WO2006128974A1

WO2006128974A1 - Method and arrangement for improving load acceptance of piston engine

Info

Publication number: WO2006128974A1
Application number: PCT/FI2006/050230
Authority: WO
Inventors: Björn HALLBÄCK; Johan KÅLAX; Mikko-Petteri Nieminen
Original assignee: Wärtsilä Finland Oy
Priority date: 2005-06-02
Filing date: 2006-06-02
Publication date: 2006-12-07
Also published as: FI20055276A0; EP1886006A4; FI20055276L; EP1886006A1

Abstract

A method of increasing load-bbearing capacity of a piston engine (1) having a turbo compressor (2) when increasing the load. In the method, combustion air is introduced into the compressor (3), pressurized combustion air is introduced into a flow plenum (6) on the pressure side of the compressor (3), pressurized combustion air is introduced from the flow plenum (6) into the cylinders (10) of the engine (1) and fuel is combusted in the cylinders (10) With the combustion air. In the method, pressurized additional air is simultaneously introduced to both the compressor (3) and the flow plenum (6).

Description

METHOD AND ARRANGEMENT FOR IMPROVING LOAD ACCEPTANCE OF PISTON ENGINE

The invention relates to a method of improving load-bearing capacity of a piston engine.

The invention also relates to an arrangement of improving load-bearing capacity of a piston engine.

Diesel engines are used as power sources in ships due to their reliability. Additionally, diesel engines can also adapt relatively fast to changes in power requirements. Usually, diesel-electric propulsion systems are used in ships, in which the electricity needed by the system is produced by means of generators driven by diesel engines. The electricity produced by the generators is then used as power for an electric motor driving the propeller and/or other drive device of the propulsion system. The electricity produced by means of the diesel engines is also used in the other electric systems of the ship.

The engines used in ships must be able to react as fast as possible to the changes of load due to the fluctuations of electricity requirements. During fast load fluctuations the running speed of the engine and the amplitude of the electricity produced by the generator connected to the engine experience a momentaneous decrease. In order to ensure as trouble-free operation as possible, ships' engines are subject to time limits inside which the running speed of the engines must return to normal at a fast load increase situation, in which the engine load is increased from 0 % to 100 % in two or three subsequent steps.

Usually, a three-step quick load increase is possible for modem, strongly turbocharged medium-fast diesel engines. However, two-step quick load increase is not possible without special arrangements because the running speed of the engine recovers too slowly in the first load increase step due lack of charge air caused by turbo lag. At low load levels the turbo lag is long, because the turbo compressors used in the engines are optimized to work at high running speeds and thus at high pressures to produce as high a specific power as possible. Further, the turbo compressors are provided with plain bearings, the friction losses of which are large at slow rotational speeds. However, use of the two-step load increase would accomplish simplifying the electrical system of the ship and thereby considerably decrease the costs related thereto.

Fast load changes are necessary in piston engines used for other applications as well.

The object of the present invention is to produce a solution by means which a turbocharged piston engine can be subjected to load increases more quickly.

The invention is based on feeding pressurized additional air simultaneously into the inlet channels leading into the combustion chambers of the cylinders and the compressor during increase of the engine load. Alternatively, pressurized additional air can be simultaneously introduced into the combustion chambers and the compressor.

More specifically, the invention is characterized by what is stated in the characterizing part of claim 1.

Furthermore, the arrangement according to the invention is characterized by what is stated in the characterizing part of claim 7.

Considerable advantages are achieved by means of the invention.

Due to the introduction of additional air the amount of combustion air fed into the cylinders increases while the engine control system increases the amount of fuel fed into the cylinders when changing the load of the engine. Due to the increased exhaust gas flow the rotation speed of the turbo compressor and thereby the pressure of the combustion air in the high pressure side of the compressor increases. Due to the introduction of additional air the decrease of engine running speed is smaller and the engine recovers its normal speed level faster in connection with an increase of load. Thus, the load of the engine can be increased faster than previously or the load can be increased during standard period in larger steps. For example, in the strongly turbocharged medium-fast diesel engines used in ships, the quick load increase can be carried out in two steps instead of three steps, whereby it is possible to use a simpler electrical system in the ship. The solution according to the invention can also be carried out inexpensively and easily installed in connection with existing engines.

In the following the invention is described in more detail by means of examples according to the appended drawings.

Figure 1 shows one arrangement according to the invention in a schematic diagrammatical drawing.

Figure 2 shows another arrangement according to the invention in a schematic diagrammatical drawing.

