DK201670927A1

DK201670927A1 - A relief valve for a large turbocharged twostroke compression-ignited internal combustion engine

Info

Publication number: DK201670927A1
Application number: DKPA201670927A
Authority: DK
Inventors: Michael Oftedal
Original assignee: Man Diesel & Turbo Filial Af Man Diesel & Turbo Se Tyskland
Priority date: 2016-11-22
Filing date: 2016-11-22
Publication date: 2017-12-18
Also published as: KR20180057527A; DK179156B9; KR101954692B1; JP6571740B2; JP2018084234A; CN108087119A; DK179156B1; CN108087119B

Abstract

A relief valve (50) for providing relief for gas in acombustion chamber of a large two-stroke compressionignited two-stroke engine in a blow-off event The relief valve (50) comprising a housing (51,70,73), a first bore (64) in the housing (51,70,73), a first piston (56) slidably disposed in the first bore and defining a first pneumatic pressure chamber (60) in the first bore (64), an valve member (52) carried by the first piston (56), the valve member (52) having a stem (53) and a head (54) that is engageable with an annular seat (55), the housing (51) being provided a relief passage between an inlet opening (57) and an outlet opening (58) with the annular seat (55) therein, the relief passage comprises a relief chamber (63) between the annular seat (55) and the outlet opening (58), a first side of the first piston (56) forms a first effective pressure surface (61) that faces the first pneumatic pressure chamber (60) and the second side of the first piston forms a second effective pressure surface (62) that faces the relief chamber (63), a first side of the head (54) forms a third effective pressure surface (59) that faces the inlet opening (57), the first effective pressure surface (61) being larger than the third effective pressure surface (59).

Description

A RELIEF VALVE FOR A LARGE TURBOCHARGED TWO-STROKE COMPRESSION-IGNITED INTERNAL COMBUSTION ENGINE

TECHNICAL FIELD

The disclosure relates to control of blow-off events in a large turbocharged two-stroke compression-ignited internal combustion engine with crossheads.

BACKGROUND

Large two-stroke turbo charged compression-ignited internal combustion engines of the cross-head type are for example used for propulsion of large oceangoing vessels or as primary mover in a power plant. Not only due to sheer size, these two-stroke diesel engines are constructed differently from any other internal combustion engines. Their exhaust valves may weigh up to 400 kg, pistons have a diameter up to 100 cm and the maximum operating pressure in the combustion chamber is typically several hundred bar. The forces involved at these high pressure levels and piston sizes are enormous.

Due to e.g. erroneous fuel injection timing or amount, excessive pressure may occur on rare occasions in one of the cylinders. In order to accommodate these excessive pressures, the force with which the cylinder cover is pressed onto the top of the cylinder liner is carefully controlled by the tension that is applied to the stay bolts that connect the cylinder cover to the bedplate and keep the engine construction together. Thus, when excessive pressure occurs the cylinder cover is lifted and the excessive pressure is blown out between the top of the cylinder liner and the bottom of the cylinder cover. This system - that is generally used in the art - is not without problems .

Cylinder cover lift is an explosive gas leakage in which uncontrolled gas is released under a loud bang of up to 170db. Any bystanders could be seriously hurt when such a sideward blow-off occurs due to exposure to a jet of hot gas, often in the form of a flame. Further, the extremely hot and high pressure gas erodes the precisely machined mating surfaces of the cylinder liner and the cylinder cover and damages the sealing ring that is placed between the top of the cylinder liner and the bottom of the cylinder cover.

Therefore, a blow-off event will typically require that these surfaces are machined and that the sealing ring is replaced in order to obtain the required fluid tightness. Consequently, the reparation costs are significant after a blow-off. Moreover, the tension in the stay bolts varies due to temperature changes of the engine and the environment and can therefore not be very accurately controlled. If a blow-off occurs at a moment that the tension in the stay bolts is relatively high, the forces on the piston and the crankshaft have in the past caused damaged big ends and other expensive engine components. Such an occurrence is even more expensive than a better controlled blow-off.

Ship insurers (Classification societies) require that large marine engines are protected with safety measures against damage from excessive pressure in the combustion chamber

Hereto, some prior art engines are provided with a rupture disk in the wall of the combustion chamber that is designed to fail in order to protect the engine against possible damage from excessive pressure in the combustion chamber. A disadvantage of these ruptured discs is that they weaken over time from the exposure to the fluctuating pressure in the combustion chamber and eventually fail already at a relatively small excess pressure, e.g. due to a small misfire. Thus, rupture discs tend to fail prematurely. This is problematic, especially since the engine has to be stopped in order to replace the failed rupture disc with a with a new disk. Conseguently, the presently most commonly used measure with the rupture discs is not optimal.

