GB2535996A

GB2535996A - A low condensation LP EGR System

Info

Publication number: GB2535996A
Application number: GB1503333.5A
Authority: GB
Inventors: Gerald Barr William
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2015-02-27
Filing date: 2015-02-27
Publication date: 2016-09-07
Anticipated expiration: 2035-02-27
Also published as: DE102016102185A1; GB201503333D0; GB2535996B

Abstract

An exhaust gas recirculation (EGR) system 100 comprising a turbocharger compressor 14a and an annular EGR duct 40 disposed about an inlet to the compressor and being arranged to direct EGR gas into the compressor, wherein the duct is insulated and/or heated. The system may comprise a heater 52 disposed around at least a portion of the annular duct. EGR gas may be injected immediately upstream or downstream of the compressor inlet, or directly into the compressor housing. The annular duct may comprise openings 48 to introduce inlet air to be mixed with EGR gas prior to injection. Preferably the EGR gas can also be cooled so that the temperature of the gases in the annular duct can be regulated. Also claimed is a method of reducing condensation within an EGR system. The invention reduces the damage caused to the compressor blades by condensing droplets resulting from the mixing of hot exhaust gases with cooler inlet air and contact between exhaust gases and the walls of the duct upstream of the compressor.

Description

A LOW CONDENSATION LP EGR SYSTEM

Technical Field

The present disclosure relates to an exhaust gas recirculation system for a motor vehicle and is particularly, although not exclusively concerned with an exhaust gas recirculation system configured to reduce the level of condensation in reintroduced gases.

Background

Fuel efficiency and exhaust pollutant levels are viewed as increasingly important characteristics for all motor vehicles. This has lead to a very high proportion of vehicle engines being fitted with turbochargers which often incorporate an exhaust gas recirculation system. Exhaust gas recirculation (EGR) is a process used to improve engine efficiency and reduce the presence of NOx compounds in the emitted exhaust gases by recirculating a portion of the exhaust gases though the engine. In a low pressure EGR system the EGR gases are reintroduced upstream of the turbocharger compressor inlet. The pressure at this location is low, even in high engine boost conditions, which allows for the low pressure recirculation of the exhaust gases.

In addition to the exhaust gases, any unburnt gases which may have leaked from the engine cylinders into the engine crankcase can also be vented and added to the gases in the EGR system. This allows the crankcase pressure to be regulated as well as the unburnt fuel in the leaked gases to be returned to the engine cylinders for combusting.

EGR gases injected upstream of the turbocharger compressor are mixed with engine inlet air before entering the compressor. The amount of EGR gases which can be introduced may determine the extent to which engine efficiency and exhaust gas pollutant levels are improved. However, the level of recirculation possible is often limited by condensation of water droplets in the exhaust gases. As the exhaust gases are mixed with the cooler inlet air, water vapour begins to condense from the exhaust gases. This may be exacerbated in cold ambient conditions. Contact between the EGR gases and the walls of the duct upstream of the turbocharger compressor also contributes to the condensation. Water droplets can be undesirable at the inlet of the compressor, especially when large water droptets are formed, which may damage the compressor blades.

Statements of Invention

According to an aspect of the present disclosure there is provided an exhaust gas recirculation (EGR) system for a motor vehicle engine, the system comprising: a turbocharger compressor and an exhaust gas recirculation duct, comprising an annular duct around which EGR gases flow, the annular duct being disposed about an inlet to the turbocharger compressor and being arranged to direct the EGR gases into the turbocharger compressor, wherein the annular duct is insulated and/or heated, so as to reduce the likelihood of condensation forming as the EGR gases meet inlet air flowing into the turbocharger compressor inlet.

The system may further comprise a heater disposed around at least a portion of the annular duct. The heater may also be configured to cool the EGR gases.

The system may further comprise an insulating layer provided around at least a portion of the annular duct.

The annular duct may be configured such that the EGR oases, e.g. all EGR gases, are directed to flow through the annular duct. The annular duct may be configured such that the EGR gases are injected at an angle closely matching the angle of inlet air flow. By way of example, the angle may be between 0° and 5° relative to the direction of bulk inlet air flow.

