DK201400395A1

DK201400395A1 - Large slow-running turbocharged two-stroke self-igniting internal combustion engine with a starting air system

Info

Publication number: DK201400395A1
Application number: DK201400395A
Authority: DK
Inventors: Niels Kjemtrup; Kim Jensen
Original assignee: Man Diesel & Turbo Deutschland
Priority date: 2014-07-17
Filing date: 2014-07-17
Publication date: 2016-02-01
Also published as: CN105020079B; JP2016023642A; JP5842078B1; KR101730062B1; KR20160010318A; DK178404B1; CN105020079A

Abstract

A large slow-running turbocharged two-stroke internal combustion engine of the uniflow type with crossheads (41). The engine comprises a plurality of cylinders (1a..1n), and a source of pressurized air (8). Each cylinder (1) is provided with scavenge ports (17) at or near the lower end of the cylinder (1a..1n) a cam controlled exhaust valve (4a..4n) at the top of the cylinder (1a..1n), the exhaust valve (4a..4n) being resiliently urged to its closed position by a pneumatic spring (30), one or more fuel injection valves (6a..6n), and a starting air valve (13a..13n) connected to the source of pressurized air. The engine further comprises a starting air distributor (11) configured for pneumatically and individually activating the starting air valves (13a...13n), and means for overruling an individual activation of a starting air valve (13a...13n) by the starting air distributor (11). The means for overruling being configured to overrule an individual activation of a starting air valve (13a...13n) when the exhaust valve (4) associated with the same cylinder is open.

Description

LARGE: SLOW-RUNNING TURRpruyARGED TWO-STROKE SELF-IGNITING internal COMBUSTION ENGlrrojJITH A STARTING AIR SYSTEM

field of THE INVENTION

The present invention relates to large slow-running turbocharged two-stroke self"igniting internal combustion engine with a starting air system and with crossheads and a camshaft.

BACKGROUND ART

Large slow running two-stroke internal combustion engines w.itn crosshead are typiCaiiy used in propulsion systems of targe ships or as prime mover in power plants. These engines have a crosshead disposed between the piston and the crankshaft.

Emission requirements have been and will be increasingly dirficuit to meet, in particular with respect to mono-nitrogen oxides levels (NOx). The formation of NOx is mainly dependent on the combustion temperature and the amount of oxygen that is present in the combustion cnamber. In order to live up to emission requirements the compression volume has been reduced because this reduces the amount of oxygen available for the combustion and thereby reduces NOx levels.

This change in compression volume is caused by a changed profile of the cams on the camshaft in the case of large slow-running uniflow turbo charged two-stroke internal combustion engines that are provided with a camshaft for controlling the opening and closing of the exhaust valves .

Reducing the compression volume increases the compression pressure. However, the mechanical construction of the engine does not allow for the compression pressure to increase significantly and therefore it has been necessary to delay the timing of the closing of the exhaust valve significantly when the compression volume was decreased.

Large slow running turbocharged two-stroke internal combustion engines are started using a so-called starting air system. The starting air system is configured to pump pressurized starting air in a suitable sequence into the cylinders of the engine to thereby start the engine. The starting air flows into the cylinder when the piston is moving down the cylinder on the power stroke.

In known large two-stroke self-igniting internal combustion engines the starting air in the starting air receivers is provided from electrically driven starting air compressors on electrical power generated by generator sets or by a generator driven by the large m a r i n e d i e s e 1 e n g i n e .

The starting air for the individual cylinders is distributed by a starting air distributor. The distributor opens and closes the air start valve associated with each of the cylinders in the correct sequence in relation to the position of the crankshaft. In order to ensure engine start at any given crankshaft position it is necessary that the crankshaft position interval where a single air start valve opens is larger than 3600/Ncyl. If this is not ensured there will be crankshaft positions where there is not. any starting air valve that opens and nothing will happen.

The delayed closing of the exhaust valve causes a substantial overlap where the starting air valve and the exhaust valve are open simultaneously (c£. Figs. 6 and 7) . This results in an large consumption of starting air that does not contribute to torque on the crankshaft since the starting air simply flows from the starting air valve to the exhaust gas receiver without delivering any energy to the piston.

The delayed closing of the exhaust valve is problematic in relation to starting the engine, in particular for engines with a few cylinders due to the overlap interval where the starting air valve and the exhaust valve are both open and the starting air thus being blown into the engine exhaust system. The overlap is particularly substantial when starting astern (reversing), which marine engines that are coupled to a fixed pitch propeller must be able to do.

