WO2022199831A1

WO2022199831A1 - Air intake port for a lean-burn gasoline engine

Info

Publication number: WO2022199831A1
Application number: PCT/EP2021/057914
Authority: WO
Inventors: Jack Johnson; Lyn Mcwilliam; Simon DRINKWATER
Original assignee: Jaguar Land Rover Limited
Priority date: 2021-03-26
Filing date: 2021-03-26
Publication date: 2022-09-29
Also published as: EP4314536A1

Abstract

An air intake port (10) for a lean-burn gasoline engine (110) comprises an air inlet (14), two air outlets (15a, 15b), and an air channel connecting the air inlet (14) to the two air outlets (15a, 15b). The air channel comprises an upstream common duct (11) and two downstream port legs (12a, 12b), the two downstream port legs (12a, 12b) branching off from the common duct (11) at a bifurcation point (13). The upstream common duct (11) has a duct floor (42) and a duct ceiling (41), each comprising a sloped portion arranged to converge on the bifurcation point (13), wherein a bifurcation angle of less than 90 degrees is formed between the sloped portions of the duct floor (42) and the duct ceiling (41) at the bifurcation point (13).

Description

Air intake port for a lean-burn gasoline engine

TECHNICAL FIELD

The present disclosure relates to an air intake port for a lean-burn gasoline engine, to a lean- burn gasoline engine and to a vehicle with such an engine.

BACKGROUND

In classic internal combustion engines, gasoline burns best when it is mixed with air in the proportions of 14.7:1 (lambda = 1). Most modern gasoline engines used in vehicles tend to operate at or near this so-called stoichiometric point for most of the time. Ideally, when burning fuel in an engine, only carbon dioxide (C02) and water (H20) are produced. In practice, the exhaust gas of an internal combustion engine also comprises significant amounts of carbon monoxide (CO), nitrogen oxides (NO_x) and unburned hydrocarbons. It is desirable to increase fuel efficiency and reduce unwanted emissions.

One possible route for increasing fuel efficiency is to burn the fuel with an excess of air. Burning fuel in such an oxygen-rich environment is usually called lean-burning. Typical lean- burn engines may mix air and fuel in proportions of, for example, 20:1 (lambda > 1.3) or even 30:1 (lambda > 2). Advantages of lean-burn engines include, for example, that they produce lower levels of C02 and hydrocarbon emissions by better combustion control and more complete fuel burning inside the engine cylinders. The engines designed for lean burning can employ higher compression ratios and thus provide more efficient fuel use and lower exhaust hydrocarbon emissions than conventional gasoline engines. Additionally, lean-burn modes help to reduce throttling losses, which originate from the extra work that is required for pumping air through a partially closed throttle. When using more air to burn the fuel, the throttle can be kept more open when the demand for engine power is reduced.

Lean burning of fuel does, however, also come with some technical challenges that have to be overcome to provide an engine that is suitable and optimised for efficiently burning hydrocarbons in an oxygen-rich environment. For example, if the mixture is too lean, the engine may fail to combust. At low loads and engine speeds, reduced flammability may affect the stability of the combustion process and introduce problems with engine misfire. A lower fuel concentration also leads to less power output. Because of such disadvantages, lean burn is currently only used for part of the engine map and most lean-burning modern engines, for example, tend to cruise and coast at or near the stoichiometric point. In order to enable the lean burning of fuel over a larger portion of the engine map, the engine needs to be designed in such a way to enable a large air flow into the combustion chamber and to ensure a reliable combustion process that will effectively burn all fuel, despite the oxygen rich conditions.

It is an aim of the present invention to provide an improved lean-burn engine.

SUMMARY OF THE INVENTION

Aspects and embodiments of the invention provide an air intake port for a lean-burn engine, a lean-burn engine and a vehicle with such an engine. The lean-burn engine may be suitable for use with gasoline as described herein. Alternatively or in addition thereto it will be appreciated that the lean-burn engine may be suitable for use with other fuels, such as hydrogen, for example. Aspects and embodiments of the invention are defined in the context of lean-burn gasoline but it will be appreciated that the fuel type can be substituted.

