DK173242B1 - of such a gas engine and a method of fuel supply Diesel-type combustion engine for combustion - Google Patents

Description

in DK 173242 B1

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a diesel-type combustion engine for gas combustion which is compressed to a high pressure suitable for supply to the engine of at least 60 bar, which has an injection system with injectors which, at high pressure, inject liquid fuel into the combustion chambers of the cylinders.

There are known dual-fuel, two-stroke cross-head engines of this kind, in which liquid fuel is injected in the form of fuel oil, which typically acts as ignition aid 10 for the injected gas. The gas in the known high-pressure injection engines is natural gas, which is gaseous upon entry into the combustion chamber. For example, an engine of this type is described in the applicant's brochure "Large Diesel Engines Using High Pressure Gas 15 Injection Technology" from 1991 and in the technical article "Development of the World's First Large-Bore Gas-Injection Engine" by T. Fukuda, P Sunn Pedersen et al, paper D51, CIMAC 1995 in Interlaken, CH. In these engines, the natural gas is supplied via a conduit supplying a well-defined gas quality, usually methane gas.

The high pressure injection of the gaseous natural gas gives the advantage that the engine can use different compositions of the natural gas. The gas can thus be of pure methane or, for example, of methane and ethane, if these are fractionated together.

Furthermore, diesel-type engines with gas-based fuel supply are known in a number of different designs which have in common that the gas is injected or introduced at low pressure of, e.g. 1-5 bar in the engine's intake air, thereby replacing part of the fuel oil, which can have environmental benefits in the form of less particle formation in the exhaust gas. Examples of such engines are reference to EP-A 0049721, which mentions the supply of LPG 35 (propane / butane) to the intake air, EP-A 0102119, which refers to the supply of LPG or methane, and EP-A 0133777, where the intake air is supplied with compressed natural gas or LPG. In the cases where the gas is supplied to the engine as liquid fuel, both evaporation and mixing of the gas in the suction air takes place before the introduction into the cylinder, while in the case of gaseous gas supply only one mixing occurs.

The gas's share of the total amount of fuel must not be too large when the gas is admixed with the intake air in a diesel-type engine, because otherwise the gas can self-ignite during the compression stroke. It is described as important in the prior art that gas ignition can only be controlled in a controlled manner by fuel oil injection. The injection of oil can usually be controlled with appropriate precise timing to achieve the desired engine operating characteristics.

In the known engines, which, as mentioned, can use high-pressure injection of gaseous gas directly into the combustion chamber or can use supply of gaseous or liquid gas to the engine's intake air, it is a prerequisite for the gas operation that the gas is refined or otherwise obtained predetermined and stabilized composition having a predictable behavior as fuel in the diesel engine so that the specific engine can be adapted to the specific fuel in its constructive design. If one of the known engines designed to supply gas with a particular ignition suddenly is supplied gas that is considerably more ignitable, self-ignition can occur during the compression stroke with consequent severe engine malfunctions.

The partial gas operation in the known engines can give a significant environmental advantage in that the engine burns less oil which, during combustion, creates environmentally harmful compounds which do not occur to the same extent in gas combustion.

The present invention has for its object to provide a diesel-type engine which, in the fuel combustion process, reduces the emission of environmentally harmful compounds substantially more than is achieved by reducing the compounds formed during combustion by combustion of gas instead of oil.

To this end, the internal combustion engine according to the invention is characterized in that the injection system contains at least liquid injectors for high-pressure injection of compressed liquid gas produced by volatile organic compounds evaporated from petroleum tanks.

15 It has been recognized for some years that the evaporation of volatile organic compounds VOC (Volatile Organic Compounds) from, among other things, crude oil constitutes a serious environmental impact, but despite various attempts to solve this and intergovernmental agreements on 20 reduction thereof, the emission of VOC growing. The volatile organic compounds evaporating from crude oil have no well-defined composition, but vary over a period of oil extracted from a particular oil field and also vary between 25 oils extracted from various fields.

By using the volatile organic compounds VOC as high-pressure injected fuel in a diesel-type internal combustion engine, emissions of the VOCs to the atmosphere are avoided, providing a significant environmental benefit, and at the same time the known effect is obtained that the exhaust gases are cleaner when gas is burned instead of oil. There is also the economic advantage that purchased refined fuel is at least partially replaced by gas compounds that were previously thrown away 35 and which in recent years have had to pay for DK 173242 B1 4 to get rid of. However, the use of the VOCs as a fuel in a diesel-type engine means that the combustion characteristics of the fuel can vary greatly over a very short period of time.

