Internal combustion engine and method for controlling internal combustion engine

Abstract

An internal combustion engine (10) comprises a combustion chamber (28), a spark plug (43), an intake port (30), and an exhaust port (31). A tip (43a) of the spark plug (43) is positioned between the intake port (30) and the exhaust port (31) and to the side thereof. Where the side of the combustion chamber (28) where the tip (43a) of the spark plug (43) is disposed, in a plan view of the combustion chamber (28), is an R-side space (SR), and the side opposite to the R-side space (SR) is an L-side space (SL), an air current (F) traveling from the R-side space (SR) to the L-side space (SR) is generated in the combustion chamber (28), and a fuel-air mixture is supplied to the combustion chamber (28) such that the concentration of ethanol-containing fuel in the fuel-air mixture included in the L-side space (SL) is higher than the concentration of the ethanol-containing fuel in the fuel-air mixture included in the R-side space (SR).

Description

[Technical field]

[0001] The present invention relates to an internal combustion engine and a method for controlling an internal combustion engine. [Background technology]

[0002] Among internal combustion engines that can take in alcohol fuel, one of the methods to achieve carbon neutrality, there are internal combustion engines that can take in fuel containing ethanol. Although ethanol has a calorific value per unit weight that is about 60% of that of diesel, it has a higher octane number than gasoline, so it can achieve a high compression ratio while suppressing the occurrence of knocking. When using ethanol as fuel for automobiles such as motorcycles, it can be mixed with gasoline or diesel at about 10 to 20% ethanol, or it can be used only with ethanol. When using ethanol-containing fuel as fuel, the internal combustion engine is controlled to operate with an air-fuel ratio (also called "A / F") that corresponds to the mixture ratio of various fuels.

[0003] A conventional internal combustion engine includes, for example, a cylinder head, a cylinder, an intake port formed in the cylinder head for taking in air into a combustion chamber, an exhaust port for exhausting the combustion chamber, and an injector for directly injecting fuel into the combustion chamber. In this internal combustion engine, the intake port forms a swirl flow in the combustion chamber, and the injector extends at an angle to the cylinder axis so that the fuel injection port faces the swirl flow (Patent Document 1).

[0004] Also, as an internal combustion engine using gasoline containing bioethanol, there is a homogeneous charge compression ignition engine equipped with an ignition unit (spark plug), a fuel injection unit (injector), and a control unit (ECU). It is disclosed that the control unit of this engine outputs a control signal to the fuel injection unit so that the fuel concentration of the mixture at the outer periphery of the combustion chamber is richer than the fuel concentration of the mixture at the center and the fuel amount of the mixture at the outer periphery is greater than the fuel amount of the mixture at the center when the engine is operated in a preset high load range, and outputs a control signal to the ignition unit so that the mixture at the center is ignited. As a result, when the engine is operated in the high load range, the mixture starts SI combustion by flame propagation due to ignition of the ignition unit, and then the unburned mixture performs CI combustion by compression ignition (Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2008-82329 A [Patent Document 2] JP 2019-39327 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, although increasing the ethanol concentration in fuel improves knocking resistance and enables even higher compression ratios to be achieved, ethanol and other alcohols have a larger latent heat of vaporization than gasoline and therefore tend to absorb heat from the combustion chamber, and cooling losses also tend to increase as compression ratios are increased, so there is room for improvement in fuel efficiency at high compression ratios.

[0007] An object of the present invention is to provide an internal combustion engine and a control method for an internal combustion engine that can improve thermal efficiency and reduce cooling loss even at a high compression ratio, thereby achieving improved fuel efficiency. [Means for solving the problem]

[0008] In order to achieve the above object, the present invention has the following configuration. [1] An internal combustion engine according to a first aspect of the present invention is an internal combustion engine (10) including a combustion chamber (28), an ignition plug (43) disposed in the combustion chamber (28), an intake port (30) that allows an air-fuel mixture containing ethanol to be drawn into the combustion chamber (28), and an exhaust port (31) through which exhaust gas flows out from the combustion chamber (28), a tip portion (43a) of the spark plug (43) is located between and to the side of the intake port (30) and the exhaust port (31); In a plan view of the combustion chamber (28), the side of the combustion chamber (28) on which the tip portion (43a) of the ignition plug (43) is disposed is referred to as an R-side space (S R ), the R-side space (S R The opposite side of the L-side space (S L ), and the R-side space (S R ) to the L side space (S L ) and generates an airflow (F) toward the L-side space (S L The concentration of the ethanol-containing fuel in the mixture contained in the R-side space (S R The mixture is supplied to the combustion chamber (28) so that the concentration of the ethanol-containing fuel is higher than the concentration of the ethanol-containing fuel in the mixture contained in the combustion chamber (28).

[0009] [2] The R-side space (S R ) to the L side space (S L The airflow (F) toward the cylinder (13) is preferably an airflow originating from a tumble flow (TF) generated within the cylinder (13) of the internal combustion engine.

[0010] [3] Moving the main flow of the tumble flow (TF) away from the tip portion (43a) of the ignition plug (43) to delay the timing of initial flame formation in the combustion chamber (28); The flame generated in the combustion chamber (28) flows from the tip portion (43a) of the ignition plug (43) into at least the L-side space (S L ) is preferred.

[0011] [4] At least the L-side space (S L A squish portion (29) is provided in a portion corresponding to a part of the By generating a reverse squish flow (f) in the squish portion (29), the reverse squish flow (f) flows into the R-side space (S R ) to the L side space (S L ) may be promoted.

[0012] [5] The internal combustion engine includes an ethanol concentration detection unit (51) that detects a concentration of ethanol supplied to the combustion chamber (28); an oil cooling passage (52) provided in at least the cylinder block (14); an opening and closing device (53) for opening and closing the oil cooling path (52); a first operation control unit (54) that controls an operation of the opening and closing device (53); Further comprising: The first operation control section (54) may block the oil cooling path (52) when the ethanol concentration detected by the ethanol concentration detection section (51) is higher than a predetermined value.