The EGR gases may be introduced into the inlet duct immediately upstream of the compressor inlet. The EGR gases may be introduced into the inlet duct downstream of the compressor inlet. For example, the annular duct may be configured to inject EGR gases directly into the area of the compressor housing swept by the compressor blades.

The annular duct may further comprise openings configured to introduce inlet air into the annular duct to be mixed with the EGR gases prior to injection into the compressor.

A temperature sensor may be configured to monitor the temperature of the EGR gases in the annular duct. The temperature sensor may be operatively connected to the heater via a controller, such that the temperature of gases in the annular duct is regulated.

According to another aspect of the present disclosure there is provided an engine or motor vehicle comprising the system according to any of the previously mentioned aspects of the present disclosure.

According to another aspect of the present disclosure there is provided a method of reducing condensation within an exhaust gas recirculation system for a motor vehicle engine, the method comprising providing a turbocharger compressor and an exhaust gas recirculation duct comprising an annular duct disposed about an inlet to the turbocharger compressor; and insulating or heating the annular duct so as to reduce the likelihood of condensation forming as the EGR gases meet inlet air flowing into the turbocharger compressor inlet.

The method may further comprise measuring the temperature of recirculated exhaust gases and comparing the measured temperature with a target temperature.

The method may further comprise heating the recirculated exhaust gases if the temperature of the recirculated exhaust gases is below the target temperature.

The method may further comprise restricting the flow of recirculated exhaust gases if the temperature of the recirculated exhaust gases is below the target temperature.

Brief Description of the Drawings

For a better understanding of the present disclosure, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a schematic view of the air and exhaust paths in an engine with an EGR system according to examples of the present disclosure; Figure 2 is a schematic view of a turbocharger compressor inlet configured with a low pressure exhaust gas recirculation system according to one example of the present disclosure; and Figure 3 is a schematic view of a turbocharger compressor inlet configured with a low pressure exhaust gas recirculation system according to a second example of the present disclosure.

Detailed Description

With reference to Figure 1, a typical air path for an internal combustion engine 10 of a motor vehicle is described. Air may enter through an inlet 12 and then pass through an air filter 13 via an inlet duct 46. The air may be throttled by a valve 36 before being passed through a compressor 14a of a turbocharger 14. The turbocharger 14 may improve the engine power output and reduce emissions. Typically, the turbocharger 14 is arranged with an exhaust gas driven turbine 14b driving the compressor 14a mounted on the same shaft. A charge air cooler 16 may further increase the density of the air entering the internal combustion engine 10, thereby improving its performance. The air may then enter the internal combustion engine 10 via a throttle 18 configured to vary the mass flow of air into the internal combustion engine.

In a particular example of the present disclosure, the internal combustion engine 10 comprises a diesel engine, however it is equally envisaged that the engine 10 may be a spark ignition engine. As depicted in Figure 1, the internal combustion engine 10 may comprise a number of cylinders 10a-d and the air may flow into each of these cylinders at an appropriate time in the engine's cycle as determined by one or more valves (not shown).

The exhaust gases leaving the internal combustion engine 10 may pass through the turbine 14b of the turbocharger. One or more exhaust treatment modules 20 may be provided downstream of the turbine 14b, e.g. to reduce emissions from the engine exhaust. The exhaust treatment modules 20 may comprise one or more of an oxidation catalyst, e.g. a diesel oxidation catalyst, and a particulate filter, e.g. a diesel particulate filter. A further exhaust treatment module 21 may be provided, e.g. downstream of the exhaust treatment module 20.

A first exhaust gas recirculation loop 32 configured to selectively recirculate exhaust gases from the internal combustion engine 10 back into the internal combustion engine may also be provided. The first exhaust gas recirculation loop 32 may be provided about the engine 10 with exhaust gases leaving the engine 10 being recirculated to the air inlet of the engine 10. The first exhaust gas recirculation loop 32 may be diverted from the main exhaust flow path, e.g. at a point between the engine 10 and the turbine 14b of the turbocharger. The first exhaust gas recirculation loop 32 may comprise a first recirculation valve 34 which may control the amount of recirculation in the first exhaust gas recirculation loop 32.

