GB2298896A

GB2298896A - I.c.engine cylinder charge stratification

Info

Publication number: GB2298896A
Application number: GB9505367A
Authority: GB
Inventors: Thomas Tsoi-Hei Ma
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1995-03-17
Filing date: 1995-03-17
Publication date: 1996-09-18
Also published as: WO1996029512A1; GB9505367D0

Abstract

At least three intake port channels 112, 113 and 122 per cylinder introduce gases of different composition into the combustion chamber 102. The channel 122 supplies a fuel and air mixture, the channel 112 supplies predominantly air and the channel 113 supplies EGR gases. The channels and the combustion chamber 102 are such as to create within the combustion chamber a stratified charge comprising three distinct regions made up of gases entering by way of the three channels. One of the regions containing air or EGR gases serves to separate the region containing the fuel and air mixture from the other of the regions containing EGR gases or air. The channels, the passages supplying the channels and the valved ports opening to the combustion chamber may take various forms (Figs. 2 to 6) to provide different forms of stratification within the combustion chamber.

Description

Intake System for an Internal Combustion Engine Field of the invention The present invention relates to an intake system for a stratified charge, spark ignition, internal combustion engine having multiple intake port channels in each cylinder.

Background of the invention British Patent Application No. 9425312.7 discloses an intake system for an engine having two intake valves per cylinder and separate intake ports leading to each valve, in which fuel is introduced only into a first of the intake ports and the two ports are designed to produce a radially stratified charge with the fuel concentrated in the centre of the combustion chamber.

The gases introduced into the outer annular region of the combustion chamber through the second, non-fuelled, port can be either air or EGR (exhaust gas recirculation) gases. If EGR gases are fed in through the second port, there will inevitably occur some mixing at the interface between the two gas flows which will result in fuel finding itself surrounded by EGR gases and consequently being unable to burn completely.

Object of the invention The present invention therefore seeks to provide an engine having a stratified charge in which mixing can be prevented between two regions of the stratified charge.

Summary of the invention According to the a first aspect of the present invention, there is provided a multi-cylinder internal combustion engine having at least three intake port channels per cylinder, gases of different composition being introduced through the individual channels into the combustion chambers, a first channel supplying a fuel and air mixture, a second supplying predominantly air and a third supplying EGR gases, wherein the design of the ports and the combustion chambers is such as to create within the combustion chamber a stratified charge comprising three distinct regions made up of gases entering by way of the three channels, one of the regions containing air or EGR gases serving to separate the region containing the fuel and air mixture from the other of the regions containing EGR gases or air, respectively.

Thus, in its broadest aspect, the invention provides three layer stratification within the combustion chamber with one region sandwiched between two others to prevent the gases in these other regions from mixing with one another.

Stratification is achieved by controlled flow of the gases from the different port channels so that they do not mix homogeneously with one another in the combustion chamber.

The controlled flow may be designed to produce swirl so that the gases rotate about the axis of the cylinder and create a radially stratified charge made up of concentric rings.

Alternatively, the controlled flow may be designed to produce tumble so that the gases rotate about an axis normal to the cylinder axis and remain in the same axial plane as they rotate so as to produce a layered structure across the width of the cylinder. This will hereinafter be termed vertical stratification as it comprises a sandwich of vertical layers (assuming the cylinder axis is vertical). In this case, a five layer sandwich is required that has a symmetrical composition about the central plane of the cylinder.

With a vertically stratified charge, if the velocity of the gases in the outer layers is significantly greater than the velocity in the central layer, the outer layers will tend to wrap around the central layer at the point on the perimeter of the combustion chamber furthest from the intake valves and on tumbling will envelope the central layer on all sides thereby producing a third form of stratification, herein termed envelope stratification, that can be likened to a sausage roll. Thus, for example, when the central layer is formed of a fuel and air mixture and the outer layers are EGR gases, a parcel is produced consisting of a horizontal cylinder of fuel and air enveloped all around in EGR gases.

In the present invention, it is possible to arrange for the central layer to be horizontally split on entering the combustion chamber so as to produce an inner horizontal cylinder of fuel and air mixture, a concentric outer hollow cylinder containing air only, the two concentric horizontal cylinders being totally enveloped in an outer layer of EGR gases.