Other engines have been provided with security valves in order to comply with the reguirements that are supposed to open for evacuating gases from the combustion chamber when excessive pressures occur in the combustion chamber. These are spring loaded poppet valves. However, the explosive nature of blow-off occurrences render these poppet valves relatively ineffective since their maximum opening is insufficient for relieving the pressure sufficiently fast.

Thus, these security valves cannot effectively provide the reguired opening area in sufficiently short time and only have the effect of an indicator or a whistle in advance of a cylinder cover lift but these known valves cannot prevent cylinder cover lift.

On such valve is disclosed in GB 817,018. This document discloses a large two-stroke diesel engine with a separate ring between the cylinder liner and the cylinder cover, the separate ring being provided with a bore for receiving a safety valve. This known safety valve was however not reliable and the use of this safety valve was discontinued.

Thus, there is a need for an improved blow-off control system for large two-stroke compression-ignited internal combustion engines of the crosshead type.

SUMMARY

It is an object of the invention to provide a relief valve for alarge two-stroke compression-ignited internal combustion engine of the crosshead type that overcomes or at least reduces the problems mentioned above.

The foregoing and other objects are achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.

According to a first aspect there is provided a relief valve for providing relief for gas in a combustion chamber of a large two-stroke compression-ignited two-stroke engine in a blow-off event, the relief valve comprising: - a housing, - a first bore in the housing, - a first piston slidably disposed in the first bore and defining a first pneumatic pressure chamber in the first bore, - an valve member carried by the first piston, the valve member having a stem and a head that is engageable with an annular seat, - the housing being provided a relief passage between an inlet opening and an outlet opening with the annular seat therein, - the relief passage comprises a relief chamber between the annular seat and the outlet opening, - a first side of the first piston forms a first effective pressure surface that faces the first pneumatic pressure chamber and the second side of the first piston forms a second effective pressure surface that faces the relief chamber, - a first side of the head forms a third effective pressure surface that faces the inlet opening, - the first effective pressure surface being larger than the third effective pressure surface.

By providing the valve member with a piston with an effective pressure surface that is significantly larger than the effective pressure surface of the head on which the combustion chamber pressure acts, the pneumatic pressure in the pneumatic pressure chamber can be kept significantly lower than the combustion chamber pressure at which the relief valve is designed to open.

Further, the provision of the second effective pressure surface facing the relief chamber causes the pressure in the relief chamber upon valve lift to act in the opening direction of the valve member on a the third effective pressure surface together with the even larger second effective pressure surface, thereby ensuring that the valve will remain open long enough to provide sufficient relief for the pressure in the combustion chamber. Without having this additional third effective pressure surface there would be a risk of the valve member closing as soon as there is a small relief, i.e. soon as there is a small drop in the pressure in the combustion chamber, which is not desirable .

According to a first possible implementation of the first aspect the first pneumatic pressure chamber is fluidly connected with a port for connection to a source of pneumatic pressure. Thus, the correct pneumatic pressure can be maintained in the 1st pneumatic pressure chamber.

According to a second possible implementation of the first aspect the first effective pressure surface is preferably at least double the size of the third effective pressure surface, even more preferably four time the size of the third effective pressure surface.

According to a third possible implementation of the first aspect the valve member is resiliently biased away from the annular seat. Thus, the valve member moves to its completely open position when the engine is shut down in the pneumatic pressure is removed. Thereby, it is ensured that the relief valve is exercised regularly.

According to a fourth possible implementation of the first aspect the housing comprises a second bore and a second piston slidably disposed in the second bore and defining a second pneumatic pressure chamber in the second bore, the second piston being operatively connected to the stem. By providing a second piston on the stem and a second pneumatic pressure chamber the closing force applied to the valve member by the pneumatic pressure is significantly increased and if the first piston and the second piston are equal in diameter the closing force is essentially doubled.

According to a fifth possible implementation of the first aspect the second pneumatic pressure chamber is fluidly connected with a port for connection to a source of pneumatic pressure. Thus, the correct pressure level in the second pneumatic pressure chamber

According to a sixth possible implementation of the first aspect the head and a portion of the stem are disposed in the relief chamber.

According to a seventh possible implementation of the first aspect the valve member is axially displaceable between a closed position and with the head resting on the annular seat and a fully open position with a range of intermediate positions between the fully open position and fully closed position .

According to an eighth possible implementation of the first aspect the outlet opening is a radial outlet opening.

According to a ninth possible implementation of the first aspect the inlet opening is an axial inlet opening.

According to a tenth possible implementation of the first aspect the second piston has a fourth effective pressure surface facing the second pneumatic pressure chamber, the fourth effective pressure surface facing the same direction as the first effective pressure surface.

