GB2215645A

GB2215645A - Separator for IC engine exhaust system

Info

Publication number: GB2215645A
Application number: GB8806326A
Authority: GB
Inventors: Peter Stanley Robertson
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1988-03-17
Filing date: 1988-03-17
Publication date: 1989-09-27
Also published as: GB8806326D0

Abstract

Particulates are removed from exhaust gas, particularly diesel engine exhaust, by passing the gas through a cyclone (10). The cyclone has a variable area entry passage, and the area of the entry passage is controlled in accordance with the volume of exhaust gas flowing at any one time. The volume is sensed in the exhaust pipe (18) upstream of the entry passase and a controller (24) thus adjusts a valve, preferably in the form of a pivoted flap (22), to vary the flow area of the entry passage, which is tangential. The cyclone is preferably included in a recirculation system allowing selection of recirculation to the IC engine of proportions of cleaned exhaust gas from cyclone outlet (14), particulates from cyclone collection box (16), and uncleaned exhaust gas (fig 4, not shown). <IMAGE>

Description

Controlling exhaust gas emissions This invention relates to the controlling of exhaust gas emissions from an internal combustion engine, and in particular to a separator for inclusion in the exhaust gas path leading from an internal combustion engine to separate out particulate components from the exhaust gases. The invention also relates to an exhaust gas recirculation system incorporating such a separator. The invention is particularly applicable to diesel engines.

The cleaning cf exhaust gas emissions from motor sehiclos is a major concern. One aspect of emissions technology relates to gaseous emissions which are usually classified either as NOX, as CO or as hydrocarbons. another aspect of emissions technology relates to non gaseous components in the exhaust gas stream, and such components are referred to as particulates. The present invention is concerned predominantly with thE- reduction of particulates in an exhaust gas stream.

According to the invention, there is provided an exhaust gas separator for inclusion in the exhaust gas path from an internal combustion engine to separate particulate matter from the exhaust as stream, the separator comprising a cyclone haing a tangential input for connection downstream of an exhaust gas manifold, an axial clean gas output and an axial output for a particle-rich fraction, wherein the tangential input has a passage of variable cross-sectional area, and wherein the separator includes means for varying the area of the passage in accordance with the rate of flow of exhaust gas through the input.

The use of a variable cross-section input allows the speed of the gas flow entering the cyclone to be maintained approximately constant by making the opening smaller when the volume of gas flowing is small and opening the passage when larger gas volumes are flowing. As a result, the speed of gas entering the cyclone can be maintained within the limits needed for proper operation of the cyclone.

The means for varying the area of the passage can be a flap pivoted at one edge which can be swung to a greater or lesser degree across the input passage.

A signal indicating the rate of flow of exhaust gas can be derived from the engine speed, or from the pressure in the exhaust gas duct upstream of the cyclone. The signal can then form an input to an actuator which controls the movement of the flap.

It ma also be possible to rake the flap self-adjusting, so that it is directly responsive to the pressure exerted by the incoming gas, against a suitably applied spring pressure.

The invention also extends to an exhaust pipe for a motor vehicle incorporating an exhaust gas separator as set forth above.

The invention will now be further described, by way of example, with reference to the accompanying drawing, in which: P'igUre I is a cross-section through a cyclone in accordance with the invention, on the section line I-I from Figure 2; Figure 2 is a section through the cyclone of Figure 1 on the line II-II; Figure 3 is a detail of the particle collection end of an alternative form of cyclone in accordance with the invention; and Figure 4 is a schematic view of an exhaust gas recirculation system in accordance with the invention.

Figure 1 shows a cyclone 10 with a tapered body 12, a clean gas outlet 14 and a collection box 16. The input for gas to be cleaned is through a tangential pipe 18 leading into a volute casing 20. At the point where the pipe 18 leads into the casing 20, a pivoted flap 22 is provided and this flap can be pivoted to produce any desired cross-sectional area of the passage between fully open and fully closed. Tne flap is under the control of a controller shown schematically at 24 in ligure 2, which receives a pressure signal from a sensor 26 mounted in the exhaust pipe upstream of the cyclone. Tne position of the flap 22 can therefore be controlled in accordance with the gas flow to the cyclone.

As an alternative to the pivoted flap shown, a linear travel valve could be used.