A second exhaust gas recirculation loop 22 configured to selectively recirculate exhaust gases from the internal combustion engine 10 back into the internal combustion engine may also be provided. The second exhaust gas recirculation loop 22 may be provided about the turbocharger 14 such that exhaust gases leaving the turbine 14b may be recirculated into the inlet of compressor 14a. The second exhaust gas recirculation loop 22 may be diverted from the main exhaust flow path, e.g. upstream or downstream of the exhaust treatment module 20. Accordingly, the exhaust gases in the second exhaust gas recirculation loop 22 may be at a lower pressure than the exhaust gases in the first exhaust gas recirculation loop 32. The second exhaust gas recirculation loop 22 may comprise a second recirculation valve 24, which may control the amount of recirculation through the second exhaust gas recirculation loop 22.

Referring now to Figures 2 and 3, an exhaust gas recirculation system 100 according to an example of the present disclosure comprises the turbocharger compressor 14a and an exhaust gas recirculation duct 42. The exhaust gas recirculation duct 42 may carry low pressure gases from the second exhaust gas recirculation loop 22 to the compressor As depicted in Figures 2 and 3, the second exhaust gas recirculation loop 22 may further comprise an injection duct 40 which receives recirculated exhaust gases from the recirculation duct 42 and is configured to inject the exhaust gases into the compressor 14a. The injection duct 40 may comprise an annular duct and may form a fully or partially circumferential channel around which the exhaust gases can flow before entering the compressor. The injection duct 40 may be circumferentially (e.g. fully or partially) disposed about the inlet duct 46 which carries air to the turbocharger compressor 14a.

The injection duct 40 may be provided adjacent to the compressor 14a. The injection duct 40 may be integral with a compressor casing 44 and/or the inlet duct 46.

Alternatively the injection duct 40 may be provided as a separate component or assembly of components, which may couple to either the inlet duct 46 or the compressor casing 44 or both.

One or more openings 50 may permit flow from the injection duct 40 to the compressor 14a. The openings 50 may be provided in a wall defining the inlet duct 46 or the compressor casing 44. In one example, there may be one opening 50 which may be circumferentially arranged, e.g. forming a circumferential slot Alternatively, there may be a plurality of openings 50, which may be circumferentially distributed. Accordingly, the openings 50 may be disposed around the injection duct 40 to direct recirculated exhaust gases into the compressor 14a As depicted in Figure 2, the openings 50 may be positioned upstream, e.g. immediately upstream, of a compressor impeller 14a. However, as depicted in Figure 3, the openings 50 may be provided axially downstream of an impeller inlet, e.g. the annular duct may be configured to inject EGR gases directly into the area of the compressor housing swept by the compressor blades.

The openings 50 may also be configured, e.g. angled, such that the direction of the flow of exhaust gases leaving the injection duct 40 is closely matched to the flow of inlet gases arriving in the inlet duct 46. For example, the angle of exhaust gases introduced via the openings 50 may be between 0° and 5° relative to the direction of inlet gases flowing in the inlet duct 46.

The position and orientation of the openings 50 may be configured such that condensation of injected EGR gases may be minimised. The amount of EGR gases being introduced may also be increased. For example, the openings 50 may be positioned immediately upstream of the compressor and may be angled such that the direction of flow of the injected exhaust gases is closely matched to the flow of inlet gases in the inlet duct 46. The recirculated exhaust gases may be introduced in a manner which minimises the mixing of exhaust gases with the inlet air within the inlet duct 46 upstream of the compressor 14a. This may minimise heat transfer from the exhaust gases into the bulk inlet air flow and may reduce the amount of condensation The openings 50 may comprise a plurality of rows of openings with varying distances from the compressor inlet and/or varying angles at which recirculated exhaust gases are injected.

By way of example, the injection duct may be configured such that the hottest exhaust gases are injected through a first row of openings 50 which is positioned further upstream than a second row of openings. The hotter exhaust gases may act as a barrier between the bulk inlet air flow and cooler recirculated exhaust gases which are injected through the second row of openings. This may have the effect of reducing condensation from the cooler exhaust gases, which may reduce overall levels of condensation. This may be achieved by ducting the exhaust gases, which flow closest to the heater (described below), towards the first row of openings 50. Additionally or alternatively, the first row of openings 50 may be heated.

