WO2010145652A1

WO2010145652A1 - A large turbocharged two-stoke diesel engine running on a fuel mixture of two or more fuel components

Info

Publication number: WO2010145652A1
Application number: PCT/DK2009/000141
Authority: WO
Inventors: Stefan Mayer
Original assignee: Man Diesel, Filial Af Man Diesel Se, Tyskland
Priority date: 2009-06-16
Filing date: 2009-06-16
Publication date: 2010-12-23
Also published as: JP2011525595A; JP5075278B2; KR20110031409A; CN102066738A; CN102066738B; KR20120135535A

Abstract

A large two-stroke turbocharged diesel engine of the crosshead type provided with a plurality of cylinders (6), one or more fuel valves (23) associated with each cylinder (6) and a hydraulically actuated fuel injection piston pump (39) associated with each cylinder. The hydraulically actuated fuel injection piston pump (39) is provided with a pump piston (45) and a pump chamber (44). The engine is also provided with an outlet port of the pump chamber (44) connected to the fuel valve or fuel valves (23), a supply of a first fuel component (72) connected to an inlet port of the pump chamber (44), and supply of a second fuel component (73) connected an inlet port of the pump chamber (44). The pump chamber (44) is filled with an amount of the first fuel component and with an amount of the second fuel component in an aspirating stroke of the hydraulically actuated fuel injection piston pump (39) and the first fuel component and the second fuel component are mixed in the pump chamber (44) to form a fuel mixture and the fuel mixture in the pump chamber (44) is expelled from the pump chamber (44) and delivered to the injection valves (23) in an injection stroke of the hydraulically actuated fuel injection piston pump (39).

Description

A LARGE TURBOCHARGED TWO-STOKE DIESEL ENGINE RUNNING ON A FUEL MIXTURE OF TWO OR MORE FUEL COMPONENTS

FIELD OF THE INVENTION

The present invention relates to large turbocharged two- stroke diesel engines that use two fuel components, and in particular to large turbocharged two-stroke diesel engines that mix the one fuel component with the other fuel component .

BACKGROUND OF THE INVENTION

Large turbocharged two-stroke diesel engines are used as prime mover in power plants and in large ocean going vessels .

Large two stoke diesel engines are typically operated with heavy fuel oil, with natural gas as the only realistic alternative. However, natural gas is only available for some stationary power plants and in gas tankers where the boil off of the natural gas can be used to as fuel of the engine. Heavy fuel oil is relatively inexpensive since this a byproduct of the refining process but it has a number of drawbacks. For example, heavy fuel oil is not liquid at ambient temperatures and needs to be heated and kept heated at all times. Further, heavy fuel oil has a high sulfur content and has a high content of other impurities. Thus, the fuel system of large two-stroke diesel engines is provided with a large number of complicated arrangements to be able to handle heavy fuel oil.

One of these arrangements is a complete heating of the fuel system at all times and a recirculation system that keeps the heavy fuel oil circulating through the fuel system and heated at the same time, also during engine stops. In order to be able to heat the fuel system the tanks are heated and the pipes are provided with stream tracing. The engines could be significantly simplified and build less expensive if they were operated on clean diesel fuel, but the costs of cleans diesel fuel prevent this.

Presently, heavy fuel oil and water mixtures or emulsifications are used to reduce emissions. In large turbocharged two-stroke diesel engines, like the one disclosed in WO2007115580 the mixture or emulsification takes place in a mixture or emulsification system upstream of the fuel injection pumps and the produced blend is stored in tanks of considerable size. Due to the size of these tanks and the length of the piping there is a very significant delay from the moment at which the water and fuel are mixed or emulsified to the moment of injection of the mixture or emulsion into the combustion chamber. This delay can be in the order of many minutes or even hours and changes in the mixing process (for example a change in the ratio between water and heavy fuel) are reflect in the combustion with considerable time delay, making a quick response to changing conditions infeasible.

