GB2445563A

GB2445563A - System for delivering stratified EGR in supercharged or turbocharged i.c. engines

Info

Publication number: GB2445563A
Application number: GB0700397A
Authority: GB
Inventors: Thomas Tsoi-Hei Ma
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-01-10
Filing date: 2007-01-10
Publication date: 2008-07-16
Also published as: GB0700397D0

Abstract

A boosted air stream containing little or no EGR is delivered via an air intake manifold 142 and intake ports 102 separately from a boosted gas stream containing a substantial quantity of EGR which is delivered via an EGR manifold 141 and swirl-producing ports 101. The two streams are delivered close to the intake ports 101, 102 such that there is insufficient time for the streams to mix fully in the cylinders before ignition. The pressure in the EGR manifold 141 is made the same as that in the air intake manifold 142 by means of a rotary gas exchanger having a rotating matrix 10 in a housing 14 and. The rotary gas exchanger has a first set 22, 22' of entry and exit ducts forming part of the engine exhaust duct 22 and a second set 24, 24' of entry and exit ducts forming part of the boosted EGR delivery duct. The matrix 10 is rotated at a sufficient speed for a substantial volumetric gas exchange to occur between the exhaust gas stream in the engine exhaust duct 22 and the boosted air stream in the boosted EGR delivery duct 24'.

Description

SYSTEM FOR DELIVERING STRATIFIED EGR IN A SUPERCHARGED OR

TURBOCHARGED IC ENGINE

Field of the invention

The present invention relates to a system for delivering, under boosted intake conditions, recirculated exhaust gases (herein called EGR) which is concentrated in a localised region of the combustion chamber of an internal combustion engine and is intentionally not well mixed with the intake air also delivered to the combustion chamber of the engine.

Background of the invention

It is known in naturally aspirated internal combustion engines to deliver EGR gases via an EGR manifold separately to each engine cylinder at close proximity to the intake port of each engine cylinder in order to produce stratified EGR within each combustion chamber of the engine. Because of the short distance between the EGR entry and the final destination within the combustion chaiber, there is insufficient time up to the time of ignition for the EGR to be fully mixed with the stream of intake air also supplied to the intake port of each engine cylinder separately via an air intake manifold. By intentionally directing the EGR stream and the air stream towards different parts of an intake port or towards separate different intake ports, the EGR gases may be urged to concentrate either near the centre of the combustion chamber or near the periphery of the combustion chamber according to different operational objectives intended by the engine designer. Examples of systems for delivering EGR in various stratification configurations in a naturally aspirated engine are described in GB2293862, GB2328716, W098/26175, W000/71881, US6073600 and GB2114660.

In all the above stratified EGR systems which rely on a higher exhaust gas pressure to drive the EGR gases into a lower intake air pressure, a problem could arises when the engine is supercharged or turbocharged with boosted air supplied to the intake ports in that the desired EGR may no longer be able to enter the intake ports or engine cylinders if the pressure in the engine exhaust system is the same as or lower than the increased boost pressure in the intake system. Indeed, the driving pressure difference along the EGR manifold could be reversed and boosted air could instead be forced to escape via the EGR manifold in the opposite direction towards the engine exhaust system. To overcome the problem, it would be necessary to throttle the engine exhaust system, increasing the exhaust back pressure well above the intake boost pressure, for the EGR to flow in the des red direction and in the desired quantities into the intake ports Throttling the exhaust however could cause severe inefficiencies in the engine and excessively high exhaust gas temperatures.

A common method of introducing GR into a boosted engine is to feed the EGR into the ambient air entry side of the air blower of the supercharger or turbocharger. But in this case, the EGR will be thoroughly mixed with the intake air, first within the air blower and then along the intake manifold over a long distance and time to the engine cylinders, making stratified EGR virtually impossible.

The exhaust emissions and combustion control benefits of homogeneously mixed EGR are well known but subjected to narrow operational limits. Stratified EGR could provide similar benefits in a more strategically localised manner over a wider operation envelope. Stratified EGR with boost could extend the benefits and operation envelope even further approaching full engine load conditions, hence the aim of the present invention for enabling stratified EGR efficiently, under supercharged or turbochargeci conditions.