With reference to Figure 3, the injection duct 40 may further comprise one or more further openings 48, which are positioned to allow inlet gases in the inlet duct 46 to be introduced and mixed with the recirculated exhaust gases from the second exhaust gas recirculation loop 22 within the injection duct 40. The one or more further openings 48 may be circumferentially disposed, e.g. distributed. Full or partial mixing may take place within the injection duct 40 prior to the injection of the recirculated gases into the compressor 14a. The further openings 48 may be provided regardless of whether the openings 50 are provided downstream of the impeller inlet.

As depicted in Figure 3, the inside diameter of the injection duct 40 may be smaller than the outside diameter of the inlet duct 46, e.g. the injection duct 40 may be provided partially or fully within the inlet duct 46. When configured with the one or more further openings 48 this may be particularly beneficial, as gases flowing in the inlet duct 46 may impinge upon the injection duct 40. When arranged in this way, inlet air may readily enter the injection duct 40 through the one or more further openings 48.

When a suitable combination of openings 50 and further openings 48 are provided on the injection duct 40, the flow of inlet air may act to provide map width enhancement to the compressor 14a, allowing the compressor 14a to achieve a desired pressure ratio across a broader range of compressor mass flow values.

With continued reference to Figures 2 and 3, one or more heaters 52 may be provided about at least a portion of the injection duct 40. For example, the heaters may be configured to cover the full circumferential length of the injection duct 40. The heaters 52 may be formed from a heat exchanger. Accordingly, the heaters 52 may comprise a channel 62 around which a heated fluid is passed. The injection duct 40 may be in thermal communication with the channel 62. The injection duct 40 and the channel 62 may not however be in fluidic communication. The heated fluid may be introduced via an inlet 54 and may exit via an outlet 56.

The fluid in channel 62 may comprise a fluid already present within the engine, such as oil, coolant, inlet or exhaust gases, and the heater may form part of an existing circuit.

For example, the heater could form part of the engine oil or coolant circuits or the heater could itself be part of the exhaust system. Alternatively, air from the turbocharger compressor, e.g. from the compressor outlet, could be used within the heater. Alternatively, the heated fluid could be provided within the engine specifically for this application and comprise a separate heating circuit.

Alternative forms of heater are also envisaged, for example the heater 52 may comprise an electric heater which may comprise a plurality of filaments or elements, which become hot when an electric current is passed through them. The heater 52 may alternatively comprise any other heater known in the art.

The system 100 may comprise a portion with a high heat conductivity which is provided in contact with the injection duct 40, e.g. between the heater 52 and the injection duct 40. The system 100 may further comprise a heat insulating portion disposed on the opposite side of the heater 52 from the injection duct 40.

Additionally or alternatively to the heater 52, an insulating layer (not shown) may be provided about at least a portion the injection duct 40. The insulating layer may be configured to reduce heat being lost from the injection duct 40. The insulating layer may be circumferentially disposed, for example the insulating layer may fully or partially cover the outside surface of the injection duct 40. The insulating layer may be provided outside the wall of the injection duct 40 and the inlet duct 46.

In the embodiments shown, the heater 52 and/or insulating layer may increase the temperature of gases in the injection duct 40 from what they may have been otherwise, thereby reducing condensation and allowing increased levels of exhaust gas recirculation. The provision of the heater 52 and/or insulating layer may be especially beneficial in the example shown in Figure 3 in which the injection duct 40 comprises the further openings 48. In this example, the heater 52 can be used to vaporise any water droplets formed though condensation occurring during the mixing of EGR gases and inlet air, within the injection duct 40, prior to injection into the compressor inlet.