[0013] [6] Either or both of an oxygen concentration detection unit (57A) that detects an oxygen concentration in the exhaust gas and an air-fuel ratio detection unit (57B) that detects an air-fuel ratio from the oxygen concentration and the unburned gas concentration; an in-cylinder pressure detection unit (58) that detects an in-cylinder pressure of the internal combustion engine; an ethanol concentration estimation unit (59) that estimates a concentration of ethanol supplied to the combustion chamber (28) based on a detection result detected by either or both of the oxygen concentration detection unit (57A) and the air-fuel ratio detection unit (57B) and a detection result detected by the in-cylinder pressure detection unit (58); an oil cooling passage (52) provided in at least the cylinder block (14); an opening and closing device (53) for opening and closing the oil cooling path (52); a first operation control unit (54) that controls an operation of the opening and closing device (53); Further comprising: The internal combustion engine according to any one of the above [1] to [4], wherein the first operation control unit (54) blocks the oil cooling path (52) when the ethanol concentration estimated by the ethanol concentration estimation unit (59) is higher than a predetermined value.

[0014] [7] The internal combustion engine includes an ethanol concentration detection unit (51) that detects a concentration of ethanol supplied to the combustion chamber (28); a louver member (61) disposed in front of the cylinder block (14) in the traveling direction of the vehicle and rotatably provided; an opening / closing device (62) for opening and closing the louver member (61); a second operation control unit (63) that controls the operation of the opening and closing device (62); Further comprising: The second operation control unit (63) may rotate the louver member (61) to reduce the airflow (F) toward the cylinder block (14) when the ethanol concentration detected by the ethanol concentration detection unit (51) is higher than a predetermined value.

[0015] [8] Either or both of an oxygen concentration detection unit (57A) that detects an oxygen concentration in the exhaust gas and an air-fuel ratio detection unit (57B) that detects an air-fuel ratio from the oxygen concentration and the unburned gas concentration; an in-cylinder pressure detection unit (58) that detects an in-cylinder pressure of the internal combustion engine; an ethanol concentration estimation unit (59) that estimates a concentration of ethanol supplied to the combustion chamber (28) based on a detection result detected by either or both of the oxygen concentration detection unit (57A) and the air-fuel ratio detection unit (57B) and a detection result detected by the in-cylinder pressure detection unit (58); a louver member (61) disposed in front of the cylinder block (14) in the traveling direction of the vehicle and rotatably provided; an opening / closing device (62) for opening and closing the louver member (61); a second operation control unit (63) that controls the operation of the opening and closing device (62); Further comprising: The internal combustion engine according to any one of the above items [1] to [6], wherein the second operation control unit (63) rotates the louver member (61) to reduce the airflow (F) flowing toward the cylinder block (14) when the ethanol concentration estimated by the ethanol concentration estimation unit (59) is higher than a predetermined value.

[0016] [9] The internal combustion engine according to any one of the above [1] to [8], wherein a crown surface (26a) of each piston (26A, 26B) in the internal combustion engine (10) is flat, or a recess (26b) is provided in the crown surface (26a).

[0017]

[10] A control method for an internal combustion engine according to a second aspect of the present invention is a control method for an internal combustion engine (10) including a combustion chamber (28), an ignition plug (43) disposed in the combustion chamber (28), an intake port (30) that enables an air-fuel mixture containing ethanol to be drawn into the combustion chamber (28), and an exhaust port (31) through which exhaust gas flows out from the combustion chamber (28), a tip portion (43a) of the spark plug (43) is located between and to the side of the intake port (30) and the exhaust port (31); In a plan view of the combustion chamber (28), the side of the combustion chamber (28) on which the tip portion (43a) of the ignition plug (43) is disposed is referred to as an R-side space (S R ), and the opposite side of the R side is the L side space (S L ), and the R-side space (S R ) to the L side space (S L ) and generates an airflow (F) toward the L-side space (S L The concentration of the ethanol-containing fuel in the mixture contained in the R-side space (S R The mixture is supplied to the combustion chamber (28) so that the concentration of the ethanol-containing fuel is higher than the concentration of the ethanol-containing fuel in the mixture contained in the combustion chamber (28).

[0018]

[11] The R-side space (S R ) to the L side space (S L The airflow (F) toward the cylinder (13) is preferably an airflow originating from a tumble flow (TF) generated within the cylinder (13) of the internal combustion engine.

[0019]

[12] Moving the main flow of the tumble flow (TF) away from the tip portion (43a) of the ignition plug (43) to delay the timing of initial flame formation in the combustion chamber (28); The flame generated in the combustion chamber (28) flows from the tip portion (43a) of the ignition plug (43) into at least the L-side space (S L ) is preferred.

[0020]

[13] At least the L-side space (S L By generating a reverse squish flow (f) in the squish portion (29) arranged in a portion corresponding to a part of the R-side space (S R ) to the L side space (S L ) may be promoted.

[0021] According to the internal combustion engine described in [1] above, in a plan view of the combustion chamber, the side of the combustion chamber where the tip of the ignition plug is located is defined as the R-side space, and the opposite side of the R-side space is defined as the L-side space. An airflow is generated in the combustion chamber from the R-side space toward the L-side space, and the air-fuel mixture is supplied to the combustion chamber so that the concentration of the ethanol-containing fuel in the air-fuel mixture contained in the L-side space is higher than the concentration of the ethanol-containing fuel in the air-fuel mixture contained in the R-side space. This makes the initial combustion period longer than before, while the main combustion period is equal to or shorter than before, and the flame is allowed to flow into the R-side space S. R From L side space S L This allows for late combustion, where rapid combustion occurs due to ignition delay, and reduces cooling loss during the expansion stroke. Therefore, even in the case of a high compression ratio using high-concentration ethanol fuel, it is possible to reduce cooling loss while improving thermal efficiency, thereby improving fuel efficiency.

[0022] According to the internal combustion engine described in [2] above, the tumble flow generated during the intake stroke is utilized to form an airflow from the R-side space to the L-side space during the compression stroke, so that the airflow can be easily and reliably formed in the combustion chamber during the compression stroke.

[0023] According to the internal combustion engine described in [3] above, the timing of initial flame formation can be reliably delayed to sufficiently lengthen the initial combustion period.

[0024] According to the internal combustion engine described in [4] above, by generating a reverse squish flow in the squish portion or in its vicinity during the compression stroke, the airflow from the R-side space to the L-side space is promoted by the reverse squish flow, thereby enabling even more rapid combustion to be achieved in the main combustion, and the main combustion period can be shortened.

[0025] According to the internal combustion engine described in [5] or [6] above, the oil cooling path of the internal combustion engine is utilized to suppress the cooling of the cylinder block and the cylinder head, thereby making it possible to increase the temperature of the combustion chamber or its surroundings, and as a result, it is possible to further suppress the cooling loss during the expansion stroke.