Summary of the Lnvention

According to the present invention, there is provided a system for delivering stratified EGR to the combustion S chambers of a supercharged or turbocharged multi-cylinder internal combustion engine supplied with boosted air, wherein a boosted air stream containing little or no EGR and a boosted gas stream containing substantial quantity of EGR are delivered separately via a boosted air intake manifold and a boosted EGR manifold respectively to each engine cylinder at close proximity to the intake port/s of the cylinder such that there is insufficient time for the streams delivered from the respective manifolds to be fully mixed within the cylinder up to the time of ignition, and is wherein the boosted gas stream containing EGR i.s delivered by the boosted EGR manifold at substantially the same pressure as the boost pressure in the boosted air intake man fold by means of a rotary gas exchanger having a housing containing a rotating matrix and first and second sets of entry and exit ducts in the housing where the first set of entry and exit ducts forms part of an engine exhaust duct connecting an exhaust gas stream from the engine exhaust manifold through the housing and matrix to the ambient atmosphere and the second set of entry and exit ducts forms part of a boosted EGR delivery duct connecting another boosted air stream supplied from the same source as the boosted air intake manifold through the housing and matrix to the boosted EGR manifold, the gas exchanger also having means for rotating the matrix at a sufficient speed for a substantial volumetric gas exchange to occur between the exhaust gas stream in the engine exhaust duct and the latter boosted air stream in the boosted EGR delivery duct leading to the boosted EGR manifold.

The present invention is an extension of a co-pending patent application GB0609674.7 in which a rotary gas exchanger is connected to an internal combustion engine serving as an EGR dispenser. In GB0609674.7, the EGR is delivered to the intake system of the engine without relying on an EGR pipe or the presence of pressure drop to drive the EGR flow in the direction towards the intake system, making it particularly suitable for delivering EGR directly into the boost pressure of a supercharger or turbocharger. In this case, the EGR is automatically mixed with the intake air as they pass through the gas exchanger and the mixture enters the engine cylinders substantially in the form of homogeneously mixed EGR.

In the present invention, the rotary gas exchanger is used to isolate only the EGR manifold from the exhaust gas pressure of the engine and at the same time expose the EGR manifold to the boost pressure from the air blower of the supercharger or turbocharger of the engine which also supplies the boosted air intake manifold. Because the pressure in both the boosted EGR manifold and the boosted air intake manifold are substantially the same, there is little or no cross-over flow between the exit ends of the branches of the two manifolds even though they are interconnected within the intake port or within the engine cyJinder (where, had there been a pressure difference, sonic gases might flow out of one manifold branch and move upstream along the other manifold branch temporarily backfilling it which would defeat any subsequent stratification) . In the present invention the gas streams within the respective manifold branches would remain unique and are stationary outside each engine cylinder during the non-induction strokes of that cylinder until the time when they are moved at speed simultaneously towards the cylinder only during the induction stroke, with little chance of mixing between themselves until after they have entered the cylinder thus keeping their distinct and separate identities and flow momentums, and ensuring substantial stratification of one boosted stream from the other boosted stream within the combustion chamber up to the time of ignition.

With the distinct and separate identities of the gas streams residing in the outlet branches of the boosted EGR and boosted air manifolds, it is possible to design a boosted engine having different types of stratified EGR within the combustion chamber according to different operational objectives chosen intentionafly by the engine designer.

In one example type, each EGR manifold branch is directed towards an intake port and valve designed for producing good volumetric flow towards the centre of the engine combustion chamber while each boosted air intake manifold branch is directed towards another intake port and valve designed for producing high swirl around the periphery of the engine combustion chamber. In this case, the EGR will be mixed with the combustib1e charge and concentrated near the centre of the combustion chamber where it has the most influence on combustion, while the boosted air will be directed to fill the peripheral parL of the combustion chamber. This allows a smaller quantity of EGR to be used to produce a similar effect on exhaust emissions as would be with a larger quantity of homogeneously mixed EGR.