If changed operating conditions would require the heavy fuel oil to water ratio to be changed, e.g. because the present mixture will not ignite properly under the current operating conditions it would take hours to adapt the heavy fuel to water ratio. For an oceangoing vessel it is dangerous if the engine does not operate properly for an hour since this affects the vessels maneuverability. Further, it is very difficult if not impossible to determine what the present ratio of the fuel components in the combustion, since it cannot be accurately determined when how fast the fuel ratio in the tanks changes and how long it takes for the changed ratio in the tank to reach the cylinders of the engine

Another difficulty in using certain mixtures of fuel- constituents, in particularly fuel-water or fuel ethanol emulsions is the long-time stability of the mixture particularly if the water content is high. This lack of stability requires the use of particular homogenizer equipment and emulsifier and stabilisator additives.

Ethanol is another fuel that can be used in large two- stroke diesel engines. However, ethanol is not self igniting and requires a pilot fuel to be injected just before or at the same time or mixed with the ethanol fuel. Known systems use a separate pilot injection for the pilot fuel.

DISCLOSURE OF THE INVENTION

On this background, it is an object of the present invention to provide a large two-stroke turbocharged diesel engine that overcomes or at least reduces the drawbacks mentioned above.

This object is achieved by providing a large turbocharged two-stroke diesel engine of the crosshead type comprising a plurality of cylinders, one or more fuel valves associated with each cylinder, a hydraulically actuated fuel injection piston pump associated with each cylinder, said hydraulically actuated fuel injection piston pump is provided with a pump piston and a pump chamber, an outlet port of said pump chamber is connected to the fuel valve or fuel valves, a supply of a first fuel component connected to an inlet port of the pump chamber, a supply of a second fuel component connected an inlet port of the pump chamber, the pump chamber is filled with an amount of the first fuel component and with an amount of the second fuel component in an aspirating stroke of the hydraulically actuated fuel injection piston pump and the first fuel component and the second fuel component are mixed in the pump chamber to form a fuel mixture and the fuel mixture in the pump chamber is expelled from the pump chamber and delivered to the fuel valves in an injection stroke of the hydraulically actuated fuel injection piston pump.

By mixing the fuel components inside the pump chamber of the hydraulically actuated fuel injection piston pump a change in the ratio of the fuel components is reflected almost instantaneously in the combustion process and actual the ratio between the fuel components is known quite exact. Thus, the fuel ratio can be quickly adapted to the actual operating conditions and there is feedback on the effect of a given ratio on the engine since the actual ratio is known .

Preferably, the engine comprises control means for controlling the ratio between the amount of the first fuel component and the amount of the second fuel component delivered to the pump chamber during the aspiration stroke.

The control can be configured to be able to change the ratio between the amount of the first fuel component and the amount of the second fuel component delivered to the pump chamber within one engine cycle. The supply of the first fuel component may comprise a common rail.

The supply of the second fuel component may comprise a common rail.

Preferably, least the supply of the first fuel component or the supply of the second fuel component comprises a valve or dosage pump for controlling the amount of the respective fuel component that is delivered to the pump chamber during the aspiration stroke.

The valve can be a simple open and close valve and the dosage of the fuel component concerned is controlled by the length of the valve open time or in response to a measured flow.

Preferably, the pump chamber is directly connected to the fuel valves by a pressure conduit.

The injection stroke of the pump piston can be powered by hydraulic pressure acting on the side of the piston opposite to the pump chamber or by hydraulic pressure acting on a piston directly connected to the pump piston.

The hydraulically actuated fuel injection piston pump can comprise an actuation chamber.

The actuation chamber can be delimited by the opposite side of the pump piston or by a booster piston directly connected to the pump piston. The effective surface area of the pump piston on the pump chamber side can be smaller than the effective surface area on the opposite side of the pump piston or can be smaller than the effective surface area of the booster piston.

