DK177713B1

DK177713B1 - Combustion engine, and a method for supplying such a gas-fueled engine

Info

Publication number: DK177713B1
Application number: DK201370268A
Authority: DK
Inventors: Stig Poulsen
Original assignee: Man Diesel & Turbo Deutschland
Priority date: 2013-05-16
Filing date: 2013-05-16
Publication date: 2014-03-31
Also published as: JP5855687B2; JP2014224524A; CN104165103A; CN104165103B; KR20140135614A; KR101622754B1; DK201370268A

Abstract

An internal combustion engine has at least one second fuel storage for liquefied gas fuel, and a fuel supply system with a gas fuel pump for providing gas at a pressure of at least 200 bar, and an injection system for injecting gaseous gas fuel. In a first heating medium flow path an outlet line for boil-off gas from the second fuel storage is connected to a heat exchanger via a compressor device, which first heating medium flow path has an outlet on the heat exchanger connected with an inlet line extending down through an upper portion of the second fuel storage to at least one expansion nozzle device located in the at least one second fuel storage.

Description

DK 177713 B1 i

The present invention relates to an internal combustion engine having at least a first fuel storage for a pilot fuel, and at least one second fuel storage for liquefied gas fuel, and a fuel supply system with a pilot fuel pump and a gas fuel pump for providing gas at a pressure of at 5 least 200 bar, and an injection system for injecting pilot fuel and injecting gaseous gas fuel, which gas fuel pump is located at least partially in the least one second fuel storage and is in connection with the injection system through a high-pressure gas conduit, the high-pressure gas conduit having at least one heat exchanger for evaporating the liquefied gas 10 fuel to gaseous gas fuel.

DK PA 2009 00434 discloses such an internal combustion engine where the gas fuel pump delivers liquefied gas fuel, and the heat exchanger is supplied with heating medium in form of ambient air, and downstream of the heat exchanger the cooled air is delivered to the 15 compressor inlet of a turbocharger on the engine. As an alternative embodiment it is suggested that the heating medium is taken from the air outlet of the compressor where the air is warmer due to the compression.

EP 1 990 272 B1 describes a fuel gas supply system to an inter-20 nal combustion engine in an LNG carrier vessel having LNG storage tanks. A first pump is installed in the LNG storage tank or just outside the tank and performs an initial compression of the LNG to a pressure of about 27 bar at the pump outlet. The LNG then passes a heat exchanger, and at the outlet thereof the LNG has a temperature of about -100°C 25 and a pressure of about 27 bar. Downstream of the heat exchanger the LNG is pressurized in a second pump to a pressure of about 250 bar and is passed through a second heat exchanger and to the injection system of the engine as liquid LNG. The first heat exchanger is supplied with boil-off gas taken out from an upper portion of the second fuel storage 30 and returned through one side at a lower portion of the second fuel storage. A compressor and a cooler are located in the boil-off gas line upstream of the heat exchanger. Downstream of the heat exchanger the boil-off gas is liquid. A pressure control valve in the line expands the pressure in the line to correspond to the pressure in the second fuel DK 177713 B1 2 storage plus the pressure head of the liquid column of LNG in the storage.

It is an object of the present invention to improve the energy utilization of the internal combustion engine in operation.

5 With a view to this the internal combustion engine according to the present invention is characterized in that in a first heating medium flow path an outlet line for boil-off gas from the second fuel storage is connected to the heat exchanger via a compressor device, which first heating medium flow path has an outlet on the heat exchanger con-10 nected with an inlet line extending down through an upper portion of the second fuel storage to at least one expansion nozzle device located in the at least one second fuel storage.

The high-pressure gas conduit delivers liquid LNG at a pressure above 200 bar to the heat exchanger, and boil-off gas is used as a first 15 heating medium to warm the gas fuel. By warming the gas fuel the boil-off gas itself is cooled, and as it has been compressed upstream of the heat exchanger possible to expand the boil-off gas and thus cool it even more. The boil-off gas exiting the heat exchanger is delivered via the inlet line to the second fuel storage, and the expansion to the gas pres-20 sure within the second fuel storage causes cooling of the boil-off gas within the second fuel storage.

In an embodiment the at least one heat exchanger has at least a second heating medium flow path connected to a liquid source, such as a fluid circuit in an air conditioning system in a ship, a water cooler in a 25 ship, a cooling fluid circuit in a freezer, or an oil cooler or an inlet air cooler of the internal combustion engine. The liquid source is delivering heat to the gas fuel and is simultaneously cooled itself, thus avoiding cooling by other means that otherwise typically are consuming electricity.