According to an eleventh possible implementation of the first aspect the fourth effective pressure surface has substantially the same size as the 1st effective pressure surface .

According to a twelfth possible implementation of the first aspect the second piston has a fifth effective pressure surface facing in the opposite direction of the fourth effective pressure surface, and wherein the second piston defines a pneumatic damping chamber in the second bore with the fifth effective pressure surface facing the pneumatic damping chamber .

By providing a pneumatic damping chamber the closing action of the valve member can be dampened and damage to the valve head can be prevented.

According to a thirteenth possible implementation of the first aspect the pneumatic damping chamber is provided with a orifice allowing the air trapped in the pneumatic damping chamber, thus ensuring that the air pressure in the pneumatic damping chamber does not act in the opening direction after the valve has closed.

According to a fourteenth possible implementation of the first aspect the first bore is disposed in a first housing part and the second bore is disposed in a second housing part, and wherein the first housing part and the second housing part are connected by a resilient element that allows for relative movement between the first housing part and the second housing part in order to compensate for dimensional differences in the relief valve due to heat expansion .

According to a fifteenth possible implementation of the first aspect the second effective pressure surface is affected by the pressure in the evacuation chamber and thereby adds a force in the opening direction on the valve member when the valve member has lift from the annular seat.

According to a sixteenth possible implementation of the first aspect the first housing part and the second housing part are connected telescopically with the resilient member there between, the resilient member preferably being a disk spring.

According to a seventeenth implementation of the first aspect the annular seat is disposed in a floating manner in the valve housing in order to allow the annular seat to be self-centering.

According to a second aspect there is provided a large turbocharged two-stroke compression-ignited internal combustion engine with crossheads, the engine comprising: a number of cylinders that serve as combustion chambers, the cylinders being provided with a cylinder cover, with an exhaust valve placed centrally in the cylinder cover, and with an exhaust duct connecting the exhaust valve to an exhaust gas receiver, the cylinder cover being provided with a relief valve according to the first aspect there any possible implementations thereof, with the inlet of the relief valve being fluidly connected to the combustion chamber and an outlet of the relief valve being fluidly connected to a discharge conduit.

According to a first possible implementation of the second aspect the relief valve allows gas flow from the inlet to the outlet when the valve member has lift from the annular seat and the relief valve preventing gas flow from the inlet to the outlet when the valve member rests on the seat.

According to a second possible implementation of the second aspect the first effective pressure surface is pressurized by pneumatic pressure in all of the positions of the valve member and wherein the second surface is pressurized by the pressure in the evacuation chamber 63 when the valve member has lift from the annular seat.

According to a third possible implementation of the second aspect the annular seat is arranged in a blow-off bore that extends through the cylinder cover.

According to a fourth possible implementation of the second aspect a main plane of the annular seat is arranged squint relative to a main direction of a the blow-off bore.

According to a fifth possible implementation of the second aspect the blow-off bore is connected to the exhaust duct or to the exhaust gas receiver via a blow-off pipe in order to bypass the exhaust valve.

According to a sixth possible implementation of the second aspect the relief valve is provided with cooling means, the cooling means preferably including a path for a cooling medium through or around the relief valve.

According to a seventh possible implementation of the second aspect the engine comprises a pneumatic system with for providing pneumatic pressure to pneumatic consumers associated with the engine, the pressure of the pneumatic system preferably increasing with increasing engine load and decreases with decreasing engine load.

These and other aspects and possible implementations will become clear from the detailed description and the drawings .

BRIEF DESCRIPTION OF THE DRAWINGS

In the following detailed portion of the present disclosure, the invention will be explained in more detail with reference to the example embodiments shown in the drawings, in which:

Fig. 1 is a front view of a large two-stroke diesel engine according to an exemplary embodiment,

Fig. 2 is a side view of the large two-stroke engine of Fig. 1,

Fig. 3 is a diagrammatic representation the large two-stroke engine according to Fig. 1,

Fig. 4 is a top view of a cylinder cover and exhaust valve with a relief valve according to an embodiment,

Fig. 5 is a sectional view along the lines A-A of Fig. 4, Fig. 6 is an elevated view of a relief valve according to an embodiment,

Fig. 7 is another elevated view of a relief valve according to an embodiment,

Figs. 8 and 9 are sectional views of the relief valve of Figs. 6 and 7, with a valve member of the relief valve in different positions, and

Fig. 10 it is a detail of a sectional view of the upper portion of the relief valve of Figs. 6 and 7.