The object above is also achieved by providing a method for preparing a fuel mixture in a large turbocharged two-stroke diesel engine of the crosshead type, said method comprising delivering and mixing an amount of a first fuel component and an amount of a second fuel component with a predetermined ratio between said amount of a first fuel component and said amount of a second fuel component to a pump chamber of a hydraulically actuated fuel injection piston pump that is associated with a cylinder of the engine during the aspiration stroke of the piston of the hydraulically actuated fuel injection piston pump to form a fuel mixture and expelling the fuel mixture in the pump chamber from the pump chamber and delivering the fuel mixture to fuel valves of the engine in an injection stroke of the hydraulically actuated fuel injection piston pump.

By delivering the fuel components to the pump chamber and mixing the fuel components inside the pump chamber of the hydraulically actuated fuel injection piston pump a change in the ratio of the fuel components is reflected almost instantaneously in the combustion process and actual the ratio between the fuel components is known quite exact. Thus, the fuel ratio can be quickly adapted to the actual operating conditions and there is feedback on the effect of a given ratio on the engine since the actual ratio is known . Further objects, features, advantages and properties of the large two-stroke diesel engines and methods according to the invention 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:

Figure 1 is a diagrammatic illustration of the fuel injection and exhaust valve actuation systems of a large two stroke diesel engine according to an embodiment of the present invention,

Figure 2 is a diagrammatic illustration of the fuel injection and exhaust valve actuation systems of a large two stroke diesel engine according to another embodiment of the invention, and

Figure 3 is a detailed diagrammatic illustration of the fuel injection system for the engine according to the embodiments of figures 1 and 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following detailed description of the large turbocharged two-stroke diesel engine of the crosshead type and the method for preparing a fuel mixture for a large turbocharged two-stroke diesel engine of the crosshead type according to the invention will be described by the preferred embodiments. The engine is a uniflow low-speed two-stroke crosshead diesel engine of the crosshead type, which may be a propulsion engine in a ship or a prime mover in a power plant. These engines have typically from 3 up to 14 cylinders in line. The total output of the engine may, for example, range from 5,000 to 110,000 kW.

The cylinders 6 are of the uniflow type and have scavenge ports 7 and drilled holes (not shown) for cylinder lubrication. The scavenge ports 7 are supplied with scavenge air from a scavenge air receiver (not shown) that is supplied with scavenge air pressurized by one or more exhaust gas driven turbochargers (not shown) .

An exhaust valve 11 is mounted centrally in the top of the cylinder 6 in a cylinder cover. At the end of the expansion stroke the exhaust valve 11 opens before the engine piston 13 passes down past the scavenge air ports 7, whereby the combustion gases in the combustion chamber 15 above the piston 13 flow out through an exhaust passage 16 opening into an exhaust receiver (not shown) and the pressure in the combustion chamber 15 is relieved. The exhaust valve 11 closes again during the upward movement of the piston 13. The exhaust valve 11 is driven upwards by a pneumatic spring (not shown) .

The exhaust valve 11 is opened by means of exhaust cams 27 on the camshaft 28. The camshaft 28 is mechanically driven by a take off from the crankshaft of the engine.

The exhaust cams 29 activate a piston pump 37 via a roller 42. The hydraulic fluid from the piston pump 37 is delivered to an exhaust valve 11 via a pressure pipe 35. A hydraulic cylinder piston type actuator 21 urges the exhaust valve 11 in the opening direction when it receives pressurized hydraulic fluid from via the pressure pipe 35. The return stroke of the exhaust valve is caused by an air spring (not shown) . The piston pump 37, the pressure pipe 35 and the exhaust valve actuator 21 form a so-call hydraulic pushrod.

In an alterative embodiment (not shown) the exhaust valve 11 is actuated by an electro-hydraulic system that does not use a camshaft.

Each cylinder 6 is provided with two or three fuel valves 23 (only one is shown) each connected by pressure conduits 51 to the outlet port or ports of a hydraulically actuated fuel injection piston pump 39 (in this embodiment the hydraulically actuated fuel injection piston pump is also a pressure booster) . The fuel valves 23 open when the pressure on their inlet port exceeds a threshold, e.g. 300 or 400 bar. The fuel valves 23 are at their tips provided with injection nozzles that vaporize the injected fuel mixture .