According to an aspect of the present invention there is provided an air intake port for a lean- burn gasoline engine, the air intake port comprising an air inlet, two air outlets, and an air channel connecting the air inlet to the two air outlets. The air channel comprises an upstream common duct and two downstream port legs, the two downstream port legs branching off from the common duct at a bifurcation point. The upstream common duct having a duct floor and a duct ceiling, each comprising a sloped portion arranged to converge on the bifurcation point, wherein a bifurcation angle of less than 90 degrees is formed between the sloped portions of the duct floor and the duct ceiling at the bifurcation point. The terms upstream and downstream are herein used to refer to parts of the air intake port relative to flow of air through the air intake port in its normal use with a lean-burn gasoline engine. The predominant air flow direction is from an upstream position to a downstream position. It follows that in normal use the engine is downstream of the air intake port.

In previously known air intake ports the duct floor and duct ceiling remain largely in parallel up to the bifurcation point, where they are joined by either a straight wall, or by a straight wall with slightly rounded edges at the interface between the straight wall and the duct floor or duct ceiling. In such air intake ports, the bifurcation angle can be considered to be approximately

180 degrees. The inventors have observed that such traditional bifurcation points may lead to a disturbance of the air flow and a reduced flow coefficient. In addition thereto, the inventors have found that the flow coefficient can be increased and flow disturbance minimised by using the sharper bifurcation angle of the present invention. This advantage is especially relevant for a lean-burn gasoline engine which uses higher volumes of intake air per piston stroke. Furthermore, it has been found that the reduced flow disturbance contributes to the controllability of the ignition process inside the combustion chamber, which again is an important advantage for especially lean-burn gasoline engines.

For the purpose of the present invention, the bifurcation angle is defined as the angle between the duct floor and the duct ceiling at the bifurcation point. Preferably the duct floor and the duct ceiling make an acute angle at this point in order to minimise the flow disturbance and to maximise the advantageous technical effects of the new design. In the event that, for ease of manufacturing or for any other reason, the angle between the two merging surfaces is less sharp and somewhat rounded, then the angle between the duct floor and the duct ceiling may be defined by the angle they make at a position of 5 mm in front of the bifurcation point.

In preferred embodiments, the bifurcation angle is less than 75, 55, or even 45 degrees. In general, smaller angles require a longer transition zone. While all bifurcation angles smaller than 90 degrees will provide at least some of the technical benefits of the current invention, the optimal bifurcation angle may depend on the exact design of the air intake port. Transition zone’ is herein to be interpreted as the zone at the downstream end of the upstream common duct, wherein the sloped portions of the duct floor and the duct ceiling are situated. The transition zone thus starts where one of the sloped portions starts and ends at the bifurcation point.

In an embodiment of the invention, a port leg length measured from the bifurcation point to one of the two air outlets is at least twice a diameter of the respective air outlet. Advantageously, due to a smooth adjustment of the flow direction, this provides a smaller disturbance to the air flow at the bifurcation than the disturbance that would be seen with a shorter port leg length. Put another way, longer port legs allow for a smoother adjustment of the flow direction. The inventors have found that when the port legs have a length of at least twice the air outlet diameter, the disturbance is sufficiently low to not have a significant detrimental effect on the performance of the lean-burn gasoline engine. This positive effect on the reduction of air flow disturbance adds to the air flow improvement already provided by the sharp bifurcation angle according to the invention. Without this sharp bifurcation angle, longer port legs (e.g. at least three or four times the air outlet diameter) might have been needed to avoid excessive disturbance of the flow.

To increase the speed with which the air flows through the air intake port and the total volume of air that can be taken in, a total cross section of the air channel may gradually decrease between the air inlet and the two air outlets. As a further measure for not disturbing the air flow, a gradient of decrease of the cross section may be locally reduced in a region immediately upstream and/or downstream of the bifurcation point.