In known engines it has been attempted, to reduce the loss of starting air by reducing the opening interval of the exhaust valve. However, this approach results in the exhaust valve closing significantly earlier, which leads to a significantly increased compression effort during engine start, which in turn worsens the engines'· starting performance.

DISCLOSURE OF THE INVENTION

On this background, it is an object of the present application to provide a large slow running turbocharged two-stroke internal combustion engine with a starting air system rhat overcomes 0r at least reduces the problems indicated above.

Tnis object xs achieved according to a first aspect by providing a rarge sxow-running turbocharged two-stroke internal combustion engine of the uniflow type with crossheaas, the engine comprising a plurality of cylinders, a source of pressurized air, each cylinder being provided with scavenge ports at or near the lower end ot the cylinder, a cam controlled exhaust valve at the top of the cylinderf the exhaust valve being resiliency urged to its closed position by a pneumatic sprinc, one or more fuel , , ^ x injection valves, and a starting- air valve connected to 1-1-,- n-e ,, ...

me source or pressurized air, a starting air distributor configured for pneumatically and individually activating the starting afr valves, means ror ov6j-Iulxiig an ind.i.vxQuaf activation of a starting air valve by the starting air distributor, the means for overruling being configured to overrule an individual activation of a starting air valve when the exhaust valve associated with the same cylinder is open.

By providing individual overruling means that prevent individual starting air valves from opening when the exhaust valve of the same cylinder is open it is prevented that starting is blown into the exist system without contributing to the start of the engine. Thus, the loss of starting air is prevented without increasing the compression effort during engine start. Since all the exhaust valves will always return to their closed position due to pressure loss in the hydraulic push rod that is used to active the exhaust valves there will the overruling means will not need to come in action at the very beginning of the engine start and there will be fully effective initial start strokes on starting air, thereby significantly improving the engines'· starting performance and reducing starting air consumption.

According to a first implementation of the first aspect the means for overruling an individual activation of a starting air valve comprises an overruling valve in a pneumatic signal conduit, the overruling valve (16a..16n) having a first position connecting the starting air distributor (11) to a starting air valve (13a...13n) and a second position connecting the starting air distributor (11) to the ambient air.

According to a second, implementation of the first aspect the position of the overruling valve is controlled by the position of the exhaust valve associated with the same cylinder .

According to a third implementation of the first aspect the overruling valve is resiliently biased to the first position and movable towards the second position by a pneumatic control pressure, the pneumatic control pressure being the pressure in an the pneumatic spring of the exhaust valve associated with the same cylinder.

According to a fourth implementation of the first aspect the starting air distributor is configured to individually activate each of the starting air valves in accordance with a predetermined activation sequence.

Further objects, features, advantages and properties of the engine according to the present disclosure will become apparent from the detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following detailed portion of the present description, the invention will be explained in more detail with reference to the exemplary 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 cross-sectional diagrammatic representation the large two stroke engine according to Fig. 1,

Fig. 4 is a diagrammatic illustration of the large internal combustion engine of Figs. 1 to 3 with a starting air system,

Fig. 5 is a diagrammatic view of one cylinder of the engine according to Fig. 4 with an overruling means according to an example embodiment,

Fig. 6 is a diagrammatic view of one cylinder of the engine according to Fig. 4 with an overruling means according to another example embodiment,

Fig. 7 is a circular diagram showing opening intervals of the exhaust valve and of starting air valve of a cylinder in astern operation, and

Fig. 8 is a circular diagram showing opening intervals of the exhaust valve and of starting air valve of a cylinder in ahead operation.

DETAILED DESCRIPTION

In the following detailed description, the large low speed two-stroke internal combustion engine will be described by the example embodiments. Figs. 1 to 3 show a large low-speed turbocharged two-stroke diesel engine with a crankshaft 42 and crossheads 43. Fig. 3 shows a diagrammatic representation of the large low speed turbocharged two-stroke diesel engine with its intake and exhaust systems in sectional view. In this example embodiment the engine has iour cylinders 1 for illustration purposes only. It should be apparent that virtually any other quantity of cylinders 1 may be employed without departing from aspects of the present invention. Large turbocharged two-stroke diesel engines have typically between four and sixteen cylinders in line, carried by an engine frame 45. The engine may e.g, be used as the main engine in an ocean going vessel. The total output of the engine may, for example, range from 5,000 to 110,000 kW.