The fuel and air mixture should occupy the central region of the combustion chamber so that it may be readily ignited by a spark plug positioned centrally in the cylinder head.

In one port configuration, it is possible to arrange for the fuel and air mixture to be separated by an air region from the or each region containing EGR gases.

In an alternative port configuration, it is possible to arrange for the fuel and air mixture to be separated by an EGR region from the or each region containing predominantly air.

According to a second aspect of the invention, there is provided an intake system for a multi-cylinder internal combustion engine having two intake valves per cylinder and separate intake ports leading to each valve, having means for injecting fuel only into the ports leading to the first intake valves and wherein the ports leading to the other intake valves are each partitioned to define two channels connected to different intake manifold branches supplying air and EGR gases respectively, the ports and the partitions being designed such that a radially stratified charge is created in each combustion chamber with the fuel containing gases concentrated in the central region of the combustion chamber and with the gases drawn in from the different port channels through the second intake valve lying in two concentric annular regions surrounding the central fuel-rich region.

This aspect of the invention differs from the proposal contained in GB-A-9425312.7 in that the second port is partitioned so that the resulting stratified charge will essentially contain three layers instead of two. The middle layer will act as a separating layer effectively preventing the gases in the central region from mixing with the gases near the cylinder wall.

Thus if EGR gases are drawn in near to the cylinder wall, the middle layer may consist only of air. Mixing between the air and the fuel-rich gases in the central region will not have any serious consequence as the fuel will still be able to burn fully. Likewise mixing between the air and the EGR gases will not degrade the combustion quality. Thus the three layer stratification will provide more robust combustion under all conditions by gradually varying the proportions of the gases contained in the three concentric gas flows.

Three layer stratification can also be used to advantage in a different way to achieve other advantages when starting an engine having an exhaust gas ignition (EGI) system. In an EGI system, an engine is overfuelled to produce hydrogen in the exhaust gases. Additional air that has not taken part in the combustion process is added to the exhaust gases and the resulting mixture is ignited in an afterburner to heat the catalytic converter and bring it rapidly to its lightoff temperature. After EGI, to prevent the converter from cooling down, the engine is overfuelled to a lesser extent and supplied with bypass air so that an exothermic catalytic reaction may take place in the converter to maintain the catalyst above its light-off temperature.

Hitherto, the additional air has needed to be injected by a special air pump directly into the exhaust system and this has added to the cost and the bulk of EGI systems. However, using three layer stratification, the invention can effectively divide a combustion chamber into regions containing air and regions having a very rich mixture while preventing these two regions from contacting each other until after the gases leave the combustion chamber. In this case, the additional air would be introduced near the cylinder wall and either EGR gases, or gases containing a stoichiometric mixture of fuel and air and exhaust gases can be introduced as the intermediate layer to prevent the excess fuel in the central region finding the excess air in the radially outermost region.

According to a third aspect of the invention, there is provided an intake system for a multi-cylinder internal combustion engine having three intake valves per cylinder and separate intake ports leading to each valve, having means for injecting fuel only into the ports leading to the central intake valves and wherein the ports leading to the other two outer intake valves are each partitioned to define two channels connected to different intake manifold branches supplying air and EGR gases respectively, the ports and the partitions being designed such that a five layer vertically stratified charge is created in each combustion chamber with the fuel containing gases concentrated in the middle layer at the centre of the chamber and with the gases drawn in from the different port channels through the other two intake valves lying in parallel layers that are symmetrically disposed one pair to each side of the middle layer.

If the same port is partitioned into two channels, one containing air and one EGR gases, it is important to provide a non-return valve in the channel containing air in order to prevent that channel from being back filled with EGR gases while the associated valve is closed.

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 is a schematic representation of part of an intake system for introducing gases of different composition through three different intake port channels into a combustion chamber in order to produce a multi-layered stratified charge.

Figure 2 is a schematic diagram of the part of the intake system associated with only one cylinder of a multicylinder engine, the intake system being designed to achieve a radially stratified charge capable of high percentage dilution with EGR gases.

