REDUCING EMISSIONS FROM AN INTERNAL COMBUSTION ENGINE

Abstract: A multicylinder engine exhaust manifold system comprises a first manifold (16) having branches leading from individual exhaust ports (14) of the engine to a downpipe, and a second manifold for interconnecting the exhaust ports. The second manifold is constructed in the form of a block (20) having individual through passages (28) communicating the engine exhaust ports (14) with the branches of the first manifold (16) and a transverse passage (24) passing through and interconnecting the individual passages (28). The transverse passage (24) has housed in it a thin-walled conduit (32). The conduit (32) partially obstructs the individual passages (28) and has openings facing the engine exhaust ports (14). The conduit (32) is in poor thermal contact with the block (20) and having a low thermal capacity relative to the block (20), in order to minimise cooling of gases transferred between exhaust ports (14).

Description: REDUCING EMISSIONS FROM AN INTERNAL COMBUSTION ENGINE Field of the invention The present invention relates to an exhaust configuration for an internal combustion engine, designed with a view to improving post flame oxidation, to allow further opportunity for unburned hydrocarbons and carbon monoxide to be oxidised by unreacted oxygen before the exhaust gases are discharged to atmosphere or supplied as so-called feedgas to a catalytic converter. Background of the invention The charge supplied to the combustion chamber of an engine is not fully burnt during the combustion cycle and it is known that the exhaust gases contain carbon monoxide and unburned hydrocarbons that continue to be oxidised in the exhaust port in the vicinity of the hot exhaust valve. A probe measuring local concentrations of hydrocarbons will show a marked reduction as the gases are discharged past the exhaust valve. However, this post-flame reaction is quenched by the cold surfaces of the exhaust port and manifold and in a conventional engine is restricted to the vicinity of the exhaust valve. There have previously been made some proposals to promote such post-flame oxidation in the exhaust port. One such proposal was to place an insulating liner in the exhaust port to reduce cooling of the gases and allow a longer time for the oxidation reaction to occur. Another proposal was to increase the exhaust gas temperature by engine management techniques, such as delaying the spark and injection timing or altering the exhaust valve timing. In a still further proposal for use during cold operation, air has been injected into each exhaust port as close as possible to the exhaust valve. The flow of exhaust gases in the exhaust ports of an internal combustion engine is not homogeneous. Instead, it is made up of pockets of rich unburned hydrocarbons and other pockets still containing excess air. These pockets are separated both across the cross section and along the length of the exhaust port. In conventional engines, a small degree of mixing between these pockets does occur and if this happens close enough to the exhaust valve, where the temperature is still sufficiently high, some degree of post flame oxidation can take place which helps to reduce the amount of unburned hydrocarbons and carbon monoxide in the exhaust gases before they reach the catalytic converter. The present invention seeks to improve the post flame reaction by promoting mixing between exhaust gases discharged at different times from the engine cylinders, while at the same time ensuring that the gases remain at a temperature high enough to permit oxidation to take place. Co-pending British Patent Application No. 9424344.2, proposes a multicylinder engine exhaust manifold system that comprises a first manifold having branches leading -from individual exhaust ports of the engine to a downpipe, and a second manifold for interconnecting the exhaust ports and also having branches leading to the individual exhaust ports of the engine, wherein the cross-sectional area of each branch of the second manifold facing the exhaust flow from the associated exhaust valve is no less than 25% of the total port area and the branches of both manifolds terminate within the ports in close proximity to the exhaust valves, whereby a large proportion of the exhaust flow discharged from the exhaust valve of one cylinder is captured by the associated branch of the second manifold and distributed by the second manifold to the exhaust ports of adjacent cylinders where the exhaust valves are closed and leaves the -exhaust ports of the adjacent cylinders through the associated branches of the first manifold, scouring the closed ends of the exhaust ports in the process. For spark ignition engines, the invention in the latter patent application attempts to reduce hydrocarbon emissions by promoting thermal oxidation in close proximity to the hot exhaust valve by mixing oxygen rich regions of the gases from one cylinder with the hydrocarbon rich regions that tend to remain stagnant in the unscavenged exhaust ports. However, the configuration of the exhaust system described in the latter patent application results in considerable heat loss to the manifold from the exhaust gases recycled to other cylinders. As a result, the gases are cooled down and this prevents them from reacting with one another efficiently to reduce the hydrocarbon content of the feedgas to the exhaust pipe. Object of the invention The present invention seeks to improve on the invention in co-pending Patent Application No. 9424344.2 by increasing the retention of heat in the exhaust gases that flow between cylinders. Summary of the invention According to one aspect of the present invention, there is provided a multicylinder engine exhaust manifold system that comprises a first manifold having branches leading from individual exhaust ports of the engine to a downpipe, and a second manifold for interconnecting the exhaust ports, characterised in that the second manifold is constructed in the form of a block having individual through passages communicating the engine exhaust ports with the branches of the first manifold and a transverse passage passing through and interconnecting the individual passages, the trans erse passage having housed therein a thin-walled conduit, the conduit partially obstructing the individual passages and having openings facing the engine exhaust ports, the conduit being in poor thermal contact with the block and having a low thermal capacity relative to the block. Preferably, the conduit has plates that extend therefrom into the exhaust ports and divide each exhaust port into separate channels, the first channels communicating via the individual through passages with the branches of the first exhaust manifold and the second channels communicating via the interior of the conduit with the exhaust ports of the other engine cylinders. 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 sectional view from above of an engine having manifold system of the invention, the section being taken along the line I-I in Figure 2, Figure 2 is a section taken along the line II-II in Figure 1, and Figure 3 is an end view of one engine exhaust port as from the right in Figure 2. Detailed description of the preferred embo iment The drawings show an engine 10 having four cylinders each with an intake port 12 and an exhaust port 14. The main exhaust manifold 16 has four separate branches that are connected to the respective exhaust ports 14 through a spacer block 20 having four through passages 28 -extending between its faces that allow each exhaust port 14 to communicate with a respective one of the branches of the exhaust manifold 16. The spacer block also contains a transverse passage 24 that interconnects the individual through passages 28. Though the described embodiment shows the spacer block 20 as being separate from the exhaust manifold 16, the two can be formed integrally. The spacer block 20 is also shown as having a front plate 22 that covers the front face of the transverse passage 24 but one can dispense with this plate in engines having a continuous face on the engine cylinder head for mating directly with the spacer block 20. The transverse passage 24, which is of rectangular cross- section, houses a thin-walled conduit 32 that is of oval cross-section and makes only line contact with the spacer block 20. The conduit 32 extends across all the exhaust ports and, as can be seen in Figure 3, it partially obstructs the through passages 28. On its side facing each exhaust port 14, the conduit 32 is cut and it wall is unravelled as shown in Figure 2 to define a partition plate 30 disposed within the exhaust port 14 and dividing it into an upper and a lower channel. The upper channel communicates with the exhaust manifold 16 through the unobstructed region of the through passage 28 while the lower channel 26 communicates with the interior of the conduit 32 through the opening created by bending back the plate 30 out of the wall of the conduit 32. By virtue of this construction, the exhaust gases from each port are split into two streams of which one exits immediately and the other flows through the conduit 32 to the other exhaust ports. The stream that flows along the conduit 32 remains hot because the conduit 32 has a low thermal capacity and is thermally isolated from the spacer block 20 by the air layer trapped between them. Only little heat transfer can occur at the line of contact between the two because of the small area involved. On reaching the other exhaust ports, the still hot exhaust gases mix with the gases trapped in the closed exhaust ports. This offers the advantage of reducing hydrocarbon emissions by promoting thermal oxidation in close proximity to the hot exhaust valve by mixing oxygen rich regions of the gases from one cylinder with the hydrocarbon rich regions that tend to remain stagnant in the unscavenged exhaust ports. Because of the poor thermal transfer between the conduit 32 and the block 20, the conduit can be made of metal. However, because the block also firmly supports the conduit 32, the need for mechanical strength and rigidity in the conduit is obviated, thereby allowing the conduit alternatively to be constructed as a thin and relatively fragile shell of an insulating material such as alumina. The present invention thus improves over that in the co- pending patent application discussed earlier by achieving higher reaction temperatures in the gases that are transferred between the cylinders and by considerably simplifying the construction of the manifold system. A more compact and more thermally efficient manifold is thereby achieved that also offers the advantage of reduced manufacturing cost.

