WO2007101567A1

WO2007101567A1 - Internal combustion engine with an exhaust gas turbocharger

Info

Publication number: WO2007101567A1
Application number: PCT/EP2007/001610
Authority: WO
Inventors: Stephan KRÄTSCHMER; Michael Stiller; Siegfried Sumser
Original assignee: Daimler Ag
Priority date: 2006-03-01
Filing date: 2007-02-24
Publication date: 2007-09-13
Also published as: DE102006009298A1

Abstract

An internal combustion engine has an exhaust gas turbocharger which comprises an exhaust gas turbine (3) in the exhaust gas line (4) and a compressor (1) in the intake duct (2), wherein the exhaust gas turbine (3) has two separate turbine inlets (6, 7), via which exhaust gas can be fed to the turbine wheel. The mass flow through the two turbine inlets (6, 7) can be set via a switching device (40) which has, in a switching housing (41), a shut-off flap (45) pivotable about a rotation axis (46) and having two at least equally long lobes (45a, 45b) on both sides of the rotation axis (46).

Description

DaimlerChrysler AG

Internal combustion engine with an exhaust gas turbocharger

The invention relates to an internal combustion engine having an exhaust gas turbocharger according to the preamble of claim 1.

In DE 103 57 925 Al an internal combustion engine with an exhaust gas turbocharger is described, the exhaust gas turbine in the exhaust line has two separate turbine flows of different sizes, via the turbine of the exhaust gas each exhaust gas can be supplied. Each of the two turbine flows is supplied via an exhaust pipe with exhaust gas, which is in each case fluidically connected to a cylinder bank of the internal combustion engine. Upstream of the exhaust gas turbine, the two exhaust pipes are mutually connected via a connecting line arranged therein, adjustable check valve, moreover, a further adjustable check valve is arranged in the exhaust pipe for the larger exhaust gas flow. Depending on the position of the check valves, the mass flows through the exhaust pipes and the associated turbine floods can be kept separate, so that a flow equalization between the exhaust pipes or between the exhaust gas is not possible, or it is the entire exhaust gas both banks led to the smaller flow tide or it the exhaust gas from both cylinder banks is supplied with equal pressure to both the smaller and the larger turbine tide. Due to the high, caused by the engine pressure pulsations in the exhaust pipes are formed on the check valves acting gas forces that may have undesirable changes in the valve position result. The check valves must therefore be designed so that caused by pressure pulsations gas forces no unwanted changes in setting, which can lead to leaks.

The invention is based on the object with simple constructive measures a supercharged internal combustion engine whose exhaust gas turbine is designed to be double-flow, to the effect that pressure pulsations in the exhaust system have no unwanted changes in setting in the exhaust gas flows to be supplied mass flows result. This should be useful to realize by means of a compact design.

This object is achieved with the features of claim 1. The dependent claims indicate expedient developments.

According to the invention, it is provided that the switching device, via which the mass flow through the two turbine flows is to be set, has a blocking flap which is pivotably mounted in a switch housing and has two flap wings of equal length on both sides of the axis of rotation of the blocking flap. This blocking flap is rotatably mounted in a connecting space in the switching housing, which communicates on the one hand with the two exhaust pipes and on the other hand with the two turbine flows of the exhaust gas turbine. The exhaust gas of the cylinder banks of the internal combustion engine is conducted into the switching device via the two exhaust gas lines and fed therefrom, depending on the position of the blocking flap, to one of the turbine flows or to both turbine flows. Possible on the one hand, a separate supply of exhaust gas of each exhaust pipe in the associated turbine flow without transfer to the other exhaust pipe or turbine flood or the blocking of an exhaust gas flow and supply of the entire exhaust gas both cylinder banks in only one turbine flood, in the latter case, the supply of the entire exhaust gas in each of the two turbine floods in question. Finally, in an intermediate position of the blocking flap, a pressure equalization between the two exhaust pipes and, accordingly, the supply of exhaust gas in each turbine flood under the same pressure possible.