DETAILED DESCRIPTION

In the following detailed description, a relief valve and large two-stroke turbocharged compression-ignited diesel internal combustion engine with crossheads will be described by example embodiments. Figs. 1 to 3 show a large low-speed turbocharged two-stroke compression-ignited engine with a crankshaft 42 and crossheads 43. Fig. 3 shows a diagrammatic representation of the engine with its intake and exhaust systems. In this example embodiment the engine has six cylinders 1 in line. Large two-stroke turbocharged compression-ignited internal combustion engines have typically between five and sixteen cylinders in line, carried by an engine frame 45. The engine may e.g. be used as the main engine in an marine vessel or as a stationary engine for operating a generator in a power station. The total output of the engine may, for example, range from 5,000 to 110,000 kW.

The engine is a compression-ignited engine of the two-stroke uniflow type with scavenge ports 19 at the lower region of the cylinders 1 and an exhaust valve 4 centrally arranged in the cylinder cover 22 at the top of the cylinders 1. The main direction of the gas flow though the cylinder is from the scavenge ports 19 at the bottom of the cylinder 1 to the exhaust valve 4 at the top of a cylinder 1, hence the name "uniflow". The charging air is passed from a charging air receiver 2 in the form of a large generally hollow cylindrical body to the scavenging air ports 19 of the individual cylinders 1. A piston 41 in the cylinder 1 compresses the charging air, fuel is injected from fuel injection valves (not shown) in the cylinder cover 22 and combustion follows and exhaust gas is generated.

When an exhaust valve 4 is opened, the exhaust gas flows through an exhaust duct 35 associated with the cylinder 1 concerned into the exhaust gas receiver 3 in the form of a large hollow cylindrical body and onwards through a first exhaust conduit 18 to a turbine 6 of the turbocharger 5, from which the exhaust gas flows away through a second exhaust conduit 7 to the atmosphere. Through a shaft 8, the turbine 6 drives a compressor 9 supplied with air via an air inlet 10. The compressor 9 delivers pressurized charging air to a charging air conduit 11 leading to the charging air receiver 2.

The intake air in the conduit 11 passes through an intercooler 12 for cooling the charging air - that leaves the compressor at approximately 200 °C - to a temperature between 36 and 80 °C.

The cooled charging air passes via an auxiliary blower 16 driven by an electric drive motor 17 that pressurizes the charging air flow in low or partial load conditions of the engine to the charging air receiver 2. At higher engine loads the turbocharger compressor 9 delivers sufficient compressed scavenging air and then the auxiliary blower 16 is bypassed via a non-return valve 15.

Figs. 4 and 5 show the exhaust valve 4 and cylinder cover 22 in greater detail in top- and sectional view, respectively. The exhaust valve 4 is securely bolted to the cylinder cover 22 with the exhaust valve spindle 44 with its integral valve disk arranged in the central opening in the cylinder cover 22. The exhaust valve spindle 44 is shown in its closed position with the disk of the exhaust valve spindle 44 resting on the valve seat. When exhaust valve 4 is open the combustion chamber 27 is connected to an exhaust duct 35. The exhaust duct 35 is connected to the exhaust gas receiver 3.

The cylinder cover 22 forms the upper portion of the combustion chamber 27. The cylinder cover 22 is provided with a plurality of cooling channels that are not visible in the figures. Further, fuel injection valves typically three fuel valves for single fuel engines for each cylinder and six fuel valves for dual fuel engines for each cylinder fuel valves (not shown) are received bores 80 in the cylinder cover 22 with the nozzle of the fuel valve protruding into the combustion chamber 27.

The exhaust valve 4 is provided with a hydraulic exhaust valve actuator 47 that includes a hydraulic pressure chamber 38 at the top of the valve spindle 44. An air spring 37 urges the valve spindle 44 upwards as upwards as in Fig. 5, i.e. in the closing direction and the hydraulic actuator 47 urges the valve spindle 44 in the opening direction when the hydraulic actuator 47 is pressurized. Thus, lift of the exhaust valve spindle 44 is achieved by applying hydraulic pressure to the hydraulic actuator 47 and the air spring 37 ensures return of the valve spindle 44 to its closed position .

The engine is provided with a blow-off conduit that extends as shown from the combustion chamber 27 to the exhaust duct 35. Alternatively, the blow-off conduit extends from the combustion chamber 27 to the exhaust gas receiver 3. The cross-sectional area of the blow-off conduit is sufficiently large for relieving the pressure in the combustion chamber 27 fast in case of a misfire or other event that causes excessive pressure in the combustion chamber 27. A relief valve 50 controls the opening and closing of the blow-off conduit and the relief valve 50 can open sufficiently fast with a sufficiently large opening for relieving the pressure in the combustion chamber 27 in case of an excessive pressure event to prevent damage to the engine. A portion of the blow-off conduit is formed by a blow-off bore 29 in the cylinder cover 22. A blow-off pipe 36 connects the blow-off bore 29 to the exhaust duct 35 or to the exhaust gas receiver 3.

