CH712921A2 - Longitudinally rinsed large engine. - Google Patents

Abstract

A longitudinally purged large engine is proposed with at least one cylinder (2), which comprises a cylinder wall (21), and in which a piston (3) is arranged to be movable back and forth along a cylinder axis (A) between a lower and an upper reversal point, with a cylinder cover (5) which, together with the piston (3) delimits a combustion chamber (6), with at least one injection nozzle (11) for introducing a fuel into the combustion chamber (6), the cylinder (2) having scavenging air openings (14) for supplying purge air into the cylinder (2), and wherein in the cylinder cover (5) an outlet valve (12) is arranged, through which combustion gases from the combustion chamber (6) can be fed to an exhaust system (13), wherein a blow-off valve (15) is provided, which is designed such that the blow-off valve (15) when a limit pressure in the cylinder (2) or in the combustion chamber (6) is exceeded from a closed state to an open state, in in which the blow-off valve (15) enables a gas flow out of the cylinder (2) or out of the combustion chamber (6).

Description

Description: The invention relates to a longitudinally flushed large engine according to the preamble of the independent patent claim.

Large engines that can be configured as two-stroke or four-stroke engines, such as longitudinally-flushed two-stroke large diesel engines are often used as drive units for ships or in stationary operation, e.g. used to drive large generators for generating electrical energy. The engines usually run for long periods in continuous operation, which places high demands on the reliability and availability. Therefore, for the operator in particular long maintenance intervals, low wear and an economical handling of the operating materials are central criteria. Large engines typically have cylinders whose inside diameter (bore) is at least 200 mm. Nowadays large engines with a bore of up to 960 mm or even more are used.

Another important issue for some years with increasing importance is the quality of the exhaust gases, in particular the nitrogen oxide concentration in the exhaust gases or sulfur. Here, the legal requirements and limit values for the corresponding emission limits are being tightened. This has in particular in two-stroke large diesel engines with the result that the combustion of the classic heavy polluted with heavy fuel oil, but also the combustion of diesel oil or other fuels is problematic, because the compliance with the exhaust limits is increasingly difficult, technically complex and thus more expensive.

From the aspects of economical and efficient operation, the compliance with exhaust emission limits and the availability of resources, one therefore seeks alternatives to the heavy fuel oil that is classically used as fuel for large engines. In this case, both liquid fuels are used, ie fuels that are introduced in the liquid state into the combustion chamber, as well as gaseous fuels, ie fuels that are introduced in the gaseous state into the combustion chamber.

Examples of liquid fuels known alternatives to heavy fuel are other heavy hydrocarbons, which remain in particular as residues in the refinery of petroleum, alcohols, especially methanol or ethanol, gasoline, diesel, or emulsions or suspensions. So it is e.g. It is known to use the emulsions referred to as MSAR (Multiphase Superfine Atomised Residue) as fuel. These are essentially emulsions of a heavy hydrocarbon, e.g. Bitumen, heavy oil or similar, and water produced in special processes. A known suspension is that of coal dust and water, which is also used as fuel for large engines. For example, natural gas such as LNG (liquefied natural gas) are known as gaseous fuels.

A likewise known alternative to pure operation with heavy oil is to design large engines so that they can be operated with two or more different fuels, the engine depending on the operating situation or environment either with the one fuel or with the other fuel is operated. Such a large engine, which is also referred to as a multi-fuel large engine, can be switched during operation from a first mode in which a first fuel is burned, in a second mode in which a second fuel is burned, and vice versa.

A known embodiment of a large engine, which can be operated with two different fuels, is the type of engine for which nowadays the term "dual-fuel engine" is in use. These engines are, on the one hand, operable in a gas mode in which a gaseous fuel, e.g. Natural gas or methane, is introduced for combustion in the combustion chamber, and on the other hand, in a liquid mode in which a liquid fuel such as heavy oil or other liquid fuels in the same engine can be burned. These large engines can be both two-stroke and four-stroke engines, especially longitudinally purged two-stroke large diesel engines.

There are also known such large engines, which can be operated with two different liquid fuels, whereby usually both fuels are in stock, so that the engine is also operable during operation either with the first or with the second fuel.