Figure 3 shows a third arrangement according to the invention in a schematic diagrammatical drawing.

The arrangement shown in figure 1 comprises a piston engine 1 that can be, for example, a medium-fast strongly turbo-charged diesel engine as used in ships. The engine 1 is used for driving a generator producing electricity to be used as a power source of the propulsion system of the ship.

The engine 1 is provided with a turbo compressor 2 comprising a compressor 3 and a turbine 4 connected to each other via a drive shaft 5. The drive shaft 5 is supported by plain bearings on the body of the turbo compressor 2. The task of the compressor 3 is to introduce pressurized air as combustion air for the engine 1. The compressor 3 comprises a rotatable rotor having blades for pressurizing the combustion air to be introduced to the engine 1. A flow plenum 6 is arranged on the high pressure side of the compressor 3, i.e. between the compressor 3 and the combustion chambers 10 of the engine for introducing the pressurized combustion air into the cylinders 10. A cooler 7 is arranged into the flow plenum 6 for cooling the combustion air. The flow plenum 6 further comprises a charge air receiver 8 arranged subsequent the cooler 7 in the flow direction of air. The flow plenum 6 also comprises inlet channels 9 arranged between each cylinder 10 and the charge air receiver 8 for introducing combustion air from the revceiver 8 to the cylinders 10.

Exhaust gas channels 11 are arranged between the cylinders 10 and the pressure side of the turbine 4 for directing the engine exhaust gases to the turbine 4. The turbine 4 also comprises a rotor having blades, the rotor being rotated by the exhaust gas from the engine 1. The engine 1 additionally comprises fuel feed means (not shown) for introducing fuel into the cylinders 10.

As the engine 1 runs, combustion air is directed into the compressor 3, in which the pressure of air is increased. The pressurized air is introduced into the flow plenum 6 located on the high pressure side 3 of the compressor. Subsequent to this the air is cooled by means of a cooler 7 and directed into the charge air receiver 8. From the charge air receiver 8 the combustion air is directed into the cylinders 10 via inlet channels 9. Fuel is introduced into the cylinders 10, such as heavy fuel oil, the fuel being combusted with combustion air in the cylinders 10. The exhaust gas formed during the combustion is directed to the turbine 4 along exhaust gas channel 11. The turbine 4 converts the energy of the exhaust gases into drive power for the compressor 3. As the exhaust gas traverses the turbine 4, it rotates the rotor of the turbine 4, the rotation being transmitted to the rotor of the compressor 3 via the drive shaft 5. As the load of the engine 1 is increased, the amount of fuel introduced in the cylinders 10 is increased, whereby also the amount of air needed for combustion is increased. In case the load is increased quickly, especially from idle or from low load levels, the amount of combustion air to be fed into the cylinders 10 can not be sufficiently increased due to the lag of the turbo compressor 2. Because of this the pressure is lowered in the flow plenum 6 and the fuel is combusted with too small an amount of air. The running speed of the engine 1 also slows down.

In order to improve the load acceptance of the engine 1 an arrangement is provided in connection therewith, whereby the pressure and amount of the air to be introduced into the engine 1 can be quickly increased. By means of the arrangement, both the compressor 3 and the flow plenum 6 are simultaneously fed pressurized additional air from a separate source of pressurized air 12. The arrangement comprises a main tube 13 being in flow connection with the source of pressurized air 12. The source of pressurized air can be, for example, the starting air tank of the engine 1 , having an air pressure of about 30 bar for air contained therein. The main tube 13 is divided into two feed tubes, the first feed tube 14 of which being connected to the compressor 3 and the second feed tube 15 being connected to the flow plenum 6. The main tube 13 is provided with a shut-off valve 16 by means which the flow of additional air from the source of pressurized air 12 to the feed tubes 14, 15 can be allowed or prevented.

The compressor 3 is provided with a so-called jet assist system for increasing the rotational speed of the rotor. Such a system comprises assist jets opening into the rotor chamber of the compressor 3 for blowing pressurized air towards the blades of the rotor. The air jets blown from the auxiliary jets collide with the blades and thus cause an additional force accelerating the rotational speed of the rotor. As the use of the jet assist system described above for increasing the rotational speed of the compressor of a turbocharged piston engine is known as such, the system is not described here in closer detail. The assist jets are in flow connection with the first feed tube 14. A pressure relief valve 17 is arranged in the first feed tube 14 for adjusting the pressure of the additional air to be introduced to the compressor 3 so as to be suitable, such as from 3 to 5 bar. There is also an adjustment valve 18 in the first feed tube 14, by means of which the mass flow of the additional air to be introduced to the compressor 3 is adjusted so as to be as desired. The pressure relief valve 17 is located prior to the adjustment valve 18 in the flow direction of the additional air.

