DK177623B1

DK177623B1 - An internal combustion engine with variable fuel gas injection pressure and duration

Info

Publication number: DK177623B1
Application number: DKPA201270379A
Authority: DK
Inventors: Anders Andreasen
Original assignee: Man Diesel & Turbo Deutschland
Priority date: 2012-06-29
Filing date: 2012-06-29
Publication date: 2013-12-16
Also published as: JP5503059B2; CN103511088A; KR20140002555A; KR101429186B1; JP2014055587A; CN103511088B

Abstract

An internal combustion engine, such as a two-stroke crosshead Diesel engine, comprising a fuel gas supply system and cylinders provided with fuel gas injectors for injecting fuel gas directly into combustion chambers in the cylinders, and an engine control unit controlling fuel gas injection into the cylinders according to an engine load index, where the fuel gas injection into the cylinders is controlled by adjusting a fuel gas injection length, wherein the fuel gas injection into the cylinders is controlled by adjusting the fuel gas injection length and a fuel gas injection pressure, and that the engine control unit accommodate the fuel gas injection to abrupt changes in the engine load by adjusting the fuel gas injection length, and that the fuel injection length and the fuel gas injection pressure is dependent on the engine load index, and the engine control unit adjusts the fuel gas injection pressure and counter adjust the fuel gas injection length to comply with the engine load index.

Description

DK 177623 B1

The present invention relates to internal combustion engine, such as a two-stroke crosshead Diesel engine, comprising a fuel gas supply system and cylinders provided with fuel gas injectors for injecting fuel gas directly into combustion chambers in the cylinders, and an engine control unit con-5 trolling fuel gas injection into the cylinders according to an engine load index, where the fuel gas injection into the cylinders is controlled by adjusting the duration of a fuel gas injection length.

There is an increasing interest in lowering carbon dioxide, nitric oxide and sulphur emissions from the operation of internal combustions engines 10 and hence alternatives to the conventional fuel oil have been investigated. Operation of large two-stroke diesel engines such as a MAN Diesel 12K80MC-GI-S has shown that operation with fuel gas as primary fuel may be both safe, reliable and environmentally desirable as to emissions compared to conventional fuel oil. As regards large two-stroke diesel engines for the mari-15 time market, engines using fuel gas are becoming increasingly interesting, especially for liquid natural gas carriers (LNG carriers), wherein boil-off gas from the gas tanks must be handled during transportation.

Usually the engine load of such internal combustion engines is controlled by adjusting the fuel gas injection length by ordering a shorter fuel 20 injection length for decreasing the engine load or a longer injection length for increasing the engine load by ordering a longer fuel injection length. This is based on the assumption that there exists a simple linear relation between the engine load and the fuel injection length, and the fuel consumption is usually optimized for high engine loads.

25 US 5,533,492 discloses a method of compensating for variations in the pressure at which fuel gas is provided to the cylinders of an internal combustion engine by a low pressure fuel gas supply system. The duration of fuel gas injections into the cylinders is adjusted in dependence of a rolling average of measured variations of the fuel gas pressure.

30 Also, US-A-2008/0103676 discloses an internal combustion engine of the diesel type comprising a fuel gas supply system and cylinders provided with fuel gas injectors for injecting fuel gas directly into combustion chambers in the cylinders. An engine control unit may use an engine map and is controlling fuel gas injection into the cylinders. The fuel gas injection is con-35 trolled by adjusting fuel gas duration of injection and a fuel gas injection. The DK 177623 B1 2 fuel gas injection is adjusted according to engine load. It is furthermore suggested to change the pulse width of the fuel gas injection and also changing the pressure of the fuel gas injection, and that the change of injection pressure is coordinated with adjustments in fuel gas injection pulse width in order 5 to counteract for the higher pressure. US-A-2008/0103676, however, is silent about operation when an abrupt increase in the required engine power output occurs.

It is a purpose of the present invention to provide an internal combustion engine with fuel gas combustion having a more optimum operation at 10 all engine loads.

With a view to this the present invention is characterized in that the fuel gas injection into the cylinders is controlled by adjusting the duration of the fuel gas injection length and a fuel gas injection pressure, and that the engine control unit accommodate the fuel gas injection to abrupt changes in 15 the engine load by adjusting the duration of the fuel gas injection length, and that the duration of the fuel injection length and the fuel gas injection pressure is dependent on the engine load index, where the engine control unit first adjusts the duration of the fuel gas injection length and secondly adjusts the fuel gas injection pressure and counter adjusts the duration of the fuel 20 gas injection length to comply with the engine load index.