The engine is in the present embodiment configured to be operated with a fuel-water mixture. The fuel components, heavy fuel and water, are delivered from the heavy fuel oil delivery installation 72 and the water delivery system 73 to the pump chamber 44 of the respective hydraulically actuated fuel injection piston pumps (pressure boosters) 39. The amount of water and the amount of heavy fuel oil delivered to the pump chamber 44 is controlled by a system that will be described in greater detail further below. The heavy fuel oil delivery installation 72 is not shown in detail in the drawings but the heavy fuel oil delivery installation 72 is so arranged that both light fuel oil (marine diesel) and heavy fuel oil can be used. From a service tank the heavy fuel oil is led to an electrically driven supply pump by means of which a pressure of approximately 4 bar can be maintained in the low pressure part of the fuel circulating system, thus avoiding gasification of the fuel in a venting box in the temperature ranges applied. From the low pressure part of the fuel system the fuel oil is led to an electrically- driven circulating pump, which pumps the heavy fuel oil through a heater and a full flow filter before the fuel is distributed at a pressure of approximately 7 bar to the respective hydraulically actuated fuel injection piston pumps (pressure boosters) 39.

The hydraulically actuated fuel injection piston pumps (pressure boosters) 39 are provided with a pump chamber 44 that is delimited by a pump piston 45.

The pump piston 45 is directly connected to a larger effective surface area booster piston 46. The booster piston 46 delimits an actuation chamber 47. The effective area of the booster piston 46 larger than the effective area of the pump piston 45 making the hydraulically actuated fuel injection piston pump 39 a pressure booster.

However, if sufficient pressure of the hydraulic fluid is available a piston (not shown) with an effective surface area smaller or equal than the pump piston can be used instead of the booster piston 46.

The fuel injection is performed by the electronically controlled hydraulically actuated fuel injection piston pumps (pressure boosters) 39, one per cylinder. The hydraulically actuated fuel injection piston pumps (pressure booster) 39 multiplies the pressure from the low- pressure (where the hydraulic fluid is applied) side to the high pressure side (the fuel side) by a fixed ratio.

The hydraulically actuated fuel injection piston pumps (pressure boosters) 39 are powered by pressurized hydraulic fluid that is applied to the actuation chamber 47 and thereby acts on the booster piston 46. The hydraulic fluid can be the engine lubrication oil. A pressure pump 60 delivers high pressure hydraulic fluid, typically a few hundred bar, via feed conduit 30 to the cylinders of the engine. If the hydraulic fluid is engine lubrication oil, the pressure pump 60 is not the engine lubrication pump which operates at a much lower pressure. Return hydraulic fluid is transported from the cylinders via conduit 65 to the tank 61 from which the hydraulic pump 60 draws its fluid.

A compression chamber 67 is in this embodiment provided for each pair of engine cylinders 6 (in case the engine has an odd number of cylinders, one of the cylinders may be served by a single compression chamber) . A conduit 69 connects the compression chamber 67 to a proportional control valves 41 (one proportional control valves 41 per cylinder) .

Each cylinder 6 of the engine 1 is associated with an electronic control unit 99 which receives general synchronizing and control signals and transmits electronic control signals to the proportional control valves 41, among others, through wires 59. There may be one control unit 99 per cylinder, or several cylinders may be associated with the same control unit (not shown) . The electronic control units 99 may also receive signals from an overall control unit (not shown) common to all the cylinders .

The electronic control unit 99 calculates the desired ratio between the fuel components, the timing, the rate shaping and the amount of the fuel injection, in accordance with the operating conditions of the engine. Hereto, the control unit receives information about the rotational position of the crankshaft, the rotational speed of the crank shaft (which could be derived by the control unit 99 from the rotational position signal) , ambient temperature, engine load and temperatures of various engine fluids. The electronic control units 99 also adapt the timing of the fuel injection for reversing the engine.

The movement of the spool in the proportional control valve 41 is controlled by the control unit 99 in a feedback control loop. The feedback control loop can alternatively be included in the proportional control valve 41 itself. The opening profile of the proportional valve 41 is matched to a desired opening profile that has been predetermined for optimal rate shaping and is stored in the control unit 99.