Figs. 6 to 10 illustrate the relief valve 50 in greater detail. The relief valve 50 can be provided with its own housing 51,70,73, as shown so that it can be used as a cartridge that is inserted into a suitable bore 28 (Fig. 5) in the cylinder cover 22 or (not shown) the relief valve can be an integral part of the cylinder cover 22.

The relief valve 50 is inserted into the bore 28 in the cylinder cover 22 with a bracket 73 protruding from the cylinder cover 22. The bracket 73, can be bolted or welded to the housing or be an integral part of the housing. The bracket 73 is provided with bores for receiving bolts (Figs. 6 and 7) that secure the relief valve 50 to the cylinder cover 22. The housing 51,70,73 is provided with an axially oriented inlet opening 27 and with a large radially oriented outlet opening 58 for allowing evacuation of exhaust gas when the relief valve 50 is open.

The relief valve 50 is provided with a valve member 52 that is displaceable between a closed position shown in Fig. 8 and a fully open position shown in Fig. 9, i.e. the valve member 52 can move back and forth over the range of positions between the closed position of Fig. 8 and the fully open position of Fig. 9. The valve member 52 can assume any intermediate position between the fully open and fully closed position. The relief valve 50 is provided with a relief passage that allows gas flow from its inlet opening 57 to its outlet opening 58 when the valve member 52 has lift, i.e. when the valve member 52 is not in its closed position. An evacuation chamber 63 in valve housing 51 connects the axial inlet opening 57 to the radial outlet opening 58. An annular seat 55 is provided around the inlet opening 57.

In an embodiment the housing is made up from several parts. The first housing part 51 is telescopically connected to a second housing part 70, with a disk spring 76 or other resilient means therebetween to accommodate effects of thermal expansion. The bracket 73 is secured to the second housing part 70.

The valve member 52 includes a stem 53 that is provided with a head 54 at one of its longitudinal ends that is engageable with the annular seat 55. The annular seat 55 is preferably disposed in a floating manner in the first housing part 51 in order to allow the annular seat 55 to be self-centering relative to the head 54.

The head 54 and a portion of the stem 53 are disposed in the relief chamber 63. A first piston 56 is secured to the stem 53 and in an embodiment a second piston 65 is also secured to the stem 53, longitudinally spaced from the first piston 56. The first piston 56 is slidably disposed in a first bore 64 in the first housing part 51 and the first piston 56 defines a first pneumatic pressure chamber 60 in the first bore 64. The second piston 56 is slidably disposed in a second bore 72 in the second housing part 70 and the second piston 65 defines a second pneumatic pressure chamber 68 in the second bore 72.

The stem 53 is slidably and sealingly received in a bore in a transverse wall 81 in the in the second housing part 70 .

The end of the stem 53 that is provided with the head 54 is extends from into the actuation chamber 63. The valve head 54 rests on the annular seat 55 when the valve member 52 is in its closed position, as shown in Fig. 8 with the surface of the valve head 54 that is exposed to the inlet opening 57 forming the third effective pressure surface 59 there is exposed to the pressure in the combustion chamber 27 .

When the valve member 52 has lift, as shown in Fig. 9 the head 54 is located in the evacuation chamber 63 and a substantial flow area is created for gas to flow from the inlet opening 57 to the outlet opening 58. In an embodiment the main plane of the annular seat 55 is arranged squint relative to the main direction to the blow-off bore 29 in order to minimize the restriction to flow through the blow-off bore 29. When the blow-off bore 29 is straight the main direction is the longitudinal direction of the blow-off bore 29. When the blow-off bore 29 is curved, its main direction is the local direction at the curve at the position where the annular seat 55 intersects with the blow-off bore 29. A first side of the first piston 56 forms a first effective pressure surface 61 that faces the first pneumatic pressure chamber 60. A second side of the first piston forms a second effective pressure surface 62 that faces the relief chamber 63. The first side of the head 54 forms a third effective pressure surface 59 that faces the inlet opening 57, i.e. is exposed to the pressure in the combustion chamber 27.

The first effective pressure surface 61 is larger than the third effective pressure surface 59, preferably at least double as large in surface area. In the shown embodiment the third effective pressure area 61 is four times the size of the first effective pressure area 61. However, it should be understood that any ratio between the first and the third pressure areas can in principle be used, depending on the maximum pressure in the combustion chamber and the available pneumatic pressure.

The second effective pressure surface 62 is affected by the pressure in the evacuation chamber 63 and thereby adds a force in the opening direction on the valve member 52 when the valve member 52 has lift from the annular seat 55. This stabilizes the opening movement of the valve member 52 by preventing the valve member 52 to close immediately when there is a slight drop in the pressure in the combustion chamber 27 due to the momentary relief provided by the lift of the valve member 52. Without the second effective pressure surface 62 creating a force in the opening direction the valve member 52 could oscillate between the closed and slightly open positions.