By adjusting the fuel gas injection length independently of the engine load index it is possible to immediately adjust the amount of energy injected into the cylinders in order to accommodate the fuel gas injection to changes in the engine load. This is advantageous for marine diesel engines 25 where e.g. manoeuvring, waves, sea current and wind blasts acting on a ship may result in sudden changes in the engine load. The provision of a predetermined engine load index defining the fuel gas injection length and the fuel gas injection pressure for operation at different engine loads along the propeller curve provides for at substantial improvement in the engine efficiency.

30 Since it is possible to change the ordered fuel gas injection length faster than the fuel gas injection pressure, the regulation of the engine load to comply with sudden changes in the engine load is achieved by first adjusting the fuel gas injection length, and then secondly the fuel gas injection pressure is adjusted while counter adjusting the fuel gas injection length until 35 both comply with the predetermined engine load index. This makes the regu- DK 177623 B1 3 lation of the engine very flexible and very efficient at a wider range of engine loads, because regulation of the fuel gas injection pressure makes it possible to optimize both fuel gas injection length and fuel gas injection pressure at a broad range of engine loads along the propeller curve.

5 The flexible regulation of the engine load is also an advantage when the fuel gas injection pressure may only be changed very slowly by the fuel gas supply system. If a significant change in the desired engine load is required, the desired engine load may readily be achieved by adjusting the duration of the fuel gas injection length at the expense of a less efficient operat-10 ing engine until the fuel gas supply system can provide the fuel gas injection pressure according to the engine load index. When the fuel gas injection pressure approaches the level according to the engine load index, the duration of the fuel gas injection length is counter adjusted until the desired operating point according to the engine load index is achieved.

15 In a preferred embodiment the cylinders are provided with fuel oil in jectors injecting fuel oil directly into the combustions chambers in the cylinder and a fuel oil supply system.

In a preferred embodiment of the invention the fuel gas supply system is a common rail fuel gas supply system.

20 In a preferred embodiment of the invention, the fuel gas injection pressure is in the range of 150 bar to 300 bar. Hence the fuel gas supply system is a high pressure fuel gas supply system from which an adjustment of the fuel injection pressure may be ordered by the engine control unit.

In a preferred embodiment of the invention at 100 % engine load 25 the engine speed is in the range from 45 rpm to 175 rpm.

In a further embodiment of the invention the fuel gas supply system providing fuel gas to the cylinders is connected to a liquid natural gas tank of a liquid natural gas carrier. Evidently, the fuel gas supply system may be connected to a dedicated fuel gas tank, i.e. with a separation of the cargo 30 and the fuel gas.

Examples of the present invention and embodiments thereof are in the following described in more detail with reference to the highly schematic drawing, in which

Fig. 1 is a general view of an engine according to the present inven- 35 tion, DK 177623 B1 4

Fig. 2 is an example of an engine a combined fuel oil and fuel gas operating mode according to a preferred embodiment of the invention.

An internal combustion engine 1 according to a preferred embodiment of the present invention may be a two-stroke crosshead diesel engine 5 as illustrated in Fig. 1. Such an engine 1 can e.g. be of the make MAN Diesel and the type MC or ME, or of the make Wårtsilå of the type Sulzer RT-flex or Sulzer RTA, or of the make Mitsubishi Heavy Industries. An engine of this type is a large engine typically used as a main engine in a ship or as a stationary engine in a power plant. The cylinders can e.g. have a bore in the 10 range from 25 cm to 120 cm, and the engine can e.g. have a power in the range from 3000 kW to 120.000 kW. The engine speed is typically in the range from 40 rpm to 250 rpm. The compression ignition internal combustion engines according to the present invention are typically capable of using heavy fuel oil as primary fuel.

15 The engine 1 of Fig. 1 has a plurality of cylinders with a cylinder liner 2 mounted in a cylinder section 3 of an engine frame 4. An exhaust valve housing 5 is mounted in a cylinder cover 6 and an exhaust gas duct 7 extends from the individual cylinder to an exhaust gas receiver 8 common to several or all cylinders. In the exhaust gas receiver pressure variations 20 caused by the exhaust gas pulses emitted from the exhaust gas ducts are equalized to a more even pressure, and one or more turbochargers 9 receive exhaust gas from the exhaust gas receiver 8 and deliver compressed air to a scavenge air system comprising at scavenge air receiver 10 which, like the exhaust gas receiver, is an elongated pressure vessel.

