GB2242226A

GB2242226A - I.C. engine intake baffle

Info

Publication number: GB2242226A
Application number: GB9005102A
Authority: GB
Inventors: John Walter Hassan
Original assignee: Jaguar Cars Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 1990-03-07
Filing date: 1990-03-07
Publication date: 1991-09-25
Also published as: GB9005102D0

Abstract

An adjustable baffle 25 deflects the flow of gas to the valve 15, so that the gas is directed past the valve into the combustion chamber 22 whereby the swirling motion of the gases within the combustion chamber may be increased. The baffle 25 may be retracted above a predetermined engine speed or its angle may be gradually reduced as engine speed rises. <IMAGE>

Description

INTERNAL COMBUSTION ENGINES The present invention relates to internal combustion engines and in particular to the reduction of NOx and other pollutants in the exhaust emissions of the engine.

One technique conventionally used to reduce NOx and other pollutants in exhaust gases of internal combustion engines, is to recirculate a portion of the exhaust gases. However, under normal circumstances the level of exhaust gases that may be recirculated is limited, typically to the order of 25%, recirculating volumes in excess of this level resulting in instability in the firing of the engine.

The present invention provides means for increasing the level of exhaust gas that may be recirculated while maintaining acceptable engine firing stability. However, the present invention will also provide improved combustion in engines where exhaust gases are not recirculated and hence is not restricted to use in engines with exhaust gas recirculation.

According to one aspect of the present invention an internal combustion engine comprises a cylinder, a piston slidably sealed within the cylinder to define a combustion chamber, valve means to control flow of gas into the combustion chamber, an inlet manifold through which gas will flow to the valve means and an adjustable baffle to deflect the gas flow to the valve means, so that the gas is directed past the valve means into the combustion chamber whereby swirling motion of the gases within the combustion chamber may be increased.

With internal combustion engines of conventional design, an air or air/fuel mixture is delivered to the inlet valve by the inlet manifold in a relative uniform manner, so that the air or air/fuel mixture will pass the valve in a relatively uniform manner on all sides of the valve. As a result, the air or air/fuel mixture within the combustion chamber will be turbulent with stagnant areas. This is particularly so at low engine speeds when the velocity of the incoming air or air/fuel mixture will be low.

With the present invention, the baffle will deflect the flow of air or air/fuel mixture to one side of the valve so that upon entering the combustion chamber, the flow will be directed to cause the incoming air to swirl around the combustion chamber. This relatively unidirectional flow of air or air/fuel mixture will improve mixing within the combustion chamber and will also enhance flame propogation upon ignition, this in turn will improve combustion so that a greater level of exhaust gases may be recirculated.

The baffle will reduce the flow area of the inlet manifold thus increasing the gas velocities and further improve mixing of the' ' air or air/fuel mixture at lower engine speeds. Reduction of the flow area will however increase the back pressure. This is not however significant at low engine speeds, for example up to 2000 rpm, and at higher speeds the increased flow rates will improve mixing of the air or air/fuel mixture within the cylinder, so that directing of the flow is less important and the baffle may be retracted to reduce the back pressure.

In order to be most effective in directing the gas flow over the valve, the adjustable baffle should be positioned as close as possible to the valve. In conventional engines, this is likely to be at the point at which the inlet manifold is connected to the head of the engine. However, in purpose built engines, the baffle may be built into the head allowing it to be located even closer to the valve.

Fuel may be injected into the inlet manifold upstream of the adjustable baffle and where exhaust gases are recirculated, these will also be introduced into the inlet manifold at a point upstream of the adjustable baffle.

An embodiment of the invention is now described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a cross-sectional elevation of the inlet manifold and valve mechanism of an engine in accordance with the present invention; Figure 2 is a section along the line II - II of Figure 1 Figure 3 is a section similar to Figure 1 but showing the adjustable baffle in its retracted position; and Figure 4 is a graph showing the relationship between swirl ratio and ignition requirement, for a typical engine formed in accordance with the present invention.