5 When the crude oil overflows into a tank, the oil crashes into the tank and is subjected to vigorous movements and circulation, which results in the release of relatively large amounts of VOC in the form of highly mixed vaporized alkanes which depend on the type of the crude oil. These alkanes typically contain relatively large amounts of each of the compounds methane, ethane, propane and butane in both normal and branched compounds as well as certain amounts of higher alkanes C5 and C6 + · Vec * ^ a subsequent storage in the tank evaporates VOC with a button such a large spread in the alkanes, this evaporation being mainly controlled by the partial pressures of the constituents of the crude oil in the tank space above the oil. Thus, the liquid phase of each constituent will seek equilibrium with the associated vapor phase, but at the same time the vapors in the tank space tend to achieve higher concentrations of the heavier constituents near the surface of the crude, slowing the evaporation of the higher alkanes. If the crude oil tank is on a ship, the ship's movements when sailing in bad weather 25 can cause a swelling of the crude oil to distribute the gases in the tank space more uniformly, resulting in stronger evaporation of the heavier constituents than when the ship sails in more calm conditions.

Thus, within a few days, there may be slow variations in the alkane composition of the VOC and within minutes or hours, rapid variations may occur that radically alter the ignition properties of the fuel, etc. These variations make it impossible to use the fuel as a premix supplement to the combustion engine's intake air. By using high-pressure injection of the fuel, premature ignition is avoided, and the rapidly varying fuel characteristics can therefore only affect the rate at which the fuel is combusted.

It is also a significant advantage that the gas at the injection in the combustion chamber is liquid. First, the liquid gas can be compressed to a high pressure suitable for the injection, which can range, for example, in the range of 200 to 1000 bar, with substantially 10 less energy consumption than when compressing gaseous gas. Second, the liquid gas allows, over a short period of time, to inject a gas amount of high energy content, and the entire injection process with any variations in the injection rate can be controlled with the means well known from oil injection. Third, most of the total energy content of the crude oil evaporated VOCs with advantageously simple and energy-efficient means can be liquidized, such as by compressing 20 to higher pressures than the condensation limit of the desired alkanes and / or by cooling. The condensate must then just be compressed up to the injection pressure before the injection.

The methane and ethane proportions in the VOCs cannot be suitably brought in liquid form. It is possible to store the methane and ethane gases temporarily by reintroducing these gases into the crude oil, but this creates increased evaporation of VOCs at a later stage, so this will only be a process to postpone the problem. The methane and ethane gases can also be discharged to the atmosphere just as it has previously been with all the VOCs. The combustion of the liquid C3 + alkanes will in any case give a considerable gain over the previous ones.

In one embodiment, the combustion engine 17174242 B1 6's injection system contains secondary injectors for high pressure injection of gaseous mixtures containing at least partially evaporated gas from crude oil tanks and possibly inert gas which has been filled with the crude oil tanks as explosion-proof gases. The secondary injectors can inject the methane and ethane gases etc. that are not brought into liquid form in the treatment of the evaporated VOCs. When emptying crude oil tanks, it is normal to add inert gas to the tank to avoid 10 gas explosions in the tank. This inert gas is an oxygen-poor mixture of gases such as nitrogen or carbon dioxide and up to approx. 7% oxygen. When crude oil is added to the tank, the oil will displace the inert gas as it fills, but at the same time the released 15 VOC gases will be mixed with the inert gas. The gaseous mixtures fed to the secondary injectors will therefore, at and immediately after a tank filling, contain large amounts of inert gas which cannot be combusted in the engine. As long as the proportion of combustible gases is sufficiently large to have an energy content more than twice the compression work by bringing the gaseous mixture into a suitable form for the injection, it would be worthwhile to inject the gaseous mixture into the engine's pre-25 combustion chamber. Environmentally, it would be advantageous to inject the gaseous mixtures into the engine's combustion chamber, even if the energy content of the combustible gases does not cover the compression work.

It is preferred that the injection system 30 comprises pilot injectors for injecting inflammatory pilot fuel which, upon injection, initiate a combustion process. The pilot fuel may be oil or other highly inflammable fuel.