Due to the special design of the blocking flap with the two at least approximately equally long flap wings on both sides of the rotation axis of the blocking flap, a gas force compensation is achieved since the exhaust gas introduced via the exhaust lines and pressurized exhaust force the two wings in the same manner around the axis of rotation of the blocking flap, so that no resulting torque arises. In the connection space in the switch housing, in which the blocking flap is pivotally mounted, the exhaust gas introduced via the mouths of the exhaust pipes mixes so that a uniform pressure is applied over the surface of the blocking flap on the side of the blocking flap facing the mouth openings of the exhaust pipes. This uniform pressure prevents the formation of resulting torques. Even with pressure pulsations in the exhaust system is a uniform application of force to the blocking flap. This has the consequence that the barrier flap is always in balance regardless of any pressure pulsations in the exhaust line and maintains its current position. Therefore, it may be possible to dispense with a monitoring of the barrier flap position, also the risk of leakage is significantly reduced. Be reached These advantages with a structurally simple and compact design.

The blocking flap is advantageously designed as a rotary valve, which has a circumferential bearing in the switch housing. A shaft bearing in the region of the axis of rotation may be provided, but is not required for the rotary valve. About an axle-side shaft but advantageously the adjusting movement of an actuator acting on the blocking flap can be initiated.

The mouth openings of the exhaust pipes on the one hand and the channels to the turbine floods on the other hand are advantageously located on opposite sides in the connecting space in the switch housing. The exhaust pipes and the channels of the exhaust gas flows are each separated by partitions, which are opposite each other diagonally in the switch housing. Because of this diagonally opposite position, the exhaust pipes and the channels of the exhaust gas flows are completely separated in terms of flow when the blocking flap is in a position connecting the end faces of the partitions. At the same time, one of the two dividing walls, preferably the dividing wall arranged between the turbine passages, can expand in an anvil shape toward the connection space and delimit the connecting space in a part-circular manner, whereby a supporting and guiding surface for the blocking flap is formed. Beyond the separating function, the partition wall thus also has a bearing and guiding function for the blocking flap.

According to an advantageous embodiment, it is provided that the blocking flap is enclosed by two axially spaced, fixedly connected to the blocking flap cover plates, for a flow-tight seal of the Verbindungsräumes in Ensure axial direction. The cover plates represent side walls of a flow channel with the blocking flap, wherein the blocking flap connects the cover plates and forms a third, the flow channel limiting side. On the opposite side of the barrier flap, the flow channel is open and communicates depending on the rotational position of the blocking flap with the mouth openings both of the two opening into the Verbindungsräum exhaust pipes and the branching, the turbine floods associated channels. On the outer surface of the cover plates additional sealing or piston rings can be arranged, which ensure the seal in the axial direction and at the same time ensure the rotation of the housing side storage of the cover plates.

The internal combustion engine is advantageously equipped with an exhaust gas recirculation device which connects one of the two exhaust gas lines to the intake tract of the internal combustion engine. Particularly in the embodiment with two turbine flows of different sizes, the exhaust line of the smaller turbine flow is coupled to the return line, which has the advantage that when the larger exhaust gas flow is blocked, the entire exhaust gas of the internal combustion engine is supplied to the smaller exhaust gas flow and an increased exhaust back pressure is generated there. which supports the exhaust gas recirculation in the direction of intake. In a further advantageous embodiment, the exhaust gas turbine is designed with variable turbine geometry for variable adjustment of the effective turbine inlet cross-section, whereby an additional degree of freedom for regulating the exhaust gas back pressure is given.

Finally, it may be appropriate to bridge the exhaust turbine by means of a bypass having an adjustable bypass valve. The blowdown over the bypass poses on the one hand, for sure that the exhaust gas turbine is not overloaded, on the other hand, this provides a further degree of freedom, are influenced by the state and characteristics of the internal combustion engine or the units of the internal combustion engine.

Further advantages and expedient embodiments can be taken from the further claims, the description of the figures and the drawings. Show it:

1 is a schematic representation of a supercharged internal combustion engine with a dual-flow exhaust gas turbine, the exhaust gas mass flows are controllable in the turbine flows of the exhaust gas turbine via a switching device,

Fig. 2, the switching device for controlling the

Mass flows into the turbine floods in an enlarged sectional view,

Fig. 3, the blocking flap of the switching device in one

Sectional view along section line III-III of Fig. 2,

4 is a sectional view of a variant of

Switching device with sealing rings and sliding rings,

Fig. 5 in a section a further variant of

Switching device, and the blocking flap in a vertical position,

Fig. 6 in a section the switching device acc. 5, and the blocking flap in an angular position and Fig. 7 in a diagram efficiencies of the exhaust gas turbine over a voltage applied to the turbine pressure ratio π _τ at a constant exhaust gas turbocharger speed.