[0026] According to the internal combustion engine described in [7] or [8] above, by utilizing outside air to suppress the cooling of the cylinder block and the cylinder head, the temperature of the combustion chamber or its surroundings can be increased, and as a result, it is possible to further suppress the cooling loss during the expansion stroke.

[0027] According to the internal combustion engine described in [9] above, it becomes easier to maintain the tumble flow formed in the cylinder, and an airflow directed from the R-side space to the L-side space in the combustion chamber can be easily generated. Effect of the Invention

[0028] According to the present invention, it is possible to reduce cooling loss while improving thermal efficiency even at a high compression ratio, thereby achieving improved fuel economy. [Brief description of the drawings]

[0029] [Figure 1] FIG. 1 is a side view showing an example of an internal configuration of an internal combustion engine according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a perspective view of the internal combustion engine of FIG. 1 as viewed obliquely from above. [Diagram 3] FIG. 3 is a schematic side view for explaining the tumble flow that occurs inside the cylinder before it approaches the top dead center. [Figure 4] FIG. 4 is a schematic side view for explaining the airflow generated in the combustion chamber near the top dead center. [Diagram 5] FIG. 5 is a view of the combustion chamber of FIG. 4 as seen from below. [Figure 6] FIG. 6 is a graph illustrating the ignition delay time of the ethanol fuel used in this embodiment. [Figure 7] FIG. 7(A) is a diagram comparing the initial flame volume in the internal combustion engine according to this embodiment with the initial flame volume in a conventional internal combustion engine, and FIG. 7(B) is a diagram explaining a method of calculating the initial flame volume. [Figure 8] FIG. 8 is a schematic side view showing a modified example of the internal configuration of the internal combustion engine of FIG. [Figure 9] FIG. 9 is a view of the combustion chamber of FIG. 8 as seen from below. [Figure 10] FIG. 10 is a diagram showing a modified example of the internal combustion engine according to this embodiment. [Figure 11] FIG. 11 is a diagram showing another modified example of the internal combustion engine according to the present embodiment. [Figure 12] FIG. 12 is a diagram showing another modified example of the internal combustion engine according to this embodiment. [Figure 13] FIG. 13 is a diagram showing another modified example of the internal combustion engine according to the present embodiment. [Figure 14] FIG. 14 is a diagram showing another modified example of the internal combustion engine according to the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0031] 1 is a side view showing an example of the internal configuration of an internal combustion engine according to an embodiment of the present invention. In this embodiment, the internal structure of a single-cylinder, two-valve engine will be described as an example of the internal combustion engine. Note that the drawings used in the following description may show characteristic parts in an enlarged manner for the sake of convenience in order to make the characteristics easier to understand, and the dimensional ratios of each component are not limited to those shown in the drawings.

[0032] 1, the internal combustion engine 10 includes a cylinder head 15, a cylinder 13 protruding from a crankcase (not shown), and a head cover (not shown) that closes an opening of the cylinder head 15. The cylinder head 15 is attached to an upper end of a cylinder block 14 of the cylinder 13. The internal combustion engine 10 is supported in such a position that a cylinder axis L1, which is the central axis of the cylinder 13, is substantially vertical (specifically, so that it coincides with a straight line extending in the vertical direction).

[0033] A piston 26A is fitted in the cylinder block 14 so as to be able to reciprocate. One end of a connecting rod 27 is connected to the piston 26A. The other end of the connecting rod 27 is connected to a crankshaft (not shown) that extends in the vehicle width direction. A combustion chamber 28 is formed in the cylinder head 15, to which the top of the piston 26A faces. The cylinder head 15 is provided with an intake port 30 that extends from the combustion chamber 28 and opens to one side surface (rear surface) of the cylinder head 15, and an exhaust port 31 that extends from the combustion chamber 28 and opens to the other side surface (front surface) of the cylinder head 15.

[0034] The intake port 30 and the combustion chamber 28 are opened and closed by an intake valve 32. The exhaust port 31 and the combustion chamber 28 are opened and closed by an exhaust valve 33. The intake valve 32 opens and closes in accordance with the swing of an intake side rocker arm 34. The exhaust valve 33 opens and closes in accordance with the swing of an exhaust side rocker arm 35. The intake side rocker arm 34 and the exhaust side rocker arm 35 are freely swingable within the cylinder head 15.

[0035] A camshaft 36 extending in the vehicle width direction is disposed in a space surrounded by the intake rocker arm 34, the exhaust rocker arm 35, the intake valve 32, and the exhaust valve 33. The camshaft 36 is rotatably supported by the cylinder head 15 via a bearing (not shown).

[0036] A driven sprocket 39 is attached to one end of the camshaft 36 that protrudes outward in the vehicle width direction from a bearing (not shown). A cam chain 40 is wound around a driving sprocket attached to one end of a crankshaft (not shown) and the driven sprocket 39. As a result, the camshaft 36 rotates in engagement with the crankshaft.

[0037] The intake side rocker arm 34 is oscillated by an intake cam 37 provided on the camshaft 36. The exhaust side rocker arm 35 is oscillated by an exhaust cam 38 provided on the camshaft 36. This causes the intake valve 32 and the exhaust valve 33 to open and close.

[0038] The injector 41 is attached to the cylinder head 15 in a state in which it extends in the front-rear direction. The injector 41 is supplied with fuel from a fuel tank (not shown). The injector 41 injects fuel into the combustion chamber 28. The fuel used in this embodiment is an ethanol-containing fuel in which ethanol is contained in a fossil fuel such as gasoline, or an ethanol fuel made of ethanol. Hereinafter, these will be collectively referred to as an ethanol-containing fuel, or simply as fuel.

[0039] FIG. 2 is a perspective view of the internal combustion engine 10 of FIG. 1 as viewed obliquely from above, and FIG. 3 is a schematic side view for explaining a tumble flow that occurs inside the cylinder before approaching top dead center.