In an embodiment the second housing part 70 is provided with a second bore 72. A second piston 65 is slidably disposed in the second bore 72 and defines a second pneumatic pressure chamber 68 in the second bore 72.

The second piston 65 is operatively connected to the stem 53, e.g. by a tapered fit connection between a tapered bore in the second piston 65 and a matching tapered section on the stem 53. The first piston 65, as well as the head 54 is preferably formed as one piece with the stem 53.

The first pneumatic pressure chamber 60 and the second pneumatic pressure chamber 68 are both connected to a source of pneumatic pressure via connecting bore 71, bore feed 77 and pneumatic port 79.

The pneumatic pressure in the first pneumatic pressure chamber 60 acts on the first effective pressure surface 61 thereby creating a force in the closing direction on the valve member 52.

The second piston 65 has a fourth effective pressure surface 66 facing the second pneumatic pressure chamber 68. The fourth effective pressure surface 66 faces the same direction as the first effective pressure surface 61. Thus, the pneumatic pressure acting on fourth effective pressure surface 66 creates a force in the closing direction of the valve member 52 and thereby assists the first piston 56 in its effort to keep the valve member 52 in the closed position.

In an embodiment the fourth effective pressure surface 66 has substantially the same size as the first effective pressure surface 61.

The second piston 65 has a fifth effective pressure surface 67 facing in the opposite direction of the fourth effective pressure surface 66. The second piston 65 defines a pneumatic damping chamber 69 in the second bore 72 with the fifth effective pressure surface 67 facing the pneumatic damping chamber 69. The pneumatic damping chamber 69 is preferably connected to the atmosphere via an orifice so that any pressure build up in the damping chamber 69 disappears over time. In an embodiment the orifice is formed by a small opening in the housing 70 that directly connects the damping chamber 69 to the surrounding atmosphere. This allows the pneumatic damping chamber 69 to act as a damper before the closing movement of the valve member 52 by the pressure in the pneumatic damping chamber 69 acting on the fifth effective pressure surface 67, i.e. creating a force opposing the closing movement of the valve member 52, thereby ensuring a smooth landing of the head 54 on the s annular eat 55.

The valve member 52 is resiliently biased away from the annular seat 55 by a helical compression spring 75 that surrounds a free end of the stem 53 that protrudes from the third housing part 73. Hereto, the helical compression spring 75 is tensioned between a flange or disc at the free end of the stem 53 and the proximal end of the housing 51,70,73. The helical spring 75 ensures that the valve member 52 moves to its fully open position when there is no pneumatic pressure applied to the first pneumatic pressure chamber 60 and the second pneumatic pressure chamber 68, i.e. when the large two-stroke diesel engine is stopped. This ensures that the valve member 52 is exercised regularly.

In an embodiment the relief valve 50 is provided with cooling means. The cooling means preferably include a path (not shown) for a cooling medium through or around the relief valve 50.

The second effective pressure surface 62 is exposed to pressure in the evacuation chamber 66 and urges the valve member 52 towards its fully open position when the pressure from the combustion chamber 27 reaches the evacuation chamber 63.

When an excessive pressure in the combustion chamber 27 occurs, the force of the pressure in the combustion chamber 27 acting on the third effective pressure surface 59 will exceed the combination of the opposing force of the pressure created by the first pneumatic pressure chamber 60 acting on the first piston 56 and the pneumatic pressure in the second pneumatic pressure chamber 68 acting on the second piston 65. Thus, the valve member 52 will start moving towards its fully open position, as shown in Fig. 9.

When the pressure in the combustion chamber 27 has been relieved the force created by the pressure in the first pneumatic pressure chamber 60 and second pneumatic pressure chamber 68 will exceed the opposing force of the pressure in the relief chamber 63 on the second effective pressure surface 61 and on the third effective pressure surface 59 and the valve member 52 will start moving to the fully closed position. This will cause the air in the pneumatic damping chamber 69 to be compressed and slowly pressed out to the atmosphere via the orifice thereby dampening the movement of the head 54 back to the seat 55. A bleed groove 82 is provided in the wall of the damping chamber 69 in order to puncture the barrier formed by second piston 65 when the letter has moved a certain distance. This causes the pressure in the damping chamber 69 to correspond to the supply pressure (before compression). There can be several bleed grooves 82 distributed around the circumference of the damping chamber 69. The bleed groove (s) 82 are designed such that both piston rings and PTFE sealing rings can be used.

When the valve member 52 moves all the way towards its fully open position its movement is dampened by a stack of disc springs 74 that is provided in the third housing part 73. The second piston 65 will engage the stack of disc springs 74 just before the fully open position is reached.