30 In an embodiment the at least one heat exchanger has at least a third heating medium flow path connected to a gaseous source, such as an inlet air flow path to the internal combustion engine. The third medium flow path can be applied without any second medium flow path.

The gaseous source is delivering heat to the gas fuel and is simultane- DK 177713 B1 3 ously cooled itself, thus obtaining a cooler state advantageously lowering the specific fuel consumption of the engine (fuel mass spent per produced kWh), or just avoiding cooling by other means that otherwise typically are consuming electricity.

5 In embodiment combining the advantages of the two previous embodiments the at least one heat exchanger has at least a second heating medium flow path connected to a liquid source, and at least a third heating medium flow path connected to a gaseous source.

In an embodiment the gas fuel pump located in the second fuel 10 gas storage has two stages, where the first stage is a primer pump feeding stage and the second stage is a centrifugal pump pressure stage. The advantage of the piston pump feeding stage is to allow the centrifugal pump to be mounted at a distance from the inner walls of the second fuel gas storage and yet be able to pump virtually all liquid LNG out of 15 the storage, because the piston pump feeding stage can draw LNG from the bottom of the storage via a suction line having an inlet opening close to the bottom of the storage.

In another aspect the present invention relates to a method of supplying an internal combustion engine with gaseous gas fuel in an in-20 jection system at a pressure of at least 200 bar, said internal combustion engine having at least a first fuel storage for a pilot fuel, and at least one second fuel storage for liquefied gas fuel, the injection system injecting pilot fuel and injecting gaseous gas fuel, which gas fuel pump is located at least partially in the least one second fuel storage and is in connection 25 with the injection system through a high-pressure gas conduit, the high-pressure gas conduit having at least one heat exchanger evaporating the liquefied gas fuel to gaseous gas fuel.

According to the present invention the boil-off gas in a first heating medium flow path from the second fuel storage is compressed to 30 a set pressure in a compressor device and is delivered to the heat exchanger for heating the gas fuel; and at least one expansion nozzle device located in the at least one second fuel storage is supplied with boil-off gas from the heat exchanger and expands this boil-off gas into the boil-off gas in the upper portion of the second fuel storage. The use of DK 177713 B1 4 boil-off gas to heat the gas fuel saves energy, and separate energy consumption for liquefying the boil-off gas is saved. The expansion of the cooled boil-off gas into the gas in the upper portion of the second fuel storage provides an efficient further cooling of the boil-offgas.

5 The set pressure of the boil-off gas is as an example set in the range from 2 bar to 5 bar, such as at about 3 bar, which allows the boil-off gas to be at a temperature approximately within -153°C to -138°C at the set pressure and cool therefrom to the temperature of -163°C when expanded to a pressure of 1 bar. Larger set pressures are also possible, 10 but the pressure should not be larger than needed because the compression consumes energy.

In some cases it may be an advantage if a flow control valve in a bypass line opens for bypass of boil-off gas from the inlet line to the outlet line when the temperature of the boil-off gas in the inlet line is 15 higher than a set temperature. If the gas fuel consumption is low, it may be an advantage to bypass the second fuel storage and let the boil-off gas circulate from the inlet line to the outlet line, and this can be controlled by the flow control valve.

Examples of embodiments of the invention are described in fur-20 ther detail in the following with reference to the highly schematic drawings, on which

Fig. 1 illustrates an LNG carrier with an internal combustion engine according to the present invention,

Fig. 2 illustrates an end outline of the engine in Fig. 1, 25 Fig. 3 illustrates a fuel supply and injection system of the engine in Fig. 2,

Fig. 4 illustrates in more detail the system in Fig. 3 viewed for a single cylinder on the engine,

Figs. 5 illustrates a Reynolds diagram for methane, and 30 Fig. 6 illustrates a second fuel storage and a heat exchanger of the internal combustion engine in Fig. 2.

An LNG carrier in Fig. 1 has a main propulsion engine in the engine room 1 located below a superstructure 2. The engine drives a propeller 3 for propulsion of the vessel. The LNG carrier has a plurality, in DK 177713 B1 5 the illustrated embodiment four, LNG storage tanks, each being a second fuel storage 4 for liquefied gas fuel to the internal combustion engine. Although the purpose of the LNG carrier is to transport LNG from a production site to a utilization site for LNG, the LNG storage tanks also acts 5 as fuel storage for the internal combustion engine during the transport.