The designated in Figure 1 by reference numeral 100 internal combustion engine, which is a diesel engine or a gasoline engine, is equipped with an exhaust gas turbocharger 20, comprising a compressor 1 in the intake tract 2 and an exhaust gas turbine 3 in the exhaust line 4, wherein the compressor wheel and the turbine wheel are rotationally coupled via a shaft 5. The exhaust gas turbine 3 is equipped with two bends and has a smaller turbine flow 6 and a larger turbine flow I _1, with the turbine flows 6 and 7 differing in the flow cross section. Exhaust gas from the exhaust line 4 of the internal combustion engine 100 can be supplied to the turbine wheel via both turbine flows 6 and 7. Furthermore, the exhaust gas turbine 3 is provided with a variable turbine geometry 8, via which the effective turbine inlet cross section between a minimum storage position and a maximum opening position is variably adjustable.

The two turbine floods 6 and 7 are connected via exhaust pipes 22 and 23 of the exhaust line 4 with the exhaust manifolds 30 and 31 respectively of a cylinder bank 10 and 11 of the engine 100. In the exhaust pipes 22 and 23 is a common switching device 40, via which the exhaust gas mass flow in each turbine flood 6 and 7 is controllable. The pipe sections in the exhaust pipes 22 and 23 upstream of the switching device 40 are provided with reference numerals 35 and 36.

Downstream of the switching device 40 branches off from the exhaust line 4 from a bypass 50, in which an adjustable bypass valve 48th is integrated. The bypass 50 comprises a first bypass line 51, which branches off from the exhaust line 22 of the smaller turbine flow 6 and opens into the bypass valve 48, and a second bypass line 52, which branches in a corresponding manner from the exhaust pipe 23 of the larger turbine flow 7 and also into the bypass valve 48 opens. Via a further bypass line 53, which branches from the bypass valve 48 and opens downstream of the exhaust gas turbine 3 in the exhaust line 4, the bypass 50 is completed.

The internal combustion engine 100 is also provided with an exhaust gas recirculation device, which is a return line

16 between the exhaust line 4 and the intake tract 2, arranged in the return line 16 exhaust gas cooler 15 and a unidirectional and appropriately adjustable return valve

17 includes. The return line 16 branches in the flow path between the switching device 40 and the exhaust gas turbine 3 from the exhaust pipe 22 of the smaller turbine flow 6 and opens downstream of a charge air cooler 14 in the intake tract second

All units of the internal combustion engine are adjusted as a function of state and parameters via StellSignale a control and control unit 18. This relates in particular to the switching device 40, the bypass valve 48, the variable turbine geometry 8 and the return valve 17.

Fig. 2 shows the switching device 40, via which the mass flows in the turbine floods 6 and 7 are controllable, in section. In a switch housing 41 of the switching device 40 is a connection space 42 which connects the opening into the switch housing line sections 35 and 36 of the exhaust pipes with channels 43 and 44, which are connected via further line sections with the turbine floods 6 and 7 respectively. In the connection space 42 is a blocking flap 45 pivotally mounted about an axis of rotation 46, wherein the axis of rotation 46 extends centrally through the center of the blocking flap 45, such that equally large flap wings 45a and 45b of the blocking flap 45 extend on both sides of the axis of rotation 46. About the current rotational position of the blocking flap 45, the mass flow supply to the turbine floods 6 and 7 is adjustable. The barrier flap 45 is enclosed between two axially spaced cover plates, of which in Fig. 2, a cover plate 62 is shown with circumferentially arranged sealing ring 64.

The designed as a rotary slide barrier 45 is mounted on the cover plate 62 and the other, axially spaced cover plate 63 (Fig. 3) in the switch housing 41 circumferentially. An anvil-shaped widening partition 61 between the channels 43 and 44 in the switch housing has a part-circular support surface on which the cover plates 62 and 63 are supported.