Figure 3 is a view generally similar to Figure 2 of a further embodiment of the intake system by appropriate switching of the various flow channels which can be used either to achieve high EGR dilution rates or to produce simultaneously air and combustible products in the exhaust system to assist in heating a catalytic converter, Figure 4 is a view generally similar to Figures 2 and 3 of a cylinder having three intake valves in which the port design is intended to promote tumble rather than swirl in the combustion chamber and thereby achieve a vertically stratified rather than radially stratified charge in the combustion chamber, Figure 5 is a view generally similar to Figures 2 to 4 of a cylinder having a single intake valve in which the port design is intended to promote radial stratification, and Figure 6 is a view generally similar to Figures 2 to 5 of a cylinder having two intake valves in which the port design is intended to promote envelope stratification.

Detailed description of the drawings In Figure 1 there is shown schematically an combustion chamber 102 with a centrally located spark plug 108. The valves of the cylinder are not shown but the part of the intake system leading to the valves can be seen to define three distinct intake port channels designated 122, 112 and 113 respectively. The channels 122 and 112 are both supplied with air from an intake manifold 116 containing an intake throttle 129. The total amount of air entering the combustion chamber is measured by an air mass flow meter 130 which is connected to an electronic control unit 132 that controls a fuel injector 128 according to a predetermined calibration to meter fuel only into the air passing through the port channel 122.The port channel 113 is connected to an EGR pipe that contains å valve 117 to regulate the proportion of EGR gases in the combustion chamber.

The gas streams of different composition are differently shaded in the drawing and it can be seen that the light grey shaded gas flow stream from the channel 122 is directed towards the spark plug 108, the dark grey shaded EGR gas flow stream from the channel 113 is directed to one side of the spark plug, and the unshaded air flow stream from the channel 112 is sandwiched between the two and acts to keep them apart.

Gas flow streams entering in this way can be used to produce either a radially stratified charge or a vertically stratified charge depending on the detail design of the intake valves and the intake ports as will be described in more detail below. The shape of the combustion chamber and in particular the piston crown also influence the gas flow and can be optimised for these different types of stratification.

In Figure 2 there is shown the intake port design required to achieve a radially stratified charge in an engine having two intake valves per cylinder. The drawing shows a combustion chamber 202 of a multicylinder engine having a centrally located spark plug 208, two exhaust valves 204 and 206, and two intake valves 210 and 220. The intake valve 220 is supplied with fuel and air by an intake port 222 that contains a fuel injector 228 and leads by way of the intake manifold branch 216a to the intake throttle 229 of the intake manifold 216. The intake port of the intake valve 210 is divided by a partition 211 into two channels 212 and 213.The channel 212 is connected to the branch 216a of the intake manifold by way of a non-return valve 218 while the channel 213 is connected to a manifold 215 to which exhaust gases are recirculated by way of a regulating valve 217 arranged in a EGR pipe leading from the EGR manifold to the exhaust system.

The intake port 222 and the channels 212 and 213 are all directed tangentially to promote swirl in the combustion chamber. The piston crown is also shaped to promote swirl in the same direction. The gases entering from the three channels therefore produce a radially stratified charge consisting of a central region containing the fuel and air mixture from the intake port 222, surrounded first by an air region entering through the channel 212 and next by an outer EGR region entering via the channel 213.

The overall air to fuel ratio in the combustion charge can be stoichiometric or lean. If a stoichiometric mixture is used then a three-way catalytic converter may be employed in the exhaust system. The EGR gases do not in this case interfere with the combustion process and act merely to reduce the air volumetric efficiency of the engine by filling a proportion of the combustion chamber with essentially inert gases. The engine can therefore be run with reduced throttling under part load operation to avoid air pumping losses. The proportion of EGR gases can be gradually reduced to increase the power output of the engine until at full load the Ego gases are totally discontinued.

The advantage of the three layer stratification achieved by sandwiching a layer of air between the fuel and air mixture and the EGR gases is that fuel is prevented from mixing with the EGR gases directly and finding itself in pockets having insufficient oxygen for it to burn completely. In this way hydrocarbon emissions in the exhaust gases can be reduced.

