GB2327983A

GB2327983A - Gasoline i.c. engine with vapour fuelling and charge stratification

Info

Publication number: GB2327983A
Application number: GB9716829A
Authority: GB
Inventors: Thomas Tsoi Hei Ma
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 1997-08-09
Filing date: 1997-08-09
Publication date: 1999-02-10
Also published as: GB9716829D0

Abstract

A gasoline spark ignition internal combustion engine is disclosed having two or more intake passages 104, 106 supplying combustion air to each engine cylinder and a flow control valve 108 regulating the air flow along one of the passages 106 to each engine cylinder. Throttling of the air flow along the passage 106 by the flow control valve 108 during part load operation of the engine results in stratification of the intake charge in the combustion chamber of the cylinder. The gases flowing along the throttled passage 106 remain in the vicinity of a spark plug 102 near the centre of the combustion chamber at the instant of spark ignition. The engine also includes a vapour extraction system for separating the gasoline fuel into a lighter vapour fraction and a heavier liquid fraction. The invention proposes introducing fuel from the vapour fraction into the intake passage 106 throttled by the flow control valve 108 to increase the concentration of the lighter fraction of the gasoline fuel in the vicinity of the spark plug 102 at the instant of spark ignition.

Description

GASOLINE INTERNAL COMBUSTION ENGINE Field of the invention The present invention relates to a stratified charge gasoline internal combustion engine.

Background of the invention Various proposals can be found in the prior art for stratifying the intake charge in an engine having one or more intake valves per cylinder by regulating the speed of the air flow along different regions of the skirts of the open valves during the induction stroke. The intake ports leading to the intake valves can be partitioned into separate passages and a flow control valve may regulate the relative air flows along the different passages by throttling one of the passages in order to direct the air flows from the other passages to different regions of the combustion chamber so as to promote charge stratification.

Depending on the geometry of the intake system and the positioning of the flow control valve, the intake charge can be made to swirl (i.e. vortex about the cylinder axis) or tumble (i.e. vortex about an axis transverse to the cylinder axis). In the case of swirl, the intake charge is radially stratified with the flow from the throttled passage remaining at the centre of the vortex near the axis of the combustion chamber. In the case of tumble, the intake charge is stratified in layers lying in planes parallel to the cylinder axis.

It has also recently been proposed by the present Applicant in GB Patent Application No. 9716156.6 to provide a fuel vapour extraction system for a gasoline engine capable of continuously separating the fuel into a lighter vapour fraction and a heavier liquid fraction, the ratio of the two fractions being adjustable and the sum of the two fractions always matching the fuel demand from the engine.

Such a vapour extraction system can continuously supply to the engine separately a vapour fraction that is easily ignitable and a liquid fraction that is more resistant to knock.

Object of the invention The present invention seeks to provide a stratified charge gasoline engine that takes advantage of the availability of the gasoline fuel in vapour and liquid fractions made possible by such a vapour extraction system.

Summary of the invention According to the present invention, there is provided a gasoline spark ignition internal combustion engine having two or more intake passages supplying combustion air to each engine cylinder and a flow control valve regulating the air flow along one of the passages to each engine cylinder, throttling of the air flow along the passage by the flow control valve during part load operation of the engine resulting in stratification of the intake charge in the combustion chamber of the cylinder with the gases flowing along the throttled passage remaining in the vicinity of a spark plug near the centre of the combustion chamber at the instant of spark ignition, wherein the engine includes a vapour extraction system for separating the gasoline fuel into a lighter vapour fraction and a heavier liquid fraction, and means are provided for introducing fuel from the vapour fraction into the intake passage throttled by the flow control valve to increase the concentration of the lighter fraction of the gasoline fuel in the vicinity of the spark plug at the instant of spark ignition.

If desired, vapour may also be supplied to the intake passage throttled by the flow control valve by purging a canister storing vapours evaporated from a fuel storage tank of the engine.

In one embodiment of the invention, the engine has two or more intake ports per cylinder supplying separate respective intake valves, one of the intake ports being deactivated during part load operation by the flow control valve so that the other intake port would create a high swirl and radial charge stratification within the cylinder.