The engine is a self-igniting (diesel) engine of the two-stroke uniflov/ type with scavenge ports 17 at the lower region of the cylinders 1 and an exhaust valve 4 at the top of the cylinders 1. The engine can be operated on various types of fuel, such as e.g. marine diesel, heavy fuel, or gas (LPG, LNG, Methanol and/or Ethanol) . The scavenge air is passed from the scavenge air receiver 2 to the scavencre ports 17 of the individual cylinders 1. A piston 41 in the cylinder 1 compresses the scavenge air, fuel is injected and combustion follows and exhaust gas is generated. When an exhaust valve 4 is opened, the exhaust gas flows through an exhaust duct 7 associated with the cylinder 1 concerned into the exhaust gas receiver 3 and onwards through a first exhaust conduit to a turbine of a. primary (constant pressure) turbocharger 5, from which the exhaust gas flows away through a second exhaust conduit. Through a shaft, the turbine of the turbocharger 5 drives a compressor supplied via an air inlet. The compressor delivers pressurized scavenge air to a scavenge air conduit leading to the scavenge air receiver 2. in an embodiment (not shown) engine has more than one primary turbocharger.

The scavenge air receiver 2 has an elongated hollow cylindrical body constructed from e,g. plate metal and an essentially circular cross-sectional outline to form a hollow cylinder. The scavenge air receiver 2 has a substantial cross-sectional diameter and a large overall volume, for absorbing pressure fluctuations caused by the scavenge ports 17 of the individual cylinders 1 opening and taking in scavenge air, i.e. to ensure a substantially constant pressure in the scavenge air receiver 2.

The exhaust gas receiver 3 has an elongated hollow cylindrical body constructed, from e.g. plate metal and an essentially circular cross-sectional outline. The exhaust gas receiver 3 receives exhaust gas from the cylinders 1 via the individual exhaust ducts 7 that extend into the exhaust gas receiver 3. The exhaust gas receiver 2 has a considerable cross-sectional diameter and a large volume, for absorbing pressure fluctuations caused by the exhaust valves 4 of the individual cylinders 1 opening and sending exhaust gas at high speed into the exhaust gas receiver 3, i.e. to ensure a substantially constant pressure in the exhaust gas receiver 3.

With reference to Figs. 4 and 5 the starting air system is described. The engine has a plurality of "n" cylinders la, lb, 1c to In, with a reciprocating piston 4 la.. 42a received in each cylinder la..In.

The piston 41a..41n is slidably received inside a cylinder la with a combustion chamber 44 there above, an exhaust valve 4a..4n and a hydraulic exhaust valve actuator 33 controlling the flow of exhaust gases to the exhaust passage 4. A linear hydraulic exhaust gas waive actuator 33 is connected to a camshaft (not shown) via a hydraulic pushrod (not shown) in a conventional manner.

A scavenge air conduit 26 delivers scavenge air to piston controlled scavenge ports 17. The top cover of the cylinders la..In is provided with one or more fuel valves 6a-6n for injecting a fuel into the combustion chamber in t h e c y1i nde r la..1n.

A starting air valve 13a-13n is also provided in the top cover of each of the cylinders la..In and these starting air valves 13a-13n are operably connected to the starting air system.

The starting air system includes one or more starting air receivers 9 which are re-filled with compressed air via a conduit by means of one or more electrically driven two-stage or three-stage starting air compressors 8 with intercooler to a pressure that is in an embodiment about 30 bar.

The total capacity of the start air receiver (s) 9 is sufficient to start the engine a plurality of times, e.g. twelve times, alternating between ahead and astern without recharging the starting air receivers 9.

The starting air receiver 9 is fitted with a relief valve (not shown) to limit the pressure rise to 10% above design pressure. A pressure sensor (not shown) can be provided in an embodiment for detecting the pressure level inside the starting air receiver 9. Initial pressure in the starting air receiver is in an embodiment about 30 bar, enough to start at the engine least a number of times.

Two starting air compressors 8 are normally provided which are capable of charging the air receiver 9 or receivers 9 from empty to full in about one hour.

Each starting air compressor 8 is driven by an electric drive motor. Electrical, power for the drive motors is provided by generator sets associated with the large slow running two-stroke internal combustion engine.

A starting air conduit 12 fluidly connects the starting air receiver 9 via a manifold to each of the starting air valves 13a..13n.