Known air intake ports are seen to have a decreasing cross section profile in order to accelerate the air flowing towards the combustion chamber and thereby increasing the total volume of air drawn through the air intake port. However, such air intake ports are generally designed such that the cross section decreases with a constant or approximately constant gradient of decrease. The present invention discloses that this common approach is not preferable for use with a lean-burn gasoline engine, which requires a relatively high air intake volume and may be more dependent on a precise control of the direction of flow of the intake air at the point where it enters the combustion chamber. By introducing a local reduction of the gradient of decrease of the total cross section in the region around the bifurcation point, any possible disturbance of the air flow caused by the splitting and deflecting of the air flow is minimised. Preferably, the local reduction of the gradient of decrease of the total cross section is realised in the region immediately upstream and downstream of the bifurcation point, but the desired flow enhancing effect is at least partly achieved when reducing the gradient of decrease at only one of the upstream and downstream sides of the bifurcation point.

The air channel has an average gradient of decrease of the total cross section along the length of the air channel. The optimal average gradient will usually be a compromise between different design considerations. One possible constraint is the desired maximum speed of the air flow at the entrance, or inlet, of the combustion chamber. Too high speeds may lead to excessive NVH (noise, vibration, and harshness) problems and to choking of the port flow. Cylinder size and space/packaging constraints may define the maximum cross section of the air outlets of the air intake port. Given a maximum cross section and air flow speed at the outlet, a preferable average gradient of decrease of the total cross section can be established. Further constraints on the length and width of the air intake port may also play a role when determining the preferable. In preferred embodiments, the gradient of decrease of the total cross section may, for example, be locally at least 15% or 20% below the average gradient of decrease in at least a portion of the region adjacent the bifurcation point. In other embodiments, the gradient of decrease at that position may even be more than 25%, 30%, 35%, 40%, 45%, or 50% below the average gradient of decrease of the total cross section.

In some embodiments, the gradient of decrease of the total cross section may locally be lower than or equal to zero in at least a portion of the region immediately upstream and/or downstream of the bifurcation point. This means that the cross section may even increase in the area around the bifurcation point in order to ensure an undisturbed air flow, even though the outlet cross section of the air intake port is significantly smaller than its inlet cross section.

According to another aspect of the invention a lean-burn gasoline engine is provided comprising at least one air intake port as described above. While the air intake port described herein is primarily designed for use with combustion chamber having a dual intake, it could be used to serve two single intake combustion chambers too.

According to another aspect of the invention, a vehicle is provided comprising a lean-burn gasoline engine with an air intake port as described above.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a vehicle in which the invention may be used;

Figure 2 shows an air intake port according to an embodiment of the invention;

Figure 3 schematically shows a bottom view of the air intake port of Figure 2;

Figures 4a and 4b schematically show side views from the plane IV-IV as shown in Figure 3, into the inside of the air intake port of Figures 2 and 3; and

Figure 5 schematically shows a bottom view of the air intake port of Figure 2, together with a diagram indicating the cross section at different positions along its length.

DETAILED DESCRIPTION

Figure 1 shows a vehicle 100 in which the invention may be used. In this example, the vehicle

100 is a car, but the invention is equally applicable to other vehicles driven by a lean-burn gasoline engine 110. As mentioned above, it is to be noted that air intake port according to the invention and as described herein can be advantageously used in engines burning other fuels or fuel mixtures than gasoline. For example, the air intake port would be useful in a hydrogen burning internal combustion engine. In this vehicle 100, the lean-burn gasoline engine 110 is positioned in the front and coupled to a drivetrain to drive the front and/or rear wheels of the vehicle 100. The energy needed for driving the vehicle 100 is provided by burning fuel in the engine’s cylinders causing the cylinder pistons to drive a crankshaft that is mechanically connected to the vehicle’s drivetrain.

Compared to classic internal combustion engines, the lean-burn engine 110 of this vehicle 100 burns the fuel with an excess of air in the air-fuel mixture. Lean-burn engines may mix air and fuel in proportions of, for example, 20:1 (lambda > 1.3) or even 30:1 (lambda > 2). Advantages of lean-burn engines include more efficient fuel use and lower exhaust hydrocarbon emissions than conventional gasoline engines.

In order to enable the lean burning of fuel over a large portion of the engine map, i.e. in a large range of different engine speeds as well as engine output power or torque, the engine 110 is designed in such a way to enable a large air flow into the combustion chamber and a good mixing with the relatively small amount of fuel that is to be burnt to ensure a reliable combustion process that will effectively burn all fuel, despite the oxygen rich conditions.