25 In the individual cylinder a piston is mounted on a piston rod that is connected with a crank pin on a crankshaft via a crosshead and a connecting rod (not illustrated). A fuel injector injects the fuel into a combustion chamber. When the injected fuel is fuel oil it auto-ignites because of the high temperature in the air above the piston. The high temperature is present because 30 the piston has compressed the inlet air during the upward compression stroke.

It is preferred that the present invention is implemented in a marine diesel engine with a dual fuel supply system, and in the following the invention is described by such example, but of course the invention may be im-35 plemented as a single fuel system. The engine is an electronically control en- DK 177623 B1 5 gine, which electronic control of both oil and gas injection, ensuring that the fuel injection and combustion is optimized. Further it is based on a high pressure gas injection principle with pilot fuel oil injection for igniting the fuel gas combustion. With this principle the diesel combustion process can be fully 5 utilized and thereby the same high thermal efficiency as for fuel oil combustion can be obtained. In Fig. 2 cylinder section 3 is illustrated with only a single cylinder 11, but the engine has a plurality of cylinders such as from 4 to 15 cylinders. As schematically shown in Fig. 2 the internal combustion engine 1 comprises a fuel oil supply system 23 and a fuel gas supply system 19 pro-10 viding a fuel oil injection system 20 and fuel gas injection system 30 with fuel oil and fuel gas to be provided into the combustion chambers of the cylinders 11. In the present example the fuel oil injection system 20 and the fuel gas injection system 30 controls injection of fuel oil and fuel gas into the combustion chambers of the cylinders 11, respectively. The general principle of the 15 fuel injection systems 20, 30 is that each cylinder 11 is associated with a cylinder control unit 12 controlling one or more fuel dosing devices 15, 16 such as fuel pumps or valves connected to fuel injectors 13, 14 in the cylinder cover 6. The number of injectors 13, 14 per cylinder depends on the power of the cylinder 11. In a preferred embodiment each cylinder comprises at least a 20 fuel oil injector 13 and a fuel gas injector 14. In smaller engines a single injector per fuel type may be sufficient to inject the amount of fuel required for one combustion process, whereas in larger, more powerful engines two or three injectors for each fuel type may be required. When several injectors are provided per cylinder 11, there may be one fuel dosing device 15, 16 per in-25 jector 13, 14. The engine control unit 12 of the fuel injection system 20, 30 are in turn controlled by an engine control unit 17 in communication with the bridge of a vessel.

It is preferred that the fuel gas supply system 19 is connected to a liquid natural gas (LNG) tank 18 of a LNG carrier vessel operated at sea. The 30 LNG tank of an LNG carrier vessel is kept at low temperatures, but is inevitably heated as external heat from the seawater and atmosphere is transferred through the insulation of tanks. By the intrusion of the external heat, a portion of the LNG is gasified, i.e. boiled off, and the tank pressure gradually increases. In order to keep the tank pressure at an acceptable level a relique-35 faction system (not shown) may be used to reliquefy boil-offgas. Alternative- DK 177623 B1 6 ly, or in combination with the reliquefaction system, a boil-off gas compressor may provide high-pressure boil-off gas when such is ordered by the fuel gas injection system 30. At the cylinders a fuel gas dosing device 16 controlled by the cylinder control unit 12 effect the timing and opening of the fuel gas in-5 jector 14. The fuel gas is preferably provided to the fuel gas injection system by a double-walled gas supply piping 26 of the common rail design, where a valve of the fuel gas injector 14 is controlled by an auxiliary control oil system. This, in principle, consists of a hydraulic control oil system and an electronic gas injection valve, supplying high-pressure control oil to the gas injec-10 tor 14, thereby controlling the timing and opening of a gas valve of the gas injector 14. The fuel gas supply system is a high pressure fuel gas supply system. An efficient gas injection is obtained when the gas delivery pressure is between 150 to 300 bar depending on the engine load, and the fuel gas has a temperature about 45° Celsius. A buffer tank 22 is used for storage of 15 boil-off gas before provided to the fuel gas injection system 30 by the fuel gas supply system 19. The amount of inevitable boil-off gas in an LNG tank of a LNG carrier is normally not sufficient as the only fuel for the operation of the internal combustion engine of the LNG carrier, but the amount of boil-off gas may advantageously be used in combination with fuel oil in an internal 20 combustion engine according to the invention. The operation of the fuel gas injection system 30 is insensitive to the gas composition as well as the variation in the gas composition. The dedicated fuel gas tank may then be an additional fuel gas pressure tank on top of the deck, which is fully separated from the cargo. Hence, also liquefied petroleum gas (LPG) that normally con-25 sists of higher hydrocarbons like propane and butane may like LNG apply as fuel gas without changing the engine's performance in terms of speed, thermal efficiency and power output, while maintaining the same rating as for fuel oil. The pressure necessary to achieve full atomization of the fuel gas is then about 550 bar and a temperature about 35° Celsius is preferred.