A second feed tube 15 is in flow connection with the flow plenum 6 between the cylinders 10 of the engine 1 , via which plenum the pressurized additional air is introduced into the cylinders 10. In an embodiment according to vfigure 1 the second feed tube 15 is connected to the charge air receiver 8. The second feed tube 15 can alternatively have branches connected to the inlet channels 9 of the cylinders 10. There is a pressure relief valve 20 in the second feed tube 15 for adjusting the pressure of air introduced into the flow plenum 6. The pressure of the additional air to be introduced into the flow plenum 6 is adjusted to be from 4 to 10 bar by means of the pressure relief valve 20. In addition, there is an adjustment valve 19 in the second feed tube 15 for adjusting the mass flow of the additional air introduced into the flow plenum 6. The pressure relief valve 20 is located in the second feed tube 15 prior to the adjustment valve 19 in the flow direction of the additional air.

If it is desired to quickly increase the load of engine 1 , the amount of fuel introduced into the cylinders 10 is increased under control of the engine control system. The introduction of additional air into both the compressor 3 and the flow plenum 6 is simultaneously begun. The introduction of additional air is also controlled by the engine control system. The amount of introduced fuel is quickly increased and the amount of fuel corresponding to the desired load (such as 50 %) is typically achieved in less than 0.2 seconds. The amount of fuel injected into the cylinders 10 is then increased so as to meet a limit value of 110 % load. The shut- off valve 16 of the additional air system is open or it is opened, whereby air is allowed to flow from the source of pressurized air 12 via the main tube 13 to the first feed tube 14 and the second feed tube 15. The pressure of the additional air and the mass flow are adjusted by means of pressure relief valves 17, 20 and adjustment valves 18, 19 so as to be suitable. The adjustment valves 18, 19 are controlled by means of the engine control system defining the suitable amount of additional air to be fed on the basis of the pressure of the combustion air in the flow plenum 6. Additional air is introduced from the first feed tube 14 to the assist jets of the compressor, from which the jets of additional air collide with the blades of the rotor, thus increasing the rotational speed of the rotor. Due to the increased rotational speed the compressor 3 feeds more pressurized combustion air into the flow plenum 6. Additional air is also introduced from the second inlet tube 15 to the flow plenum 6. Additional air can also be introduced into the charge air receiver 8 as shown in figure 1 , or alternatively into the inlet channel 9 of each cylinder 10. If necessary, introduction of additional air into the inlet channels 9 can be timed by means of the control system and a valve located in the feed tube 15, near the inlet channel 9, so as to take place only when the inlet valves of the cylinders 10 are open.

Introduction of additional air into both the compressor 3 and the flow plenum 6 is especially used in situations in which the load of the engine is quickly increased at idle or low load levels, typically when the load of the engine 1 is less than 50 % of its maximum load. The rotational speed of the turbo compressor 2 is in this case about 15 - 70 % of its maximum rotational speed. Introduction of additional air into the compressor 3 and the flow plenum 6 increases the amount of combustion air in the cylinders 10, whereby the fuel is combusted more efficiently and the output of the engine 1 is increased faster. Further, the turbo lag of the turbo compressor 2 is decreased because the mass flow of the exhaust gas traversing the turbine 4 increases as a result of the inlet of additional air.

Typically the mass flow of the additional air introduced into the compressor 3 is 2-5 % of the mass flow of the combustion air introduced into the cylinders 10. Accordingly, the mass flow of the additional air introduced into the flow plenum 6 is at least about as large as the mass flow of the air introduced to the compressor 3, i.e. the mass flow is about 2-5 % of the mass flow of the combustion air introduced into the cylinders 10. The mass flow of the additional air introduced into the flow plenum 6 must not be too large so as to avoid stalling of the compressor 3. The mass flows of the additional air introduced into the compressor 3 and the flow plenum 6 can be kept constant during the whole load increase or their rates can be adjusted by means of adjustment valves 18, 19. Thus the mass flow of the additional air is at its largest at the rotational speed of the turbo compressor 2 corresponding to the idle speed of the engine 1 and the mass flow is decreased as the rotational speed of the turbo compressor 2 increases. When the engine 1 has reached the desired load level, introduction of additional air into the compressor 3 and the flow plenum 6 is stopped and the amount of injected fuel is decreased to the level corresponding to the desired load.