Large engines that can be operated with at least two or more different liquid or gaseous fuels are often operated depending on the currently used fuel in different operating modes. In the operating mode, often referred to as diesel operation, the combustion of the fuel is usually carried out according to the principle of compression ignition or auto-ignition of the fuel. In the mode frequently referred to as Ottobetrieb combustion takes place by the spark ignition of an ignitable fuel-air mixture. This spark ignition can be done, for example, by an electric spark, e.g. with a spark plug, or by the auto-ignition of a small amount of injected fuel, which then causes the spark ignition of another fuel. In the case of the abovementioned dual-fuel engines, it is known, for example, for the gas mode, to mix the gas in the gaseous state with the purging air so as to produce an ignitable mixture in the combustion chamber of the cylinder. In this low-pressure method then the ignition of the mixture in the cylinder is usually carried out by a small amount of liquid fuel is injected into the combustion chamber of the cylinder or in an antechamber at the right moment, which then leads to the ignition of the air-gas mixture.

Furthermore, mixed forms from the Otto operation and the diesel operation are known.

Large engines are designed differently due to their enormous size and the extremely strong forces that occur in them as small internal combustion engines as they are used for example for driving automobiles and therefore also require other safety precautions. In large engines, it may happen, for example, due to a faulty amount of the fuel introduced into the combustion chamber or due to a wrong time of fuel introduction, that the pressure in the cylinder or in the combustion chamber exceeds an allowable limit for which the cylinder is designed. In such cases, it is known today with large engines, that the cylinder cover is lifted from the cylinder or from the cylinder cover so that the excessive pressure can escape. Usually, this pressure, at which it comes to lifting the cylinder cover, at least roughly be adjusted by the bias with which the cylinder cover is mounted on the cylinder or the cylinder liner.

However, this lifting of the cylinder cover also has some disadvantages. If an inadmissible overpressure occurs in the cylinder and the cylinder cover is lifted off the cylinder, so that the pressure between the top of the cylinder liner and the bottom of the cylinder cover can escape, this means an uncontrolled escape of an ignitable mixture and / or the escape of flames, usually accompanied by a very loud bang. This represents a very high risk of injury to personnel located near the cylinder.

In addition, such an event often leads to damage to the cylinder or the engine, which make time-consuming and costly repair or service work necessary.

Based on this prior art, it is therefore an object of the invention to propose a large engine, in which an inadmissible overpressure in the cylinder is safely degradable.

The object of the invention solving this object is characterized by the features of the independent claim.

According to the invention, therefore, a longitudinally rinsed large engine is proposed with at least one cylinder, which comprises a cylinder wall, and in which a piston along a cylinder axis between a lower and an upper reversal point is arranged back and forth, with a cylinder cover, which together with the Piston defines a combustion chamber, with at least one injection nozzle for introducing a fuel into the combustion chamber, wherein the cylinder scavenging air openings for supplying scavenging air into the cylinder, and wherein in the cylinder cover an exhaust valve is arranged, through which combustion gases from the combustion chamber can be fed to an exhaust system, wherein a blow-off valve is provided, which is designed such that the blow-off valve when a limit pressure in the cylinder or in the combustion chamber is exceeded from a closed state to an open state in which the blow-off valve ode a gas flow from the cylinder r out of the combustion chamber allows.

If an impermissible pressure prevails in the cylinder or in the combustion chamber, as a specifiable limit pressure is exceeded, this pressure can be reduced using the blow-off valve in a secure manner, so that a lifting of the cylinder cover can be avoided by the cylinder. The blow-off valve can be designed so that it automatically changes from the closed state to the open state when the predeterminable limit pressure is exceeded. But it is also possible that the blow-off valve is designed to be controllable and is then moved when the limit pressure is exceeded by a valve control unit from the closed to the open state.

Also, the blow-off valve may be configured so that it still has one or more intermediate states between the closed state and the open state, in which the blow-off valve is open, but only a smaller flow area for the outflowing gas releases as in the open state ,

According to one embodiment, the blow-off valve is arranged in the cylinder cover.

According to a further embodiment, the blow-off valve is arranged in the outlet valve.

In another embodiment, the blow-off valve is arranged on the cylinder and in particular in or on the cylinder wall.

In possible embodiments, the blow-off valve is configured as a mechanical blow-off valve or as a hydraulic blow-off valve or as a mechanical-hydraulic blow-off valve.