Figure 2 shows an air intake port 10 according to an embodiment of the invention. The air intake port 10 has an air inlet 14 and two air outlets 15a, 15b. An air channel connects the air inlet 14 to the two air outlets 15a, 15b. The first, upstream portion of the air channel, starting at the air inlet 14 forms a common duct 11. At a bifurcation point 13, at a downstream end of the common duct 11 , the common duct 11 branches off in two port legs 12a, 12b that provide the two respective air outlets 15a, 15b. The terms upstream and downstream are used to refer to parts of the air intake port 10 relative to flow of air through the air intake port 10 in its normal use with a lean-burn gasoline engine 110. The predominant air flow direction is from an upstream position to a downstream position. It follows that in normal use the engine 110 is downstream of the air intake port 10. The air outlets 15a, 15b are configured to connect to two respective inlets of the combustion chamber. Near the downstream ends of the port legs 12a, 12b, two valve guides 16a, 16 are provided, each being configured to receive a valve stem that is used for controlling the valve that selectively opens and closes the combustion chamber inlets. To ensure a smooth air flow in use between the air inlet 14 and the two air outlets 15a, 15b, the air intake port 10 is designed such that any disturbances by the bifurcation are minimised. A key aspect of this minimisation of the air flow disturbance is the sharp bifurcation angle at the bifurcation point 13. In this embodiment, the sharp bifurcation angle 13 turns into a sloped portion 131 of the ceiling of the common duct 11. A similar sloped portion may be provided in the bottom surface of the common duct 11 (see Figures 3 and 4). In other embodiments, the floor and ceiling of the common duct 11 may be flat and the sharp bifurcation angle 13 may be formed by additional structures provided entirely inside the common duct 11.

Additionally, the air flow disturbance may be reduced by having port legs 12a, 12b that are long enough for splitting and redirecting the incoming air flow in a gradual way. Preferably, a port leg length, measured from the bifurcation point 13 to one of the two air outlets 15a, 15b, is at least twice a diameter of the respective air outlet 15a, 15b. Without the sharp bifurcation angle, however, longer port legs 12a, 12b may be necessary to obtain the air intake flow that is needed for the desired lean combustion process. An advantage of the sharp bifurcation angle is therefore that the relatively short port legs 12a, 12b allow for a more compact design of the air intake port 10 and the engine 110.

Figure 3 schematically shows a bottom view of the air intake port 10 of Figure 2. In addition to what has already been shown in and described with reference to Figure 2, Figure 3 shows the air outlets 15a, 15b, and a sloped portion 132 in the common duct floor which leads to the bifurcation point 13. Figure 3 further shows a plane IV-IV through the air intake port 10, from which the views on the inside of the air intake port 10 as shown in Figures 4a and 4b are taken. In addition thereto, Figure 3 indicates, with three arrows 33, the direction from which the cross section is viewed in the view of Figures 4a and 4b.

The side views shown in Figures 4a and 4b thus show the inside of the air intake port 10 as seen from the plane IV-IV indicated in Figure 3. As will be explained below, Figures 4a and 4b show two different embodiments of the sharp bifurcation angle 133 according to the invention.

From this viewpoint inside the common duct 11, we look directly upon a side wall 43 of the common duct 11 and a side wall 44 of one of the leg ports 12a. In addition to a side walls 43,

44, the common duct 11 and the port legs 12a, 12b may have a ceiling 41 , a floor 42, and another side wall (not shown). It is noted that the common duct 11 and the port legs 12a are preferably not rectangularly shaped. Depending on the exact shape of the air intake port 10, the boundaries of its floor 42, side walls 43, 44, and ceiling 41 may not be easy to define. The common duct 11 and the port legs 12a, 12b may, e.g., be tubular, oval, rectangular with rounded corners, or have flat floors 42 and/or ceilings 41 with curved side walls. Combinations and variations of such shapes are possible too. In preferred embodiments, however, at least the floor 42 of the common duct 11 is substantially flat.