The pneumatic system of the large two-stroke diesel engine comprises a compressor or compressor station (not shown) that supplies a pneumatic supply conduit with pressurized air. The pressure in the supply conduit can be anywhere between 10 and 50 bar and is supplied to various consumers of pressurized air associated with the large two-stroke diesel engine 1. In an embodiment the pneumatic system is formed by a conventional starting air supply system which a large two-stroke turbocharged compression-ignited internal combustion engine with crosshead normally is provided with. The inlet port 79 of the relief valve 50 is connected to the pneumatic supply system to ensure a constant or variable pressure in the pneumatic pressure chambers of the relief valve 50.

The normal maximum pressure in the combustion chamber 27 increases with increasing engine load and decreases with decreasing engine load. Therefore, in an embodiment, the pressure in pneumatic system is adjusted accordingly.

Thus, by dimensioning the size of the area of the first effective pressure surface 61 and the fourth effective pressure surface 66 relative to the size of the area of the first effective pressure surface 59 the relief valve 50 can be dimensioned to open at a pressure that is higher with a margin than the normal pressure in the combustion chamber 27 for the actual engine load. The margin could be a constant pressure differential or increase with increasing engine load and vice versa.

The relief valve 50 can also be operated with a constant pneumatic pressure supplied to port 79. In this case the pressure should be such that the relief valve 50 opens when the highest pressure in the combustion chamber 27 during normal engine operation is exceeded by a margin, e.g. the relief valve 50 is set to open at a pressure of 230 Bar when the maximum expected pressure i.e. at 100% engine load is 200 Bar. The relief valve 50 can be set to open at the required pressure by adjusting the ratio between the third effective pressure surface 59 and the sum of first effective pressure surface 61 and the fourth effective pressure surface 66 in view of the pneumatic pressure applied at port 79.

In an embodiment (not shown) the relief valve 50 is coupled to electronic control unit (not shown) of the engine and issues an alarm upon a blow-off event. Hereto, the relief valve 50 is in an embodiment provided with a pressure sensor (not shown) that senses the pressure in the pneumatic damping chamber 69. If the pressure in the pneumatic damping chamber 69 exceeds a threshold an alarm is issued. Alternatively, the valve member 52 can be monitored with a movement sensor and an alarm is issued when the valve member 52 moves away from its closed position.

In an embodiment, the balance of forces that determines whether the valve member 52 is urged to the closed position or to the fully open position is only determined by the balance of the force of the pressure of the gas in the combustion chamber 27 acting on the valve member 52 and the force of the pressure of the air supplied to the relief valve 15 acting on the first piston 56 and second piston 65. Thus, if there is any resilient means for exercising the relief valve when the engine is stopped these resilient means will have a minor strength so that they do not have any significant influence on the movement of the valve member 52 during engine operation.

The invention has been described in conjunction with various embodiments herein. However, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality- The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage .

The reference signs used in the claims shall not be construed as limiting the scope.

Claims

1. A relief valve (50) for providing relief for gas in a combustion chamber of a large two-stroke compression-ignited two-stroke engine in a blow-off event, said relief valve (50) comprising: - a housing (51,70,73), - a first bore (64) in said housing (51,70,73), - a first piston (56) slidably disposed in said first bore and defining a first pneumatic pressure chamber (60) in said first bore (64), - an valve member (52) carried by said first piston (56), said valve member (52) having a stem (53) and a head (54) that is engageable with an annular seat (55), - said housing (51) being provided a relief passage between an inlet opening (57) and an outlet opening (58) with said annular seat (55) therein, - said relief passage comprises a relief chamber (63) between said annular seat (55) and said outlet opening (58) , - a first side of said first piston (56) forms a first effective pressure surface (61) that faces said first pneumatic pressure chamber (60) and the second side of said first piston forms a second effective pressure surface (62) that faces said relief chamber (63), - a first side of said head (54) forms a third effective pressure surface (59) that faces said inlet opening (57), - said first effective pressure surface (61) being larger than said third effective pressure surface (59).

2. A relief valve (50) according to claim 1, wherein said first pneumatic pressure chamber (60) is fluidly connected with a port (79) for connection to a source of pneumatic pressure .

3. A relief valve (50) according to any one of the preceding claims, wherein said first effective pressure surface (61) is at least double the size of said third effective pressure surface (59).

4. A relief valve (50) according to any one of the preceding claims, wherein said valve member (52) is resiliently biased away from said annular seat (55).

5. A relief valve (50) according to any one of the preceding claims, wherein said housing (51,70,73) comprises a second bore (72) and a second piston (65) slidably disposed in said second bore (72) and defining a second pneumatic pressure chamber (68) in said second bore (72), said second piston (65) being operatively connected to said stem (53).