The dividing wall 61 diagonally opposite is another, narrowing partition wall 60 in the switch housing, which separates the channels for the line sections 35 and 36. Laterally of the partition 60, the mouths of the channels for the line sections 35 and 36 of wall sections of the switching housing are limited in such a way that contact points A and B can come into contact with the radially outer end faces of the blocking flap 45. FIG. 2 shows an angular position for the blocking flap 45 in which the radially outer end face of the flap 45b of the blocking flap rests against the contact point B, which is located on a side wall which delimits the channel for the line section 36. In this angular position of the blocking flap 45, an inflow of exhaust gas is possible both via the line section 35 and via the line section 36. The inflow exhaust gas mass flows are introduced as shown by the solid arrows in the channel 43, which communicates with the smaller turbine trough 6. The second channel 44 in the switch housing 41, however, is shut off by the blocking flap 45, so that no exhaust gas is supplied to the larger turbine flow 7. In a corresponding manner, the channel 43 and the turbine trough 6 is shut off and the entire exhaust gas is conducted via the channel 44 into the larger flow trough 7 when the blocking flap 45 is in an angular position in which one of the radially outer end faces of the blocking flap at the contact point A is present.

On the other hand, if the blocking flap 45 is in a vertical position, in which the end face of the dividing wall 60 is contacted by the radially outer face of a wing 45a or 45b of the blocking flap 45, then the channels in the switching housing 41 are completely separated, so that the exhaust gas mass flows are introduced via the channels assigned to the line sections 35 and 36, are not mixed and continue to flow into the associated channels 43 and 44, respectively. This case corresponds to a flow separation of the turbine flows 6 and 7.

In an intermediate position of the blocking flap 45, either between the tip of the dividing wall 60 and the contact point A or in an intermediate position between the dividing wall 60 and the contact point B - ie in each case in the middle of the mouth opening of the channel for the line section 35 or the channel for the line section 36 - There is a thorough mixing of the supplied exhaust gas mass flows, so that a pressure equalization between the mass flows is achieved. At the same time both outgoing channels 43 and 44th open, so that the respective turbine flows 6 and 7, the same pressure is supplied.

The sectional view of Fig. 3 it can be seen that the locking flap 45 is enclosed between the axially spaced cover plates 62 and 63, which have on their outer side in each case a sealing ring 64 and 65, whereby the space between the cover plates sealed against the switching housing 41 is. The composite of cover plates 62 and 63 with blocking flap 45 is rotatably mounted on a shaft 66 in the switch housing 41, wherein via the shaft 66, the applied via an actuator adjusting movement is introduced to the locking flap 45.

4 shows a variant of the switching device 40, wherein a section of the switching device 40 is shown, which essentially shows the cover plates 62, 63. The sealing rings 64, 65 receiving cover plates 62, 63 additionally have slip rings 67, 68, whereby leakage can be reduced. With the aid of the sliding rings 67, 68, a pressure compensation chamber 72 can be formed, which contributes to the reduction of the friction forces occurring. The pressure compensating space 72 is the sealing ring 64; 65 partially formed bounded, so that a pressure P on opposite sides of the sealing ring 64; 65 and can partially compensate.

For realizing a first annular region 73 of the pressure compensating space 72, the sliding rings 67, 68 are arranged next to the sealing rings 64, 65, wherein a first side surface 69 of the sealing ring 64; 65 a second side surface 70 of the sliding ring 67; 68 is arranged opposite. An outer diameter DAG of the sliding rings 67, 68 is smaller than an outer diameter DAD of the sealing rings 64, 65, wherein an inner diameter DIG of the seal rings 67, 68 is made larger than an inner diameter DID of the seal rings 64, 65. Between the first side surface 69 and the second side surface 70, a contact surface 71 smaller than the second side surface 70 is formed Contact surface 71 is arranged extending from the outer diameter DAG in the direction of the inner diameter DIG.

A first end face 74 of the sealing ring 64; 65 and a second end face 75 of the sliding ring 67; 68 are positioned away from the switch housing 41, wherein a second annular portion 76 of the pressure compensating space 72 is formed between the first end face 73 and an opposite first cover disk wall 79.

A third annular region 77 of the pressure compensation chamber 72 is located between a third side surface 78 of the sealing ring 64, which is remote from the first side surface 69; 65 and an opposite second Abdeckscheibenwandung 80 is formed.

The sealing rings 64, 65 and the sliding rings 67, 68 are ideally positioned in groove-shaped openings 81, 82 of the cover disks 62, 63, wherein the sliding rings 67, 68 predominantly rest unmoved due to the exhaust gas pressure in the openings 81, 82.