As illustrated in the accompanying drawings, an internal combustion engine comprises cylinder 10 with a piston 11 slidably sealed therein. Cylinder 10 is closed by cylinder head 12 defining inlet and exhaust ports 13 and 14. The inlet and exhaust ports 13 and 14 are controlled by poppet type valves 15 and 16 respectively, of conventional design, the valves 15 and 16 being driven by overhead cam shafts 18 and 19.

An inlet manifold 20 is connected to the inlet port 13 by duct 21, the manifold 20 being bolted to cylinder head 12 in conventional manner. A flap valve 25 is pivotally mounted on a spindle 26 to the base of the inlet manifold 20 adjacent the end of the inlet manifold 20 secured to the cylinder head 12. The flap valve 25 is adjustable between a retracted position in which it lies along the base of the inlet manifold 20 as illustrated in Figure 3 and a raised position in which it is inclined upwardly towards the cylinder head 12 as illustrated in Figure 1. A fuel injector 27 opens into the upper part of inlet manifold 20 adjacent the flap valve 25 but on side thereof remote from cylinder head 12. The injector 27 is arranged to direct a jet of fuel over the top of the flap valve 25, when in its raised position.The end of inlet manifold 20 remote from the cylinder head 12 is connected to suitable air metering means (not shown).

As illustrated in Figure 1, the flap valve 25 is controlled by means of lever 30 which is attached to spindle 26. A solenoid 31 is arranged to move the lever 30 between the first position in which the flap valve 25 is in a raised position as illustrated in Figure 1 and a second position in which the flap valve 25 is in a retracted position as illustrated in Figure 3. The solenoid 31 is controlled by suitable means, for example the electronic control module that controls engine management, so that the flap valve 25 is moved to its raised position when the engine is running below a pre-determined speed, for example 2000 rpm.

Alternatively, a solenoid plunger may be arranged to act against the underside of the flap valve 25 to move it from its retracted to its raised position. In a further alternative embodiment, the lever 30 may be operated by a cam mechanism. Furthermore, cam means, an electrical stepper motor or similar means may be used to provide continuous adjustment of the flap valve 25, so that the angle of inclination thereof may be varied with engine speed. With multi-cylinder engines, flap valves 25 will be provided for each cylinder 10, each flap valve 25 may be controlled by independent means or the flap valves 25 may be mounted on a common spindle 26 and controlled by common operating means.

As illustrated in Figures 1 and 2, when the flap valve 25 is in its raised position, the flow area of the inlet manifold 20 is substantially reduced, thus creating a significant increase in the velocity of air drawn into the combustion chamber 22 defined by the cylinder 10, on the induction stroke of the engine. Furthermore, the flap valve 25 deflects the flow of air and fuel away from the lower surface of the inlet duct 21 and over one side of the head 35 of valve 15, thus directing the flow of air and fuel into the combustion chamber 22, so that it will swirl around the combustion chamber 22 in a relatively unidirectional manner, as illustrated by the arrows in Figure 1. This swirling action improves mixing of the air and fuel and also flame propagation on ignition of the mixture, thus improving ignition and also providing more complete combustion.As a result, a leaner air/fuel mixture may be used resulting in lower emission polutants and also enabling greater volumes of exhaust gas to be recirculated thus further reducing emission polutants.

As illustrated in Figure 2, the upper edge 40 of the flap valve 25 is contoured, the outer edges 41 being extended so that when in its raised position, the lower boundary regions of the air flow will be controlled to avoid the air flow being dragged back down to the lower portions of the inlet duct 21.

Reduction in the flow area of the inlet manifold 20 will produce a back pressure which will become significant at high engine speeds, say above 2000 rpm. Consequently, at such speeds the flap valve 25 is retracted, so that the full bore of the inlet manifold 20 is open. As illustrated in Figure 3, when the flap valve 25 is retracted, the air/fuel mixture is delivered substantially uniformly to the inlet port 13 and will pass valve head 35 on all sides, thus creating turbulent flow within the combustion chamber 22 as illustrated by the arrows in Figure 3. The resultant low levels of swirl will result in poorer mixing of the air and fuel within the combustion chamber 22 although this will be compensated to some extent by the increased air speed at higher engine speeds.

