WO2017078597A1

WO2017078597A1 - Four stroke internal combustion engine

Info

Publication number: WO2017078597A1
Application number: PCT/SE2016/051070
Authority: WO
Inventors: Johan Linderyd; Henrik HÖGLUND; Matthias USSNER; Jonas ASPFORS; Eric Olofsson; Daniel Norling
Original assignee: Scania Cv Ab
Priority date: 2015-11-03
Filing date: 2016-11-01
Publication date: 2017-05-11
Also published as: SE1551416A1; DE112016004553T5; SE539658C2; CN108368773A

Abstract

Herein an internal combustion engine (2) comprising at least one cylinder arrangement (4) forming a combustion chamber (23) is disclosed. The engine (2) further comprises at least one turbine (21) comprising a turbine wheel (26) and having a turbine wheel inlet area, A_TIN. An exhaust conduit (6) extends from a port (15) arranged in a lower half of a cylinder bore (12) of the cylinder arrangement (4) to the turbine wheel inlet area, A_TIN. The piston (10) has different piston stroke lengths, the power and exhaust strokes being longer than the intake and compression strokes, such that the port (15) is uncovered by the piston (10) during part of the power and exhaust strokes and is covered by the piston (10) during the intake and compression strokes.

Description

Four Stroke Internal Combustion Engine

TECHNICAL FIELD

The present invention relates to a four stroke internal combustion engine comprising a turbine.

BACKGROUND

In a four stroke combustion engine comprising a turbine such as e.g. a turbocharger, exhaust gas pressure in a cylinder is utilised to drive a turbine wheel of the turbine.

A piston of a four stroke internal combustion engine performs four strokes, an intake stroke, a compression stroke, a power stroke, and an exhaust stroke. An exhaust arrangement of the internal combustion engine, comprising e.g. ordinary exhaust poppet valves, has to be opened before the piston reaches its bottom dead centre, BDC, during the power stroke. Otherwise, if the exhaust arrangement would open later, e.g. when the piston reaches the BDC, the internal pressure from the exhaust gases inside the cylinder would impede the movement of the piston towards the top dead centre, TDC, during the exhaust stroke.

Available engine power would thus be reduced. The opening of the exhaust arrangement before the BDC of the piston during the power stroke permitting a portion of the exhaust gases to escape through the exhaust arrangement before the piston reaches the BDC, is referred to as blowdown. The term blowdown may also be used for the exhaust gases escaping through the exhaust arrangement prior to the piston reaching the BDC and after the piston has reached the BDC, while the pressure inside the cylinder exceeds the pressure in the exhaust system downstream of the exhaust

arrangement. The energy (work) of the blowdown, the blowdown energy, escapes through the exhaust arrangement and is not transferred to a crankshaft of the internal combustion engine via the piston. US 4535592 discloses a turbo compound engine of internal combustion type having conventional reciprocally movable pistons, cylinders, manifolds, fuel-oxygen admixing apparatus or fuel injection, firing apparatus or compression ignition, and incorporating the improvement of respective nozzle means for conveying the hot, moderately high pressure combustion products (exhaust gases) from the respective cylinders to one or more turbines. The nozzle means have its inlet and discharge ends connected, respectively, with the respective boundary walls of respective combustion chambers or cylinders and with the inlet to a turbine. A quick opening nozzle valve admits exhaust gas from the respective cylinder to the nozzle means.

US 5775105 discloses a cam driven plug that opens and closes exhaust valve ports in an engine cylinder bore. The plug moves to and forms an optimum variable geometry nozzle for the exhaust gasses exiting from the cylinder to impart maximum velocity energy to these exhaust gasses for delivery first at supersonic speed and then lower velocities as the cylinder pressure decays to drive a turbine that delivers power to the shaft of the internal combustion engine or other service loads.

Nozzle valves and cam driven plugs as discussed in the above mentioned documents may prove to be arrangements which are complicated to realise in practice.

SUMMARY

It is an object of the present invention to provide a four stroke combustion engine comprising a turbine, wherein a reliable arrangement is provided to utilise exhaust gas energy.

According to an aspect of the invention, the object is achieved by a four stroke internal combustion engine comprising at least one cylinder arrangement forming a combustion chamber and a crankshaft. The at least one cylinder arrangement comprises a piston, a connecting rod, a cylinder bore, and an exhaust arrangement for outflow of exhaust gas from the cylinder bore. The piston is pivotably connected to the connecting rod at a first end of the connecting rod and arranged to reciprocate in the cylinder bore in an intake stroke, a compression stroke, a power stroke, and an exhaust stroke. The exhaust arrangement comprises a port arranged in a lower half of the cylinder bore. The four stroke internal combustion engine further comprises at least one turbine comprising a turbine wheel and having a turbine wheel inlet area, A™. An exhaust conduit extends from the port to the turbine wheel inlet area, A™ .The piston has different piston stroke lengths, the power and exhaust strokes being longer than the intake and compression strokes, such that the port is uncovered by the piston during part of the power and exhaust strokes and is covered by the piston during the intake and compression strokes.

Since the piston has different piston stroke lengths, the power and exhaust strokes being longer than the intake and compression strokes, such that the port is uncovered by the piston during part of the power and exhaust strokes and is covered by the piston during the intake and compression strokes, there is no requirement for any separate valve in the exhaust conduit for opening and closing the exhaust conduit. As a result, the above mentioned object is achieved.

Moreover, since the exhaust arrangement comprises a port arranged in a lower half of the cylinder bore and the exhaust conduit extends from the port to the turbine wheel inlet area, ATIN, the blowdown energy of the exhaust gases is efficiently utilised in the turbine.

The four stroke internal combustion engine may comprise more than one cylinder arrangement each having a piston and an exhaust arrangement. The four stroke internal combustion engine may comprise more than one turbine. The turbine may for instance be a turbocharger, it may form part of a turbo compound engine, or may be a turbine driving an electric generator. The piston may be connected via the connecting rod to the crankshaft of the internal combustion engine. Suitably, the connecting rod may be indirectly connected to the crankshaft. The port may comprise one single port. However, the expression port herein also encompasses a port which is divided into two or more port sections, as well as more than one singular port in a cylinder bore connecting to one and the same exhaust conduit.