In their rest position the proportional control valves 41 connect the pressure chamber at the low pressure side

(actuation chamber 47) of the pressure booster 39 to tank.

When the control unit 99 sends a signal to start the fuel injection for a given cylinder, one of the proportional control valves 41 opens to a certain extend and connects thereby the low pressure side of the pressure booster 39 to the compression chamber 67 via conduit 69. The length of the stoke of the pump piston is preferably controlled by the electronic control unit 99 by allowing the pump piston 45 to return completely to is bottom position at the end of the aspiration stroke of the hydraulically actuated piston fuel pump 39 and by allowing it to move to a controlled position during the fuel injection stroke. The aspiration stroke is largely driven by the pressure of the first fuel component (heavy fuel oil) .

However, in another embodiment the pump piston 45 is returned to a controlled position during the aspiration stroke and the pump piston 45 allowed to move to its top position (emptying the pump chamber substantially completely) during the fuel injection stroke. In jet another embodiment the pump piston 45 is returned to a controlled position during the aspiration stroke and the pump piston 45 is moved to another controlled position during the fuel injection stroke.

The pressure in the actuation chamber 47 is multiplied, typically to reach an injection pressure for the fuel mix in the pump chamber 44 between approximately 400 and 1500 bar. A feed conduit 51 transports the high pressure fuel directly from the pump chamber 44 to the fuel valves 23 which atomize the fuel mixture by injecting the fuel mixture into the combustion chamber 15 via a nozzle at the tips of the fuel valves 23.

Figure 2 shows another embodiment of the engine according the invention. This embodiment is essentially the same as the embodiment of figure 1, except that the hydraulic fluid for actuating the hydraulically actuated piston fuel pump (fuel booster) is delivered by a piston pump 25 that is actuated by a fuel cam 27 on the camshaft 28. The piston pump 25 has a variable output for regulating the volume of the fuel delivered to the conduit 25 from one cam actuation to control the volume of fuel mixture that is injected in on fuel injection event.

Further, no boosting of the pressure is required in this embodiment and therefore the hydraulically actuated fuel injection piston pump 39 is a cylinder with a single piston 45 therein. The piston 45 has equal effective surface areas on each side and divides the cylinder into a pump chamber 44 and an actuation chamber 47.

Figure 3 shows the pump chamber 44 and the supply of the first fuel component 72 (in this embodiment heavy fuel oil) and the supply of the second fuel component 73 (in this embodiment water) in greater detail.

Heavy fuel oil is delivered at approximately 7 bar from the heavy fuel oil system 72 to the pump chamber 44 via in inlet port of the pump chamber, non-return valve 83 and conduit 82. In an embodiment the pump piston 45 always returns to its initial bottom position at which the pump chamber 44 has its maximum and known volume at the end of the aspiration stroke in the period between two successive fuel injection events.

The second fuel component (in this embodiment water) is delivered from a source of water 73 to the pump chamber 44 via an inlet port of the pump chamber 44, a non-return valve 85, conduit 86 and a dosage pump 94. The inlet ports of the pump chamber 44 can in en embodiment be provided with nozzles the improve mixing of the fuel components in the pump chamber 44.

The electronic control unit 99 commands the dosage pump via an electronically controlled valve 91 that selectively connects the dosage pump 94 to a source of pressurized hydraulic fluid 90. The dosage pump 94 is in an embodiment provided with a sensor (not shown) that registers the position of the piston of the dosage pump. An electronic controller (can be electronic control unit 99) determines when the pump stroke of the dosage pump 94 corresponds to the desired amount of the second fuel component to be delivered during the aspiration stoke of pump piston 45 of the hydraulically actuated fuel injection piston pump 39.

Alternatively, the dosage pump may have its own control loop and simply receives a command from the electronic control unit 99 to deliver the desired amount of the second fuel component. The dosage pump 94 is shown as a hydraulically driven pump, but could just as well be a pneumatically or electrically driven dosage pump.

The supply of water 73 can be a rail that supplies several or all of the cylinders of the engine with the second fuel component (water) .