[0040] 2 and 3, the spark plug 43 is attached to the cylinder head 15 so that the tip 43a is exposed to the combustion chamber 28. The tip 43a of the spark plug 43 is located between the intake port 30 and the exhaust port 31 and to the side of them. In this embodiment, in a plan view of the combustion chamber 28, the side of the combustion chamber 28 on which the tip 43a of the spark plug 43 is located is referred to as the R-side space S. R The opposite side of the R side space is the L side space S L It is defined as:

[0041] In the intake stroke, the piston 26A descends and the intake port 30 opens, forming a tumble flow TF of air in the combustion chamber 28 and the cylinder 13. The tumble flow TF is a swirling flow around an axis intersecting the cylinder axis, and is a vertical vortex that descends or ascends in the cylinder axial direction. In this embodiment, the main stream of the tumble flow TF is configured to be as far away as possible from the tip 43a of the spark plug 43. For example, the port shape of the intake port 30 is adjusted to control the inflow direction of the air or mixture, thereby making it possible to separate the main stream of the tumble flow TF from the tip 43a of the spark plug 43. To control the inflow direction of the air or mixture, the air or mixture is made to have a directionality in the flow of the intake port 30 (or the intake valve 32) and, for example, the air or mixture is made to flow from the intake port 30 to the L-side space S of the combustion chamber 28. L into the R side space S R It is possible to prevent as much as possible of this from entering the

[0042] In the compression stroke, as shown in FIG. 4, as the piston 26A rises, the tumble flow TF is crushed in the vertical direction by the combustion chamber 28, and the main stream of the tumble flow TF flows through the exhaust port 31 or the L-side space S. L As a result, as shown in FIG. 5, at the top dead center of the piston 26A, the R-side space S of the combustion chamber 28 is filled in the combustion chamber 28. R From L side space S L In this embodiment, this airflow is also referred to as an airflow derived from a Dumbledore flow. R From L side space SL In FIG. 5, the area defined by the outer periphery 28A of the combustion chamber 28 and the two-dot chain line L1 on the R side is the R-side space S. R On the L side, the area defined by the outer periphery 28A of the combustion chamber 28 and the two-dot chain line L2 is the R-side space S L It is.

[0043] At this time, the L-side space S in the combustion chamber 28 L The concentration of the ethanol-containing fuel in the mixture in the R-side space S R The mixture is supplied to the combustion chamber 28 so that the concentration of the ethanol-containing fuel in the mixture is higher than that of the ethanol-containing fuel in the L-side space S. For example, the injection timing of the ethanol fuel or the ethanol-containing fuel and the ignition timing of the spark plug 43 are adjusted to adjust the concentration of the ethanol-containing fuel in the L-side space S. L The concentration of ethanol-containing fuel in the mixture in the R-side space S R The concentration of the ethanol-containing fuel in the air-fuel mixture can be made higher than the concentration of the ethanol-containing fuel in the air-fuel mixture contained in the fuel tank. As a method for adjusting the injection timing, for example, the oxygen concentration, air-fuel ratio, intake temperature, atmospheric pressure, etc. of the exhaust gas are detected, and the injection timing can be adjusted by the ECU 50 based on one or more of these detection results. As a simple method, a map showing the correlation between the concentration of the ethanol-containing fuel in the air-fuel mixture and / or the ethanol concentration in the ethanol-containing fuel and the injection timing can be obtained in advance, and the injection timing can be adjusted based on the map. Furthermore, the cylinder pressure can be detected, and the detection result of the cylinder pressure is added to the above detection result to adjust the injection timing by the ECU 50, thereby making it possible to perform more accurate adjustment. The ignition timing can be adjusted in the same manner as the above-mentioned injection timing adjustment method.

[0044] In this embodiment, when a fuel containing ethanol is used, an ignition delay occurs when the ratio of ethanol added to the fuel is increased due to the presence of intermediate products such as aldehydes generated in the oxidation process of alcohol. For example, as shown in Figure 6, under conditions of a compression ratio of 13.9, an intake temperature of 40°C, and an equivalence ratio of 0.4, the ignition delay time of a mixture in which normal heptane is mixed with ethanol is longer than the ignition delay time of a mixture in which normal heptane is mixed with toluene or isooctane (PRF). It can also be seen that the difference in delay time for each fuel increases as the mixture ratio (mass%) of each fuel increases.

[0045] In this embodiment, this characteristic is utilized to intentionally delay the timing of initial flame formation by moving the tumble flow TF away from the tip 43a of the spark plug 43. As a result, there is an ignition delay immediately after ignition by the spark plug 43, but the flame then extends toward the wall surface of the combustion chamber 28 in the flow direction of the airflow F (flame propagation direction D in FIG. 5), accelerating combustion all at once. At this time, the flame generated in the combustion chamber 28 flows into the R-side space S. R From L side space S L and / or the exhaust port 31, specifically, from the tip portion 43a of the ignition plug 43 to the L-side space S L and / or propagates towards the exhaust port 31.

[0046] Also, the L side space S L Mixture concentration of L side space S L The ethanol concentration in the R-side space S R As described above, there is an ignition delay immediately after ignition by the spark plug 43, but L The ethanol concentration in the R-side space S R By making the mixture richer than the front side, the ignition delay is reversed and the flame spreads rapidly, resulting in a faster laminar combustion speed and promoting rapid combustion.

[0047] FIG. 7(A) is a diagram comparing the initial flame volume in the internal combustion engine according to this embodiment with the initial flame volume in a conventional internal combustion engine, and FIG. 7(B) is a diagram explaining a method of calculating the initial flame volume. As shown in Fig. 7(A) and Fig. 7(B), the initial flame was assumed to be an elliptical sphere, and one side A and one side B of each initial flame were rotated around the major axis as the rotation axis, and the average value was calculated as the initial flame volume. The measurement period of the initial flame was an average of 200 cycles, and the measurement conditions were an internal combustion engine speed of 3000 rpm / min, BMEP (breakdown mean effective pressure) of 300 kPa, and A / F of 14.7. As a result, the initial flame in the internal combustion engine according to this embodiment propagates toward the L-side space (or the L-side space and exhaust port) compared to the conventional one, and the initial flame volume in this embodiment is smaller than the conventional initial flame volume. Therefore, it can be seen that the flame volume is small and the initial flame growth is small due to late combustion in which rapid combustion occurs due to ignition delay.

