WO1994013936A1

WO1994013936A1 - An internal combustion engine

Info

Publication number: WO1994013936A1
Application number: PCT/DK1993/000385
Authority: WO
Inventors: Thomas Synnestvedt Knudsen
Original assignee: Man B&W Diesel A/S
Priority date: 1992-12-09
Filing date: 1993-11-29
Publication date: 1994-06-23
Also published as: KR950704597A; JP3242662B2; KR100271291B1; DK169824B1; JPH08504494A; DK147892A; DK147892D0

Abstract

In a V-engine a reactor (24; 24') for reducing the content of undesired compounds in the exhaust gas, such as NOx, is disposed between the two rows of cylinders (4). With this positioning the reactor does not occupy space in the engine room around the engine and at the same time the reactor is kept hot by the radiation and convection heat generated by the engine when the exhaust gas is not flown through the reactor. The reactor (24') may be integral with the exhaust gas receiver (18') of the engine, preferably so that the internal cavity of the receiver is separated from the reactor by means of a partition wall (28'), thereby making it possible to pass only exhaust gas through the reactor when there is a need for purification of the gas.

Description

An internal combustion engine

The invention relates to an internal combustion engine having an engine frame box on which two rows of cylinders are mounted in V-shape, and having a reactor for reduction of undesired compounds in the exhaust gas disposed between the two rows of cylinders together with an air intake.

US-A-4 138 843 discloses a four-stroke V-engine of the trunk type having a reactor assembled of a small reaction chamber for each two cylinders and a larger secondary reaction chamber positioned between the two rows of cylinders. The reactor is of the type where unburnt hydrocarbons in the gas react with oxygen, and CO is converted into C0₂, i.e., a reactor which primar- ily requires a high temperature. The reaction chambers are empty cavities of such a limited size that the gas temperature is kept high.

In large two-stroke in-line engines it is known that the small and light reaction chambers known from car engines do not have a great purifying effect, as the large engines are operated at such a large air excess that unburnt hydrocarbons only escape with the exhaust gas to a slight extent. But the exhaust gas contains other impurities, such as N0_X which require the use of catalysts with a large content of catalyst material which may, for example, remove the N0_X content of the exhaust gas by reduction of N0_X into N₂ and water when the exhaust gas passes through the reactor at a suitable flow velocity and gas temperature. To produce an efficient conversion of the undesired compounds in the exhaust gas, the catalyst material must have a large volume, the result of which is that the reactor takes up a lot of space and is heavy. This problem is particu¬ larly great in large two-stroke crosshead engines developing considerable power. In the known in-line engine plants, the size and weight of the reactor have caused it to be independently supported and disposed beside the engine, where the reactor takes up space in the engine room. This disposal of the reactor has furthermore resulted in unsuitably long pipe connections in the exhaust system.

The object of the invention is to provide a large engine with catalytic exhaust gas purification, which engine is very compact in relation to its output.

With this object in view, the internal combustion engine according to the invention is characterized in that the engine is a large two-stroke crosshead engine having a longitudinal scavenging air receiver and having an exhaust gas receiver extending in the longitudinal direction of the engine and being disposed between the two rows of cylinders, and that a cavity in the reactor extending in the longitudinal direction of the engine is separated from the cavity of the exhaust gas receiver and contains catalyst material for reduction of the undesired compounds, such as N0_X.

The V-engine has the well-known advantage of being short in relation to the number of its cylinders. Letting the V-engine be a large two-stroke crosshead engine enables the engine to have a till now unknown large output in relation to its dimensions. The V-shape permits the prior known large tubular scavenging air and exhaust gas receivers projecting sidewards to be repositioned from the side of the engine to a position between the cylinder rows, which, in the direction of width, compensates for the increased top width of the engine caused by the V-shape. In addition to this it has surprisingly turned out to be possible to dispose the separate, very large and heavy reactor with the reactor material up between the cylinders together with the two receivers.