A starting air distributor 11 ensures the correct timing of the activation of the respective starting air valves 13a-13n. in an embodiment the air distributor 11 comp rises of a series of pilot valves, one for each cylinder arranged radially around a cam. Timed to the engine (crankshaft position) and driven from the camshaft, the distributor opens and closes the air start valves 13a..13n in the correct sequence.

In another embodiment the air distributor 11 comprises a rotary disk with holes corresponding to ports in a housing in which the disk is received. The rotary disk is timed to the engine (crankshaft position) and driven from t-je camshaft and opens and closes the air start valves 13a..I3n in the correct sequence.

T'hv. air distributor li is connected via individual PteuiridL-ic »ignal conduits 15a. . 15n to a control port on 'a''“ the starting air valves 13a. ,13n. An overruling vali/e ^ 6a. . 16n is provided in each of the pneumatic signal uonauits 15a..15n. The starting air valves l->a.. r3n nave an open and a closed position and the otaruing air varves 13a..lin are resiliently biased to tneir closed position. When the control port of a starting air valve ua. .13n is pressurized it is urged, to i t s ope n po s i tiο n.

When is necessary to start the engine, master valve 10 is opened and tne inlet port of the starting air valves 13a..13n is pressurized. The individual starting air valves i3a.,13n are activated in the correct order by the pneumatic signals from the starting air distributor 11 via the pneumatic signal conduits 15a..15n and thus the cylinders la..In are supplied with starting air from the starting air receiver 9 via conduit 12 under control of starting air distributor 11.

The starting air valves I3a-13n can be independently controlled from each other so that one or more cylinders la, lb, 1c to In are supplied with compressed air from starting air receiver 9 in order to start the engine.

) It should, be noticed in that in Fig. 5 only one cylinder la is shown and referred thereto. However, the description applies in addition or separately to any of the other cylinders from lb to In.

The overruling means comprise in an embodiment overruling valves 16a.· 16n. As can be seen in Fig. 5 the overruling valve 16a has two positions. In a first position (shown) the overruling valve 16a.. 16n connects the starting air-distributor 11 to the control port of the starting air valve 13a. In a second position the overruling valve 16a connects the starting air distributor to the ambient air, thereby preventing a pneumatic signal from the starting air distributor reaching the starting air valve 13a. The overruling valve 16a is resiliently biased to the first position. The overruling valve is provided is a control port and can be urged to the second position by applying pneumatic pressure to the control port. The control port is in this example embodiment connected to the spring chamber 34 of the pneumatic spring 30 via a pneumatic signal conduit 19a.

The pneumatic spring 33 comprises a cylinder with a spring piston 31 slidably received therein. The spring piston 31 is secured to the stem of the exhaust valve 4.

A hydraulic linear actuator 33 urges the valve stem and the spring piston 31 downwards against the pressure in the spring chamber 34 in order to move the exhaust valve 4 to its open position (shown) . The linear actuator 33 receives hydraulic pressure via a hydraulic push rod that connects to a piston pump (not shown) that is activated by a cam on a camshaft (not shown) in a conventional manner.

When tne exhaust valve 4 is moved to the open position by the hydraulic actuator 33 the pressure in the spring chamber 34 increases and the pneumatic signal conduit 19a communicates this increased pressure to the control port of the overruling valve 16a, thereby moving the overruling valve 16a to its second position and connecting the pneumatic signal conduit 15a to the ambient air (e.g· engine room) so that the starting air valve 13a cannot be activated when the exhaust valve 4 is open.

When the exhaust valve 4 xs closed the pressure in the spring chamber 34 decreases and the overruling valve 16a returns to its first position thereby no longer overruling the pneumatic signal from the starting air distributor 11 in the pneumatic signal conduit 15a and thus, the starting air valve 13a can be activated and used for starting the engine.

In another embodiment, that is similar to the embodiment according to Fig. 5, the overruling means also comprises a two-way overruling valve 16a..16n. However, the two a valve this in this embodiment resiliently biased to the position where it allows the pneumatic; signal from the starting at distributor 11 to pass through the signal conduit 15a..I5n to the corresponding starting air valves 13a..13n. In the second position of the overruling valve 16a..16n the pneumatic signal from the starting at distributor n to the corresponding starting a valve 13a..13n is blocked. The overruling valve 16a..16n Can be urgea to move to its second position by applying pneumatic pressure to the control port of the overruling valve I6a..-i,6n. ihe control port of the overruling valve 16a..xbn is connected via a signal conduit 19a..19n to a port in the cyxinaer of the pneumatic spring 30. The port is positioned such that it will communicate to the spring cnamber 34 under the spring piston 31 when the exhaust valve 4 xs ciosecl and position such that it will communicate with air chamber above the spring piston 31 when the exhaust valve 4 is in its open position. The pressure in the spring chamber 34 is significant-!-y higher than the pressure in the air cnamber 35. ihns, overruling valve 16a..l6n will have a hign pressure on its control port when the exhaust valve is closed and thereby assume its first position where it allows the pneumatic signal from the air distributor rl to ieatu corresponding starting air valve 13a..r3u ana nw overruling valve 16a..I6n will have a iow pressure on its control port when the exhaust vaive rs open and i_.ne.teoy assume its second position wnere iu prevents the pneumatic signal from the air aistncuLor rl Lo reacn one corresponding starting axr valve loa..J..:>n, thereby overruling the signal of the starring your aistributor 11.