[0048] In addition, the flame generated in the combustion chamber 28 flows along the air flow F into the L side space S L and / or the exhaust port 31, the total initial combustion period becomes longer. On the other hand, it is known that the flame propagation speed when the mass fraction burned (MFB) is 10% or more is the same as in the conventional case, and as a result, the main combustion period becomes the same as in the conventional case or shorter. Therefore, by making the initial combustion period longer than in the conventional case while maintaining the main combustion period the same as in the conventional case or shorter, and controlling the direction of flame stretch as described above, it is possible to realize late combustion in which rapid combustion occurs due to ignition delay, and it becomes possible to reduce cooling loss during the expansion stroke.

[0049] FIG. 8 is a schematic side view showing a modified example of the internal configuration of the internal combustion engine 10 of FIG. 4, and FIG. 9 is a view of the combustion chamber 28 of FIG. 7 as seen from below. As shown in FIGS. 8 and 9, at least the L-side space S in the outer circumferential portion 28A of the combustion chamber 28 LA squish portion 29 may be provided in a portion corresponding to a part of the R-side space S. The squish portion 29 forms a reverse squish flow f from the center of the combustion chamber 28 to the outer periphery during the compression stroke. By generating the reverse squish flow f in the squish portion 29 or in its vicinity, the R-side space S R From L side space S L The airflow F toward the center of the cylinder is promoted by the reverse squish flow f, so that further rapid combustion can be achieved in the main combustion, and the main combustion period can be shortened.

[0050] The structure of the squish portion 29 is not particularly limited. For example, the squish portion 29 may be formed in the L-side space S of the combustion chamber 28, which is circular in plan view. L A squish surface (not shown) that protrudes radially outward more than other portions can be provided in a portion corresponding to a part of the exhaust port 31 and a part of the exhaust port 32. During the compression stroke, the squish surface comes close to the upper surface of the piston 26A that faces the squish surface, thereby forming a squish portion 29.

[0051] The range in which the squish portion 29 is formed is, for example, the L-side space S of the outer peripheral portion 28A in a plan view. L 9. The boundary between the outer peripheral portion 28A and the exhaust port 31 of the outer peripheral portion 28A (the outer peripheral portion 28A and the L-side space S in FIG. 9) is taken as a reference. L The grooves are formed in a range of 1 / 2, 1 / 3, or 1 / 4 along the circumferential direction from the intersection with the two-dot chain line L1 that defines the grooves.

[0052] Similarly, the squish portion 29 is, for example, in a plan view, defined by taking the entire range of the portion of the outer peripheral portion 28A corresponding to the exhaust port 31 as a reference, and the L-side space S L The boundary between the outer periphery 28A and the L-side space S in FIG. L The entire range of the portion of the outer circumferential portion 28A corresponding to the exhaust port 31 may be, for example, the range of the outer circumferential portion 28A and the L-side space S in FIG. L From the intersection with the two-dot chain line L2 that defines the outer circumferential portion 28A and the R-side space SR The range is up to the intersection with the two-dot chain line L2 which defines the above.

[0053] In FIG. 8 and FIG. 9, the squish portion 29 is disposed in the L-side space S of the outer circumferential portion 28A of the combustion chamber 28. L and a part of the exhaust port 31, but is not limited thereto. L That is, the squish portion 29 may be disposed only in a portion corresponding to a part of the L-side space S. L may be disposed in a portion corresponding to at least a part of The squish surface is disposed in the L-side space S of the combustion chamber 28, which is circular in plan view. L The portion corresponding to at least a part of the groove may protrude radially inward further than the other portions.

[0054] As described above, according to the present embodiment, the side of the combustion chamber 28 on which the tip portion 43a of the ignition plug 43 is disposed in a plan view of the combustion chamber 28 is defined as the R-side space S. R The opposite side of the R-side space is the L-side space S L The combustion chamber 28 includes an R-side space S R From L side space S L It generates airflow F toward the L side space S L The concentration of the ethanol-containing fuel in the mixture in the R-side space S R The mixture is supplied to the combustion chamber 28 so that the concentration of the ethanol-containing fuel in the mixture is higher than that in the mixture contained in the R side space S. Therefore, the initial combustion period is longer than before, while the main combustion period is equal to or shorter than before, and the flame is in the R side space S. R From L side space S LThe ignition delay causes rapid combustion, resulting in late combustion, and the cooling loss during the expansion stroke can be reduced. Therefore, even in the case of a high compression ratio using a high-concentration ethanol fuel, the cooling loss can be reduced while improving the thermal efficiency, and fuel efficiency can be improved. The high compression ratio may be, for example, 14 or more, or may be 14. In addition, since the laminar burning speed tends to become higher in the fuel characteristics when the ethanol concentration is increased, it is possible to further improve fuel efficiency by increasing the concentration of ethanol in the fuel and increasing the compression of the internal combustion engine.

[0055] FIG. 10 is a diagram showing a modified example of the internal combustion engine 10 according to the present embodiment. As shown in FIG. 10, the internal combustion engine 10 includes an ethanol concentration detection unit 51 that detects the concentration of ethanol supplied to the combustion chamber 28 (see FIG. 1), an oil cooling path 52 provided in at least the cylinder block 14, an opening / closing device 53 that opens and closes the oil cooling path 52, and a first operation control unit 54 that controls the operation of the opening / closing device 53.

[0056] The ethanol concentration detection unit 51 is disposed between the fuel tank 55 and the fuel injection valve 56, and detects the ethanol concentration in the fuel f supplied into the cylinder 13. The ethanol concentration in the fuel f refers to the content of ethanol when the mass of the entire fuel is taken as 100% by mass, and the predetermined value of the ethanol concentration differs depending on the specifications and the operating state, but is, for example, a value within a range of 20% by mass or more. The predetermined value of the ethanol concentration is stored, for example, in a storage unit (not shown). The fuel injection valve 56 supplies the fuel f into the cylinder 13 via a pump. The ethanol concentration detection unit 51 is electrically connected to the first operation control unit 54.

[0057] The oil cooling path 52 is provided, for example, in the cylinder block 14, and forms a circulation path via an oil cooler (not shown). The oil cooling path 52 only needs to be provided mainly in the cylinder block 14, and the form of the path is not limited.

[0058] The opening and closing device 53 is composed of an actuator such as a solenoid valve, and the opening and closing operation of the actuator blocks or opens the oil cooling path 52. The opening and closing device 53 is electrically connected to a first operation control unit .