The arrangement described in Figure 3 has many items in common with that of Figure 2 and to avoid unnecessary repetition of the description the same reference numerals have been used but falling within the 300 series rather than the 200 series. The important difference between Figures 2 and 3 resides in the fact that by means of an arrangement consisting of valves 325, 327, 325a and 327a, the positions of the air and EGR regions in the stratified charge can be interchanged. With the valves in the illustrated position, EGR gases are introduced into the channel 312 and air is introduced through the channel 313 whereas if all these valve rotated to their other positions, the gas flows will be no different from that previously described with reference to Figure 2.

Forming in this way a radially stratified charge in which a central fuel and air mixture is isolated from further air by a ring of EGR gases means that one can ensure in an engine having an overall stoichiometric mixture that the combustion in the central region will be incomplete and will supply hydrocarbons to the exhaust gases at the same time as unconsumed oxygen is supplied to the exhaust gases from the outer ring. These combustion products can now be reacted with one another outside the engine to create in the exhaust system exothermic reaction for heating the catalytic converter.In an extreme case of charge separation, it is possible to achieve an exhaust mixture which is ignitable in an afterburner for initial heating of the catalytic converter whereas less degree of charge separation can be used to produce a mixture that is not ignitable but will nevertheless react in a partly active catalytic converter to maintain a high temperature under certain conditions such as warm up and prolonged idling. The position of the valves illustrated is therefore only useful for catalyst warm up and once light-off is achieved the valves can be switched to allow system to operate in the manner previously described in Figure 2.

Figure 3 also shows how additional steps may be taken to improve the swirl. While the introduction of gases tangentially through the intake port channels 311 and 312 automatically ensures air rotation about the axis of the cylinder, the gases entering through valve 320 should ideally be rotating as the same speed to avoid turbulence at the interface between the different streams. To achieve swirl of the gases drawn in through the port 322, it is possible to provide vanes 323 on the head of the valve to promote the formation of a vortex as the gas leaves the valve. A further possibility illustrated in Figure 3 is to create a vortex in the gas flow even before it reaches the valve 320 by drawing in air from upstream of a throttle 326 and introducing it tangentially to the wall of the port 322 through a pipe 324.The pressure drop that is created by the throttle 326 causes the flow in the pipe 324.

In Figures 2 and 3, a partitioned port has been used in which one side contains air and the other side contains EGR gases. In such a configuration it is possible, in the absence of a non-return valve such as the valves 218 and 318, for the air channel to be back filled with EGR gases during the time when the associated intake valve is closed.

It is for this reason that the non-return valves are provided in the embodiment described.

Figure 4 is a further embodiment designed to produce a five layer vertical stratification with a tumbling charge rather than a swirling charge. The reference numerals is this case lie in the 400 series and like reference numerals are again used to designate like components. The cylinder is this case has three intake valves, two being designed 410 and the third being designed 420. The intake valves 410 together with their partitioned intake port channels 412 and 413 are symmetrically disposed about the valve 420 and each side behaves in a manner entirely analogous to the valve 210 and 310 previously described by reference to the previous embodiments.The difference resides essentially in that the gas flows are not this time directed tangentially but diametrically forwards so that they create five tumbling layers across the width of the combustion chamber, the central layer is located in the vicinity of the spark plug 408 and is flanked by two air layers which separates the fuel containing central region from two further regions consisting of EGR gases.

Referring now to Figure 5 and retaining the same approach to the allocation of reference numerals, there is shown a cylinder 502 having a single large intake valve 510, an exhaust valve 506 and a spark plug 508. The intake valve 510 has two intake ports leading to it, a first port 522 being the port through which air and fuel are introduced into the combustion chamber, the fuel injector 528 being positioned within this port. The other port is divided by a partition 511 into two channels 512 and 513, the channel 512 being for air and the channel 513 being connected to an EGR manifold 515 having a control valve 517.