The large engine is designed for example as a longitudinally flushed two-stroke large diesel engine.

It is also possible that the large engine is designed as a multi-fuel large engine, which can be operated with a first fuel, and which can be operated with at least one second fuel, which is different from the first fuel.

According to another possible embodiment of the large engine is designed as a dual-fuel large diesel engine, which is operable in a liquid mode, in which a liquid fuel is introduced for combustion in the combustion chamber, and which is further operable in a gas mode in which a Gas is introduced as fuel into the combustion chamber.

Further advantageous measures and embodiments of the invention will become apparent from the dependent claims.

In the following the invention will be explained in more detail with reference to embodiments and with reference to the drawing. In the drawing shows:

Fig. 1: a schematic representation of an embodiment of an inventive large engine.

Fig. 1 shows a schematic representation of an embodiment of an inventive large engine, which is designated overall by the reference numeral 1. Since it is sufficient for the understanding, only one of the usually multiple cylinders 2 of the large engine 1 is shown in FIG. The cylinder axis of the cylinder 2 is designated by the reference symbol A. In the circumferential direction of the cylinder 2 is bounded by a cylinder wall 21, which is usually configured as a cylinder liner or as a cylinder liner.

The term "large engine" means such engines as commonly used as main propulsion units for ships or in stationary operation, e.g. be used to drive large generators for generating electrical energy. Typically, the cylinders 2 of a large engine 1 each have an inner diameter (bore) that is at least about 200 mm.

The large engine 1 can be configured as a four-stroke or two-stroke engine. In particular, the large engine can be configured as a large diesel engine, especially as longitudinally purged two-stroke large diesel engine. By the term "large diesel engine" are meant such large engines that are operable in a diesel operation. In the idealized limit, diesel operation is a constant pressure (steady pressure combustion) process based on diffusion combustion. In diesel operation, the combustion of the fuel is usually carried out according to the principle of auto-ignition. In the context of this application, the term "large diesel engine" also means those large engines which can be operated except in diesel mode, alternatively also in an Otto mode. The Otto operation is in the idealized borderline case a Gleichraumverbrennung, in which the combustion is typically carried out according to the principle of the spark ignition of the fuel. It is also possible that the large diesel engine can be operated in mixed forms from the diesel operation and the Otto operation.

Further, the term "externally ignited fuel" refers to such a fuel that burns as determined by spark ignition in the cylinder 2, in which therefore a self-ignition should be avoided as intended. In contrast, with a "self-igniting fuel" refers to such a fuel that burns as intended by auto-ignition in the cylinder 2, for example, heavy oil or diesel fuel.

As "liquid fuel", a fuel is referred to, which is introduced in the liquid state in the cylinder 2. The term "gaseous fuel" refers to a fuel which is introduced into the cylinder 2 in the gaseous state.

In the following description of the invention is taken by way of example the practical case of a large diesel engine, which is designed as a longitudinally flushed two-stroke large diesel engine 1, and which is used as the main propulsion unit of a ship. However, for example, this large diesel engine 1 may not necessarily be configured as a dual fuel large diesel engine so that it can be operated with two different fuels, e.g. with a liquid fuel such as heavy oil and with a gaseous fuel, e.g. Natural gas. The dual-fuel large diesel engine can be switched during operation from burning the first fuel to the burning of the second fuel and vice versa.

It is understood that the invention is not limited to this type of large diesel engine 1 and to this use, but relates to large engines in general. It is also possible that the large engine is designed only for the combustion of a single fuel, such as heavy oil, marine diesel or diesel. It is also possible that the large engine 1 is designed as a multi-fuel large engine, which can be operated with a first fuel, and which can be operated with at least one second fuel, which is different from the first fuel. Of course, the large engine is also designed for the combustion of more than two fuels.

In each cylinder 2 of the large diesel engine 1 (see Fig. 1), a piston 3 is provided in each case, which is arranged reciprocally in the direction of the cylinder axis A between an upper and a lower reversal point, and its upper side together with a Cylinder cover 5 limits a combustion chamber 6. The piston 3 may optionally comprise one or more piston rings 31, 32 in a manner known per se, the piston ring 31 closest to the combustion chamber 6 being referred to as the uppermost piston ring 31.