If the compressed liquid gas has a quality that makes ignition assistance unnecessary, pilot injectors can be dispensed with on the cylinders that have fluid injectors. Still, there may be advantages to placing at least one pilot injector at each cylinder. If the production of VOC is insufficient to meet the total fuel demand of the engine 5 over a longer period of time, the engine can for periods of time be operated solely on oil injected through the pilot injectors.

In one embodiment, a plurality of the liquid injectors and of the secondary injectors are combined into a corresponding number of dual-fuel injectors capable of injecting both the liquid gas and the gas-containing, gaseous mixtures. The dual-fuel injector requires less space in the cylinder cover than a liquid injector and a secondary injector, and is therefore easier to place, especially if there are already injectors for injecting oil on the same cylinder.

The reliability of the gas injection can be improved by the fact that the injection system periodically activates the secondary injector, even when no gaseous fuel is to be injected into the associated cylinder. For example, the activation can occur at least once every ten minutes, and upon activation, the nozzle holes are blown clean of any deposits. If no gaseous mixture is available upon activation, compressed air or a gaseous gas such as inert gas may be used instead. The period between each clean-blow activation does not have to be 10 minutes, but can range from once per motor cycle to once per day. The period is selected taking into account the fuel burned when no gas is blown. If the fuel gives rise to stronger particle and soot formation, choose a short period.

If, for a long time, the engine is supplied with gaseous and liquid gas under certain conditions, a simplification of the injection system can be achieved by the fact that only some of the cylinders of the engine are provided with secondary injectors, while others of the cylinders are provided with liquid injectors. all of the cylinders may additionally optionally have pilot and / or fuel oil injectors. The simplification lies in the fact that not all engines have three different types of fuels. For example, if the VOC composition is such that only 10-15% of the VOC's calorific value is derived from methane and ethane, one or two of the engine's cylinders 10 can burn off all the gaseous gas so that no distribution and injection system for gaseous fuel for the other cylinders.

It is preferred that the engine be the main engine of a crude oil tanker such as a shuttle tanker or a crude oil carrier and that evaporated volatile organic compounds which may have temporally varying ignition characteristics, calorific values and / or evaporation rates are significant. share of main engine fuel consumption. A very large amount of the 20 VOCs that are released to the atmosphere today are released by loading crude oil at offshore oil extraction sites or at coastal oil terminals and during the subsequent voyage to the refinery or other unloading site. By using these VOCs as fuel 25 in the ship's main engine, the volatile compounds are suitably removed soon after release from the crude oil.

The engine may have an electronic control unit which, on the basis of monitoring the instantaneous cylinder pressure, controls at least the injection pressure of the gaseous fuel gas. With continuous monitoring of the pressure flow in a cylinder, the combustion in the cylinder can be analyzed in the electronic control unit, the energy development of the combustion and the combustion rate can be determined, and on the basis of this the control unit 35 can determine fuel parameters for use in subsequent injection processes. When the engine is supplied with gaseous gaseous mixtures collected from crude oil tanks, the gas may contain varying amounts of inert gas. The non-combustible inert gas affects the combustion of the combustible 5 VOCs so that the combustion rate is greater when the content of inert gas is greater. In order to achieve a more uniform combustion, it is preferred that the control unit controls the injection pressure to be lower when the gas content of inert gas is greater. This also gives the advantage of reducing the compression work for high pressure gas compression.

The invention further relates to a method of supplying a combustion engine of the aforementioned kind, characterized in that volatile organic compounds evaporated from crude oil tanks after possible temporary storage and compression are added to the engine's fuel system and used as fuel in the engine. time varying ignition characteristics, 20 burn values and / or evaporation rates. The method achieves the above-mentioned advantages that the environment is spared from the emission of at least part of the VOCs while the engine uses a cleaner fuel than oil and that the shipowner gains an economic advantage by using as a fuel a waste product in instead of purchased bunker oil.

In an environmentally optimal further development of the process, the evaporated and compressed compounds comprise both a gaseous and a liquid phase 30 which are substantially spaced apart from each other upon application to the engine. By using both the liquid and the gaseous phase as fuel, virtually all of the evaporated amount of VOC can be burnt. For the engine, it is essential that the two phases be kept separate from each other by the feed to the engine, because there would be disproportionately large variations in the burn value in the fuel supplied for combustion if, for example, a gas phase suddenly a saturated liquid phase came through the same injector.