In an alternative embodiment of the invention, the engine may have two or more intake ports per cylinder supplying a common intake valve, one of the intake ports being de-activated by the flow control valve during part load operation so that the other intake port would create a high swirl within the cylinder.

In a further embodiment of the invention, the engine may have more than one intake valve per cylinder supplied by a common intake port, one side of the flow cross-section of the intake port passage being throttled by the flow control valve during part load operation- to concentrate the air flow along the other side of the intake passage and thereby promote swirl and radial charge stratification within the cylinder.

In a still further embodiment of the invention, the air flow to one or more intake valves may be supplied by three transversely spaced passages, the outer two passages being unthrottled and the central passage being throttled by the flow control valve, the air flows from all three passages being directed to flow into the combustion chamber parallel to a diameter of the cylinder bore. In this case, the intake system promotes tumble with the flow from the throttled passage tumbling in a diametral plane of the combustion chamber thereby forming a sandwiched charge stratification.

In the invention, the lighter fraction of the gasoline fuel is concentrated in the vicinity of the spark plug at the instant of spark ignition and this improves the ignitability of the charge especially when operating with a total charge that is on average on the lean side of stoichiometry.

The invention can be applied to engines where the heavier fraction of the gasoline fuel is introduced separately into each combustion chamber by being injected either into an unthrottled intake passage or directly into the combustion chamber.

When the liquid fraction of the gasoline fuel is injected into the unthrottled intake passage of the engine cylinder, it will be distributed around the periphery of the cylinder. The invention will then achieve a readily ignitable mixture containing the lighter fraction of the gasoline fuel surrounding the spark plug, and a more knock resistant mixture containing the heavier fraction of the gasoline fuel occupying the end-gas regions of the combustion chamber.

When the liquid fraction of the gasoline fuel is injected directly into the combustion chamber during the intake stroke or early in the compression stroke, it will be distributed uniformly within the cylinder and a similar stratification of the composition of the fuel to that previously described will be attained.

When the liquid fraction of the gasoline fuel is injected directly into the combustion chamber late in the compression stroke, a local cloud of rich mixture containing this fuel may be formed in the vicinity of the spark plug.

The invention will then achieve two separately produced mixture clouds surrounding the spark plug at the time of spark, a first cloud containing the readily ignitable lighter fraction of the gasoline fuel and the second cloud containing the heavier fraction. Such a combination would produce a more reliable ignition of the cylinder charge compared with a direct injection engine injecting all of its fuel late in the compression stroke to form a single ignitable cloud.

The presence of the flow control valve in an intake passage will create a vacuum in the intake passage with each induction stroke of the engine to drive the vapour extraction system. The same vacuum can also be used to advantage in purging a vapour canister. The presence of a flow control valve throttling an intake passage ensures that an ample supply of the lighter fraction of the gasoline fuel can be drawn under all engine operating conditions. Such conditions could include cranking and starting of the engine as well as idling with a delayed spark timing during warm up. They could also include stratified charge operation where the main throttle of the engine is opened wide and the intake manifold is substantially at ambient pressure.

Hitherto, vapour produced during purging of a vapour.

canister could not be used in a controlled manner. When such vapour is dumped into the intake system without the engine fuel system compensating for its presence, it disturbs the fuel calibration of the engine and is not burnt efficiently.

If the engine operates with a stratified charge, this vapour can also find its way into a region of the charge where it cannot burn at all and will add to the hydrocarbon emissions in the exhaust gases discharged from the engine.

In the present invention, the fuel vapour drawn from a vapour canister during purging of the canister is included in the vapour fuel fraction. This vapour will be burnt completely, thereby providing an efficient and reliable manner of disposing of the purge vapour from the vapour canister.

In a preferred embodiment of the invention, though the purge flow drawn from the vapour canister may have a variable vapour content, it may be buffered and equilibrated by routing the flow through the vapour extraction system proposed in GB Patent Application No. 9716156.6. In this way, the purge vapour will merge with the overall vapour flow supplied to the engine and allowance will automatically be made for it by the engine management system.