Figure 4 shows'a graph with a plot of; swirl ratio, that is the ratio of the speed of incoming gas in the direction of swirl relative to piston speed, and angle of inclination of the flap valve 25; against the minimum ignition requirement which is measured as the minimum advance at which firing may take place in order to achieve optimum fuel consumption.

This graph clearly illustrates that as the angle of inclination of the flap valve 25 increases and the advance necessary for optimum fuel consumption reduces indicating improved combustion.

Various modifications may be made without departing from the invention. For example, while in the above embodiment, a flap valve is used to control flow of air through the inlet manifold, inlet duct and past the valve, a gate valve which may be raised and lowered transverse to the flow of air, may alternatively be used. Also, while in the above embodiment, fuel is injected into the inlet manifold, the present invention may be used where a fuel/air mixture is introduced into the inlet manifold by conventional carburation means or where the fuel is injected directly into the combustion chamber. Alternatively, the fuel may be injected into the inlet duct, between the flap valve and inlet valve.

Claims

1. An internal combustion engine comprising a cylinder, a piston slidably sealed within the cylinder to define a combustion chamber, valve means to control flow of gas into the combustion chamber, an inlet manifold through which gas will flow to the valve means and an adjustable baffle to deflect the gas flow to the valve means, so that the gas is directed past the valve means into the combustion chamber whereby swirling motion of the gases within the combustion chamber may be increased.

2. An internal combustion engine according to Claim 1 in which the adjustable baffle is in the form of a flap valve.

3. An internal combustion engine according to Claim 2 in which the flap valve is pivotally mounted to the lower surface of the inlet manifold and adapted to be moved between a retracted position in which it lies parallel to the lower surface of the inlet manifold and a raised position in which it is inclined upwardly towards the valve means.

4. An internal combustion engine according to Claim 3 in which a mechanism is provided for moving the flap valve between its raised and its retracted positions.

5. An internal combustion engine according to Claim 4 in which the flap valve is mounted on a spindle which is rotated by suitable control means.

6. An internal combustion engine according to Claim 5 in which the spindle is controlled by a solenoid or cam operated lever.

7. An internal combustion engine according to Claim 4 in which a solenoid plunger acts directly on the flap valve to move it between its retracted and raised positions.

8. An internal combustion engine according to any one of Claims 4 to 7 in which the mechanism moves the flap valve from its raised to its retracted position when the speed of the engine rises above a predetermined value.

9. An internal combustion engine according to Claim 4 in which the mechanism moves the flap valve to one or more positions intermediate of its retracted and raised positions, depending on engine speed.

10. An internal combustion engine according to Claim 9 in which the flap valve is controlled by a cam operated lever mechanism or electrical stepper motor.

11. An internal combustion engine according to any one of Claims 2 to 10 in which the edge of the flap valve opposite to the pivotted edge is contoured.

12. An internal combustion engine according to Claim 11 in which the contoured edge of the flap valve is curved, the outer edges extending away from the pivotted edge.

13. An internal combustion engine according to any one of Claims 1 to 12 in which the adjustable baffle is positioned adjacent to the valve mechanism.

14. An internal combustion engine according to Claim 13 in which the adjustable baffle is provided at the end of the inlet manifold connected to the cylinder head.

15. An internal combustion engine according to any one of Claims 1 to 14 in which a fuel injector is provided adjacent the adjustable baffle, upstream thereof.

16. An internal combustion engine according to any one of Claims 1 to 15 in which exhaust gases are introduced into the inlet manifold upstream of the adjustable baffle.

17. An internal combustion engine substantially as described herein with reference to, and as shown in, Figures 1 to 4 of the accompanying drawings.