30 The fuel gas supply system may receive fuel gas directly from the cargo of a ship or from a dedicated fuel tank which may be a fuel tank on the deck of a ship. And the fuel gas supply system may receive fuel gas from a boil-off gas reliquefaction system e.g. from the manufacturer Hamworthy or directly from the cargo or a dedicated fuel gas tank. The fuel gas supply sys-35 tern may also be from the manufacturer Hamworthy and generally comprises DK 177623 B1 7 a booster pump, a high-pressure pump and a heater unit. After pumping the fuel gas to the required pressure by the booster pump to the required pressure, the fuel gas is heated to the required temperature and then provided to the engine cylinders via the double-walled gas supply piping 26. An additional 5 booster pump may be provided after heating of the fuel gas to fuel adjust the fuel gas pressure to the desired level.

In the fuel oil injection system 20 the fuel oil dosing device 15 may be a fuel pump, and in that case the fuel oil supply system 23 needs only deliver fuel oil from a fuel oil tank 21 to the fuel dosing device at a relatively 10 low feeding pressure in a fuel feeding pipe 24, such as a pressure in the range from 2 bar to 15 bar. Alternatively, the fuel oil dosing device 15 may be a valve or a valve in connection with a metering device, and the fuel feeding pipe is then a high-pressure pipe in which the fuel is at a pressure higher than the injection pressure, such as a feeding pressure in the range of 500 15 bar to 1500 bar. Such a fuel oil supply system 23 is called a common-rail system. In either case, the fuel oil dosing device 15 is connected to fuel feeding pipe 24 by a branch conduit with a valve that is maintained in open position during normal engine operation. Fuel oil dosing device 15 is connected to fuel oil injectors 13 via high-pressure fuel oil conduits. A return conduit leads from 20 the fuel oil injectors to a fuel oil return line (not shown). The fuel oil provided to the cylinders is typically heavy fuel oil or marine diesel oil.

An internal combustion engine 1 according to the invention may be provided by installing a fuel gas supply system 19 and a fuel gas control system 30 on an existing engine with a fuel oil supply system as described 25 above. In order to simplify installation and generally to make the control strategy of the combustion process least complex, it is generally preferred that independent cylinder control units 12a, 12b control the amount of fuel oil and the fuel gas provided into the combustion chambers of the cylinders 11, respectively. Likewise, both the fuel oil control system 20 and the fuel gas 30 control system 30 comprise independent engine control units 17a, 17b. Evidently, as known in the art of marine diesel engine at least the fuel oil control system 20 is preferably redundant, viz. a further engine control unit with redundant cabling to the cylinder control units is present. When operating an internal combustion engine according to the invention, the engine regulation 35 of fuel injection is either with the fuel oil injection system 20 or the fuel gas DK 177623 B1 8 injection system 30. Generally, the engine control unit 17 receives an engine speed signal and other engine operating parameters from a sensor arrangement 40, and controls the amount and rate of fuel to be provided into the combustion chambers of the cylinders 11, which is also known as the 5 engine's governor control. The internal combustion engine according to the invention may be operated in a fuel oil operating mode, fuel gas operating mode and a combined fuel oil and fuel gas operating mode. The operating modes may be ordered from the bridge of a ship. Switching between operating modes may be performed by an engine switch unit 25 connected to 10 the fuel oil injection system 20 and the fuel gas control system 30, and preferably the engine switch unit is a part of the fuel gas supply system 19.

In the combined fuel oil and fuel gas operating mode the engine switch control unit 25 determines if the critical timing and regulation of the combustion process in the internal combustion engine is with the fuel oil injection system 15 20 or the fuel gas injection system 30, i.e. the engine switch unit 25 switches the governor control between the fuel oil control system 20 and the fuel gas control system 30. Hence in the combined fuel oil and fuel gas operating mode, operation is automatically alternated between the fuel oil operating mode and the fuel gas operating mode. Switching between the operating 20 modes may be ordered from the bridge or for safety reasons in case of a gas leak, which immediately will switch the engine to the fuel oil operating mode.

In the fuel gas operating mode the fuel gas injection and the timing of the combustion process is controlled by the fuel gas injection system 30.