Once the exhaust gas enters the cyclone, it is subjected tc the conditions normally found therein, ie an outer vortical flow is produced which precesses towards the small end of the housing 12. Any particulate matter in the gas is flung outwardly by centrifugal forces. As the outer vortica; flow precesses towards the small end of the cyclone, an inner vortical flow (of cleaned sir) arises and precesses in the opposite direction, to the large end of the cyclone where it is drawn off through the offtake 14 and passed to the atmosphere, through a silencer if necessary. Ultimately the outer vortical flow together with the particulate matter enters a collection chamber 16 where the sudden increase in volume causes the particLes to be released from the gas stream and deposited.

The chamber 16 can be periodically emptied and can be constructed to that it will only need emptying at acceptable service intervals. Alternatively however the collection chamber 16 can have an outlet passage 28 closed by a poppet valve 30, and the poppet valve can be opened or closed as required.

Figure 4 shows schematically how the cyclone separator can form part of an exhaust gas recirculation system. In this figure, an engine block is shown at 38 with an inlet 40 and an exhaust gas outlet 42. The exhaust flowing through the outlet 42 is passed to the cyclone 10 as already As-ç^ribeA. ; ex eust cas recircul2tion passage 44 with e flow control valve 46 is provided to recirculate exhaust gas to the engine intake in a known manner.Upstream of the valve is a cistribution valve 48 which allows the EGR passage 44 to be connected to a source of exhaust gas either from the passage 28 or from the exhaust gas manifold 42 or from the exhaust gas pipe 50 downstream of the cyclone or from any combination of these sources in any desired proportions. It may be necessary to draw exhaust gas downstream of the cyclone to avoid interfering with the functioning of the cyclone.

With this arrangement, when the valve 30 in the passage 28 is opened a particle-rich gas stream can be drawn into the EGR system and recirculated through the engine. Because the rate of exhaust gas recirculation will vary in accordance with the engine operating load and speed, it is desirable to be able to control the recirculation of particulates from the cyclone in accordance with these parameters, and to avoid an excess quantity of particulate matter from being drawn into the engine at any stage.

A baffle 32 can be placed at the end of the cyclone body 12 to ensure that the particle-rich gas entering the collection chamber 16 is properly distributed.

Claims

1. An exhaust gas separator for inclusion in the exhaust gas path from an internal combustion engine to separate particulate matter from the exhaust gas stream, the separator comprising a cyclone having a tangential input for connection downstream of an exhaust gas manifold, an axial clean gas output and an axial output for a particle-rich fraction, wherein the tangential input has a passage of variable cross-sectional area, and wherein the separator includes means for varying the area of the passage in accordance with the rate of flow of exhaust gas through the irput.

2. An exhaust gas separator as claimed in Claim 1, wherein the means for varying the area of the passage is a flap pivoted at one edge which can be swung to a greater or lesser degree across the input passage.

3. An exhaust gas separator as claimed in Claim 1 or Claim 2, wherein a signal indicating the rate of flow of exhaust gas is derived from the engine speed and forms an input to an actuator which controls the movement of the flap.

4. An exhaust gas separator as claimed in Claim 1 or Claim 2, wherein a signal indicating the rate of flow of exhaust gas is derived from the pressure in the exhaust gas duct upstream of the cyclone and forms an input to an actuator which controls the movement of the flap.

5. An exhaust gas separator as claimed in Claim 1 or Claim 2, wherein the cross-cectional area of the input passage is self-adjusting to maintain the speed of the gas entering the cyclone at a substantially constant level irrespective of the flow volume.

6. An exhaust gas separator substantially as herein described with reference to the accompanying drawing.

7. An exhaust pipe for a motor vehicle incorporating an exhaust gas separator as claimed in any preceding claim.

8. An exhaust gas recirculation arrangement wherein an exhaust gas separator as claimed in any one of Claims 1 to 6 is mounted in an exhaust pipe and an exhaust c-s recirculation passage is connected to the separator output for the particle-rich fraction to recirculate the particle-rich fraction to the engine.

9. An exhaust gas recirculation arrangement as claimed in Claim 8, including a distributor valve arranged to connect to the recirculation passage exhaust gas either from the separator particle-rich fraction, or from the exhaust pipe downstream of the separator or from the exhaust pipe upstream of the separator.