As has been mentioned in the above, the solution according to the invention can be used in, for example, strongly turbo-charged medium fast diesel engines, the maximum running speed of which is about 300-1200 rpm. In such engines the turbo lag is long when the load is increased at low levels, such as less then 50 %. Naturally, the solution according to the invention can also be used in otto cycle engines having a turbocharger and in other types of diesel engines. If necessary, the introduction of additional air can be arranged so that air is simultaneously introduced into both the charge air receiver 8 and the inlet channels 9. If necessary, additional air can be introduced only to the charge air receiver 8 with no introduction of additional air into the compressor 3.

Figure 2 illustrates another embodiment of the invention. In this embodiment pressurized additional air is introduced simultaneously into both the inlet channels 9 located between the charge air recceiver 8 and the cylinders 10 and the compressor 3. The inlet channels 9 are forked so that additional air is introduced into two different cylinders via one inlet channel 9. Going further towards the chargge air receiver 8 the inlet channel 9 is divided into two branch channels 9' being in flow connection with the combustion chambers 22 of different cylinders, preferably with the combustion chambers of adjacent cylinders. The first end of the inlet channel 9 opens into the combustion air feed tank 8 and the second ends open to the cylinder combustion chambers 22. A so-called distribution piece is located between the combustion air feed tank 8 and the engine cylinder head, into which distribution piece the inlet channel 9 is arranged. Additionally, a channel is arranged into the header for directing exhaust gases from the cylinder via cylinder head to the exhaust channel 11 and a channel for directing cylinder cooling water from the cylinder head to the cooling water systems. The distribution piece can, for example, like the one shown in US 5,213,068. Between the distribution piece and the combustion chamber 22 the inlet channel 9 is arranged in the cylinder head of the engine. The location of the branch of the inlet channel 9 is in the portion located in the cylinder head.

A feed tube 15 connected to a source 12 of pressurized air, such as the starting air tank of the engine 1 , is divided into branch tubes 23 being in connection with the inlet channels 9 for introducing pressurized additional air into inlet channels 9. The opening of the branch tube 23 in the inlet channel 9 opens into the flow direction of the combustion air. Thus, the jet of additional air being discharged from the branch tube 23 into the inlet channel 9 is parallel with the flow direction of the combustion air. The opening of the branch tube 23 in the inlet channel 9, i.e. the point of introduction of additional air in the inlet channel 9 is in the cylinder head or in the distribution piece in the vicinity of the cylinder head. The point of introduction of the additional air is prior to the branch in the inlet channel 9 in the flow direction of the combustion air, whereby the flow of additional air is divided into branch channels 9' leading into combustion chambers 22. Additional air is introduced into the inlet channel 9 only during the intake stroke of the cylinders 10 connected thereto. Each branch tube 23 has a valve 25, such as an electronically operated solenoid valve, by means of which the introduction of additional air into the inlet channel 9 is controlled. Valves 25 are controlled, i.e. opened and closed by means of the control system 21 on the basis of, for example, the rotational angle of the crankshaft of the engine. The rotational angle of the crankshaft is measured by means of a measuring device 24 and the measurement result is directed to the control system 21. The pressure of the additional air is adjusted by means of a pressure relief valve 20 so as to be between 4 - 30 bar. Typically the mass flow of the additional air introduced into the compressor 3 is 2-5% of the mass flow of the combustion air introduced into the cylinders 10. Correspondingly, the mass flow of the additional air introduced into the inlet channels 9 is at least about as large as the mass flow of the additional air introduced to the compressor, i.e. 2-5% of the total mass flow of combustion air. Otherwise, the embodiment of figure 2 corresponds to that of figure 1. The embodiment of figure 2 can be carried out so that additional air is introduced only into the inlet channels 9, with no introduction of additional air into the compressor 3. The inlet channels 9 can be arranged similarly to those in the embodiment of figure 1, whereby a separate inlet channel 9 leads to each cylinder from the charge air receiver 8.