In prior art air intake ports with one air intake and two air outlets, the bifurcation point is typically formed as a straight and substantially vertical wall or pillar that connects the air intake floor 42 to the air intake ceiling 41. This vertical wall is situated centrally in the air intake port 10, at the end of the common duct 11. From there, the two port legs 12a, 12b and there opposing inner walls diverge.

In this case, as can be seen in the side views of Figures 4a and 4b, the bifurcation is a gradual transition and not, as in the prior art, a straight wall perpendicular to the air flow 34 through the common duct 11. In a transition zone 134 at the downstream end of the common duct 11, and in or around the centreline of the common duct 11 , the ceiling 41 and the floor 42 of the common duct 11 start approaching each other, until the sloped portions 131 , 132 of the ceiling 41 and the floor 42 meet each other in the bifurcation point 13. If these sloped portions 131 , 132 are sufficiently long, they make a sharp bifurcation angle 133 at this bifurcation point 13. The inventors have found that with such a sharp bifurcation angle, the air flow 34 is allowed to split in two, with far less disturbance than if the bifurcation is formed by a simple vertical wall (or an approximation thereof). In order to achieve this advantageous effect, a bifurcation angle 133 of less than 90° is preferred, however even better results may be obtained with even sharper bifurcation angles of, e.g., less than 75° 55°, or 45°.

In this example, the bifurcation point 13 is located centrally in the common duct 11, i.e. midway between the two side walls and at equal distances from the floor 42 and the ceiling 41. However, other, less symmetric configurations may be provided without departing from the scope of the invention. For example, the bifurcation point 13 may be positioned somewhat closer to the floor 42, the sloped portion 131 at the ceiling 41 being steeper and/or longer than the sloped portion 132 near the floor 42. In other embodiments the bifurcation point 13 may be somewhat rounded to further reduce air flow disturbances and/or because manufacturing constraints. It is noted that in the event of a slightly rounded bifurcation point 13, the bifurcation angle 133 may be defined as the angle between the duct floor 42 and the duct ceiling 41 measured at a point beyond the rounded edge, e.g. at a position of 5 mm in front of the bifurcation point.

Although the sloped portions 131, 132 are shown as straight lines with a constant slope in

Figure 4a, the actual slope of these sloped portions 131, 132 may vary. For example, the sloped portions 131 , 132 may have a curved profile as shown in Figure 4b with a larger slope near the bifurcation point 13 than where the sloped portions 131 , 132 meet the ceiling 41 or the floor 42 of the common duct 11. In addition to a slope in the longitudinal direction, i.e. in the direction of the air flow 34, the sloped portions 131 , 132 are preferably sloped in the transverse direction too, thereby forming an aerodynamically shaped wedge-like structure.

Figure 5 schematically shows a bottom view of the air intake port 10 of Figure 2 together with a diagram indicating the cross section at different positions along its length. In addition to what has already been shown in and described with reference to Figure 2, the bottom view also shows the air outlets 15a, 15b. As can be seen in Figure 5, the total cross section of the air intake port 10 gradually decreases from Am at the air inlet to A_out at the two air outlets. Am therein is the cross section at the start of the common duct and A_out is the sum of the cross sections at the end of the two port legs 12a.12b. The decrease of the cross section does not follow a continuous and linear profile but is specifically designed to provide preferable air flow conditions with an aim to provide an undisturbed, high speed and high-volume flow of air at the outlets 15a, 15b of the air intake port 10. It is noted that, if the common duct 11 and the leg ports 12a, 12b are tubular or have a constant height-width ratio, the change in cross- section size may alternatively be visualised by showing the development of the radius, height, or width between the air inlet 14 and the air outlets 15a, 15b. Even though the overall profile of the cross section does not follow a linear pattern, the cross section may decrease linearly over parts of the common duct 11 and or the port legs 12a, 12b. This may particularly happen in sections where, e.g., the width of the common duct 11 or leg ports 12a, 12b is kept constant while the height decreases linearly (or vice versa).