[0059] The first operation control unit 54 is provided in the ECU 50 that comprehensively controls a vehicle such as a motorcycle. This first operation control unit 54 blocks the oil cooling path 52 when the ethanol concentration detected by the ethanol concentration detection unit 51 is higher than a predetermined value. For example, the first operation control unit 54 inputs a signal corresponding to the ethanol concentration detected by the ethanol concentration detection unit 51 and reads out the predetermined value of the ethanol concentration from the storage unit. Then, the first operation control unit 54 determines whether the ethanol concentration detected by the ethanol concentration detection unit 51 is higher than the predetermined value, and when the detected ethanol concentration is higher than the predetermined value, sends a signal to the opening / closing device 53 to close the opening / closing device 53 and block the oil cooling path 52. In addition, when the ethanol concentration detected by the ethanol concentration detection unit 51 is equal to or lower than a predetermined value, the first operation control unit 54 sends a signal to the opening and closing device 53 to open the opening and closing device 53 and open the oil cooling path 52.

[0060] According to this modified example, the first operation control unit 54 blocks the oil cooling path 52 when the ethanol concentration detected by the ethanol concentration detection unit 51 is higher than a predetermined value. Therefore, by utilizing the oil cooling path 52 of the internal combustion engine 10 to suppress cooling of the cylinder block 14 and the cylinder head 15, the temperature of the combustion chamber 28 or its surroundings can be increased, and as a result, cooling loss during the expansion stroke can be further suppressed.

[0061] 11, the internal combustion engine 10 may have, instead of the ethanol concentration detection unit 51, an oxygen concentration detection unit 57A that detects the oxygen concentration in the exhaust gas, an in-cylinder pressure detection unit 58 that detects the in-cylinder pressure of the internal combustion engine 10, and an ethanol concentration estimation unit 59 that estimates the concentration of ethanol supplied to the combustion chamber 28 based on the detection results detected by the oxygen concentration detection unit 57A and the in-cylinder pressure detection unit 58. In this configuration, the first operation control unit 54 blocks the oil cooling path 52 when the ethanol concentration estimated by the ethanol concentration estimation unit 59 is higher than a predetermined value. From the viewpoint of detecting the air-fuel ratio with high accuracy, instead of the oxygen concentration detection unit 57A, an air-fuel ratio detection unit 57B (LAF sensor) that detects the air-fuel ratio from the oxygen concentration and the unburned gas concentration may be provided. Also, the oxygen concentration detection unit 57A and the air-fuel ratio detection unit 57B may be used in combination.

[0062] According to the modified example of FIG. 11, the first operation control unit 54 blocks the oil cooling path 52 when the ethanol concentration estimated by the ethanol concentration estimation unit 51 is higher than a predetermined value. Therefore, even when the ethanol concentration detection unit 51 is not provided, it is possible to further suppress the cooling loss during the expansion stroke.

[0063] FIG. 12 is a diagram showing another modified example of the internal combustion engine 10 according to the present embodiment. As shown in FIG. 12, the internal combustion engine 10 includes an ethanol concentration detection unit 51, a louver member 61 that is rotatably arranged in front of the cylinder block 14 in the vehicle's traveling direction, an opening / closing device 62 that opens and closes the louver member 61, and a second operation control unit 63 that controls the operation of the opening / closing device 62.

[0064] The louver member 61 changes the amount of air passing near the cylinder block 14 while the vehicle is running. The louver member 61 is composed of, for example, a plurality of long plates arranged side by side, and effectively reduces or increases the airflow while saving space. There are no particular limitations on the material of the louver member 61, and metal, resin, or a composite material thereof can be used.

[0065] The opening and closing device 62 is composed of an actuator such as a motor, and adjusts the angle of the louver member 61. The opening and closing device 62 is electrically connected to a second operation control unit 63.

[0066] The second operation control unit 63 is provided in the ECU 50, similarly to the first operation control unit 54. When the ethanol concentration detected by the ethanol concentration detection unit 51 is higher than a predetermined value, the second operation control unit 63 rotates the louver member 61 to reduce the airflow toward the cylinder block 14. For example, the second operation control unit 63 inputs a signal corresponding to the ethanol concentration detected by the ethanol concentration detection unit 51 and reads out the predetermined value of the ethanol concentration from the storage unit. Then, the second operation control unit 63 determines whether the ethanol concentration detected by the ethanol concentration detection unit 51 is higher than the predetermined value, and when the detected ethanol concentration is higher than the predetermined value, transmits a signal to the opening and closing device 62 and rotates the louver member 61 in a direction to reduce the airflow toward the cylinder block 14. In addition, when the ethanol concentration detected by the ethanol concentration detection unit 51 is below a predetermined value, the second operation control unit 63 sends a signal to the opening and closing device 62 to rotate the louver member 61 in a direction that increases the airflow toward the cylinder block 14.

[0067] 12, when the ethanol concentration detected by the ethanol concentration detection unit 51 is higher than a predetermined value, the second operation control unit 63 rotates the louver member 61 to reduce the airflow toward the cylinder block 14, thereby using outside air to suppress cooling of the cylinder block 14 and the cylinder head 15, thereby making it possible to increase the temperature of the combustion chamber 28 or its surroundings, thereby making it possible to further suppress cooling loss during the expansion stroke. Also, by combining the configuration of this modification with the configuration of the modification of FIG. 10, it becomes possible to further suppress cooling loss during the expansion stroke.

[0068] 13, the internal combustion engine 10 may have, instead of the ethanol concentration detection unit 51, an oxygen concentration detection unit 57A that detects the oxygen concentration in the exhaust gas, an in-cylinder pressure detection unit 58 that detects the in-cylinder pressure of the internal combustion engine, and an ethanol concentration estimation unit 59 that estimates the concentration of ethanol supplied to the combustion chamber 28 based on the detection results detected by the oxygen concentration detection unit 57A and the in-cylinder pressure detection unit 58. In this configuration, the second operation control unit 63 rotates the louver member 61 to reduce the air flow toward the cylinder block 14 when the ethanol concentration estimated by the ethanol concentration estimation unit 59 is higher than a predetermined value. From the viewpoint of detecting the air-fuel ratio with high accuracy, instead of the oxygen concentration detection unit 57A, an air-fuel ratio detection unit 57B (LAF sensor) that detects the air-fuel ratio from the oxygen concentration and the unburned gas concentration may be provided. Also, the oxygen concentration detection unit 57A and the air-fuel ratio detection unit 57B may be used in combination.