Figure 3 illustrates a third embodiment of the invention. In this embodiment pressurized additional air is introduced simultaneously directly into both the combustion chambers 22 and the compressor 3. Additional air is introduced to the combustion chambers 22 by means of starting air valves 26 connected to the cylinders 10. The starting air valves 26 are connected to the source of pressurized air 12, i.e. the starting air tank of the engine, via branch tubes 23 and a feed tube 15. Normally, pressurized air is introduced via starting air valve 26 into the combustion chamber 22 during the combustion stroke during start-up of the engine. In the embodiment of this figure the starting air valves are also used for introducing additional air into the combustion chambers 22 during operation of the engine when the load is increased. The introduction of additional air into the combustion chamber 22 is adjusted by opening and closing the starting air valves 26 at the desired times. The starting air valves are controlled by means of the engine control system 21. Pressure relief valve 20 is used for adjusting the pressure of the additional air to between 15-30 bar. Typically the mass flow of the additional air introduced into the compressor 3 is 2-5% of the mass flow of the combustion air introduced into the cylinders 10. Correspondingly, the mass flow of the additional air introduced into the combustion chambers via the starting air valves is at least about as large as the mass flow of the additional air introduced to the compressor, i.e. 2-5% of the total mass flow of combustion air. The mass flow of the additional air is 2-8% of the mass flow of the combustion air directed into the cylinders.

In the embodiment of figure 3 additional air is introduced into the combustion chamber 22 during the inlet stroke. Introduction of additional air is commenced not earlier than at the start of the inlet stroke, and ended during compression stroke at the latest, when the pressure in the combustion chamber has risen to the same level as that of the additional air. A one-way valve is arranged in the branch tube 23 for allowing flow therethrough in one direction only, i.e. from the source 12 of pressurized air towards the combustion chamber 22. Additional air can alternatively be introduced into the combustion chamber during the scavenging phase of the cylinder, i.e. when both the inlet and outlet valve are simultaneously open. Otherwise, the embodiment of figure 3 corresponds to that of figure 2.

In all above-mentioned embodiments additional air is introduced into desired objects when the load of the engine is increased. The engine control system 21 detects the changes of load from, for example, the changes of pressure of the charge air receiver 8 and controls the introduction of additional air as desired. The introduction of additional air is started in situations, for example, in which the change of load exceeds a certain percentage of the current engine load.

Claims

CLAIMS:

1. A method of increasing load-bearing capacity of a piston engine (1) having a turbo compressor (2) when increasing the load, in which method - combustion air is introduced into the compressor (3),

- combustion air is pressurized in a compressor (3),

- pressurized combustion air is directed to the combustion chambers (22) of the cylinders (10) via inlet channels (9), and

- fuel is combusted in the combustion chambers (22) by means of combustion air, characterized in that pressurized additional air is simultaneously introduced into the compressor (3) and the inlet channels (9) or into the compressor (3) and the combustion chambers (22).

2. A method according to claim 1 , characterized in that additional air is introduced into the inlet channel (9) or the combustion chamber (22) during the inlet stroke.

3. A method according to claim 1 or 2, characterized in that additional air is introduced into the combustion chamber (22) during the scavenging phase of the cylinder.

4. A method according to any of previous claims 1-3, characterized in that additional air is introduced into the combustion chamber (22) via a starting air valve (26) in connection with the cylinder.

5. A method according to claim 1 or 2, characterized in that the inlet channel (9) is divided into two branch channels (9¹) being in flow connection with different combustion chambers (22), and that additional air is introduced into the inlet channel (9) at a place prior to the branching point in the flow direction of the flow gas.

6. A method according to any of the above claims, characterized in that additional air is introduced at a pressure of 4-30 bar.

7. An arrangement for increasing load-bearing capacity of a piston engine (1) having a turbo compressor (2) when increasing the load, the arrangement comprising

- a compressor (3) for pressurizing combustion air to be introduced into cylinders (10) of the engine (1), and

- inlet channels (9) being in connection with combustion chambers (22) of the cylinders (10) for introducing pressurized combustion air into the combustion chambers (22), characterized in that the arrangement comprises means (14) for introducing pressurized additional air into the compressor (3) and feed means (23, 25, 26) for introducing pressurized additional air into the inlet channels (9) or the combustion chambers (22).

8. An arrangement according to claim 7, characterized in that the inlet channel (9) is divided into two branch channels (9¹) being in flow connection with different combustion chambers (22).

9. An arrangement according to claim 8, characterized in that the additional air feed means comprise a branch tube (23) opening into the inlet channel (9), the opening of the branch tube being prior to the branching point of the inlet channel (9) in the flow direction of the combustion air.

10. An arrangement according to claim 7, characterized in that the additional air feed means comprise a starting air valve (26) being in connection with the cylinder (10).