For the sealing rings 64, 65 and seal rings 67, 68 comparable schleißresistente material combinations are to be selected, which have, taking into account the high exhaust gas temperatures, for example in the Otto engine about 1050 ⁰ C and the diesel engine 850 ⁰ C, a high temperature strength. Furthermore, the materials should have a high resistance to oxidation, a high compressive strength and a low rate of crack propagation. have rate.

Preferably, combinations of metallic materials and ceramic or graphite-containing materials are to be selected, in particular ceramics with silicon nitrides, silicon carbides or aluminum oxides being used as the ceramic material.

In a further variant of the switching device 40 shown in FIGS. 5 and 6, the switching device 40 is associated with guide devices 83, 84 for increasing the efficiency η of the exhaust gas turbine 3. The Verbindungsräum 42 has a fluidly lossy zone 85, which is formed in particular in the region of the wing 45a. High flow losses can cause a reduction of the enthalpy of the exhaust gas in the turbine floods 6, 7 and thus low efficiencies of the exhaust gas turbine 3. With the aid of the guide devices 83, 84, which are designed projecting into the connection space 42, leakage of lossy waste gas from the zone 85 into the channels 43, 44 can be avoided.

The lossy exhaust gas can flow back into the region of the Verbindungsräumes 42 outside of the zone 85 via stomata 88, 89, which are arranged between 42 positioned in the Verbindungsräum 42 ends 87, the guide devices 83, 84 and the blocking flap. With the help of the stomata 88, 89 a pressure equalization between the zone 85 and the remaining Verbindungsräum 42 can be realized, so that the possibility of gas-force compensation is maintained.

The guide devices 83, 84 are fastened to a circumference of the dividing wall 61 adjoining the connecting space 42, in particular the transition between the dividing wall 61 and the guide devices 83, 84 is to perform flow-tight. Ideally, the guide devices 83, 84 and the partition 61 are formed as one component.

Flow cross sections, which are arranged starting from the ends 86, 87 in the direction of the turbine wheel of the exhaust gas turbine 3, are designed by means of the guide devices 83, 84 tapering in the direction of the turbine wheel, whereby a flow acceleration to increase the efficiencies η of the exhaust gas turbine 3 by a Reduction of the tendency to detach the flow is achieved.

Advantageously, the blocking flap 45 are arranged facing inner surfaces 90, 91 of the guide devices 83, 84 opposite surfaces 92, 93 of the blocking flap 45 adapted adapted.

FIG. 7 shows in a diagram efficiencies of the exhaust gas turbine 3 above a pressure ratio π _τ applied to the exhaust gas turbine 3 at a constant exhaust gas turbocharger speed, wherein the lines marked with a dot describe the achieved efficiencies η with the switching device 40 and the guide devices 83, 84. The lines marked with a cross describe the achieved efficiencies η of the switching device 40 without guide devices 83, 84.

Claims

DaimlerChrysler AGPatent claims

1. Internal combustion engine with an exhaust gas turbocharger, the exhaust gas turbine (3) in the exhaust line (4) and a compressor (1) in the intake (2), wherein the exhaust gas turbine (3) has two separate turbine floods (6, 7) over which can be fed to the turbine wheel exhaust gas, and the mass flow through the two turbine floods (6, 7) via a switching device (40) is adjustable, characterized in that the switching device (40) in a switch housing (41) one about an axis of rotation (46) pivotable, impenetrable barrier flap (45) with two at least approximately equally long wings (45a, 45b) on both sides of the axis of rotation (46), wherein the blocking flap (45) in a connecting space (42) in the switch housing (41) stored and the connecting space (42) is connected both to the two turbine passages (6, 7) of the exhaust gas turbine (3) and to two exhaust passages (22, 23), which are each assigned to a cylinder bank (10 or 11) of the internal combustion engine (100) ,

2. Internal combustion engine according to claim 1, characterized in that in the connecting space (42) in the switch housing (41) each have a partition (60) between channels (43, 44) of the exhaust pipes (22, 23) and between channels (43, 44) the turbine floods (6, 7) opens, and that the partitions (60, 61) are located diagonally opposite each other in the switch housing (41).

3. Internal combustion engine according to claim 2, characterized in that the turbine flows (6, 7) associated partition wall (61) to the connection space (42) towards anvil-shaped and the connection space (42) bounded part-circular.