In certain circumstances, the temperature of the recirculated exhaust gases in the injection duct 40 may be higher than necessary to prevent condensation. The temperature of the recirculated exhaust gases may exceed the temperature of the heated fluid provided in the heater 52. In these circumstances it may be beneficial for the heater 52 to cool the exhaust gases rather than heating them. Cooling the recirculated gases may increases their density. This may allow more air and exhaust gas mixture to enter the engine cylinders 10a-d. The reduced temperature may also reduce the amount of NOx compounds produced in the subsequent combustion. This may be particularly useful in engine conditions where low levels of EGR are demanded and hence condensation levels are acceptable.

With further reference to Figures 2 and 3, a temperature sensor 58 may be provided within the injection duct 40 and may be configured to measure the temperature of the recirculated exhaust gases. Measurement of EGR gas temperature may be used to predict EGR condensation levels and may be used to vary EGR flow rate accordingly.

The temperature sensor 58 may be connected to the heater 52 via a controller (not shown). The system may thus be configured to maintain the EGR gases in the injection duct 40 at a predetermined target temperature. For example, the temperature of the EGR gases measured by the temperature sensor 58 may be compared to the target temperature. If the temperature of the EGR gases is lower than the target temperature, the heater 52 may be turned on. Alternatively or additionally, if the temperature of the EGR gases is lower than the target temperature, second recirculation valve 24, and/or another suitable valve, may be operated to restrict the flow of exhaust gases in the second exhaust gas recirculation loop 22, such that the heater 52 is able to maintain the recirculated exhaust gases at the target temperature.

In this case, if desirable, the heater 52 may be permanently turned on, and/or it may be controlled separately.

A temperature sensor 60 may also or alternatively be provided to measure the temperature of the heated fluid within heater 52, if present.

It will be appreciated by those skilled in the art that although the invention has been described by way of example, with reference to one or more examples, it is not limited to the disclosed examples and that alternative examples could be constructed without departing from the scope of the invention as defined by the appended claims.