Inside the cylinder arrangement, above the piston, there is a combustion chamber. Intake air enters the combustion chamber through an intake arrangement of the cylinder arrangement during the intake stroke of the piston. The intake air may be compressed by the

turbocharger. The internal combustion engine may be e.g. a compression ignition (CI) engine, such as a Diesel type engine, or a spark ignition (SI) engine, such as an Otto type engine and comprises in the latter case a sparkplug or similar device in the cylinder arrangement. Fuel may be injected into the combustion chamber during part of the intake or compression stroke of the piston, or may be entrained with the intake air. The fuel may ignite near the TDC between the compression stroke and the power stroke of the piston.

According to embodiments, a port area, A_PORT, of the port may have a size of at least twice the turbine wheel inlet area, ATIN, of the turbine when the piston is at a bottom dead centre, BDC, between the power stroke and the exhaust stroke. In this manner it may be ensured that the port area, A_PORT, does not restrict an outflow of the exhaust gases during blowdown. Thus, the blowdown energy of the exhaust gases may be efficiently utilised in the turbine.

According to embodiments, a height of the port may be within a range of 8 - 16 % of a piston stroke length between a top dead centre, TDC of the piston and the bottom dead centre, BDC, between the power stroke and the exhaust stroke. In this manner the port may be uncovered in a manner to ensure that the blowdown energy of the exhaust gases are released to the turbine for efficient use therein. According to some embodiments the port will be fully uncovered by the piston when the piston reaches the BDC. In such embodiments, the height of the port will extend a height upwardly from the BDC within a range of 8 - 1 6 % of the piston stroke length between a top dead centre, TDC of the piston and the bottom dead centre, BDC, between the power stroke and the exhaust stroke.

According to embodiments, the at least one cylinder arrangement may have a maximum volume, V_MAX, between the bottom dead centre, BDC, of the piston between the power stroke and the exhaust stroke, and an upper inner delimiting surface of the combustion chamber. The port may be configured to expose the port area, A_PORT, at a size of at least 0,44*V_MAX, when the piston is at the bottom dead centre, BDC, between the power stroke and the exhaust stroke. In this manner, the port area, APORT, when the piston is at the bottom dead centre, BDC, may be sized such that the blowdown energy of the exhaust gases may be efficiently utilised in the turbine.

It has been discovered by the inventors that a port area, APORT, which has been opened to correspond to at least the size of 0.44 times the maximum volume, VMAX, when the piston is at the BDC, between the power stroke and the exhaust stroke, results in a large portion of the blowdown energy being transferred to the turbine. That is, an initial burst of exhaust gases produced by the blowdown, in an unrestricted manner, passes through the exhaust flow area, A_PORT, and is transferred via the exhaust conduit to the turbine wheel inlet area, ATIN, to be utilised in the turbine.

According to embodiments, the cylinder arrangement may have a maximum volume, V_MAX, between a bottom dead centre, BDC, of the piston between the power stroke and the exhaust stroke, and an upper inner delimiting surface of the cylinder bore. A momentary cylinder volume, V, of the cylinder arrangement may be defined by a momentary position of the piston in the cylinder bore during its reciprocation, wherein

APORT(V) expresses a port area of the port as a function of the momentary cylinder volume, V, during a power stroke of the piston, wherein

an exhaust flow area coefficient, δ, of the port is defined as

δ = A_PORT(V)/(0,22*VMAX) , A_PORT being expressed in m² and VMAX being expressed in m³, wherein

the port has an opening speed coefficient, β, defined as

β = (V(5= 1 ) - V(5=0, 1 ))/VMAX , and wherein

the port area, A_PORT, has an opening speed coefficient β < 0,06. In this manner, the port area, A_PORT, may be opened at a speed providing low flow resistance in the exhaust arrangement. Thus, an efficient transfer of the blowdown energy from the combustion chamber into the exhaust conduit may be promoted. Put differently, the opening speed coefficient β < 0.06 means that the cylinder volume increases less than 6 % while A_PORT increase from 1 0 % to 1 00 % of 0,22*V_MAX during a power stroke.

According to embodiments, the cylinder arrangement may have a maximum volume, V_MAX, between a bottom dead centre, BDC, of the piston between the power stroke and the exhaust stroke and an upper inner delimiting surface of the cylinder bore. The exhaust conduit may have an exhaust conduit volume, VEXH, wherein VEXH is≤ 0,5 times the maximum volume, VMAX. In this manner the blowdown energy of the exhaust gases may be efficiently transferred through the exhaust conduit to be utilised in the turbine.

Moreover, the defined maximum exhaust conduit volume, VEXH, in combination with the above defined and discussed opening speed coefficient, β, may ensure that an initial burst of exhaust gases produced by the blowdown energy is available to be utilised in the turbine. According to embodiments, the four stroke internal combustion engine may comprise a movable cylinder wall portion configured for varying a size of the port. The movable cylinder wall portion may be movable between a first position, in which the movable wall portion forms a portion of the port, and a second position, in which the movable wall portion is removed from the port. In this manner, a variable port size may be achieved. For instance, when the speed of the internal combustion engine is to be increased, the port size may be increased by positioning the movable wall portion in the second position in order to rev up the speed of the turbine to assist in the speed increase of the internal combustion engine. Once the turbine has revved up, the movable wall portion may be again position in its first position. According to embodiments, the exhaust arrangement may comprise a valve arrangement at an upper inner delimiting surface of the cylinder bore, the valve arrangement being fluidly connected with an exhaust line extending to downstream of the turbine. In this manner remaining exhaust gases in the cylinder arrangement just prior to the port being covered by the piston, or after the port has been covered, during an exhaust stroke may be ejected through the valve arrangement. Since during a large portion of the exhaust stroke the exhaust gases do no longer contribute to extracting work from the exhaust gases in the turbine, i.e. during so-called scavenging, bypassing the turbine with the exhaust line downstream of the turbine may avoid energy being wasted in the turbine.