The vessel need not be an LNG carrier, but can also be a vessel of any another type, where the second fuel storage 4 is serving only as a fuel storage, independent from the cargo areas of the vessel. Examples of such other types of vessels are RoRo-vessels, container vessels, tank-10 ers, car carriers, bulk-carriers, product tankers, shuttle carriers, etc.

In Fig. 2 the main propulsion engine is shown in more detail as an internal combustion engine. The internal combustion engine is piston engine, and preferably a two-stroke crosshead internal combustion engine, generally designated 5. The engine can have from 4 to 15 cylin-15 ders. The engine can e.g. be of the make MAN Diesel & Turbo and the type ME or MC, or of the make Wårtsilå, or of the make Mitsubishi. The cylinders can have a bore in the range of e.g. 25 to 120 cm, preferably from 60 to 120 cm. The two-stroke crosshead internal combustion engines used as main propulsion engines typically have a speed indicated 20 as rpm in the range from 60 to 200 rpm. These engines are named low speed engines. The low speed is required for transferring the propulsion thrust via the propeller to the water in the wake of the vessel. In order to transfer the thrust to the water the propeller needs a large area, and thus a large diameter. As cavitation at the propeller is undesired it is 25 necessary to limit the speed of the propulsion engine to the low speed range, such as from 60 to 200 rpm.

The engine 5 has a plurality of cylinders, each having a reciprocating piston in the cylinder. In the two-stroke crosshead internal combustion engines the cylinders are typically of the uniflow scavenging type 30 where an exhaust valve 6 is located on top of the cylinder and scavenge air ports (not shown) are located at the lower end of the cylinder. The exhaust gas from the cylinder is passed to an exhaust gas receiver 7 and onwards to the turbine part of a turbocharger 8, the compressor part of which supplies compressed inlet air to an inlet air chamber 9. From his DK 177713 B1 6 chamber the inlet air may pass through an inlet air cooler 10 to an area surrounding the scavenge air ports in the cylinders.

The engine has an injection system for injecting pilot fuel and for injecting gaseous fuel, and for safety reasons the system for injecting 5 gaseous fuel is provided with an air intake system and an inert gas system. The air intake system is provided in a pipe 15 surrounding the gas fuel pipe 16, and the annular space between the two pipes allows for monitoring for gas leaks from the inner pipe. The air intake is effected at 11, and if the system is operating normally the air outlet is effected at 10 12. A pair of hydrocarbon detectors 13 is placed downstream of the en gine in the conduit leading to air outlet 12. A source of pressurized inert gas 14 is connected to gas fuel pipe 16, and at shutdown of the engine the inert gas is supplied to the gas fuel pipe for purging the same for gas.

15 A first fuel storage 17 supplies pilot fuel to fuel injectors 18 on each cylinder 19 of the internal combustion engine. The pilot fuel is supplied at a pressure of e.g. 300 bar and is used to initiate each fuel injection sequence in the cylinder. The pilot fuel can be fuel oil and is able to self-ignite in the combustion chamber at the compression pressure 20 available in the combustion chamber at the end of the combustion stroke. Gas injectors 20 on each cylinder 19 are provided with control oil from a pump 21 when the required pilot oil pressure is detected, and the control oil pressure is required at the gas injectors 20 in order to inject gas. The control oil ensures that gas is not injected into the cylinder if 25 the pilot oil fails to inject. Gas injectors 20 are also supplied with pressurized sealing oil via sealing oil line 22. The sealing oil prevets gas from escaping from the gas injector otherwise than through the injection nozzle.

Gas from the second fuel storage 4 is supplied to gas fuel pipe 30 16 and flows to an accumulator 23 and a control valve 24 opens for gas to the injectors 20 when gas injection is to take place. There may be a common rail pipe between the gas fuel pipe 16 and the injectors 20 and in that case it may be possible to dispense with accumulator 23.