Before each fuel injection event, the pump piston 45 performs an aspiration stoke back to its predefined initial position so that the volume of the pump chamber 44 is known. The dosage pump 94 delivers the amount of the second fuel component (in this embodiment water) as determined by the electronic control unit during the aspiration stroke of the pump piston 45. Simultaneously, the pump chamber is 44 filled with first fuel component (in this embodiment heavy fuel oil) . The pressure of the first fuel component powers the aspiration stoke and ensures that the pump chamber 44 is completely filled at the end of the aspiration stroke with the pump piston at its bottom position.

The total volume of the fuel mixture in the pump chamber 44 is known at the end of the aspiration stroke and the volume of the second fuel component in the pump chamber 44 is known (by using the dosage pump) . The volume of the first fuel component in the pressure chamber is determined by subtracting the volume of the second fuel component in the pump chamber 44 from the total (known) volume of the pump chamber 44 at the end of the aspiration stroke.

The injection stoke of the pump piston 45 will normally not be a full stoke completely emptying the pump chamber 44. Thus, at the beginning of the aspiration stoke there will be a volume of fuel mixture in the pump chamber.

The ratio between the first fuel component and the second fuel component in the pump chamber 44 at the end of the aspiration stroke is influenced by the fuel mixture that is in the pump chamber 44 at the beginning of the aspiration stroke.

However, if a change in the desired ratio between the first fuel component and the second fuel component is carried out by the electronic control unit 99 it will only take a few engine (injection) cycles before the actual ratio between the fuel components in the pump chamber 44 corresponds accurately to the desired ratio between the fuel components . A change in the desired ratio between the first fuel component and the second fuel component is thus reflected in the combustion after only a few engine cycles, i.e. the change is reflected in the combustion in seconds rather than hours as is the case in the known large two-stroke diesel engines described in the introductory part of this document .

The time available for the aspiration stroke is relatively long compared to the length of the time of the fuel injection stroke. Therefore there is relatively much time available for the aspiration stroke and the demands on the speed of e.g. the dosage pump are not high. Also, the time for the fuel components mixing in the pump chamber 44 is relatively long.

In an embodiment an emulsifier can be used to emulsify the fuel mixture in the pump chamber 44. The emulsifier can be a third fuel component or the emulsifier be mixed in advance with one of the fuel components.

In an embodiment (not shown) the mixing of the fuel components in the pump chamber 44 can be enhanced by the shape of the pump piston 45.

In an embodiment the volume of the second fuel component delivered during the aspiration stroke of the pump piston is not controlled by a dosage pump nut instead any another suitable means for dosage of the second fuel component. Such dosage means can be a valve in combination with a flow meter or a valve with controlled open times. The fuel components can be delivered to the pump chamber simultaneously or sequentially. In an embodiment the volume of each fuel component delivered during the aspiration stroke of the pump piston is controlled through dosage or measuring.

In an embodiment (not shown) the hydraulically actuated piston fuel pump 39 has a single piston 45 received in a cylinder with a pump chamber on one side of the piston and an actuation chamber on the pother side of the piston. The effective surface are of the piston 45 on the pump chamber side may be equal to or different from the effective surface area of the piston on the actuation chamber side, depending on the need for boosting the pressure that actuated the hydraulically actuated piston fuel pump 39.

The embodiments described above have been illustrated with two fuel components being mixed in the pump chamber of the hydraulically actuated piston fuel pump. However, the invention can also be used to mix more than two fuel components in the in the pump chamber of the hydraulically actuated piston fuel pump.

The invention has been illustrated with heavy fuel oil and water as the fuel components. However, the invention can also be used for other fuel components such as fuel oil, ethanol, bio-fuel and pilot oil. A fuel component as used in the present invention does not need to be a pure component and a fuel component can therefore be a mixture of substances. For example, the second fuel component can be a mixture of water and an emulsifier.