In another example type, each EGR manifold branch is directed towards an intake port and valve designed for producing high swirl around the periphery of the engine combustion chamber while each boosted air intake manifold branch is directed towards another intake port and valve designed for producing good volumetric flow towards the :30 centre of the engine combustion chamber. In this case, most of the EGP. will be directed to act as inert filler gases in the peripheral part of the combustion chamber where it has the least influence on combustion, while the combustible charge mixed with the boosted air will be concentrated near the centre of the combustion chamber. This allows large quantities of EGR to be delivered into the engine without adversely affecting the combustion stability of the engine.

Thus an engine may be developed capable of accepting a very large quantity of EGR, which consequently could enable the stratified EGR to be used to extend further the range of engine load control without throttling by "drive-by-exhaust" S described in another co-pending patent application GB0613090.O which is a further extension of the co-pending patent application GB0609674.7.

Finally, in having the option of stratified EGR, derived from the distinct and separate identities of the gas streams residing in the outlet branches of the boosted EGR manifold and the boosted air intake manifold according to the present invention, it would also be feasible to have a further option of providing the engine with well mixed EGR when required. This may be achieved by including in the system means to selectively reduce or stop the flow in the boosted air intake manifold so that the boosted EGR manifold will take over supplying to the engine substantially all the boosted air and boosted EGR which are homogeneously mixed as they pass through the rotary gas exchanger. In this case, the EGR system etfectively reverts to that described in the co-pending patent application GB0609674.7.

Brief description of the drawings

The invention will now be described further by way of example with reference to a single drawing which is a schematic view of a system for delivering stratified EGR in a turbocharged reciprocating internal combustion engine according to the present invention.

Detailed description of the preferred embodiment

Figure 1 shows a system for delivering stratified EGR to the combustion chamber of the turbocharged reciprocating internal combustion engine. The engine 100 has first and second intake ports 101, 102 opened and closed by respective poppet intake valves (101) (102) in the cylinder head of each cylinder of the engine. The first intake port 101 is a swirl producing port directing gases to swirl around the periphery of the combustion chamber and the second intake port 102 is a volumetric efficiency port directing gases to concentrate near the centre of the combustion chamber. The system comprises a boosted EGR manifold 141 and a boosted air intake manifold 142 supplied via a boosted EGR delivery duct 24' and a boosted air intake duct 42 respectively for delivering separate streams of gases to the first and the second intake ports and valves 101, 102 of the engine cylinders. An exhaust manifold 112 is connected to an exhaust duct 22 for discharging exhaust gases from the engine cylinders. The system further comprises a rotary gas exchanger having a housing 14 containing a rotating matrix 10, a first set of entry and exit ducts 22, 22' in the housing forming part of the engine exhaust duct connecting an exhaust gas stream from the engine through the housinq and matrix to the ambient atmosphere, and a second set of entry and exit ducts 24, 24' forming part of a boosted EGR delivery duct 24' connecting a boosted air stream supplied from the same source 124 as the boosted air intake manifold 142 through the housing and matrix to the boosted EGR manifold 141. The gas exchanger also has means for rotating the matrix 10 at a sufficient speed for a substantial volumetric gas exchange to occur between the exhaust gas stream in the engine exhaust duct 22 and the boosted air stream in the boosted EGR delivery duct 24' leading to the boosted EGR manifold 141.

In the invention, because the boosted EGR manifold 141 and the boosted air intake manifold 142 are connected to the same air source coming from the air blower 124, and because the EGR manifold 141 is isolated by the rotary gas exchanger 14, 10 from the gas pressure in the exhaust system 112, 122, 22, 22' of the engine, both manifolds 141, 142 will have substantially the same manifold pressure at all engine speeds and loads. As a consequence, there is little or no cross flow between the exit ends of the two manifolds 141, 142 where and when they are interconnected, such as where the intake ports 101, 102 are siamesed at the connection with the manifolds 141, 142, and when both the intake valves (101) (102) are open into the engine cylinder at the beginning of the induction stroke of that cylinder.