As can be seen in Figure 5, the gradient of decrease of the total cross section is locally reduced in a region 31 adjacent the bifurcation point 13. The present invention discloses that by introducing this local reduction of the gradient of decrease of the total cross section in the region 31 around the bifurcation point 13, any possible disturbance of the air flow caused by the splitting and deflecting of the air flow is minimised. Preferably, the local reduction of the gradient of decrease of the total cross section is realised in the region immediately upstream and downstream of the bifurcation point 13, but the desired flow enhancing effect is at least partly achieved when reducing the gradient of decrease at only one side of the bifurcation point 13.

The air channel has an average gradient of decrease of the total cross section. The preferable average gradient will usually be a compromise between different design considerations. One possible constraint is the desired maximum speed of the air flow at the entrance of the combustion chamber. Too high speeds may lead to excessive NVH (noise, vibration, and harshness) problems and to choking of the port flow. Cylinder size and space constraints may define the maximum cross section of the air outlets of the air intake port. Given a maximum cross section and air flow speed at the outlet, a preferable average gradient of decrease of the total cross section can be established. Further constraints on the length and width of the air intake port may also play a role when determining the preferred. In preferred embodiments, the gradient of decrease of the total cross section may, for example, be locally at least 20% below the average gradient of decrease in at least a portion of the region adjacent the bifurcation point. In other embodiments, the gradient of decrease at that position may even be more than 25%, 30%, 35%, 40%, 45%, or 50% below the average gradient of decrease of the total cross section.

Optionally, like in the embodiment shown in Figure 5, the gradient of decrease of the total cross section is locally about zero in at least a portion of the region 31 adjacent the bifurcation point 13. In this embodiment, the cross section of the air intake port 10 remains substantially constant in the region around the bifurcation point, thereby allowing the air flow to move through undisturbed. In some embodiments, the gradient of decrease of the total cross section may even be locally below zero in at least a portion of the region 31 adjacent the bifurcation point 13, which means that the cross section locally increases in the region 31 around the bifurcation point 13.

Preferably, the gradient of decrease of the total cross section increases downstream of the region adjacent the bifurcation point 13. As soon as the air flow is split in two branches 12a, 12b, the cross section can be decreased again in order to further increase the air flow.

In the embodiment shown in Figure 5, the gradient of decrease of the total cross section is also locally reduced in the region 32 immediately upstream of the two air outlets. The air outlets 15a, 15b of the air intake port 10 connect to the air inlets of the combustion chamber. Like near the bifurcation point 13 of the air intake port 10, there may be a risk of undesired flow disturbances when the air flow reaches the intake valves and the transition point between the air intake port 10 and the combustion chamber. To minimise such disturbances, it may be preferred to bring the gradient of decrease of the total cross section down to or below zero in the region 32 immediately upstream of the air outlets 15a, 15b.

It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.

Claims

1. An air intake port for a lean-burn gasoline engine, the air intake port comprising: an air inlet, two air outlets, and an air channel connecting the air inlet to the two air outlets and comprising an upstream common duct and two downstream port legs, the two downstream port legs branching off from the common duct at a bifurcation point, the upstream common duct having a duct floor and a duct ceiling each comprising a sloped portion arranged to converge on the bifurcation point, wherein a bifurcation angle of less than 90 degrees is formed between the sloped portions of the duct floor and the duct ceiling at the bifurcation point.

2. An air intake port according to claim 1 , wherein the bifurcation angle is less than 75 degrees.

3. An air intake port according to any preceding claim, wherein the bifurcation angle is less than 55 degrees.

4. An air intake port according to any preceding claim, wherein the bifurcation angle is less than 45 degrees.

5. An air intake port according to any of the preceding claims, wherein a port leg length measured from the bifurcation point to one of the two air outlets is at least twice a diameter of the respective air outlet.

6. An air intake port according to any of the preceding claims, wherein a total cross section of the air channel gradually decreases between the air inlet and the two air outlets, and wherein a gradient of decrease of the total cross section is locally reduced in a region immediately in front of and/or behind the bifurcation point.

7. An air intake port according to claim 6, wherein the gradient of decrease of the total cross section is locally lower than or equal to zero in at least a portion of the region immediately in front of and/or behind the bifurcation point.

8. A lean-burn gasoline engine comprising at least one air intake port according to any of the preceding claims.

9. A vehicle comprising a lean-burn gasoline engine according to claim 8.