According to embodiments, the turbine may have a normalised effective flow area, γ, defined as

γ = ATURB/VMAX , wherein γ > 0.22 ητ¹ , wherein

ATURB = (ATIN/ATOT) ^* m'RED ^* (R/(K(2/(K +1 )^x)))^1/2 , wherein X = (κ + 1 )/(κ -1 ), wherein Α_ΤΟτ is a total inlet area of the turbine, and wherein ATURB is obtained at a reduced mass flow, m'_RED, of the turbocharger at 2.5 - 3.5 pressure ratio between an inlet side and an outlet side of the turbine and at a tip speed of 450 m/s of the turbine wheel.

In this manner, a turbine may be provided in which an initial burst of exhaust gases, produced by the blowdown from one cylinder arrangement and transferred via the defined port area, A_PORT, and the defined exhaust conduit volume, VEXH, to the turbine wheel inlet area, A™, may be utilised. Moreover, in a turbine having such defined normalised effective flow area, γ, the blowdown energy may be extracted from the exhaust gases over a crank angle of the crankshaft of < 80 degrees. Thus, blowdown energy may be extracted individually from each of the cylinder arrangements connected to the turbine, as exhaust gases from the different cylinder arrangements reach the turbine at different crank angles of the crankshaft.

Besides the improved blowdown energy utilisation in the turbine, the four stroke internal combustion engine of the above discussed kind also has excellent gas exchange properties. That is, due to the quick opening of the port and the large available exhaust flow area in the port, as well as the above defined properties of the turbine, the exhaust gases are subjected to a low back pressure. A low back pressure in an exhaust system of the internal combustion engine promotes efficient, low energy, ejection of the exhaust gases. In a four stroke internal combustion engine as defined in some of the embodiments above, such low energy ejection is achieved while still a large amount of the blowdown energy is utilised in the turbine having the above defined properties. Put differently, a large amount of the available blowdown energy is recovered in the turbine without penalising the exhaust stroke with a high in- cylinder pressure, which would result in high negative piston pumping work.

According to a further aspect of the present invention there is provided a vehicle comprising a four stroke internal combustion engine according to any aspect and/or embodiment discussed herein. Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of the invention, including its particular features and advantages, will be readily understood from the example embodiments discussed in the following detailed description and the accompanying drawings, in which:

Figs. 1 a and 1 b illustrate schematically a four stroke internal combustion engine according to embodiments,

Figs. 1 c and 1 d illustrate partial cross sections of alternative embodiments of a four stroke internal combustion engine,

Fig. 2 illustrates a diagram of mass flow rate across an exhaust arrangement of a four stroke internal combustion engine,

Fig. 3 illustrates a diagram of exhaust flow areas of exhaust arrangements,

Fig. 4 illustrates a schematic example of a turbine map of a turbocharger,

Fig. 5 illustrates example embodiments of four stroke internal combustion engines and embodiments of a vehicle comprising a four stroke internal combustion engine, and

Figs. 6 and 7 illustrate embodiments wherein two cylinder arrangements are connected to a turbine.

DETAILED DESCRIPTION

Aspects of the present invention will now be described more fully. Like numbers refer to like elements throughout. Well-known functions or constructions will not necessarily be described in detail for brevity and/or clarity.

Figs. 1a and 1 b illustrate schematically a four stroke internal combustion engine 2 according to embodiments. The four stroke internal combustion engine 2 comprises at least one cylinder arrangement 4 forming a combustion chamber 23, an exhaust conduit 6, and at least one turbine (21 ), in these embodiments schematically exemplified as part of a turbocharger 8, see Fig. 1 a.

The at least one cylinder arrangement 4 comprises a piston 10, a connecting rod 22, a cylinder bore 12, an exhaust arrangement 14 for outflow of exhaust gases from the cylinder bore 12, an inlet port arrangement 16, and a fuel injection arrangement 18, and/or an ignition device. The piston 10 is pivotably connected to the connecting rod 22 at a first end of the connecting rod 22 and is arranged to reciprocate in the cylinder bore 12 in an intake stroke, a compression stroke, a power stroke, and an exhaust stroke. The exhaust arrangement 14 comprises a port 15 arranged in a lower half of the cylinder bore 12. The exhaust conduit 6 extends from the port 15 to the turbine wheel inlet area, ATIN .The piston 10 has different piston stroke lengths, the power and exhaust strokes being longer than the intake and compression strokes, such that the port 15 is uncovered by the piston 10 during part of the power and exhaust strokes and is covered by the piston 10 during the intake and compression strokes. In Figs. 1a and 1 b the piston 10 is shown in broken lines at its TDC. In Fig. 1a the piston 10 is shown with continuous lines at its BDC between the intake stroke and the compression stroke with the port 15 covered. In Fig. 1 b the piston 10 is shown with continuous lines at its BDC between the power stroke and the exhaust stroke with the port 15 uncovered. Thus, a port area, A_PORT, of the port 15 of the exhaust arrangement 14 is opened and closed as the piston reciprocates in the piston bore 12. A height of the port 15 is within a range of 8 - 16 % of a piston stroke length between the TDC of the piston 10 and the BDC, between the power stroke and the exhaust stroke. In these embodiments the port 15 is fully uncovered by the piston 10 only when the piston 10 reaches the BDC. In alternative embodiments, the port may be positioned higher along the cylinder bore such that the port is fully uncovered prior to the piston reaching the BDC. The advantage of utilising a port in the cylinder bore for ejecting exhaust gases is the fast opening speed of at least part of an exhaust flow area, i.e. the port area, A_PORT. In embodiments wherein the port is fully uncovered prior to the piston reaching the BDC, the further advantage is achieved that the opening speed of the port area, A_PORT, is even faster than the opening speed of the port area, A_PORT, in embodiments where the port is fully uncovered only when the piston reaches the BDC. In Figs. 1a and 1 b the piston 10 has been illustrated shorter than in practice. Namely, in practice the piston 10 should suitably have a length such that the port 15 is covered by the piston 10 when it is at its TDC in order to avoid the exhaust conduit 6 communicating with the crankcase of the four stroke internal combustion engine 2. The different piston stroke lengths of the piston 10 may be achieved by a mechanism 27 connecting the connecting rod 22 with a crankshaft 20 of the internal combustion engine 2. The mechanism 27 is schematically illustrated in Figs. 1 a and 1 b. Various such mechanisms are known, e.g. as in the so-called Atkinson cycle engine disclosed in patent document US 367,496, or as in the variable stroke engine disclosed in patent document US 4,517,931 . In these embodiments, the port 15 is formed by fixed parts only. That is, the port 15 is formed by one or more openings of fixed size in the cylinder bore 12. Accordingly, the port area, APORT, is not variable in these embodiments. During the reciprocation of the piston 10, the cylinder arrangement 4 has a momentary cylinder volume, V. That is, the momentary cylinder volume, V, of the cylinder arrangement is defined by a momentary position of the piston 10 in the cylinder bore 12. Accordingly, the port area, A_PORT, may be expressed as a function of the momentary cylinder volume, V, i.e. APORT(V) . AS will be discussed below, A_PORT(V) during a power stroke of the piston 10 is utilised to define an opening speed of the port 15. The exhaust arrangement 14 further comprises a valve arrangement 17 at an upper inner delimiting surface 24 of the cylinder bore 12. The valve arrangement 17 is fluidly connected with an exhaust line 19 extending to downstream of the turbine 21 . The valve arrangement 17 has an exhaust flow area, A_CYL, which varies during the piston reciprocation. More specifically, the exhaust flow area, A_CYL, starts opening just prior to, or just after, the piston 10 fully covers the port 15 during the exhaust stroke.

