second electrode 32 extending longitudinally of the spark plug body 17. On the other hand! the direction of the fuel as it is injected from the hole 40 is opposite to the tumble flow 24, and the pilot-injected fuel interacts with the low pressure area in the wake 80, and as a result, the fuel injected from the pilot injector 15 vaporizes very rapidly. This allows a locally rich-mixture region 81 to be formed within the spark gap but not around the spark gap 35. When the spark plug 16 is energized, it ignites the rich-mixture situated within the spark gap 81 so as to form a flame kernel. This flame kernel develops and propagates towards the ultra-lean-mixture region 82 assisted by the tumble flow 24 and the high tumble turbulence.

The pressure in the combustion chamber 11 becomes low as the exhaust stroke proceeds. Therefore, the pressure in the first chamber 54 of the amplifier 50 also becomes low and the first and second pistons 56,58 move backwards under the force of the spring 61. At this time, the pressure in the compression chamber 62 also becomes low, thus allowing fuel for the next injection to be supplied through the check valve 67.

Instead of the longitudinal section 34 of the side electrode 32, a narrow plate 85 may act as an obstructor.

The plate 85 generates a wake 80 of the tumble flow 24, as shown in Figure 7. In this case, the plate 85 is located upstream of the spark gap 35 and the spark gap 35 is located upstream of the hole 40 of the pilot injector 15, with respect to the tumble flow 24 in the combustion chamber 11.

Claims

1. An ignition system for a spark-ignition internal combustion engine, comprising: a main injector for injecting fuel into an intake port of the engine and creating a tumble flow of an ultra-lean fuel-air mixture past a spark plug in a combustion chamber of the engine; an obstructor in the flow path of the ultra-lean fuel-air mixture, creating a wake in the flow path; and a pilot injector incorporated into the spark plug and having an injection nozzle near the spark gap for injection fuel towards the spark gap and into the wake; whereby the obstructor is located immediately upstream of the spark gap and the spark gap is located immediately upstream of the injection nozzle of the pilot injector, with respect to the direction of the tumble flow of the ultra-lean fuel-air mixture in the combustion chamber.

2. An ignition system according to claim 1, wherein the spark plug comprises a first electrode extending longitudinally from the spark plug body and a second electrode comprising a first portion extending longitudinally from the spark plug body and a second portion extending transversely of the first portion and overlying the first electrode to establish the spark gap; and the obstructor is the first portion of the second electrode.

3. An ignition system according to claim 1, wherein the obstructor is a narrow plate extending from the spark plug body immediately upstream of the spark plug gap.

4. An ignition system according to any preceding claim, wherein an electrode of the spark plug is shaped to direct fuel injected from the injection nozzle of the pilot injector into the spark plug gap.

5. An ignition system according to any preceding claim, wherein the spark plug electrodes, the pilot injector and the obstructor are all contained within the diameter of the spark plug body.

6. An ignition system according to any preceding claim, further comprising a pressure amplifier driven by the increasing pressure in the combustion chamber during the combustion stroke, for increasing the pressure of fuel supplied to the pilot injector and thereby controlling the timing of the injection of fuel by the pilot injector.

7. An ignition system substantially as described herein with reference to the accompanying drawings.