6. A relief valve (50) according to claim 5, wherein said second pneumatic pressure chamber (68) is fluidly connected with a port (7 9) for connection to a source of pneumatic pressure .

7. A relief valve (50) according to any one of the preceding claims, wherein said head (54) and a portion of said stem (53) are disposed in said relief chamber (63).

8. A relief valve (50) according to any one of the preceding claims, wherein said valve member (52) is axially displaceable between a closed position and with said head (54) resting on said annular seat (55) and a fully open position with a range of intermediate positions between said fully open position and fully closed position.

9. A relief valve (50) according to any one of the preceding claims, wherein said outlet opening (58) is a radial outlet opening.

10. A relief valve (50) according to any one of the preceding claims, wherein said inlet opening (57) is an axial inlet opening.

11. A relief valve according to any one of the preceding claims, wherein said second piston (65) has a fourth effective pressure surface (66) facing said second pneumatic pressure chamber (68), said fourth effective pressure surface (66) facing the same direction as said 1st effective pressure surface (61).

12. A relief valve (50) according to claim 11, wherein said fourth effective pressure surface (66) has substantially the same size as said first effective pressure surface (61) .

13. A relief valve (50) according to any one of claims 5 to 12, wherein said second piston (65) has a fifth effective pressure surface (67) facing in the opposite direction of said fourth effective pressure surface (66), and wherein said second piston (65) defines a pneumatic damping chamber (69) in said second bore (72) with said fifth effective pressure surface (67) facing said pneumatic damping chamber (69) .

14. A relief valve (50) according to any one of claims 5 to 13, wherein said first bore (64) is disposed in a first housing part (51) and said second bore (72) is disposed in a second housing part (70), and wherein said 1st housing part (51) and said second housing part (70) are connected by a resilient element 76 that allows for relative movement between said first housing part (51) and said 2nd housing part (70) in order to compensate for dimensional differences in the relief valve due to heat expansion.

15. A relief valve (50) according to any one of receiving claims, wherein said second effective pressure surface (62) is affected by the pressure in said evacuation chamber (63) and thereby adds a force in the opening direction on the valve member (52) when the valve member (52) has lift from the annular seat (55).

16. A relief valve (50) according to any one of claims 5 to 13, wherein said first housing part (51) and said second housing part (70) are connected telescopically with said resilient member (76) there between, said resilient member preferably being a disk spring (76).

17. A relief valve (50) according to any one of the preceding claims, wherein said annular seat (55) is disposed in a floating manner in said valve housing (51, 70, 73) in order to allow the annular seat (55) to be selfcentering .

18. A large turbocharged two-stroke compression-ignited internal combustion engine with crossheads (43), said engine comprising: a number of cylinders (1) that serve as combustion chambers (27) , said cylinders being (1) provided with a cylinder cover (22), with an exhaust valve (4) placed centrally in said cylinder cover (22) , and with an exhaust duct (35) connecting said exhaust valve (4) to an exhaust gas receiver (3), said cylinder cover (22) being provided with a relief valve (50) according to any one of claims 1 to 17, with the inlet (57) of said relief valve (50) being fluidly connected to said combustion chamber (27) and an outlet (58) of said relief valve (50) being fluidly connected to a discharge conduit (36).

19. An engine according to claim 18, wherein said relief valve (50) allows gas flow from said inlet (57) to said outlet (58) when said valve member (52) has lift from said annular seat (55) and said relief valve (50) preventing gas flow from said inlet (57) to said outlet (58) when said valve member (52) rests on said seat (55).

20. An engine according to claim 18 or 19, wherein said first effective pressure surface (61) is pressurized by pneumatic pressure in all of the positions of said valve member (52) and wherein said second surface (62) is pressurized by the pressure in said evacuation chamber 63 when said valve member (52) has lift from said annular seat (55) .

21. An engine according to any one of claims 18 to 20, wherein, said annular seat (55) is arranged in a blow-off bore (29) that extends through said cylinder cover (22).

22. An engine according to claim 21, wherein a main plane of said annular seat (55) is arranged squint relative to a main direction of a said blow-off bore (29).

23. An engine according to claim 21 or 22, wherein said blow-off bore (29) is connected to said exhaust duct (35) or to said exhaust gas receiver (3) via a blow-off pipe (36) in order to bypass said exhaust valve (4).

24. An engine according to any one of claims 18 to 23, wherein said relief valve (50) is provided with cooling means, said cooling means preferably including a path for a cooling medium through or around the relief valve (50).

25. An engine according to any one of claims 18 to 24, wherein said engine comprises a pneumatic system with for providing pneumatic pressure to pneumatic consumers associated with the engine, the pressure of said pneumatic system preferably increasing with increasing engine load and decreases with decreasing engine load.