With this position between the cylinder rows, the reactor is formed as an integral part of the engine, and the V-engine with the reactor does not take up substan¬ tially more space than a corresponding engine without the reactor. Furthermore, the reactor will be close to the natural passageway for the exhaust system, as the pipe sections passing the exhaust gas away from the individual cylinders usually extend inwards towards a common exhaust passage positioned between the two rows of cylinders. The position of the reactor thus renders it possible to design the exhaust system with advantage¬ ously short pipe sections. Normally, the reduction of the undesired compounds in the exhaust gas cannot take place until the reactor has been heated to an operating temperature, such as from 300 to 400°C, which is substantially above the ambient temperature. The position of the reactor between the cylinder rows therefore also has the advantage that the reactor is positioned in a relatively hot position, which is particularly an advantage if the reactor is to be on stand-by during certain periods of operation. When the reactor is to be connected up for purification of the exhaust gas after a long period of engine running, it will be heated by the radiation and convection heat from the surrounding engine parts so that it is immedi¬ ately able to purify the exhaust gas or only has to be heated by it to a slight extent, and so that the reactor does not cool the exhaust gas immediately after its being connected, to such an extent that a risk of condensation arises in the exhaust system.

The reactor may be disposed above or below the receiver. The position between the receiver and the engine frame box is preferred, as the engine thus becomes most compact.

A particularly compact design, which also ensures good heating of the reactor, has been provided in a preferred embodiment in that the reactor is integral with the exhaust gas receiver of the engine, suitably so that a partition wall separates the internal cavity of the receiver from the reactor which is connected with a gas outlet on the exhaust gas receiver via a flow passage.

The engine according to the invention is particu¬ larly applicable as the propulsion engine of a ship where it is of great importance that the engine takes up the least possible space so that the largest possible part of the ship may be used for payload. In ocean-going vessels where the reactor only needs to be in operation while the vessel is sailing in coastal waters, it is possible in particular to take advantage of the fact that the heat from the engine keeps the reactor hot and ready for use at short notice.

Examples of embodiments of the invention will now be described below in further detail with reference to the schematic drawing, in which

Fig. 1 is a partial cross-sectional view through an engine according to the invention,

Fig. 2 shows a side view of a reactor and an exhaust gas receiver with associated pipe system, and

Figs. 3 and 4, respectively, show a side view and a cross-sectional view through a reactor integral with an exhaust gas receiver.

Fig. 1 shows a two-stroke crosshead engine gen¬ erally designated 1 and having a frame box 3 mounted on a bedplate 2, which frame box on its upper side carries two rows of cylinders 4 which are mounted in pairs in V-shape on the engine frame box. Via respective piston rods 5 with associated crossheads 6 and connecting rods 7, the pistons of each cylinder pair are connected with a common crank pin journal 8 on the crankshaft. The crosshead is guided in the transverse direction by means of crosshead shoes 9 sliding on associated guide planes 10 fastened to transverse walls 11 in the engine frame box.

Each piston is mounted in a cylinder liner 12 which is closed upwards by a cover 13 with an exhaust valve 14. The cylinders are longitudinally scavenged and are supplied with scavenging and charging air from a turbocharger 15, the compressor of which passes the air to a scavenging air receiver 16, from where the air may flow into the cylinder through scavenging air slots in the lower part of the cylinder liner when the piston has uncovered the ports.

From the exhaust valve 14, the exhaust gas is passed through pipe sections 17 to an exhaust gas receiver 18 extending longitudinally along the engine and being disposed between the two cylinder rows. The receiver is formed with an inlet opening 19 aligned with each pipe section 17, and at its one end it is attached to an outlet pipe 20 which, via a regulating means 21 in the form of a throttle or a valve, is connected with an inlet pipe 22 leading to the turbine inlet of the turbocharger. Via a flow passage in the form of a conduit 23, the other end of the receiver 18 is in connection with a reactor 24, the gas outlet of which is connected with the inlet pipe 22 of the turbine via an outlet pipe 25 and a regulating means 26 in the form of a throttle of a valve.