A gas fuel pump 25 at the second fuel storage 4 (Fig. 6) is DK 177713 B1 7 mounted through the upper portion of the storage. The pump may be a single stage pump, but preferably it has at least two stages where the first stage is a primer pump, such as a piston pump, and the second stage is a centrifugal pump. The centrifugal pump may have a plurality 5 of pump stages. The pump is a cryogenic pump, and examples are model TC-34 from Cryogenic Industries, CA, USA, and high pressure centrifugal LNG pumps as disclosed in Hydrocarbon Processing, July 2011, pages 37-41. The gas fuel pump 25 delivers the liquid LNG gas fuel to a high pressure gas conduit 26 at a pressure of at least 200 bar, 10 such as a pressure in the range of 200 to 500 bar, and preferably at about 300 bar.

The high pressure gas conduit 26 for gas fuel is connected to a heat exchanger 27 and to a second heat exchanger 28 and continues into the gas fuel pipe 16. Heat exchanger 27 has a first heating medium 15 flow path comprising an outlet line 29 for boil-offgas from the second fuel storage 4. The outlet line 29 extends from the upper portion of the second fuel storage to a compressor 30, and from the compressor to the heat exchanger 27. Outlet line 29 is connected to the heat exchanger in such a manner that the boil-off gas is in counterflow with the gas fuel in 20 high pressure gas conduit 26. From an outlet on the heat exchanger 27 the first heating medium flow path has an inlet line 31 extending down through the upper portion of the second fuel storage 4 to an expansion nozzle 32 located in the uppermost portion of the second fuel storage 4 in an area that is normally filled with boil-offgas.

25 The first heating medium flow path also has a bypass line 33 with a flow control valve 34, which is normally closed. If the flow of gas fuel through heat exchanger 26 is so low that the boil-off gas may be reused to heat the gas fuel, then control valve 34 may open for recirculation of the boil-offgas from outlet line 29 to inlet line 31.

30 The second heat exchanger has a second heating medium flow path 35 connected to a liquid source 36, such as the coolant fluid circuit in an air conditioning unit in the ship. The second heat exchanger has a third heating medium flow path 37 connected to a gaseous source 38, such as an inlet air flow path to the internal combustion engine. The DK 177713 B1 8 gaseous source may thus be part of the inlet air cooler 10. When the gas fuel flows out of heat exchanger 28 it has been heated to gaseous state and a temperature in the range of 30 to 60°C, preferably 45°C.

An example of the process is illustrated in the Reynolds chart in 5 Fig. 5. The chart illustrates on a logaritmic scale the pressure in bar, and the enthalpy in kJ/kg of methane, and temparature curves are shown.

An inverted U-curve indicates the area where the methane is partly gaseous and partly liquid. The temperature in the second fuel storage 4 is about -163°C and the pressure is about 1 bar. Depending on where 10 the second fuel storage 4 is located in the vessel in relation to the compressor 30 the outlet line 29 may have considerable length, such as from a few m to 400 m. In case the outlet line 29 has considerable length, as may be the case when the compressor is located near the engine room and the second fuel storage is in the forward end of the vessel, the boil-15 off gas may be warmed somewhat when it arrives at the compressor. In Fig. 5 the boil-off gas is assumed to have a temperature of -100°C at the compressor inlet, indicated at point 40. The compressor increases the pressure of the boil-off gas, such as to a pressure of 3 bar, indicated at point 41. In the heat exchanger 27 the boil-offgas is cooled, which is 20 indicated by the horizontal line at 3 bar pressure. If the cooling does not liquify the boil-off gas and it is expanded to a pressure of 1 bar, the boil-off gas may have a temperature of -163°C as indicated at point 42. If the cooling does fully liquify the boil-off gas and it is expanded to a pressure of 1 bar, the boil-off gas may have a temperature of -163°C as in-25 dicated at point 43. If the cooling progresses to a temperature of about -150°C, and the boil-off gas is expanded to a pressure of 1 bar, the boil-off gas may have a temperature of -163°C as indicated at point 44. The gas fuel pump 25 pressurerize the liquid gas fuel from the pressure of 1 bar at -163°C, indicated at point 45, to a pressure of e.g. 300 bar at a 30 temperature of about -150°C, indicated at point 46. In the heat exchanger 27 the gas fuel may be heated to a temperature of e.g. -50°C, indicated at point 47, and in the second heat exchanger 28 the gas fuel may be heated to a temperature of e.g. 45°C, indicated at point 48.

The first fuel storage, the pilot fuel pump and the injection sys- DK 177713 B1 9 tem for injecting pilot fuel serves to initiate combustion within the combustion chamber so that injected gaseous fuel combusts when injected.

The pilot fuel has the function of being ignition aid for the gaseous fuel.