As a further refinement of the invention, additional steps may be taken to ensure that the fuel drawn from the vapour fraction has an increased concentration of reactive components which are even more readily ignitable. Such steps may include heating the vapour fraction in a heat exchanger and mixing the vapour fraction with hot exhaust gases before introducing it into the throttled intake passage.

Pre-conditioning of the vapour fraction in this way could produce active radicals having a sufficiently long lifetime to remain in the stratified charge up to the time of spark ignition.

Brief description of the drawings The invention will now be described further, by way of example, with reference to the accompanying drawings, in which Figure 1 shows an intake system designed to promote swirl and radial charge stratification when one of two intake passages is throttled, and Figure 2 is a block diagram similar to the single drawing in copending Patent Application No. 9716156.6 that shows a continuous fuel vapour extraction system.

Detailed description of the preferred embodiment The present invention relies on the availability of separate continuous supplies of vapour fuel and liquid fuel of different composition. These can be derived from separation of gasoline into a lighter and a heavier fraction in the manner that will now be described with reference to Figure 2, this being the subject of the above mentioned copending GB Patent Application No. 9716156.6.

An engine 10 has an intake manifold 16, a main throttle 14 and an intake passage containing a venturi 12. A fuel injection system for the engine comprising a fuel circulation pump 32 that supplies fuel under pressure into a fuel rail 34 from which fuel is dispensed to the individual cylinders of the engine by fuel injectors 18. The pressure in the fuel rail 34 is regulated by a relief valve 36 that derives a reference pressure from the intake manifold 16.

Surplus fuel is spilled by the relief valve 36 into a fuel return pipe 38.

While it is conventional for the pump 32 and the return pipe 38 to be directly connected to the main fuel storage tank, designated 20 in the drawing, they are connected instead to a volatising chamber 30 that contains a much smaller quantity of fuel. The volatising chamber 30 is connected to the main fuel tank 20 by a supply pipe 24 containing a fuel lifter pump 22 and the level of fuel within the chamber 30 is maintained constant by means of a float 28 and a valve 26.

An evaporator 40 is disposed in the vapour filled space of the chamber 30 above the liquid level and in the path of the fuel returned by way of the fuel return pipe 38. The return fuel is sprayed over the evaporator and the latter is designed to have a large surface area that is coated with a film of fuel. The large surface area may be achieved by using a matrix of capillaries or a porous or sintered block for the evaporator 40. Neither the evaporator 40 nor the fuel in the chamber 30 is heated and evaporation relies on the reduced pressure in the vapour space, the dispersion of the spray droplets, the large surface area of the evaporator 40 and such heat as the return fuel picks up during its circulation flow. The matrix of the evaporator 40 may be formed of a hydrocarbon storage material such as activated carbon to increase the quantity of vapour that can readily be extracted under dynamic conditions.

To maintain the vapour space in the volatising chamber 30 below atmospheric pressure, a pipe 42 leading from it is connected by way of a first pipe 46 and a regulating valve 56 to the venturi 12, by way of a second pipe 44 and a regulating valve 54 to the intake manifold 16 and by way of a third pipe 110 containing a regulating valve 112 to a throttle passage of the engine intake system, as will be described below by reference to Figure 1.

The pipe 42 is also connected by way of a pipe 48 and a regulating valve 58 to a vapour canister 50 that is itself connected to the ullage space of the main fuel tank 20 by a pipe 52. Instead of the pipe 48 being connected to the pipe 42 to allow fuel vapour stored in the vapour canister 50 to be purged directly into the venturi 12, it is alternatively possible as represented by the pipe 48' shown in dotted lines to route the purge flow from the vapour canister 50 through the volatising chamber 30.

Figure 1 shows the intake system of one of the engine cylinders 100. The cylinder 100 has a central spark plug 102 and two intake valves (the exhaust valves are not shown as they not relevant to the present invention) . The intake port of the lower intake valve as viewed in Figure 1 is a helical swirl port connected to an intake passage 104. The intake port of the upper intake valve is supplied with air by a passage 106 that contains a butterfly throttle 108 acting as a flow control valve. Both the intake passages 104, 106 are connected to the intake manifold 16.

