EP4314537A1

EP4314537A1 - Air intake port for a lean-burn gasoline engine

Info

Publication number: EP4314537A1
Application number: EP21716624.8A
Authority: EP
Inventors: Jack Johnson; Lyn Mcwilliam; Simon DRINKWATER
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2021-03-26
Filing date: 2021-03-26
Publication date: 2024-02-07
Also published as: WO2022199834A1

Abstract

An air intake port (10) for a lean-burn gasoline engine (110), the air intake port (10) comprising 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) and comprising 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 two port legs (12a, 12b) diverge from the bifurcation point (13) and are shaped to be parallel or converge proximal to the two air outlets (15a, 15b).

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 gasoline 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 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 two port legs diverge from the bifurcation point and are shaped to be parallel or converge proximal to the two air outlets. 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 the prior art, as well as in the air intake port according to the invention, the two port legs diverge when branching off from the common duct at the bifurcation point. In the prior art, the air flow of the air entering the combustion chamber is commonly directed outward, toward the circular wall of that combustion chamber. When approaching the far end of the combustion chamber relative to the position of the entering air, the two originally divergent airflow streams are deflected inward toward the centre of the combustion chamber and then backward toward the position of the entering air, thereby resulting in a swirl pattern that is commonly called omega swirl. With the air intake port according to the invention, however, the direction of the omega swirl is reversed. By delivering the intake air to the combustion chamber through two port legs that do not diverge towards the air outlets of the air intake port and into the combustion chamber, the air flow of the air entering the combustion chamber will first be directed down the centre of the chamber and then splits to move outward before returning. This reverses the omega swirl compared to the prior art. The inventors have found that by reversing the omega swirl it is ensured that a larger part of the combustion will take place closer to the centre of the combustion chamber, with a small push towards the exhaust valves. As a result, this leaves the unburnt end gas under the cooler intake valves. This helps to reduce knock and thus to increase the performance and durability of the engine.

Each one of the two port legs may be defined as having a respective centre line. A tangent to the centre line of one of the two port legs at its respective air outlet makes a port exit angle with a tangent to the centre line of the other one of the two port legs at its respective air outlet. When the two port legs run in parallel when reaching the two air outlets of the air intake port, the port exit angle is 0 (zero). For converging port legs, the port exit angle is greater than 0. In exemplary embodiments of the invention, the port exit angle is larger than 5 degrees. In further embodiments, the port exit angle may be larger than 10 or 15 degrees.

In an embodiment of the air intake port according to 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 present invention discloses that when the port legs each have a length of at least twice the respective 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 parallel or convergent course of the port legs when approaching the air outlets of the air intake port. Reduced air flow disturbance thereby further allow for increased control and predictability of the swirl pattern inside the combustion chamber.

According to a further aspect of the invention, a lean-burn gasoline engine is provided comprising at least one air intake port as described above and a combustion chamber with two air inlets, the two air outlets of the air intake port being connected to the two air inlets of the combustion chamber. 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;

Figure 4a schematically shows a cross-sectional view of an air intake port according to the prior art and a combustion chamber to which the air intake port is attached; and

Figure 4b schematically shows a cross-sectional view of an air intake port according to an embodiment of the invention and a combustion chamber to which the air intake port is attached.

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.

The port legs 12a, 12b diverge from the bifurcation point 13 to provide for two separate air flow channels to two separate combustion chamber air inlets. At some point in between the bifurcation point 13 and the air outlets 15a, 15b, the port legs 12a, 12b stop diverging and start running in parallel, or may even converge. These directional changes are preferably designed such that any disturbance of the air flow is avoided or minimised. The advantages of the non diverging port legs 12a, 12b and the thus obtained non-diverging air flows will be discussed in more detail below with reference to Figures 4a and 4b. 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 airoutlets 15a, 15b. Figure 3 further indicates the respective longitudinal axes 111, 112a, 112b of the common duct 11 and the port legs 12a, 12b. Looking at the longitudinal axes 112a, 112b of the port legs 12a, 12b, it can be seen how they first diverge and then bend towards each other until they slightly converge near the air outlets 15a, 15b.

Figure 4a schematically shows a cross-sectional view on a combustion chamber 50 to which an air intake port according to the prior art is attached. Like most known air intake ports with a single air inlet and two air outlets, this one has two straight port legs 42a, 42b that branch off and extend in a straight line from the bifurcation point. As a result, the air flow of the air entering the combustion chamber 50 is directed outward, toward the circular wall of that combustion chamber 50. When hitting or approaching the opposite chamber wall, the two air flow streams are then deflected inward and backward, thereby resulting in a swirl pattern that is commonly called omega swirl. Also shown in Figure 4a are two exhaust outlets 56 through which the exhaust air is expelled by the piston stroke following the combustion. Exhaust valves close off these exhaust outlets 56 before and during combustion.

Figure 4b schematically shows a cross-sectional view on a combustion chamber 50 to which an air intake port 10 according to an embodiment of the invention is attached. With this air intake port 10, the direction of the omega swirl is reversed. By delivering the intake air to the combustion chamber 50 through two port legs 12a, 12b that converge towards the air outlets 15a, 15b of the air intake port 10, the air flow of the air entering the combustion chamber 50 will first be directed down the centre of the chamber 50 and then splits to move outward. The inventors have found that by reversing the omega swirl it is ensured that a larger part of the combustion will take place closer to the centre of the combustion chamber 50, with a small push towards the exhaust valves. As a result, this leaves the unburnt end gas under the cooler intake valves. This helps to reduce knock and thus to increase the performance and durability of the engine 110.

Each one of the two port legs 12a, 12b defines a respective centre line 112a, 112b. A tangent to the centre line 112a, 112b of one of the two port legs 12a, 12b at its respective air outlet makes a port exit angle 34 with a tangent to the centre line 112a, 112b of the other one of the two port legs 12a, 12b at its respective air outlet 15a, 15b. In exemplary embodiments of the invention, the port exit angle 34 is larger than 5 degrees. In further embodiments, the port exit angle 34 may be larger than 10 or 15 degrees. It is, however, to be noted that the desired reversal of the omega swirl direction has also be obtained with a port exit angle 34 just above or even as small as 0 degrees, i.e. when the port legs 12a, 12b run in parallel when approaching the combustion chamber 50. 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. This positive effect on the reduction of air flow disturbance adds to the air flow improvement already provided by the parallel or convergent course of the port legs when approaching the air outlets of the air intake port. Reduced air flow disturbance thereby further allow for increased control and predictability of the swirl pattern inside the combustion chamber.

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, wherein the two port legs diverge from the bifurcation point and are shaped to be parallel or converge proximal to the two air outlets.

2. An air intake port according to claim 1 , wherein each one of the two port legs has a respective centre line, wherein a tangent to the centre line of one of the two port legs at its respective air outlet makes a port exit angle with a tangent to the centre line of the other one of the two port legs at its respective air outlet, and wherein the port exit angle is equal to or larger than 0 degrees.

3. An air intake port according to claim 2, wherein the port exit angle is larger than 5 degrees.

4. An air intake port according to claim 3, wherein the port exit angle is larger than 10 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 outlet.

6. A lean-burn gasoline engine comprising at least one air intake port according to any of the preceding claims and a combustion chamber with two air inlets, the two air outlets of the air intake port being connected to the two air inlets of the combustion chamber.

7. A vehicle comprising a lean-burn gasoline engine according to any of claims 6.