4. Internal combustion engine according to claim 2 or 3, characterized in that the side regions of the part-circular extension of the turbine floods (6, 7) associated partition (61) outer boundary walls of the Abgas1eitungen (22, 23) associated with channels (43, 44) are diagonally opposite ,

5. Internal combustion engine according to one of claims 2 to 4, characterized in that the exhaust pipes (22, 23) associated with the partition (61) for Verbindungsräum (42) is formed narrow.

6. Internal combustion engine according to one of claims 1 to 5, characterized in that the pivotable blocking flap (45) is designed as a rotary valve with peripheral side storage.

7. Internal combustion engine according to one of claims 1 to 6, characterized in that the blocking flap (45) of two axially spaced, fixedly connected to the locking flap cover plates (62, 63) is enclosed, which are rotatably mounted in the switch housing (41) ,

8. Internal combustion engine according to claim 7, characterized in that on the outside of the cover plates (62, 63) sealing rings (64, 65) are arranged.

9. Internal combustion engine according to claim 8, characterized in that on the outside of the cover plates (62, 63) sliding rings (67, 68) are arranged, which are positioned next to the sealing rings (64, 65).

10. Internal combustion engine according to claim 9, characterized in that the sliding rings (67, 68) are formed smaller than the sealing rings (64, 65).

11. Internal combustion engine according to claim 9 or 10, characterized in that in each case one of the sealing rings (64, 65) at least partially delimiting pressure compensation chamber (72) can be formed.

12. An internal combustion engine according to any one of claims 8 to 11, characterized in that a first side surface (69) of the sealing ring (64; 65) and a second side surface (70) of the sliding ring (67; 68) are arranged opposite one another, wherein a contact surface (71) which is smaller than the second side surface (70) can be formed.

13. Internal combustion engine according to one of claims 2 to 12, characterized in that the partition wall (61) has guide devices (83, 84) for flow conditioning, wherein the guide devices (83, 84) projecting into the connecting space (42) are formed.

14. Internal combustion engine according to claim 13, characterized in that the guide devices (83, 84) on one of the connection space (42) adjacent the periphery of the partition (61) are provided.

15. An internal combustion engine according to claim 13 or 14, characterized in that the guide devices (83, 84) a lossy zone (85) of the connecting space (42) are configured such that a separation of exhaust gas from the lossy zone (85) in the channels (43, 44) is avoidable.

16. Internal combustion engine according to one of claims 13 to 15, characterized in that between in the connecting space (42) projecting ends (86, 87) of the guide devices (83, 84) and the blocking flap (45) stomata (88, 89) are formed ,

17. Internal combustion engine according to any one of claims 13 to 16, characterized in that the blocking flap (45) facing arranged inner surfaces (90, 91) of the guide devices (83, 84) surfaces (92, 93) of the blocking flap (45) are adapted adapted.

18. Internal combustion engine according to one of claims 13 to 17, characterized in that from the ends (86, 87) of the guide devices (83, 84) formed flow cross sections in the direction of the Turbine wheel of the exhaust gas turbine (3) are tapered.

19. Internal combustion engine according to one of claims 1 to 18, characterized in that the switching device (40) in the exhaust manifold (30, 31) is integrated.

20. Internal combustion engine according to one of claims 1 to 19, characterized in that the switching device (40) in the exhaust gas turbine (3) is integrated.

21. Internal combustion engine according to any one of claims 1 to 20, characterized in that the turbine flows (6, 7) are designed differently sized with different flow cross sections.

22. Internal combustion engine according to one of claims 1 to 21, characterized in that a first flow cross section of the first turbine tide and a second flow cross section of the second tide itself

23. Internal combustion engine according to one of claims 1 to 22, characterized in that an exhaust gas recirculation device is provided which connects an exhaust pipe (22, 23) which is associated with a turbine flow (6, 7) with the intake tract (2).

24. Internal combustion engine according to one of claims 1 to 23, characterized in that the exhaust gas turbine (3) bridging bypass (50) is provided with adjustable bypass valve (51).

25. Internal combustion engine according to one of claims 1 to 24, characterized in that the exhaust gas turbine (3) is equipped with variable turbine geometry (8) for variable adjustment of the effective turbine inlet cross-section.