The piston 3 is connected in a conventional manner via a piston rod 7 with a crosshead 8, which is connected via a push rod 9 with a crankshaft 10, so that the movement of the piston 3 via the piston rod 7, the crosshead 8 and the Push rod 9 is transmitted to the crankshaft 10 to rotate it.

In the combustion chamber 6, the fuel can be injected by means of at least one injection nozzle 11. Of course, it is also possible for each cylinder 2 to have a plurality of injection nozzles 11 for injecting the fuel into the combustion chamber 6. In Fig. 1, two injection nozzles 11 are shown. If the large engine 1 can be operated with different fuels, different injection nozzles or injection devices can also be provided for the different fuels. Both injection nozzles 11 are arranged in the cylinder cover 5 in this embodiment (FIG. 1).

In the cylinder cover 5, a mostly centrally disposed exhaust valve 12 is provided, through which the combustion gases can be discharged from the cylinder 2 into an exhaust system 13 after the combustion process.

The further construction and the individual components of the large diesel engine 1, such as details of the injection system, the gas exchange system, the exhaust system or the turbocharger system for the provision of purge or charge air, and the control and control system for a large diesel engine 1 are the Professional well known both for the design of a two-stroke engine as well as for the design of a four-stroke engine and therefore require no further explanation here.

In the embodiment described here of a longitudinally purged two-stroke large diesel engine 1 are usually in the lower part of each cylinder 2 and cylinder liner scavenging air 14, for example designed as scavenging air slots, provided for supplying scavenging air into the cylinder 2, wherein the scavenging air through the movement of the piston 3 in the cylinder 2 are periodically closed and opened, so that the provided by the turbocharger under a boost pressure scavenging air can flow through the scavenging air slots 14 in the cylinder 2, as long as they are open.

The control and control system is in modern large diesel engines an electronic system with which usually all engine or cylinder functions, in particular the injection (start and end of the injection) and the actuation of the exhaust valve, set or control or can be regulated.

According to the invention, a blow-off valve 15 is also provided, which changes when a limit pressure in the cylinder 2 is exceeded from a closed state to an open state, in which the blow-off valve 15 enables a gas flow out of the cylinder 2 or out of the combustion chamber 6. As a result, in the case of an impermissibly high overpressure in the cylinder 2 or in the combustion chamber 6 in a secure manner, a pressure relief can be made because the gas or a fuel-gas mixture can be discharged via the open blow-off valve 15.

The discharge valve 15 is arranged in the embodiment shown here on the cylinder 2, namely on the cylinder wall 21. The blow-off valve 15 is provided in a cavity 16, which is open to the interior of the cylinder 2. This cavity 16 may be configured, for example, as a nozzle, as a recess or as a conduit. Downstream, the blow-off valve 15 or the cavity 16, in which the blow-off valve 15 is arranged, preferably connected via a discharge line 17 to the exhaust system 13, so that the gas or the fuel-gas mixture in the open state of the blow-off valve 15 from the cylinder 2 or from the Combustion chamber 6 through the cavity 16 and the discharge line 17 can flow into the exhaust system 13.

In the closed state of the blow-off valve 15, the flow connection between the cavity 16 and the discharge line 17 is closed, so that thereby no gas can flow out and the duty cycle of the cylinder 2 can proceed normally with the combustion process in a conventional manner.

Only when the predeterminable limit pressure is exceeded, the blow-off valve 15 changes from the closed to the open state, so that then the flow connection between the cavity 16 and the discharge line 17 is opened.

With regard to the arrangement of the blow-off valve 15 and / or the cavity 16, several variants are possible. As shown in Fig. 1, the blow-off valve 15 may be provided on the cylinder 2 and in particular in or on the cylinder wall 21, but it is also possible to provide the blow-off valve 15 on or in the cylinder cover 5, for example laterally adjacent to the outlet valve 12 or in the Side regions in which the injection nozzles 11 are shown in Fig. 1. A further variant consists of arranging the blow-off valve 15 in the outlet valve 12, for example in the valve plate or in the valve stem of the outlet valve 12. Another variant is to arrange the blow-off valve 15 in the piston 3. It is only essential that the gas or the fuel-gas mixture in the opened state of the blow-off valve 5 can flow out of the combustion chamber 6 or out of the cylinder 2, even if the outlet valve 12 is closed.