According to some embodiments, the valve arrangement 17 may be selectively fluidly connectable with the exhaust conduit 6 upstream of the turbine. In this manner, under certain operating conditions, the valve arrangement 17 may be connected upstream of the turbine. For instance, in order to improve engine load response during acceleration. As shown in Fig. 1 b, a two-way valve 25 may be provided for selectively connecting the exhaust line 19 to the exhaust conduit 6. The two-way valve 25 may be controlled by a control system (not shown) of the four stroke internal combustion engine 2.

The turbine 21 comprises a turbine wheel 26. The turbine 21 comprises a turbine wheel inlet area, A™. The turbine wheel inlet area, A™, is provided at an opening of a housing of the turbine 21 where the exhaust gases are admitted to the turbine wheel 26. The turbine wheel inlet area, A™, may suitably be the nozzle throat area of the turbine. The nozzle throat area may also be referred to as turbine house throat area, turbine house critical area, or similar and may often be specified for a specific turbine. In case the nozzle throat is not specified for a specific turbine, and/or the position of the nozzle throat area is not specified, the turbine wheel inlet area, A™, extends perpendicularly to a flow direction of the exhaust gases. In embodiments of turbines where the exhaust conduit extends along a portion of the turbine wheel e.g. in a volute, such as e.g. in a twin scroll turbocharger, the turbine wheel inlet area, A™, is defined at the section of the exhaust conduit where the turbine wheel is first exposed to the exhaust gases emanating from the relevant cylinder arrangement. The cylinder arrangement 4 has a maximum volume, VMAX, between the BDC of the piston 1 0 between the power stroke and the exhaust stroke, and the upper inner delimiting surface 24 of the combustion chamber 23. The combustion chamber 23 is formed above the piston 1 0 inside the cylinder arrangement 4. The piston 1 0 is connected to the crankshaft 20 of the internal combustion engine 2. More specifically, the piston 1 0 may be indirectly connected to the crankshaft 20 via the connecting rod 22 and the mechanism 27.

The cylinder arrangement 4 has a total swept volume, V_s, in the cylinder bore 1 2 between the BDC and the TDC during the power and exhaust strokes. The cylinder arrangement 4 has a geometrical compression ratio, ε = VMAX / V_Min . VMAX may be expressed as:

The exhaust conduit 6 connects the port 1 5 with the turbine 21 . The exhaust conduit 6 has an exhaust conduit volume, VEXH. In Figs. 1a and 1 b the exhaust conduit volume, VEXH, is illustrated as a box. In practice, the exhaust conduit 6 extends between the port area, A_PORT, and the turbine wheel inlet area, A™. Accordingly, the exhaust conduit volume, VEXH is formed by the volume of the exhaust conduit between the port area, APORT, and the turbine wheel inlet area, A™. The exhaust conduit 6 fluidly connects only the port 1 5 with the turbine wheel inlet area, A™. That is, the exhaust conduit 6 forms a separate conduit extending between the port area, APORT, and the turbine wheel inlet area, ATIN. The separate conduit does not have any other inlets or outlets for exhaust gases. Thus, the turbine wheel inlet area, A™, is a dedicated inlet area of the turbocharger 8 for the port 1 5 connected thereto via the exhaust conduit 6.

The exhaust conduit volume, VEXH, is≤ 0.5 times the maximum volume, VMAX,

i.e. VEXH≤ 0.5 * VMAX. Further, the port area, A_PORT, of the port 1 5 may have a size of at least twice the turbine wheel inlet area, ATIN, of the turbine when the piston is at a bottom dead centre, BDC, between the power stroke and the exhaust stroke. An additional, or alternative, criteria of a size of the port 1 5 may be that it is configured to expose the port area, A_PORT, at a size of at least 0,44*V_MAX, i.e. APORT≥ 0.44 * VMAX, when the piston is at the bottom dead centre, BDC, between the power stroke and the exhaust stroke. Accordingly, the criteria: APORT / VMAX≥ 0.44 nr¹ may be fulfilled when the piston 1 0 is at the BDC between the power and exhaust strokes.

The turbine wheel 26 of the turbine 21 , in a turbocharger 8 is connected to an impeller (not shown) for compressing and transporting intake air to the intake port arrangement 1 6. According to some embodiments, the turbine wheel 26 may be an axial turbine wheel. A turbine comprising an axial turbine wheel may provide the low back pressure discussed herein. However, according to alternative embodiments the turbine wheel may be a radial turbine wheel, which also may provide the low back pressure discussed herein. The turbine 21 may be an impulse turbine or a reaction turbine.