The pipe 110 mentioned in the description of Figure 2 opens into the passage 106 to feed the vapour fraction of the gasoline fuel into the passage 106 downstream of the flow control valve 108. At the same time the vacuum created in the passage 106 during each induction stroke of the cylinder is applied by the pipe 110 to the vapour space of the volatising chamber 30 in Figure 2.

Under idling and low load conditions, the bulk of the fuel requirement will be delivered to the engine in vapour form. A small quantity of liquid fuel corresponding to the unvaporised fraction of the fuel will be supplied by the fuel injection system so as to maintain the composition of the fuel consumed overall the same as that present in the fuel storage tank 20.

As the engine load is increased progressively, by suitable selection of the positions of the regulating valves 54, 56 and 112, the vacuum pressure in the volatising chamber 30 can be set to supply vapour at any desired rate while the balance of the fuel to make up the original composition of the fuel is injected by the fuel injectors.

During this mode of operation the vacuum alone would not be sufficient to maintain the rate of vapour supply continuously but as a large proportion of the fuel is recirculated in the loop 32, 34, 36, 38 the cooling of the evaporator 40 will be compensated by heat picked up by the recirculating fuel and the evaporation rate will stabilise.

The rate of supply of fuel in vapour form to the engine depends upon the pressure and temperature prevailing in the volatising chamber 30 and the position of the regulating valves 54, 56 and 112. The engine control system will first decide the total quantity of fuel to be burnt and the fractions to be supplied in vapour and liquid forms. Based upon these variables, as can be prior determined by conventional engine fuel calibration maps, the engine management system can set the positions of the regulating valves 54, 56 and 112 to achieve the desired vapour flow rate and the pulse width of the fuel injectors 18 to achieve the desired liquid flow rate.

Under high load conditions, it is not desirable to supply fuel vapour as it would reduce the volumetric efficiency and maximum power output of the engine, for which reason the valves 54, 56 and 112 can be closed so that all the fuel requirement is met by the injected liquid fuel.

The fact that fuel vapour is used efficiently in running the engine allows proper use of such vapour as is stored in the vapour canister 50. Whereas normally fuel purged from the canister 50 is merely dumped into the intake system in an uncontrolled fashion to regenerate the canister 50, by routing the purge flow through the volatising chamber 30, such vapour flow is taken into consideration in determining the total amount of fuel vapour to be metered to the engine.

The vapour extraction system of Figure 2 copes well with a steady demand for fuel vapour as the operating pressure and temperature will move automatically to match the demand. To cope with sudden changes in the vapour demand, there is a need for a vapour store to act as a buffer. Such a vapour store is already present in the form of the canister 50 the content of which may be used by opening the valve 58 whenever a sudden surge occurs in the demand for fuel vapour. A second vapour store can be formed by using a storage material, such as activated carbon, in the evaporator 40 which will be replenished more rapidly than the vapour canister 50.

The invention takes advantage of the availability of the gasoline fuel in vapour and liquid fractions made possible by the vapour extraction system. It can be applied to any geometry of charge stratification, the described preferred embodiment, shown in Figure 1, being one in which the intake system is designed to promote swirl during part load operation.

Under high load conditions, the flow control valve 108 is fully opened and the charge is homogeneous. Under these conditions the vapour and liquid fractions of the fuel are both evenly distributed throughout the combustion chamber and the mixture strength is sufficiently high to ensure reliable ignition.

Under part load conditions, the flow control valve 108 is closed as illustrated in Figure 1. The air drawn through the passage 104 will swirl in the combustion chamber because of the design of the helical port and will be blown towards the outer periphery of the cylindrical combustion chamber.

The other intake valve would be open but cannot draw air past the closed flow control valve 108. The resultant vacuum in the passage 106 will draw fuel vapour via the pipe 110 from the vapour space of the volatising chamber 30 and this vapour will dwell near the centre of the cylinder.

The liquid fraction of the gasoline fuel is injected either solely into the passage 104 or partly into both passages 104 and 106. The amount of liquid fuel will be related to the amount of vapour fuel such that the overall composition of the fuel that is burnt matches that of the stored gasoline in the fuel tank 20.