[0069] 13, when the ethanol concentration estimated by the ethanol concentration estimation unit 59 is higher than a predetermined value, the second operation control unit 63 rotates the louver members 61 to reduce the airflow toward the cylinder block 14, making it possible to further reduce cooling loss during the expansion stroke even when the ethanol concentration detection unit 51 is not provided. Also, by combining the configuration of this modification with the configuration of the modification of FIG. 11, it is possible to further reduce cooling loss during the expansion stroke.

[0070] In the above embodiment, the crown surface 26a of the piston 26A of the internal combustion engine 10 is flat (FIG. 1), but this is not limiting, and the crown surface 26a of the piston 26B may have a recess 26b as shown in FIG. 14. When the crown surface 26a of the piston 26A is flat or the crown surface 26a of the piston 26B is provided with a recess 26b in this manner, the tumble flow TF formed in the cylinder 13 is more easily maintained and the R-side space S in the combustion chamber 28 is more efficiently maintained than when a protrusion is provided on the crown surface 26a of the piston 26A of the internal combustion engine 10. R From L side space S L It is easy to generate an air flow F toward the

[0071] The above describes the form for carrying out the present invention using an embodiment, but the present invention is not limited to such an embodiment, and various modifications and substitutions can be made within the scope that does not deviate from the gist of the present invention. [Explanation of symbols]

[0072] 10 Internal combustion engine 13 Cylinder 14 Cylinder block 15 Cylinder head 26A Piston 26B Piston 26a Crown surface 26b Recess 27 Connecting rod 28 Combustion chamber 28A outer periphery 29 Squish Club 30 Intake port 31 Exhaust port 32 Intake valve 33 Exhaust valve 34 Intake side rocker arm 35 Exhaust side rocker arm 36 Camshaft 37 Intake cam 38 Exhaust cam 39 Driven sprocket 40 Cam chain 41 Injector 43 Spark plug 43a Tip 50 ECU 51 Ethanol concentration detector 52 Oil cooling path 53 Switchgear 54 First motion control section 55 Fuel Tank 56 Fuel Injection Valve 57A Oxygen concentration detector 57B Air-fuel ratio detector 58 Cylinder pressure detector 59 Ethanol concentration estimation section 61 Louver parts 62 Switchgear 63 Second operation control section S R R side space S L L side space

Claims

1. The engine comprises a combustion chamber (28), an ignition plug (43) disposed in the combustion chamber (28), an intake port (30) that allows an air-fuel mixture containing ethanol to be drawn into the combustion chamber (28), and an exhaust port (31) through which exhaust gas flows out from the combustion chamber (28), an ethanol concentration detection unit (51) for detecting the concentration of ethanol supplied to the combustion chamber (28); an oil cooling passage (52) provided in at least the cylinder block (14); an opening and closing device (53) for opening and closing the oil cooling path (52); A first operation control unit (54) that controls the operation of the opening and closing device (53); An internal combustion engine (10) further comprising: A tip portion (43a) of the spark plug (43) is located between the intake port (30) and the exhaust port (31) and to the side of them, In a plan view of the combustion chamber (28), the side of the combustion chamber (28) where a tip portion (43a) of the ignition plug (43) is located is defined as an R-side space (SR), and the opposite side of the R-side space (SR) is defined as an L-side space (SL), and an airflow (F) is generated in the combustion chamber (28) from the R-side space (SR) toward the L-side space (SL), and an air-fuel mixture is supplied to the combustion chamber (28) so that a concentration of ethanol-containing fuel in the air-fuel mixture contained in the L-side space (SL) is higher than a concentration of ethanol-containing fuel in the air-fuel mixture contained in the R-side space (SR), The first operation control unit (54) blocks the oil cooling path (52) when the ethanol concentration detected by the ethanol concentration detection unit (51) is higher than a predetermined value.

2. The engine comprises a combustion chamber (28), an ignition plug (43) disposed in the combustion chamber (28), an intake port (30) that allows an air-fuel mixture containing ethanol to be drawn into the combustion chamber (28), and an exhaust port (31) through which exhaust gas flows out from the combustion chamber (28), an oxygen concentration detection unit (57A) for detecting an oxygen concentration in the exhaust gas, and / or an air-fuel ratio detection unit (57B) for detecting an air-fuel ratio based on the oxygen concentration and the unburned gas concentration; an in-cylinder pressure detection unit (58) that detects an in-cylinder pressure of the internal combustion engine; an ethanol concentration estimation unit (59) that estimates a concentration of ethanol supplied to the combustion chamber (28) based on a detection result detected by either or both of the oxygen concentration detection unit (57A) and the air-fuel ratio detection unit (57B) and a detection result detected by the in-cylinder pressure detection unit (58); an oil cooling passage (52) provided in at least the cylinder block (14); an opening and closing device (53) for opening and closing the oil cooling path (52); An internal combustion engine (10) further comprising a first operation control unit (54) that controls an operation of the opening and closing device (53), In a plan view of the combustion chamber (28), the side of the combustion chamber (28) where a tip portion (43a) of the ignition plug (43) is located is defined as an R-side space (SR), and the opposite side of the R-side space (SR) is defined as an L-side space (SL), and an airflow (F) is generated in the combustion chamber (28) from the R-side space (SR) toward the L-side space (SL), and an air-fuel mixture is supplied to the combustion chamber (28) so that a concentration of ethanol-containing fuel in the air-fuel mixture contained in the L-side space (SL) is higher than a concentration of ethanol-containing fuel in the air-fuel mixture contained in the R-side space (SR), The first operation control unit (54) blocks the oil cooling path (52) when the ethanol concentration estimated by an ethanol concentration estimation unit (59) is higher than a predetermined value.

3. The engine comprises a combustion chamber (28), an ignition plug (43) disposed in the combustion chamber (28), an intake port (30) that allows an air-fuel mixture containing ethanol to be drawn into the combustion chamber (28), and an exhaust port (31) through which exhaust gas flows out from the combustion chamber (28), an ethanol concentration detection unit (51) for detecting the concentration of ethanol supplied to the combustion chamber (28); a louver member (61) disposed in front of the cylinder block (14) in the traveling direction of the vehicle and rotatably provided; an opening / closing device (62) for opening and closing the louver member (61); A second operation control unit (63) that controls the operation of the opening and closing device (62); An internal combustion engine further comprising: In a plan view of the combustion chamber (28), the side of the combustion chamber (28) where a tip portion (43a) of the ignition plug (43) is located is defined as an R-side space (SR), and the opposite side of the R-side space (SR) is defined as an L-side space (SL), and an airflow (F) is generated in the combustion chamber (28) from the R-side space (SR) toward the L-side space (SL), and an air-fuel mixture is supplied to the combustion chamber (28) so that a concentration of ethanol-containing fuel in the air-fuel mixture contained in the L-side space (SL) is higher than a concentration of ethanol-containing fuel in the air-fuel mixture contained in the R-side space (SR), The second operation control unit (63) rotates the louver member (61) to reduce the airflow (F) toward the cylinder block (14) when the ethanol concentration detected by the ethanol concentration detection unit (51) is higher than a predetermined value.