According to some embodiments, the cylinder arrangement 4 may have a total swept volume, V_s, in the cylinder bore 12 between the bottom dead centre, BDC, between the power stroke and the exhaust stroke, and a top dead centre, TDC, of the piston, and wherein 0,3 < V_s < 4 litres. Mentioned purely as an example, in the lower range of Vs, the cylinder arrangement 4 may form part of an internal combustion engine for a passenger car, and in the middle and higher range of Vs, the cylinder arrangement 4 may form part of an internal combustion engine for a heavy load vehicle such as e.g. a truck, a bus, or a construction vehicle. Also in the higher range of Vs, the cylinder arrangement 4 may form part of an internal combustion engine for e.g. a generator set (genset), for marine use, or for rail bound (train) use.

Figs. 1 c and 1d illustrate partial cross sections of alternative embodiments of a four stroke internal combustion engine 2. These embodiments resemble in much the embodiments of Figs. 1a and 1 b however, the four stroke internal combustion engine 2 comprises a movable cylinder wall portion 31 configured for varying a size of the port 15. The movable cylinder wall portion 31 is movable between a first position, in which the movable wall portion 31 forms an upper portion of the port 15, and a second position, in which the movable wall portion 31 is removed from the port 15. Thus, the port area, A_PORT, of the port 15 may be varied during operation of the four stroke internal combustion engine 2. In order to control the size of the port 15, movable cylinder wall portion 31 may be controlled by a control system (not shown) of the four stroke internal combustion engine 2. In Fig. 1 c the movable cylinder wall portion 31 is shown in its first position forming an extension of the cylinder bore 12 in the port 15, and in Fig. 1 d the movable cylinder wall portion 31 is shown in its second position removed from the port 15 and the cylinder bore 12.

In Figs. 1 c and 1d the piston 10 has been illustrated shorter than in practice. Namely, in practice the piston 10 should suitably have a length such that the port 15 is covered by the piston 10 when it is at its TDC in order to avoid the exhaust conduit 6 communicating with the crankcase if the four stroke internal combustion engine 2. According to alternative embodiments, more than one cylinder arrangement may be connected to a turbine 21 at one position of the turbine 21 . Fig. 6 illustrates embodiments wherein two cylinder arrangements 4 are connected to a turbine 21 via one turbine wheel inlet area, A™, i.e. the two cylinder arrangements 4 share the same turbine wheel inlet area, ATIN. Accordingly, the exhaust conduit branches 6', 6" from the ports 15 of the two cylinder arrangements 4 are connected to form a common exhaust conduit 6 leading to the turbine 21 and the turbine wheel inlet area, ATIN. Since there exists a certain degree of crossflow between the two exhaust conduit branches 6', 6" as exhaust gases flow from one of the cylinder arrangements 4 to the turbine wheel inlet area, A™, the above discussed criteria: VEXH≤ 0.5 * VMAX is valid for the collective exhaust conduit volume, VEXH, of both exhaust conduit branches 6', 6" and the common exhaust conduit 6. Fig. 7 illustrates embodiments wherein the ports 15 of two cylinder arrangements 4 are connected to a turbine 21 via two separate exhaust conduits 6, each leading to one turbine wheel inlet area, ATIM , ATIN2. The turbine wheel inlet areas, A™i , A_TIN2, are positioned adjacent to each other such that they may be considered to be connected to the turbine 21 at one position of the turbine 21 . The crossflow between two turbine wheel inlet areas, A™i , A_TIN2, is negligible. Accordingly, for each of the exhaust conduits 6 the above discussed criteria: VEXH≤ 0.5 * VMAX is valid.

In general, volumes of connections to/from the exhaust conduits 6 are not considered to form part of the exhaust conduit volume, VEXH, if such connections have a cross sectional area below a limit value. According to embodiments the exhaust conduit volume, VEXH, excludes all volumes connected to the exhaust conduit 6 via a connection having a connection cross section area, A_CON,≤ 0.022 nr¹ times the maximum volume, VMAX, at its narrowest portion. That is, the limit value of the cross sectional area, A_CON, is 5 % of the above discussed criteria related to the port area, A_PORT, when the piston 10 is at the BDC between the power and exhaust strokes. With such a small cross sectional area, A_CON, any crossflow of exhaust gases through a connection is negligible. In Fig. 7 two example connections 7 with connection cross section areas, AGON, have been indicated. Mentioned purely as an example, such connections 7 may form part of an exhaust gas recirculation (EGR) system, or may be connect to sensors, etc.

Fig. 2 illustrates a diagram of mass flow rate across an exhaust arrangement of a four stroke internal combustion engine. Along the X-axis of the diagram the four strokes, power stroke 30, exhaust stroke 32, intake stroke 34, and compression stroke 36 of a piston in a cylinder bore of a cylinder arrangement of the internal combustion engine are indicated between the bottom dead centres, BDC, and top dead centres, TDC, of the piston. The angle of the crankshaft of the internal combustion engine is also given on the X-axis. 0 degrees crankshaft angle is set at the TDC between the exhaust stroke 32 and the intake stroke 34. An example mass flow rate in kg/s through the exhaust arrangement is given on the Y-axis.

The graph of the diagram shows the mass flow rate across the exhaust arrangement. At point 38 the exhaust arrangement starts to open. At point 40 the exhaust arrangement has closed again. Thus, during a period in between points 38 and 40, an exhaust flow area is exposed and increases to a maximum, then decreases and closes. During the period in between points 38 and 40 the exhaust gases are ejected from the cylinder arrangement via the exhaust arrangement. The period inbetween points 38 and 40 may be roughly divided into two parts, blowdown 42 and scavenging 44. During blowdown 42 an excessive pressure prevails in the exhaust gases in the cylinder bore, compared to a pressure downstream of the exhaust flow area. The excessive pressure causes spontaneous outflow of the exhaust gases from the cylinder bore via the exhaust flow area. The excessive pressure may be utilised e.g. in a turbine. In accordance with the present invention, during blowdown 42, the port of the exhaust arrangement is uncovered by the piston. Thus, an efficient ejection of the exhaust gases via the port to the turbine is achieved, which promotes a high degree of utilisation of the blowdown energy in the turbine. During scavenging 44 there no longer prevails an excessive pressure in the exhaust gases in the cylinder bore compared to a pressure downstream of the exhaust flow area and the exhaust gases are ejected across the exhaust arrangement by the piston as it travels upwardly in the cylinder bore. In particular, the exhaust gases may be ejected during scavenging through a valve arrangement 17 as discussed above in connection with Figs. 1a and 1 b.