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

CLAIMS :

1. A large turbocharged two-stroke diesel engine (1) of the crosshead type comprising:

a plurality of cylinders (6),

one or more fuel valves (23) associated with each cylinder ( 6) ,

a hydraulically actuated fuel injection piston pump (39) associated with each cylinder,

said hydraulically actuated fuel injection piston pump (39) is provided with a pump piston (45) and a pump chamber (44) ,

an outlet port of said pump chamber (44) is connected to the fuel valve or fuel valves (23) ,

a supply of a first fuel component (72) connected to an inlet port of the pump chamber (44),

a supply of a second fuel component (73) connected an inlet port of the pump chamber (44),

the pump chamber (44) is filled with an amount of the first fuel component and with an amount of the second fuel component in an aspirating stroke of the hydraulically actuated fuel injection piston pump (39) and the first fuel component and the second fuel component are mixed in the pump chamber (44) to form a fuel mixture and the fuel mixture in the pump chamber (44) is expelled from the pump chamber (44) and delivered to the fuel valves (23) in an injection stroke of the hydraulically actuated fuel injection piston pump (39) .

2. A large turbocharged two-stroke diesel engine (1) according to claim 1, further comprising control means (71,99,91,94) for controlling the ratio between the amount of the first fuel component and the amount of the second fuel component delivered to the pump chamber (44) during the aspiration stroke.

3. A large turbocharged two-stroke diesel engine (1) according to claim 2, wherein the control means (71,99,91,94) is configured to be able to change the ratio between the amount of the first fuel component and the amount of the second fuel component delivered to the pump chamber (44) within one engine cycle.

4. A large turbocharged two-stroke diesel engine (1) according to claim 1, wherein the supply of the first fuel component (72) comprises a common rail.

5. A large turbocharged two-stroke diesel engine (1) according to claim 1, wherein the supply of the second fuel component (73) comprises a common rail.

6. A large turbocharged two-stroke diesel engine (1) according to claim 1, wherein least the supply of the first fuel component (72) or the supply of the second fuel component (73) comprises a valve or dosage pump for controlling the amount of the respective fuel component that is delivered to the pump chamber (44) during the aspiration stroke.

7. A large turbocharged two-stroke diesel engine (1) according to claim 6, wherein the valve is a simple open and close valve (71) and the dosage of the fuel component concerned is controlled by the length of the valve open time or in response to a measured flow.

8. A large turbocharged two-stroke diesel engine (1) according to claim 1, wherein the pump chamber (44) is directly connected to the fuel valves (23) by a pressure conduit (51) .

9. A large turbocharged two-stroke diesel engine (1) according to claim 1, wherein the injection stroke of the pump piston (45) is powered by hydraulic pressure acting on the side of the piston opposite to the pump chamber (44) or by hydraulic pressure acting on a piston (46) directly connected to the pump piston (45) .

10. A large turbocharged two-stroke diesel engine (1) according to claim 1, wherein the hydraulically actuated fuel injection piston pump comprises an actuation chamber (47) .

11. A large turbocharged two-stroke diesel engine (1) according to claim 10, wherein the actuation chamber is delimited by the opposite side of the pump piston (45) or by a piston (46) directly connected to the pump piston (45) .

12. A large turbocharged two-stroke diesel engine (1) according to claim 11, wherein the effective surface area of the pump piston (45) on the pump chamber side is smaller than the effective surface area on the opposite side of the pump piston (45) or is smaller than the effective surface area of the piston (46) .

14. A method for preparing a fuel mixture in a large turbocharged two-stroke diesel engine (1) of the crosshead type, said method comprising delivering and mixing an amount of a first fuel component and an amount of a second fuel component with a predetermined ratio between said amount of a first fuel component and said amount of a second fuel component to a pump chamber of a hydraulically actuated fuel injection piston pump (39) that is associated with a cylinder (6) of the engine during the aspiration stroke of the pump piston (45) of the hydraulically actuated fuel injection piston pump (39) to form a fuel mixture and expelling the fuel mixture in the pump chamber

(44) from the pump chamber (44) and delivering the fuel mixture to fuel valves (23) of the engine in an injection stroke of the hydraulically actuated fuel injection piston pump (39) .