In Figure 1, a stream of gases containing substantial quantity of EGP. coming from the rotary gas exchanger 10, 14 enter the engine cylinders via the boosted EGR manifold 141 and the first intake valve (101), while another stream of boosted air containing little or no EGR enters the cylinders via the boosted air intake manifold 142 and the second is intake valve (102). Because the two manifolds 141, 142 are at substantlaily the same pressure so that there is little or no cross flow between the interconnected ends of each branch of the two manifolds 141, 142 leading to each engine cylinder, the two streams within the respective manifold branches would remain unique and are stationary outside each engine cylinder during the non-induction strokes of that cylinder until the time when they are moved at speed simultaneously towards the cylinder only during the induction stroke, with little chance of mixing between themselves until after they have entered the cylinder thus keeping their separate identities and flow momentums, and ensuring substantial stratification of one boosted stream from the other boosted stream within the combustion chamber up to the time of ignition.

In Figure 1, the swirl producing port 101 is a helical port designed to induce relatively high velocity and high angular momentum. The volumetric efficiency port 102 is a low restriction flow port designed to admit gases at relatively low velocity and low momentum. The intake ports 101, 102 may be separate and connected to the manifolds 141, 142 respectively as shown in Figure 1 Alternatively the intake ports may be siamesed upstream of the intake valves at the connection with the manifolds 141, 142 (not shown) The first and the second intake ports 101, 102, operating in combination with the distinct and separate identities of the gas streams residing in the outlet branches of the boosted EGR manifold 141 and the boosted air intake rnanifo]d 142 respectively, would produce stratified EGR where the stream containing EGR is directed to swirl around the periphery of the engine combustion chamber while the stream containing boosted air with little or no EGR is directed towards the centre of the engine combustion chamber. In this case, most of the EGR will be directed to act as inert filler gases in the peripheral part of the combustion chamber where it has the least influence on combustion, while the combustible charge mixed with the boosted air will be concentrated near the centre of the combustion chamber where the spark plug and/or fuel injector are usually located in the engine cylinder (not shown) This allows large quantities of EGP. to be delivered into the engine without adversely affecting the combustion stability of the engine.

Figure 1 shows the system for delivering stratified EGR in an engine supplied with boosted air from a turbocharger in which the air blower 124 is driven by an exhaust turbine 122. In the case of an engine supplied with boosted air from a supercharger, Figure 1 would still apply except there is no exhaust turbine and the air blower 124 is driven by the engine drive train or by an electric motor.

Claims

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1. A system for delivering stratified EGR to the combustion chambers of a supercharged or turbocharged multi-cylinder internal combustion engine supplied with boosted air, wherein a boosted air stream containing little or no GR and a boosted gas stream containing substantial quantity of EGR are delivered separately via a boosted air intake manifold and a boosted EGR manifold respectively to each engine cylinder at close proximity to the intake port/s of the cylinder such that there is insufficient time for the streams delivered from the respective manifolds to be fully mixed within the cylinder up to the time of ignition, and wherein the boosted gas stream containing EGR is delivered by the boosted EGR manifold at substantially the same pressure as the boost pressure in the boosted air intake manifold by means of a rotary gas exchanger having a housing containing a rotating matrix and first and second sets of entry and exit ducts in the housing where the first set of entry and exit ducts forms part of an engine exhaust duct connecting an exhaust gas stream from the engine exhaust manifold through the housing and matrix to the ambient atmosphere and the second set of entry and exit ducts forms part of a boosted EGR delivery duct connecting another boosted air stream supplied from the same source as the boosted air intake manifold through the housing and matrix to the boosted EGR manifold, the gas exchanger also having means for rotating the matrix at a sufficient speed for a substantial volumetric gas exchange to occur between the exhaust gas stream in the engine exhaust duct and the latter boosted air stream in the boosted EGR delivery duct leading to the boosted EGR manifold.