An exhaust sequence starts at point 38, ends at point 40, and is indicated with reference number 46. Moreover, at the BDC in between the power stroke 30 and the exhaust stroke 32 (- 180.0 degrees), the port area, APORT, has been opened to such an extent that

APORT≥ 0.44 ^* VMAX.

Fig. 3 illustrates a diagram of exhaust flow areas of exhaust arrangements. Each such exhaust arrangement forms part of a cylinder arrangement further comprising a piston arranged to reciprocate in a cylinder bore. Along the Y axis example exhaust flow area of the exhaust arrangement is given in mm². Along the X axis relative cylinder volume is given, i.e. the ratio between the momentary cylinder volume, V, and the maximum volume, VMAX, which ratio is calculated, V/VMAX. Accordingly, at the ratio 1 the piston is at its BDC, i.e. the BDC between the power and exhaust strokes in embodiments of the present invention. Two graphs 50, 54 are shown in the diagram. A first graph 50 relates to an exhaust arrangement comprising standard camshaft controlled exhaust poppet valves. The first graph 50 shows that the poppet valves are opened at a ratio of approximately 0.82, and that the exhaust flow area of the poppet valves increases gradually as the piston travels towards the BDC and reaches its maximum exhaust flow area at a ratio of approximately 0.88 as the piston is travelling towards the TDC. A second graph 54 relates to an exhaust arrangement comprising a port arranged at a lower half of the cylinder bore. The second graph 54 shows that the exhaust arrangement is opened at a ratio of approximately 0.88 and that the port area increases gradually as the piston travels towards the BDC between the power and exhaust strokes.

As will be discussed below, the first graph 50 illustrates the characteristics of a prior art exhaust arrangement, whereas the second graph 54 illustrate characteristics of an exhaust arrangements of embodiments discussed herein.

According to embodiments, a momentary cylinder volume, V, of the cylinder arrangement is defined by a momentary position of the piston in the cylinder bore during its reciprocation. APORT(V) expresses a port area of the port as a function of the momentary cylinder volume, V, during a power stroke of the piston. An exhaust flow area coefficient, δ, of the port is defined as δ = A_PORT(V)/(0,22^*VMAX) , A_PORT being expressed in m² and VMAX being expressed in m³. In the diagram of Fig. 3, the power stroke of the piston is in a rightward direction, as the ratio increases. The power stroke ends at the ratio 1 . An exhaust stroke of the piston is in a leftward direction in the diagram, as the ratio decreases. Further, the port has an opening speed coefficient, β, defined as β = (V(5=1 ) - V(5=0,1 ))/V_MAX. That is, V(5=1 ) represents the momentary cylinder volume V when δ equals 1 , and V(5=0.1 ) represents the momentary cylinder volume, V, when δ equals 0.1 . Since δ is based on the exhaust flow area, the opening speed coefficient, β, represents a value for how fast opening a particular exhaust arrangement of a cylinder arrangement is. The lower the opening speed coefficient, β, the faster a particular exhaust arrangement will expose the exhaust flow area.

According to embodiments discussed herein, the port area, A_PORT, may have an opening speed coefficient β < 0.06 in order to efficiently utilise the blowdown energy in the turbine.

In the diagram of Fig. 3 the opening speed coefficient, β, of an exhaust arrangement for cylinder arrangements having a particular V_MAX is represented by a respective line extending through the points 56, 60 representing V(5=1 ) and the points 64, 66 representing V(5=0.1 ) on the relevant graphs 50, 54. Thus, the opening speed coefficient, βι, for the exhaust arrangement comprising standard camshaft controlled exhaust poppet valves represented by the first graph 50, βι = 0.09. For the exhaust arrangement represented by the second graphs 54, β₂ = 0.025. Thus, the exhaust arrangement represented by the second graph 54 fulfils the requirement β < 0.06.

The exhaust sequence mentioned in connection with embodiments herein, starts on the graph 54 where the port is uncovered by the piston and then follows along the graph 54 to the right in the diagram to the BDC, and then follows along the graph to the left in the diagram towards the TDC while the valve arrangement is open. Only the beginning of the exhaust sequence is represented in the diagram. Ratios below 0.80 are not shown in the diagram. Due to the comparatively large exhaust flow area of the port, A_PORT, and the quick opening speed of the port, the second graph 54 at the ratio 1 extends outside the diagram. Thus, for the exhaust arrangement represented by the second graph 54, a shorter portion of the exhaust sequence is illustrated in the diagram than for the prior art exhaust arrangement represented by the first graph in 50.

For a particular turbine, turbine rig test results are plotted in a turbine map. Based on such turbine maps a suitable turbine may be selected for a particular four stroke internal combustion engine. In one type of turbine map a number of turbine speed lines may be plotted against a corrected flow and pressure ratios over the turbine. Such turbine speed lines may represent e.g. so-called reduced turbine rotational speeds, RPM RED. The corrected flow may be represented e.g. by a reduced mass flow, m'_RED.

wherein m' is an actual mass flow rate through the turbine wheel, T is the exhaust gas temperature before the turbine wheel, and P is the exhaust gas pressure before the turbine wheel. In Fig. 4 a schematic example of a turbine map of a turbocharger is illustrated. The standards SAE J 1 826 and SAE J922 relate to test procedures, nomenclature and

terminology of turbochargers, and are incorporated herein by reference for further details of turbine maps and parameters related to turbochargers.