With regard to the embodiment of the blow-off valve 15, several variants are possible.

The blow-off valve 15 may be configured, for example, as an electrically or electronically controllable switching valve.

The blow-off valve 15 may be configured with a valve body and a valve seat cooperating with the valve body. In the closed state of the blow-off valve 15, the valve body, for example by means of a spring force, pressed into the valve seat, so that the valve body sealingly cooperates with the valve seat. In the open state, the valve body is lifted out of the valve seat, so that a flow connection between the valve seat and the valve body is opened.

The blow-off valve 15 may be configured as an automatic valve, which automatically changes from the closed state to the open state when the predeterminable limit pressure is exceeded.

The blow-off valve can also be designed as an actively controllable blow-off, which is switched when the limit pressure in the cylinder 2 and in the combustion chamber 6 is actively exceeded by the closed in the open state. The pressure in the combustion chamber 6 is a variable which is usually detected by measurement in the large engine.

Claims (8)

The blow-off valve may also be designed so that it can be brought in one or more intermediate state / intermediate states in addition to the closed state and the open state. In each intermediate state, the flow connection via the blow-off valve 15 is opened, however, the open flow cross-section is smaller in each intermediate state than in the opened state of the blow-off valve 15. The blow-off valve 15 can be designed as a purely mechanical valve, for example, the valve body can by a Spiral spring or one or more plate spring (s) sealingly pressed into the valve seat. When the limit pressure is exceeded, the force caused by the force in the combustion chamber 6 or in the cylinder 2 on the valve body exceeds the spring force, so that the valve body is lifted from the valve seat, whereby the blow-off valve 15 changes to the open state. The limit pressure at which the blow-off valve 15 opens can then be adjusted via the geometry and / or via the spring force which presses the valve body into the valve seat. The blow-off valve 15 can also be designed as a mechanical-hydraulic blow-off valve, in which hydraulic elements or hydraulic forces are combined with mechanical forces, such as the spring force described above. Similar or mutatis mutandis identical embodiments are known for example from the exhaust valve 12 in large engines. Further, it is possible to design the blow-off valve 15 in a conventional manner as a hydraulic blow-off valve. claims 1. A longitudinally purged large engine with at least one cylinder (2), which comprises a cylinder wall (21), and in which a piston (3) along a cylinder axis (A) between a lower and an upper reversal point is arranged back and forth, with a Cylinder cover (5) which defines together with the piston (3) a combustion chamber (6), with at least one injection nozzle (11) for introducing a fuel into the combustion chamber (6), wherein the cylinder (2) scavenging air openings (14) for supplying of purge air in the cylinder (2), and wherein in the cylinder cover (5) an outlet valve (12) is arranged, through which combustion gases from the combustion chamber (6) an exhaust system (13) are fed, characterized in that a blow-off valve (15 is provided, which is designed such that the blow-off valve (15) when a limit pressure in the cylinder (2) or in the combustion chamber (6) is exceeded from a closed state to an open state, in in which the blow-off valve (15) enables a gas flow out of the cylinder (2) or out of the combustion chamber (6). 2. Large engine according to claim 1, wherein the blow-off valve (15) in the cylinder cover (5) is arranged. 3. Large engine according to one of the preceding claims, wherein the blow-off valve (15) in the outlet valve (12) is arranged. 4. Large engine according to claim 1, wherein the blow-off valve (15) on the cylinder (2) and in particular in or on the cylinder wall (21) is arranged. 5. Large engine according to one of the preceding claims, wherein the blow-off valve (15) as a mechanical blow-off valve (15), or as a hydraulic blow-off valve (15) or as a mechanical-hydraulic blow-off valve (15) is configured. 6. Large engine according to one of the preceding claims, designed as a longitudinally flushed two-stroke large diesel engine. 7. Large engine according to one of the preceding claims, designed as a multi-fuel large engine, which can be operated with a first fuel, and which can be operated with at least one second fuel, which is different from the first fuel. 8. Large engine according to one of the preceding claims, configured as a dual-fuel large diesel engine, which is operable in a liquid mode, in which a liquid fuel for combustion in the combustion chamber (6) is introduced, and which is further operable in a gas mode, in which a gas is introduced as fuel into the combustion chamber (6).