The essential difference between this embodiment and that of Figure 2 resides in the fact that the cylinder has only a single intake valve thereby allowing the possibility for the air and fuel channel 522 to communicate directly with the EGR channel 513. For this reason it is in this case necessary to provide a further one-way valve 518a which act in the same way as the one-way valve 518 to prevent back filling with EGR gases. Though separate valves 518a and 518 are shown for the port 522 and the channel 512 respectively, these may be combined into a single one-way valve positioned further upstream.

The engine of Figure 6 is one designed to promote envelope stratification which is desirable during low load operation when the volume of EGR gases is significantly greater than the volume of the fuel and air mixture. This embodiment has a cylinder 602 with two exhaust valves 604 and 606, two intake valves 610 and 620 and a spark plug 608. Two separate ports lead to the intake valves, both of the ports having a central vertical partition 611 dividing the port into two channels. The two central channels 612 are connected to the air and fuel intake manifold branch 622 whereas the two outer channels 613 are connected to an EGR manifold 615. Once again because of the risk of EGR back flow a one-way valve 618 is used in the air intake branch.

Three layer stratification is achieved in this embodiment by horizontally partitioning the channels 612, that is to say in the plane of the paper, and directing the fuel spray from the fuel injector 628 below the horizontal partition so that the air entering the combustion chamber through the channels 612 is vertically stratified with the fuel and air mixture stream being located below the air stream. When these two streams tumble in the combustion chamber, the air is wrapped around the fuel and air mixture to form a cylinder within which the fuel is concentrated in the centre. The EGR gases drawn in from the channels 613 envelopes this cylindrical charge on all sides under low load conditions. In this case it is desirable to extend the tip of the spark plug to be able to reach the ignitable region of the charge.

From the description of Figure 6, it will be appreciated that the same advantage of envelope stratification at low load can be achieved in the embodiment of Figure 4 by providing a horizontal partition in the intake port 422 leading to the central intake valve. Such an embodiment will achieve three layer stratification in all planes and thereby optimise the separation of the fuel from the EGR gases under all operating conditions.

The various manifolds described above as EGR manifolds do not obstruct the intake valve area because they only act to supply EGR gases to the combustion chamber under low load conditions. At high load when the EGR valve is closed, the EGR manifold acts only to transfer air between cylinders and the normal breathing of the intake port is unimpaired.

During intermediate load conditions, air and fuel can be drawn into the EGR manifolds 215 - 515 and if allowed to mix with EGR gases there will be a risk of fuel becoming trapped in pockets of EGR gases. To mitigate this problem, one can avoid operating under such conditions by fully shutting off the EGR gases once a certain load limit is reached.

Alternatively, as shown in'Figure 6, one may lengthen the branches 615a of the EGR manifold leading to the intake valves 610 so that within these branches 615a a stratified column may be stored in which the fuel and air mixture remains separate from the EGR gases in the plenum 615 of the EGR manifold. These gases are later admitted sequentially into the combustion chamber when the intake valve 610 opens.

While the provision of a one-way valve in the air channel may have disadvantages at wide-open-throttle by interfering with the normal breathing of the engine, it provides significant advantages during idling, in particular in the embodiments described in Figure 5 and 6. Under idle conditions, the amount of internal EGR is so great that one needs to close the external EGR supply. In this context it should be explained that internal EGR refers to exhaust gases entering the intake system directly during the valve overlap period. The advantage of the one-way valves 518 and 618 in this mode of operation is that they prevent the internal EGR gases from entering the fuel and air supply channels 522 and 622, and divert the EGR gases for storage in the EGR channels 513 and 613.When the intake charge enters the combustion chamber, the internal EGR gases would be stratified in just the same way as has been described with reference to the external EGR gases. This improves the purity of the ignitable mixture which directly affects idling quality.

In the case of the embodiments of Figures 2, 3 and 4, stratified internal EGR for improved idling can be achieved in the absence of one-way valves in the channels 222, 322, and 422 by setting the timing of the intake valves 210, 310, 410 such that they open earlier than the other intake valves 220, 320 and 420.