The proportions of the vapour and liquid fractions can be varied relative to one another to control the composition of the fuel in the different stratified layers by varying the vacuum in the volatising chamber 30 and the pulse width of the liquid fuel injectors 18. This can control the ignitability of the vapour fraction near the spark plug and the knock resistance of the liquid fraction remote from the spark plug.

The invention is not exclusively applicable to the intake geometry shown in Figure 1 and can be applied to different intake geometries designed to promote either radial or lateral stratification (swirl or tumble) in the intake charge.

The invention may also be applied to an engine where charge stratification may also be achieved by direct fuel injection into the combustion chamber. In this case, the liquid fraction of the gasoline fuel may be injected in two phases into the combustion chamber. A first phase timed to occur in the intake stroke or early in the compression stroke will result in a homogeneous distribution of the liquid fraction throughout the combustion chamber, while a second phase timed to occur late in the compression stroke will result in a local rich cloud containing the liquid fraction in the vicinity of the spark plug at the time of spark ignition. As it is difficult to time the second phase to ensure that this rich cloud of ignitable mixture will surround the spark plug under all operating conditions, the vapour fraction of the fuel may be introduced through the intake port into the vicinity of the spark plug to enhance the ignitability of the mixture.

Claims

1. A gasoline spark ignition internal combustion engine having two or more intake passages supplying combustion air to each engine cylinder and a flow control valve regulating the air flow along one of the passages to each engine cylinder, throttling of the air flow along the passage by the flow control valve during part load operation of the engine resulting in stratification of the intake charge in the combustion chamber of the cylinder with the gases flowing along the throttled passage remaining in the vicinity of a spark plug near the centre of the combustion chamber at the instant of spark ignition, wherein the engine includes a vapour extraction system for separating the gasoline fuel into a lighter vapour fraction and a heavier liquid fraction, and means are provided for introducing fuel from the vapour fraction into the intake passage throttled by the flow control valve to increase the concentration of the lighter fraction of the gasoline fuel in the vicinity of the spark plug at the instant of spark ignition.

2. An engine as claimed in claim 1, wherein means are provided for additionally supplying vapour to the intake passage throttled by the flow control valve by purging a canister storing vapours evaporated from a fuel storage tank of the engine.

3. An engine as claimed claim 1 or 2, wherein the engine has two or more intake ports per cylinder supplying separate respective intake valves, one of the intake ports being de-activated during part load operation by the flow control valve so that the other intake port creates a high swirl and radial charge stratification within the cylinder.

4. An engine as claimed claim 1 or 2, wherein the engine has two or more intake ports per cylinder supplying a common intake valve, one of the intake ports being de-activated by the flow control valve during part load operation so that the other intake port creates a high swirl within the cylinder.

5. An engine as claimed claim 1 or 2, wherein the engine has more than one intake valve per cylinder supplied by a common intake port, one side of the flow cross-section of the intake port passage being throttled by the flow control valve during part load operation to concentrate the air flow along the other side of the intake passage and thereby promote swirl and radial charge stratification within the cylinder.

6. An engine as claimed claim 1 or 2, wherein the air flow to one or more intake valves of each cylinder is supplied by three transversely spaced passages, the outer two passages being unthrottled and the central passage being throttled by the flow control valve, the air flows from all three passages being directed to flow into the combustion chamber parallel to a diameter of the cylinder bore thereby forming a sandwiched charge stratification.

7. An engine as claimed in any preceding claim, wherein means are provided for separately introducing the liquid fraction of the gasoline fuel into each combustion chamber by injection into an unthrottled intake passage of the cylinder.

8. An engine as claimed in any one of claims 1 to 6, wherein means are provided for separately introducing the liquid fraction of the gasoline fuel into each combustion chamber by injection directly into the combustion chamber.

9. An engine as claimed in any preceding claim, further comprising means for pre-conditioning the vapour fraction to increase its ignitability prior to its introduction into the intake air to the engine.

10. An engine as claimed in claim 9, wherein the preconditioning means include means for heating the vapour fraction in a heat exchanger.

11. An engine as claimed in claim 9, wherein the preconditioning means include means for mixing the vapour fraction with hot recirculated exhaust gases.

12. A gasoline spark ignition internal combustion engine constructed, arranged and adapted to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.