This is done according to a predetermined engine load index specifying a fuel 25 injection length and a fuel injection pressure required to operate the engine optimally at a given engine load. Before taken into operation the engine is tested at different loads along the propeller curve to determine the optimum fuel injection length and fuel injection pressure at different loads. Hence when the engine control unit makes a look-up in the engine maps for finding 30 e.g. the correct timing of fuel gas injection, timing of opening and closing of the exhaust valve and the hydraulic pressure, it is dependent on both an ordered fuel injection length and an ordered fuel injection pressure required to operate the engine at a desired engine load.

The fuel injection length may be adjusted on a very short time scale 35 from one fuel gas injection to a following fuel gas injection, i.e. in the range DK 177623 B1 9 of 1 to 2 seconds or less dependent on the engine speed, and in practice the possible adjustment is only limited by general safety requirements limiting the possible change of the fuel injection length from one fuel gas injection to a following fuel gas injection. By adjusting the fuel gas injection length the 5 amount of energy injected into the cylinders is adjusted. Whereas the engine control unit may control the fuel injection length from fuel gas injection to fuel gas injection by communication of the desired fuel injection length to the cylinder control unit 12, a change in the fuel gas injection pressure ordered by the engine control unit 17b from the fuel gas supply system 19 is more 10 time consuming. By adjusting the fuel gas injection pressure the amount of energy injected into the combustion chamber per time unit is adjusted. Depending on the configuration of the fuel gas supply system and the required change of fuel gas injection pressure, an ordered fuel gas injection pressure may be provided by the fuel gas supply system 19 to the fuel gas injection 15 system 30 within 2 seconds to 15 seconds. However, a longer response time for providing the desired fuel gas injection pressure is possible.

The possible fast adjustment of the fuel injection length allows the engine control unit to control the engine load by first adjusting the fuel injection length to immediately accommodate changes in the engine load, and 20 thereafter adjusting the fuel injection pressure and counter adjusting the fuel injection length in accordance with the predetermined engine load index that provides the most optimum operation of the engine. Hence in order to accommodate the fuel gas injection to changes in the engine load, the fuel gas injection length is first adjusted independently of the predetermined engine 25 load index by adjusting the fuel gas injection length and thereby the amount of energy injected into the cylinders. However, this is achieved with a less optimum operation of the engine, because neither the fuel gas injection length nor the fuel gas injection pressure is in compliance with the engine load index. Therefore, while the fuel gas injection length is ordered by the 30 engine control unit to comply with abrupt changes in the engine load, an adjusted fuel gas injection pressure is ordered from the fuel gas supply system 19. While the fuel gas injection pressure delivered by the fuel gas supply system 10 to the cylinders is adjusted to the ordered fuel gas injection pressure, the fuel gas injection length is counter adjusted by the engine control unit 35 until the both the fuel gas injection pressure and the fuel gas injection length DK 177623 B1 10 corresponds to the predetermined engine load index.

Claims

An internal combustion engine (1), such as a two-stroke cross-head diesel engine comprising a fuel gas supply system (19) and cylinders (11) with fuel gas injectors (14) for injecting fuel gas directly into combustion chambers in the cylinders (11), and an engine control unit (12) controlling fuel gas injection into the cylinders (11) according to a motor load index, wherein the fuel gas injection into the cylinders (11) is controlled by adjusting a duration of a fuel gas injection length, characterized in that the fuel gas injection into the cylinders (11) is controlled by adjusting the length of the fuel gas injection length and a fuel gas injection pressure, and the engine control unit (12) adjusts the fuel gas injection to steep changes in the engine load by adjusting the duration of the fuel gas injection length and the duration of the fuel injection gas injection and the fuel gas injection length. seen as the engine control unit it (12) first adjusts the duration of the fuel gas injection length and then adjusts the fuel gas injection pressure and counteracts the duration of the fuel gas injection length to follow the engine load index.

Combustion engine (1) according to claim 1, characterized in that the cylinders (11) are provided with fuel oil injectors which inject fuel oil directly into the combustion chambers of the cylinder (11) and a fuel oil supply system (20).

Combustion engine (1) according to claims 1 to 2, characterized in that the fuel gas supply system (20) is a common rail gas supply system.

Combustion engine (1) according to any one of the preceding claims, characterized in that the fuel gas injection pressure is in the range 150 bar to 300 bar.

An internal combustion engine (1) according to any one of the preceding claims, characterized in that the engine speed at 100% engine load is in the range 45 rpm to 175 rpm.

Combustion engine (1) according to any one of the preceding claims, characterized in that the fuel gas supply system (19), which supplies fuel gas to the cylinders (11), is connected to a tank (18) for liquid natural gas. on a tanker for liquefied natural gas.