The various embodiments of the invention that have been described are all capable of running at all times with an overall stoichiometric mixture so that a three-way catalyst may be used in the exhaust system. The proportion of the EGR under low load conditions can be much greater than normally contemplated because of the effect of stratification that avoids dilution of the combustible charge. As well as permitting high efficiency of conversion of all three pollutants (HC, CO and NOx) in the exhaust gases by the three-way catalyst, the high percentage of EGR reduces pumping losses and improves fuel economy under low load conditions.

Claims

1. A multi-cylinder internal combustion engine having at least three intake port channels per cylinder, gases of different composition being introduced through the individual channels into the combustion chambers, a first channel supplying a fuel and air mixture, a second supplying predominantly air and a third supplying EGR gases, wherein the design of the ports and the combustion chambers is such as to create within the combustion chamber a stratified charge comprising three distinct regions made up of gases entering by way of the three channels, one of the regions containing air or EGR gases serving to separate the region containing the fuel and air mixture from the other of the regions containing EGR gases or air, respectively.

2. A multi-cylinder internal combustion engine as claimed in claim 1, wherein stratification is achieved by controlled flow of the gases from the different port channels so that they do not mix homogeneously with one another in the combustion chamber, the controlled flows being designed to produce radial stratification as herein defined.

3. A multi-cylinder internal combustion engine as claimed in claim 1, wherein stratification is achieved by controlled flow of the gases from the different port channels so that they do not mix homogeneously with one another in the combustion chamber, the controlled flows being designed to produce vertical stratification as herein defined.

4. A multi-cylinder internal combustion engine as claimed in claim 1, wherein stratification is achieved by controlled flow of the gases from the different port channels so that they do not mix homogeneously with one another in the combustion chamber, the controlled flows being designed to produce envelope stratification as herein defined.

5. A multi-cylinder internal combustion engine as claimed in any preceding claim, wherein the fuel and air mixture occupies the central region of the combustion chamber.

6. A multi-cylinder internal combustion engine as claimed in any preceding claim, wherein the port configuration results in the fuel and air mixture being separated by an air region from the or each region containing EGR gases.

7. A multi-cylinder internal combustion engine as claimed in any of claims 1 to 5, wherein the port configuration results in the fuel and air mixture being separated by an EGR region from the or each region containing predominantly air.

8. An intake system for a multi-cylinder internal combustion engine having two intake valves per cylinder and separate intake ports leading to each valve, having means for injecting fuel only into the ports leading to the first intake valves and wherein the ports leading to the other intake valves are each partitioned to define two channels connected to different intake manifold branches supplying air and EGR gases respectively, the ports and the partitions being designed such that a radially stratified charge is created in each combustion chamber with the fuel containing gases concentrated in the central region of the combustion chamber and with the gases drawn in from the different port channels through the second intake valve lying in two concentric annular regions surrounding the central fuel-rich region.

9. An intake system as claimed in claim 8, wherein EGR gases are drawn into the combustion chamber to lie near to the cylinder wall and the middle layer comprises predominantly air.

10. An intake system as claimed in claim 8, operative to produce a gaseous mixture in the exhaust system containing combustible components, wherein air is drawn into the combustion chamber to lie near to the cylinder wall and the middle layer comprises predominantly EGR gases.

11. An intake system for a multi-cylinder internal combustion engine having three intake valves per cylinder and separate intake ports leading to each valve, having means for injecting fuel only into the ports leading to the central intake valves and wherein the ports leading to the other two outer intake valves are each partitioned to define two channels connected to different intake manifold branches supplying air and EGR gases respectively, the ports and the partitions being designed such that a five layer vertically stratified charge is created in each combustion chamber with the fuel containing gases concentrated in the middle layer at the centre of the chamber and with the gases drawn in from the different port channels through the other two intake valves lying in parallel layers that are symmetrically disposed one pair to each side of the middle layer.

12. An intake system as claimed in any preceding claim, wherein the same port is partitioned into two channels of which one channel contains EGR gases, and wherein a nonreturn valve is provided in the other channel in order to prevent said other channel from being back filled with EGR gases while the associated intake valve is closed.

13. An intake system constructed, arranged and adapted to operate substantially as herein descried with reference to and as illustrated in the accompanying drawings.