4. The engine comprises a combustion chamber (28), an ignition plug (43) disposed in the combustion chamber (28), an intake port (30) that allows an air-fuel mixture containing ethanol to be drawn into the combustion chamber (28), and an exhaust port (31) through which exhaust gas flows out from the combustion chamber (28), an oxygen concentration detection unit (57A) for detecting an oxygen concentration in the exhaust gas, and / or an air-fuel ratio detection unit (57B) for detecting an air-fuel ratio based on the oxygen concentration and the unburned gas concentration; an in-cylinder pressure detection unit (58) that detects an in-cylinder pressure of the internal combustion engine; an ethanol concentration estimation unit (59) that estimates a concentration of ethanol supplied to the combustion chamber (28) based on a detection result detected by either or both of the oxygen concentration detection unit (57A) and the air-fuel ratio detection unit (57B) and a detection result detected by the in-cylinder pressure detection unit (58); a louver member (61) disposed in front of the cylinder block (14) in the traveling direction of the vehicle and rotatably provided; an opening / closing device (62) for opening and closing the louver member (61); A second operation control unit (63) that controls the operation of the opening and closing device (62); An internal combustion engine further comprising: In a plan view of the combustion chamber (28), the side of the combustion chamber (28) where a tip portion (43a) of the ignition plug (43) is located is defined as an R-side space (SR), and the opposite side of the R-side space (SR) is defined as an L-side space (SL), and an airflow (F) is generated in the combustion chamber (28) from the R-side space (SR) toward the L-side space (SL), and an air-fuel mixture is supplied to the combustion chamber (28) so that a concentration of ethanol-containing fuel in the air-fuel mixture contained in the L-side space (SL) is higher than a concentration of ethanol-containing fuel in the air-fuel mixture contained in the R-side space (SR), The second operation control unit (63) rotates the louver member (61) to reduce the airflow (F) directed toward the cylinder block (14) when the ethanol concentration estimated by the ethanol concentration estimation unit (59) is higher than a predetermined value.

5. The internal combustion engine according to any one of claims 1 to 4, wherein an airflow (F) flowing from the R-side space (SR) to the L-side space (SL) is an airflow originating from a tumble flow (TF) generated in a cylinder (13) of the internal combustion engine.

6. A main flow of the tumble flow (TF) is moved away from a tip portion (43a) of the ignition plug (43) to delay the timing of initial flame formation in the combustion chamber (28); 6. The internal combustion engine according to claim 5, wherein a flame generated in the combustion chamber (28) propagates from a tip portion (43a) of the ignition plug (43) toward at least the L-side space (SL).

7. A squish portion (29) is provided in a portion of an outer circumferential portion (28A) of the combustion chamber (28) that corresponds to at least a part of the L-side space (SL), The internal combustion engine according to any one of claims 1 to 6, wherein a reverse squish flow (f) is generated in the squish portion (29), and the reverse squish flow (f) promotes the air flow (F) from the R-side space (SR) to the L-side space (SL).

8. The internal combustion engine according to any one of claims 1 to 7, wherein a crown surface (26a) of a piston (26A, 26B) in the internal combustion engine (10) is flat or has a recess (26b) in the crown surface (26a).

9. The engine comprises a combustion chamber (28), an ignition plug (43) disposed in the combustion chamber (28), an intake port (30) that allows an air-fuel mixture containing ethanol to be drawn into the combustion chamber (28), and an exhaust port (31) through which exhaust gas flows out from the combustion chamber (28), an ethanol concentration detection unit (51) for detecting the concentration of ethanol supplied to the combustion chamber (28); an oil cooling passage (52) provided in at least the cylinder block (14); an opening and closing device (53) for opening and closing the oil cooling path (52); A first operation control unit (54) that controls the operation of the opening and closing device (53); A method for controlling an internal combustion engine (10) further comprising: A tip portion (43a) of the spark plug (43) is located between the intake port (30) and the exhaust port (31) and to the side of them, In a plan view of the combustion chamber (28), the side of the combustion chamber (28) where the tip portion (43a) of the ignition plug (43) is located is defined as an R-side space (SR), and the opposite side to the R side is defined as an L-side space (SL), and an airflow (F) directed from the R-side space (SR) to the L-side space (SL) is generated in the combustion chamber (28), and an air-fuel mixture is supplied to the combustion chamber (28) so that a concentration of ethanol-containing fuel in the air-fuel mixture contained in the L-side space (SL) is higher than a concentration of ethanol-containing fuel in the air-fuel mixture contained in the R-side space (SR), The method for controlling an internal combustion engine (10), wherein the first operation control unit (54) blocks the oil cooling path (52) when the ethanol concentration detected by the ethanol concentration detection unit (51) is higher than a predetermined value.

10. The control method for an internal combustion engine according to claim 9, wherein the airflow (F) flowing from the R-side space (SR) to the L-side space (SL) is an airflow originating from a tumble flow (TF) generated in a cylinder (13) of the internal combustion engine.

11. A main flow of the tumble flow (TF) is moved away from a tip portion (43a) of the ignition plug (43) to delay the timing of initial flame formation in the combustion chamber (28); 11. The method for controlling an internal combustion engine according to claim 9 or 10, wherein a flame generated in the combustion chamber (28) propagates from a tip portion (43a) of the spark plug (43) toward at least the L-side space (SL).

12. A control method for an internal combustion engine as described in any one of claims 9 to 11, wherein a reverse squish flow (f) is generated in a squish portion (29) arranged in a portion of the outer periphery (28A) of the combustion chamber (28) that corresponds to at least a part of the L-side space (SL), and the reverse squish flow (f) promotes the air flow (F) from the R-side space (SR) to the L-side space (SL).

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