According to embodiments, the turbine has a normalised effective flow area, γ, defined as γ = ATURB/VMAX . Thus, the turbine wheel inlet area, A™, may be defined in relation to the maximum volume, VMAX, of the cylinder arrangement. Namely,

ATURB = (ATIN/ATOT) ^* m'RED ^* (R/(K(2/(K + 1 )^X)))^1/2 ,

wherein X = (κ + 1 )/(κ -1 ). As mentioned above, A™, is the turbine wheel inlet area connected to the exhaust arrangement of a cylinder arrangement. The turbine may have more than one inlet area. Accordingly, A_TOT is a total inlet area of the turbine, i.e. A™ and any additional turbine wheel inlet areas, ATINX, etc. (Ατοτ = A™ + ATINX + . . .)■ ^R is the specific gas constant. An example value of R may be 287. κ = C_P / C_V , where C_P is the specific heat capacity at constant pressure of the exhaust gases and C_V is the specific heat capacity of the exhaust gases at constant volume. An example value of κ may be 1 .4 at a temperature of 293 K.

ATURB is obtained at a reduced mass flow, m'_RED, of the turbine at 2.5 - 3.5 pressure ratio between an inlet side and an outlet side of the turbine and at a tip speed of 450 m/s of the turbine wheel. ATURB for a particular turbine may be obtained e.g. by extracting the reduced mass flow, m'_RED, from a relevant turbine map for a turbine speed corresponding to the relevant tip speed at the relevant pressure ratio, and calculating ATURB with relevant data for the turbine and its operating conditions. Thereafter, γ may be calculated. According to embodiments herein γ > 0.22 m^~1 . As discussed above, the exhaust arrangement is configured to expose the port area, A_PORT, at a size of at least 0.44*V_MAX, when the piston is at the BDC between the power and exhaust strokes. In a turbine having a normalised effective flow area γ > 0.22 nr¹ , the turbine wheel inlet area, A™, may correspond to the above defined port area, A_PORT, ( A_PORT≥ 0.44*V_MAX ), when the piston is at the BDC between the power and exhaust strokes. Put differently, the exhaust flow area coefficient is δ≥ 2 at the BDC of the piston between the power and exhaust strokes. In combination with the defined VEXH≤ 0.5 * VMAX thus, an efficient transfer of the blowdown energy from the exhaust arrangement to the turbine wheel inlet area, A™, may be achieved. Accordingly, a low pressure drop may be provided as the exhaust gases are transferred from the cylinder arrangement to the turbine and the blowdown energy may be transformed into useful work as the exhaust gases expand over the turbine wheel of the turbine. Also, the above discussed fast opening of the exhaust valve arrangement with the opening speed coefficient β < 0.06 may contribute to the low pressure drop from the cylinder arrangement to the turbine. Fig. 5 illustrates first example embodiments of a four stroke internal combustion engine 2, and second example embodiments of a four stroke internal combustion engine 2, as well as embodiments of a vehicle 1 comprising a four stroke internal combustion engine 2.

With continuous lines, the first example embodiments of a four stroke internal combustion engine 2 comprising three cylinder arrangements 4 are illustrated in Fig. 5. Each cylinder arrangement 4 comprises an exhaust arrangement comprising a port 1 5, wherein a separate exhaust conduit 6 fluidly connects only one of each port 1 5 with a separate inlet area, A™, of a turbine 21 . Each cylinder arrangement 4 is a cylinder arrangement 4 as discussed in connection with Figs. 1a and 1 b.

The above discussed and defined opening speed coefficient, β, and normalised effective flow area, γ, apply to at least one of the cylinder arrangements 4. According to embodiments, each cylinder arrangement 4 has an opening speed coefficient β < 0.06, as defined herein. According to some embodiments the above discussed and defined opening speed coefficient, β, and normalised effective flow area, γ, apply to each of the cylinder

arrangements 4 and the thereto connected turbine 21 .

According to embodiments, each of the three cylinder arrangements 4 may be arranged to fire at an approximately 240 degrees crankshaft angle separation interval.

According to the second example embodiments illustrated in Fig. 5, the four stroke internal combustion engine 2 comprises six cylinder arrangements 4, 4'. These embodiments comprise the three cylinder arrangements 4 of the previous embodiments as well as the three cylinder arrangements 4' indicated with dashed lines. Again, each cylinder

arrangement 4, 4' comprises an exhaust arrangement comprising a port 15, 15' wherein a separate exhaust conduit 6, 6' fluidly connects only one of each port 15, 15' with a separate inlet area, A™, of a turbine 21 , 21 '. In these embodiments the internal combustion engine comprises two turbines 21 , 21 '. Three separate exhaust conduits 6 are connected to a first turbine 21 , and three separate exhaust conduits 6' are connected to a second turbine 21 '. Again, each cylinder arrangement 4, 4' is a cylinder arrangement 4, 4' as discussed in connection with Figs. 1 a and 1 b. The above discussed and defined opening speed coefficient, β, and normalised effective flow area, γ, apply to at least one of the cylinder arrangements 4, 4'. According to some embodiments the above discussed and defined opening speed coefficient, β, and normalised effective flow area, γ, apply to each of the cylinder arrangements 4, 4' and the thereto connected turbines 21 , 21 '. According to embodiments, three cylinder arrangements 4, 4' of the six cylinder

arrangements 4, 4' may be arranged to fire at an approximately 240 degrees crankcase angle separation interval.

According to further embodiments, the four stroke internal combustion engine may comprise a different number of cylinder arrangements 4, such as e.g. two, four, five, or eight cylinder arrangements 4. A vehicle 1 is schematically illustrated in Fig. 5. The vehicle 1 comprising a four stroke internal combustion engine 2 according to the first example embodiments or according to the second example embodiments illustrated in Fig. 5. This invention should not be construed as limited to the embodiments set forth herein. A person skilled in the art will realize that different features of the embodiments disclosed herein may be combined to create embodiments other than those described herein, without departing from the scope of the present invention, as defined by the appended claims.

Although the invention has been described with reference to example embodiments, many different alterations, modifications and the like will become apparent for those skilled in the art. For instance, in the embodiments discussed in connection with Figs. 1 - 5, at least one turbine in the form of a turbocharger has been discussed. Alternatively, the turbine may be a turbine connected to a crankshaft of the internal combustion engine, or a turbine connected to an electric generator. Therefore, it is to be understood that the foregoing is illustrative of various example embodiments and that the invention is defined only by the appended claims.

As used herein, the term "comprising" or "comprises" is open-ended, and includes one or more stated features, elements, steps, components or functions but does not preclude the presence or addition of one or more other features, elements, steps, components, functions or groups thereof.