Claims: CLAIMS 1. A multicylinder engine exhaust manifold system that comprises a first manifold having branches leading from individual exhaust ports of the engine to a downpipe, and a second manifold for interconnecting the exhaust ports, characterised in that the second manifold is constructed in the form of a block having individual through passages communicating the engine exhaust ports with the branches of the first manifold and a transverse passage passing through and interconnecting the individual passages, the transverse passage having housed therein a thin-walled conduit, the conduit partially obstructing the individual passages and having openings facing the engine exhaust ports, the conduit being in poor thermal contact with the block and having a low thermal capacity relative to the block. 2. A manifold system as claimed in claim 1, wherein the conduit has plates that extend therefrom into the exhaust ports and divide each exhaust port into separate channels, the first channels communicating via the individual through passages with the branches of the first exhaust manifold and the second channels communicating via the interior of the conduit with the exhaust ports of the other engine cylinders. 3. A manifold system constructed, arranged and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.

Inventors: MA THOMAS TSOI-HEI, MA, THOMAS, TSOI-HEI
Applicants: FORD FRANCE, FORD MOTOR CO, FORD WERKE AG, MA THOMAS TSOI HEI, FORD FRANCE S.A., FORD MOTOR COMPANY, FORD MOTOR COMPANY LIMITED, MA, THOMAS, TSOI-HEI
Application year: 1996
Main classification: F01N7
IPC codes: F01N7