It is possible, according to an aspect of the present invention, to replace 5 the first fuel storage, the pilot fuel pump and the injection system for injecting pilot fuel with another ignition aid, such as electrical spark ignition supplied by an electrical source and controlled by a control unit and an electrical switching device. In this case, an internal combustion engine has at least one second fuel storage for liquefied gas fuel, and a fuel 10 supply system with a gas fuel pump for providing gas at a pressure of at least 200 bar, an injection system for injecting gaseous gas fuel, and a gas ignition aid. The gas fuel pump is located at least partially in the least one second fuel storage and is in connection with the injection system through a high-pressure gas conduit. The high-pressure gas conduit 15 has at least one heat exchanger for evaporating the liquefied gas fuel to gaseous gas fuel. In a first heating medium flow path an outlet line for boil-off gas from the second fuel storage is connected to the heat exchanger via a compressor device, which first heating medium flow path has an outlet on the heat exchanger connected with an inlet line extend-20 ing down through an upper portion of the second fuel storage to at least one expansion nozzle device located in the at least one second fuel storage.

Details of the various embodiments described can be combined into further embodiments within the scope of the claims. Heat exchang-25 ers 27 and 28 may e.g. be combined into a single heat exchanger, or heat exchanger 28 may be sub-divided into several heat exchangers.

Claims

An internal combustion engine having at least one pilot fuel storage tank and at least a second liquid gas fuel storage facility and a fuel supply system having a pilot fuel pump and gas fuel pump for supplying gas at a pressure of at least 200 bar and an injection system for injection of pilot fuel and injection of gaseous gas fuel, said gas fuel pump being located at least partially in the at least one other fuel storage and connected to the injection system via a high pressure gas line, said high pressure gas line having at least one heat exchanger for evaporating the liquid gas fuel for gaseous gas fuel; in that in a first heating medium flow path, a discharge line for boiled gas from the second fuel storage is connected to the heat exchanger via a compressor device, said first heating medium flow path having an outlet on the heat exchanger t with an inlet line extending through an upper portion of the second fuel stock to at least one expansion nozzle device located in the at least one other fuel stock.

Internal combustion engine according to claim 1, characterized in that the at least one heat exchanger has at least one other heating medium flow path connected to a liquid source, such as a liquid circuit in an air conditioning system of a ship.

Combustion engine according to claim 1, characterized in that the at least one heat exchanger has at least a third heating medium flow path connected to a gaseous source, such as an intake air flow path for an internal combustion engine.

Combustion engine according to claim 1, characterized in that the at least one heat exchanger has at least one second heating medium flow path connected to a liquid source, such as a liquid circuit in an air conditioning system in a ship, and at least a third heating medium flow path connected to a gaseous source such as an intake air flow path for an internal combustion engine.

An internal combustion engine according to one or more of claims 1-4, characterized in that the gas fuel pump has two stages, the first stage being a dilute-pump feed stage and the second stage being a centrifugal pump pressure stage.

Internal combustion engine according to one or more of claims 1 to 5, characterized in that the internal combustion engine is a two-stroke cross-head, piston engine.

Internal combustion engine according to one or more of claims 1-6, characterized in that an bypass line extends from the inlet line to the outlet line and is provided with a flow control valve.

A method of supplying a combustion engine with gaseous gas fuel in an injection system at a pressure of at least 200 bar, the combustion engine having at least a first fuel fuel storage tank and at least a second liquid gas fuel storage tank, where the injection system gas injection fuel injector and pilot fuel injection system are injected. and wherein a gas fuel pump is located at least partially in the at least one other fuel storage and is connected to the injection system via a high pressure gas line, said high pressure gas line having at least one heat exchanger for evaporating the liquid gas fuel to gaseous gas fuel, characterized by boiling gas in a first heating medium flow path from the second fuel storage is compressed to a predetermined pressure in a compressor device and supplied to the gas exchanger heat exchanger at least one expansion nozzle device located in the at least one other 25 fuel storage, the boiler is supplied with boiled gas and expands this boiled gas into the boiled gas in the upper section of the second fuel storage.

Method according to claim 8, characterized in that the predetermined pressure is in the range of 2 bar to 5 bar.

Method according to claim 8 or 9, characterized in that a flow control valve in an inlet line opens for circulation of boiled gas from the inlet line to the outlet line when the temperature of the boiled gas in the inlet line is higher than a predetermined temperature. 35