Claims

1 . A four stroke internal combustion engine (2) comprising at least one cylinder arrangement (4) forming a combustion chamber (23) and a crankshaft (20), wherein

the at least one cylinder arrangement (4) comprises a piston (10), a connecting rod (22), a cylinder bore (12), and an exhaust arrangement (14) for outflow of exhaust gas from the cylinder bore (12), wherein

the piston (10) is pivotably connected to the connecting rod (22) at a first end of the connecting rod (22) and arranged to reciprocate in the cylinder bore (12) in an intake stroke, a compression stroke, a power stroke, and an exhaust stroke, wherein

the exhaust arrangement (14) comprises a port (15) arranged in a lower half of the cylinder bore (12), wherein

the four stroke internal combustion engine (2) further comprises at least one turbine (21 ) comprising a turbine wheel (26) and having a turbine wheel inlet area, A™, and wherein

an exhaust conduit (6) extends from the port (15) to the turbine wheel inlet area, A™

characterised in that

the piston (10) has different piston stroke lengths, the power and exhaust strokes being longer than the intake and compression strokes, such that the port (15) is uncovered by the piston (10) during part of the power and exhaust strokes and is covered by the piston (10) during the intake and compression strokes.

2. The four stroke internal combustion engine (2) according to any one of the preceding claims, wherein a port area, A_PORT, of the port (15) has a size of at least twice the turbine wheel inlet area, A™, of the turbine (21 ) when the piston (10) is at a bottom dead centre, BDC, between the power stroke and the exhaust stroke.

3. The four stroke internal combustion engine (2) according to claim 2, wherein a height of the port (15) is within a range of 8 - 16 % of a piston stroke length between a top dead centre, TDC of the piston (10) and the bottom dead centre, BDC, between the power stroke and the exhaust stroke.

4. The four stroke internal combustion engine (2) according to claim 2 or 3, wherein the at least one cylinder arrangement (4) has a maximum volume, VMAX, between the bottom dead centre, BDC, of the piston (10) between the power stroke and the exhaust stroke, and an upper inner delimiting surface (24) of the combustion chamber (23), wherein the port (15) is configured to expose the port area, A_PORT, at a size of at least 0,44*V_MAX, when the piston (1 0) is at the bottom dead centre, BDC, between the power stroke and the exhaust stroke.

5. The four stroke internal combustion engine (2) according to any one of the preceding claims, wherein the cylinder arrangement (4) has a maximum volume, V_MAX, between a bottom dead centre, BDC, of the piston (1 0) between the power stroke and the exhaust stroke and an upper inner delimiting surface of the cylinder bore ( 1 2), wherein a momentary cylinder volume, V, of the cylinder arrangement (4) is defined by a momentary position of the piston (1 0) in the cylinder bore (1 2) during its reciprocation, wherein

APORT(V) expresses a port area of the port (1 5) as a function of the momentary cylinder volume, V, during a power stroke of the piston (1 0) , wherein

an exhaust flow area coefficient, δ, of the port ( 1 5) is defined as

the port (1 5) has an opening speed coefficient, β, defined as

β = (V(5= 1 ) - V(5=0, 1 ))/VMAX , and wherein

the port (1 5) has an opening speed coefficient β < 0,06.

6. The four stroke internal combustion engine (2) according to any one of the preceding claims, wherein the cylinder arrangement (4) has a maximum volume, VMAX, between a bottom dead centre, BDC, of the piston (1 0) between the power stroke and the exhaust stroke and an upper inner delimiting surface (24) of the cylinder bore ( 1 2) , wherein the exhaust conduit (6) has an exhaust conduit volume, VEXH, and wherein VEXH is≤ 0,5 times the maximum volume, VMAX.

7. The four stroke internal combustion engine (2) according to any one of the preceding claims, wherein the exhaust conduit (6) fluidly connects only the port ( 1 5) with the turbine wheel inlet area, A™.

8. The four stroke internal combustion engine (2) according to any one of the preceding claims, wherein the port ( 1 5) is formed by fixed parts only.

9. The four stroke internal combustion engine (2) according to any one of claims 1 - 7, comprising a movable cylinder wall portion (31 ) configured for varying a size of the port (1 5) , wherein the movable cylinder wall portion (31 ) is movable between a first position, in which the movable wall portion (31 ) forms a portion of the port ( 1 5), and a second position, in which the movable wall portion (31 ) is removed from the port (1 5).

10. The four stroke internal combustion engine (2) according to any one of the preceding claims, wherein the exhaust arrangement (14) comprises a valve arrangement (17) at an upper inner delimiting surface of the cylinder bore (12), the valve arrangement (17) being fluidly connected with an exhaust line (19) extending to downstream of the turbine (21 ).

1 1 . The four stroke internal combustion engine (2) according to claim 10, wherein the valve arrangement (17) is selectively fluidly connectable with the exhaust conduit (6) upstream of the turbine (21 ).

12. The four stroke internal combustion engine (2) (2) according to any one of the preceding claims, wherein the turbine (21 ) has a normalised effective flow area, γ, defined as γ = ATURB/VMAX , wherein γ > 0.22 m^~1 , wherein

ATURB = (ATIN/ATOT) ^* m'RED ^* (R/(K(2/(K +1 )^x)))^1/2 , wherein X = (κ + 1 )/(κ -1 ), wherein Α_ΤΟτ is a total inlet area of the turbine (21 ), and wherein ATURB is obtained at a reduced mass flow, m'RED, of the turbine (21 ) at 2.5 - 3.5 pressure ratio between an inlet side and an outlet side of the turbine (21 ) and at a tip speed of 450 m/s of the turbine wheel.

13. The four stroke internal combustion engine (2) according to any one of the preceding claims, wherein the cylinder arrangement (4) has a total swept volume, V_s, in the cylinder bore (12) between the bottom dead centre, BDC, between the power stroke and the exhaust stroke, and a top dead centre, TDC, of the piston (10), and wherein 0,3 < V_s < 4 litres.

14. A vehicle (1 ) comprising a four stroke internal combustion engine (2) according to any one of the preceding claims.