The overruling valve can in embodiment giot shown) os an electronically controlled valve tnat receives an elect.ron.ic signal from a pressure sensor or a. position sensor indicative of the position of the exhaust vaive. The pressure sensor can in embodiment trie eonnectea to the hydraulic pushrod. Further, in an embodiment the starting air valves can oe electronically controlled valves that, receive an overruling signal based on a signal from a pressure sensor or position sensor that detects the position of the exhaust valve.

During an engine stop all the exhaust valves 4 will return to their closed position under influence of the ) pneumatic spring 30 because the nydrauxic pusn rod will slowly lose pressure. Thus, regardless of the position of the crankshaft, there will not be any starting air valves 13a. ,Ί3η that are overruled, at the beginning of an engine start and a full starting air activation without overruling or pressure loss to the exhaust gas receiver is achieved at the beginning of the engine start, thereby significantly improving the engine start performance.

Fig. 7 illustrates the opening interval 52 of the exhaust valve and the opening interval 51 all the starting air valve for starting the engine "astern". For starting in "astern" the overlap between the two intervals is very significant.

Fig. 8 illustrates the opening interval 52 of the exhaust valve and the opening interval 51 of the starting air-valve for starting "ahead". For starting in "ahead" the o v e r1ap be t ween t h e t wo i nt erva1 s i s quite s i gn if i c a n t.

The term "comprising” as used in the claims does not exclude other elements or steps. The term "a" or "an" as used in the claims does not exclude a plurality.

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

Although the present invention has been described in detail for purpose of illustration, it is understood that such detail is solely for that purpose, and variations can be made therein by those skilled in the art without departing from the scope of the invention.

Claims

1. A large slow---running turbocharged two-stroke internal combustion engine of the uniflow type with crossheads (41), s a i d e ng ine c omp r is i ng: a plurality of cylinders (la..in), a source of pressurized air (8), each cylinder (la..In) being provided with: scavenge ports (17) at or near the lower end of said cylinder (la . . In) , a cam controlled exhaust valve (4a..4n) at the top of said cylinder (la..In), said exhaust valve (4a..4n) being resiliently urged to its closed position by a pneumatic spring (30), one or more fuel injection valves (6a..6n), and a starting air valve (13a..13n) connected to said source of pressurized air, a starting air distributor (11) configured for pneumatically and individually activating said starting air valves (13a...13n), means for overruling an individual activation of a starting air valve (13a. . . 13n) by said starting- air distributor (11), said means for overruling being configured to overrule an individual activation of a starting air valve (13a...13n) when the exhaust valve (4) associated with the same cylinder (la..In) is open.

2. An engine according to claim 1, wherein said means for overruling an individual activation of a starting air valve (13a...13n) comprises an overruling valve (16a..16n) in a pneumatic signal conduit (15a..15n), said o ve rru1 i n g va1ve (16 a ..16n) hav i n g a f i r s t p o s i t i ο n connecting the starting air distributor (11) to a starting air valve (13a...13n) and a second position connecting the starting air distributor (11) to the ambient air.

3. An engine according to claim 1, wherein the position of said overruling valve (16a..16n) is controlled by the position of the exhaust valve (4) associated with the same cylinder (la..In).

4. An engine according to claim 3, wherein said overruling valve (16a..16n) is resiiiently biased to said first position and movable towards said second position by a pneumatic control pressure, the pneumatic control pressure being the pressure in an the pneumatic spring (30) of the exhaust valve (4) associated with the same cy 1 irider (1 a . . 1 n) .

5. An engine according to claim 1, wherein said starting air distributor (11) is configured to individually activate each of said starting air valves (13a...13n) in accordance with a predetermined activation sequence.