Claims

Claims 1. An exhaust gas recirculation (EGR) system for a motor vehicle engine, the system comprising: a turbocharger compressor; and an exhaust gas recirculation duct, comprising an annular duct around which EGR gases flow, the annular duct being disposed about an inlet to the turbocharger compressor and being arranged to direct the EGR gases into the turbocharger 10 compressor; wherein the annular duct is insulated and/or heated, so as to reduce the likelihood of condensation forming as the EGR gases meet inlet air flowing into the turbocharger compressor inlet.
2. The exhaust gas recirculation system of claim 1, further comprising a heater disposed around at least a portion of the annular duct.
3. The exhaust gas recirculation system of claim 1 or 2, further comprising an insulating layer provided around at least a portion of the annular duct.
4. The EGR system according to any of the preceding claims wherein the annular duct is configured such that the EGR gases are directed to flow through the annular duct.
5. The EGR system according to any of the preceding claims, wherein the annular duct is configured such that the EGR gases are injected at an angle closely matching the angle of inlet air flow.
6. The EGR system according to claim 5, wherein the angle is between 0° and 5° relative to the direction of bulk inlet air flow.
7. The EGR system according to any of the preceding claims, wherein EGR gases are introduced into the inlet duct immediately upstream of the compressor inlet.
8. The EGR system according to any of the preceding claims, wherein EGR gases are introduced into the inlet duct downstream of the compressor inlet.
9, The EGR system according to any of the preceding claims, wherein the annular duct is configured to inject EGR gases directly into the area of the compressor housing swept by the compressor blades.
10. The EGR system according to any of the preceding claims, wherein the annular duct further comprises openings configured to introduce inlet air into the annular duct to be mixed with the EGR gases prior to injection into the compressor.
11. The EGR system according to any of the preceding claims when dependent on claim 2, wherein the heater is also configured to cool the EGR gases.
12. The EGR system according to any of the preceding claims, wherein a temperature sensor is configured to monitor the temperature of the EGR gases in the annular duct.
13. The EGR system according to claim 12 when dependent on claim 2, wherein the temperature sensor is operatively connected to the heater via a controller, such that the temperature of gases in the annular duct is regulated.
14. An engine or motor vehicle comprising the EGR system according to any of the preceding claims.
15. An exhaust gas recirculation system, engine or motor vehicle substantially as described herein with reference to and as shown in Figures 2 and 3.
16. A method of reducing condensation within an exhaust gas recirculation system for a motor vehicle engine, the method comprising: providing a turbocharger compressor and an exhaust gas recirculation duct comprising an annular duct disposed about an inlet to the turbocharger compressor; and insulating or heating the annular duct so as to reduce the likelihood of condensation forming as the EGR gases meet inlet air flowing into the turbocharger compressor inlet.
17. The method of claim 16, further comprising: measuring the temperature of recirculated exhaust gases; and comparing the measured temperature with a target temperature.
18. The method of claim 17, further comprising: heating the recirculated exhaust gases if the temperature of the recirculated exhaust gases is below the target temperature.
19. The method of claim 17 or 18, further comprising: restricting the flow of recirculated exhaust gases if the temperature of the recirculated exhaust gases is below the target temperature.
20. A method of reducing condensation within recirculated exhaust gases substantially as described herein and with reference to the Figures 2 and 3.Amendement to the claims have been filed as follows Claims 1. An exhaust gas recirculation (EGR) system for a motor vehicle engine, the system comprising: a turbocharger compressor; and an exhaust gas recirculation duct, comprising an annular duct around which EGR gases flow, the annular duct being disposed about an inlet to the turbocharger compressor and being arranged to direct the EGR gases into the turbocharger 10 compressor; wherein the annular duct is insulated and/or heated, so as to reduce the likelihood of condensation forming as the EGR gases meet inlet air flowing into the turbocharger compressor inlet.1.0 15 2. The exhaust gas recirculation system of claim 1, further comprising a heater disposed around at least a portion of the annular duct. C\13 The exhaust gas recirculation system of claim 1 or 2, further comprising an insulating layer provided around at least a portion of the annular duct a) 20 4. The EGR system according to any of the preceding claims, wherein the annular duct is configured such that the EGR gases are injected at an angle closely matching the angle of inlet air flow.5. The EGR system according to claim 4, wherein the angle is between 0° and 5° relative to the direction of bulk inlet air flow.6. The EGR system according to any of the preceding claims, wherein EGR gases are introduced into the inlet duct immediately upstream of the compressor inlet.7. The EGR system according to any of the preceding claims, wherein EGR gases are introduced into the inlet duct downstream of the compressor inlet.8. The EGR system according to any of the preceding claims, wherein the annular duct is configured to inject EGR gases directly into the area of the compressor housing swept by the compressor blades.9. The EGR system according to any of the preceding claims, wherein the annular duct further comprises openings configured to introduce inlet air into the annular duct to be mixed with the EGR gases prior to injection into the compressor.10. The EGR system according to any of the preceding claims when dependent on claim 2, wherein the heater is also configured to cool the EGR gases.11. The EGR system according to any of the preceding claims, wherein a temperature sensor is configured to monitor the temperature of the EGR gases in the annular duct.12. The EGR system according to claim 11 when dependent on claim 2, wherein the temperature sensor is operatively connected to the heater via a controller, such that the temperature of gases in the annular duct is regulated.CO preceding claims.13. An engine or motor vehicle comprising the EGR system according to any of the 14. An exhaust gas recirculation system, engine or motor vehicle substantially as described herein with reference to and as shown in Figures 2 and 3.15. A method of reducing condensation within an exhaust gas recirculation system for a motor vehicle engine, the method comprising: providing a turbocharger compressor and an exhaust gas recirculation duct comprising an annular duct disposed about an inlet to the turbocharger compressor; 30 and insulating or heating the annular duct so as to reduce the likelihood of condensation forming as the EGR gases meet inlet air flowing into the turbocharger compressor inlet.16 The method of claim '15, further comprising: measuring the temperature of recirculated exhaust gases; and comparing the measured temperature with a target temperature.17 The method of claim 16, further comprising: heating the recirculated exhaust gases if the temperature of the recirculated exhaust gases is below the target temperature.18. The method of claim 16 or 17, further comprising: restricting the flow of recirculated exhaust gases if the temperature of the recirculated exhaust gases is below the target temperature.19. A method of reducing condensation within recirculated exhaust gases substantially as described herein and with reference to the Figures 2 and 3.