The reactor contains a catalyst (27' in Fig. 4), which, at the passage of the exhaust ga^'sses through the reactor, reduces the undesired compounds in the gas into compounds which are not harmful to the environment. The catalyst may, for example, reduce the exhaust gas content of N0_X into N₂ and water. When the reactor is to reduce the N0_X content of the exhaust gas, it may, for example, be of the type SCR (Selective Catalytic Reduction). A reactor of this type is manufactured, for example, by the Danish company Haldor Topsøe A/S. To give an expression of the size of the reactor, it may be mentioned that in an engine with an output of about 40 MW, about 13^ tonnes of catalyst material has to be used to obtain a fully satisfactory conversion of the N0_X content of the exhaust gas.

It is possible to arrange the reactor at a higher level than the exhaust gas receiver, but preferably, the reactor 24 is disposed as shown between the receiver 18 and the engine frame box 3 so that the engine has the smallest total height possible. In the first embodiment shown in Figs. 1 and 2, the reactor and the receiver are designed as two separate units.

In a second embodiment shown in figs. 3 and 4, the receiver 18' and the reactor 24' are integral, which partly reduces the total space taken up by these two units, partly results in the convection heat from the receiver 18' keeping the reactor 24' hot when the exhaust gas bypasses the reactor. In the second embodi- ment, the reactor is separated from the internal cavity of the receiver, through which exhaust gas flows, by means of a partition wall 28 ' . By cutting off the reactor from the outlet pipe 25 ' by means of the regulating means 26' and opening the regulating means 21 ' , the exhaust gas may be completely prevented from flowing through the reactor 24' when the exhaust gas does not require purification. Thus, the exhaust gas may be prevented from dirtying the catalyst material 27 ' during the periods of operation when the exhaust gas may be passed unpurified into the atmosphere. By gradual opening of one regulating means and gradual closure of the other regulating means (21 or 26; 21' or 26' ), the reactor may be gradually put more or less into operation. This renders it possible to pass a large or small part of the exhaust gas through the reactor in dependency of the operating conditions of the engine and the desired degree of purification of the exhaust gas, while the remaining part of the exhaust gas is passed directly from the exhaust gas receiver 18, 18' to the turbine of the turbocharger. In the setting of the regulating means shown in the drawing, all the exhaust gas is passed through the reactor. At full shifting of both regulating means, all the exhaust gas may also bypass the reactor and be passed directly to the turbocharger.

In the embodiments shown, the reactor and the receiver extend in parallel and have the same length. If special reasons should so dictate, it is, of course, possible to let the length of the reactor deviate from the length of the receiver, just as the reactor may be disposed in another position in relation to the receiver.

Claims

P A T E N T C L A I M S

1. An internal combustion engine ( 1 ) having an engine frame box (3) on which two rows of cylinders (4) are mounted in V-shape, and having a reactor (24; 24' ) for reduction of undesired compounds in the exhaust gas disposed between the two rows of cylinders together with an air intake, c h a r a c t e r i z e d in that the engine is a large two-stroke crosshead engine having a longitudinal scavenging air receiver (16) and having an exhaust gas receiver (18; 18' ) extending in the longi¬ tudinal direction of the- engine and being disposed between the two rows of cylinders, and that a cavity in the reactor extending in the longitudinal direction of the engine is separated from the cavity of the exhaust gas receiver and contains catalyst material for reduc¬ tion of the undesired compounds, such as N0_X.

2. An internal combustion engine according to claim 1, c h a r a c t e r i z e d in that the reactor (24; 24' ) is positioned between the exhaust gas receiver and the engine frame box (3) .

3. An internal combustion engine according to claim 1 or 2, c h a r a c t e r i z e d in that the reactor (24') is integral with the exhaust gas receiver (18' ) of the engine.

4. An internal combustion engine according to claim 3, c h a r a c t e r i z e d in that a partition wall ( 28 ' ) separates the internal cavity of the receiver (18' ) from the reactor (24') which is connected with a gas outlet on the exhaust gas receiver via a flow passage ( 23' ) .

5. An internal combustion engine according to any one of the claims 1-4, c h a r a c t e r i z e d in that the engine is a propulsion engine of a ship.

6. An internal combustion engine according to any one of the claims 3-5, c h a r a c t e r i z e d in that the engine comprises a turbocharger (15), and that the exhaust gas system is designed for supplying gas to the turbocharger turbine either from the reactor (24; 2 ' ) alone or at least partially directly from the exhaust gas receiver (18; 18').