In order to avoid liquid phase separation in the gas phase, it is preferred that the temperature of the gaseous phase in the engine's fuel and injection system be kept higher than the temperature which the gaseous phase had after the compression to the pressure at which it was delivered to. engine fuel system. In an advantageous design, the temperature of the gaseous phase of the fuel system is controlled to rise towards the engine so that any risk of condensation is removed. Alternatively, at the gaseous phase approach 15 to the engine fuel system, there may be a freeze trap for condensate separation from the gas phase.

It is preferred that said liquid phase and said gaseous phase are both supplied to all the cylinders of the engine, thus keeping the injectors for the gas phase functional in all cylinders and all cylinders can be controlled in the same way.

When the engine is the main engine of a crude oil tanker from which volatile organic constituents are evaporated, it is preferred that the engine be supplied with only 25 fuel oil to the extent necessary as auxiliary fuel or required because the engine's current fuel demand exceeds the supply of fuel gas to the engine. This saves as much as possible on bunkered fuel oil. The control of the supply of 30 fuel gas to the engine does not have to be dictated by the engine's fuel needs or by the immediate VOC production, but can very well be subject to overall control of burning the environmentally friendly fuel gas in the coastal areas where 35 environmentally harmful emissions products to be avoided.

11 DK 173242 B1

Furthermore, the delivery of the gaseous and liquid fuel gas can be controlled individually, for example, so that the gaseous fuel gas is supplied to the engine as it is produced to avoid storage, while the liquid liquid gas gas is, as needed, stored on the ship and supplied at those times when the environmental benefit is greatest.

The engine may be associated with a shaft generator in a shuttle tanker or in a vessel for collecting 10 hydrocarbons from a drilling or production well, and in this case it is preferred that at least a portion of the volatile organic compounds evaporated by the oil load be combusted in the engine operating the shaft generator for power generation for drive units in the dynamic positioning system of the tanker or vessel. Since the greatest amount of VOC is generated during the loading of the crude oil, it is particularly advantageous to provide the engine with a shaft generator of such size that the electric power requirement for bow thrusters, etc. used in the 20 dynamic positioning of the vessel can be covered by the shaft generator and then drive the main engine on the VOC during the loading.

The invention further relates to a diesel-type combustion engine for gas combustion which is compressed to a high pressure suitable for injection into the cylinders of the engine at least 200 bar, which is pressurized to a charge pressure of at least 3 bar absolute and has a volumetric compression ratio. of at least 1:14 as well as an average pressure of at least 15 bar and having an injection system with injectors which inject high liquid fuel into the combustion chambers of the cylinders at high pressure.

Such an engine is known from the applicant's aforementioned brochure "Large Diesel Engines ...", in which the liquid 35 fuel is pilot oil and the gas is gaseous natural gas, which is pre-compressed to a supply pressure of about 250 bar. The gas is blown at this pressure after the control oil has opened for the injector. The natural gas used consists primarily of 5 methane.

Older four-stroke engines are also known where LPG has been used as fuel, see for example the above-mentioned writings, where LPG is evaporated in the engine's intake air. These older engines were relatively small, 10 fast-running engines with a compression ratio of no more than 1:13, and it is well known that the requirement for a suitably high metal number is greatly increasing with the engine's compression ratio, its cylinder diameter, its mean pressure and with lower rpm.

15 The metal number is an expression of the gas's ignition properties, roughly like the octane number it is for gasoline, and a gas with a metal number of 100 self-igniting as pure methane, while a gas with a metal number of 0 self-igniting as pure hydrogen. The ignition characteristics are important in order to make good use of the fuel value in the fuel. It is not desirable for the ignition to be explosive as this gives a steep rise in pressure and a very high combustion pressure which usually leads to damage to the combustion chamber components with a risk of a total of 25 engine failures.

Normally, therefore, the gas is desired with a high number of metals. Ordinary natural gas has a metal number of about 90 when the gas is clean, and when carbon dioxide or nitrogen is mixed, the metal number can vary between 90 30 and 130, ie. the metal number can be higher, which is seen by the engine as a variation to the positive side. The high volumetric compression ratio of at least 1:14 in combination with the high mean pressures of at least 16 bar in the newer diesel engines presupposes that gas operation 35 at full load is possible only on gaseous natural gas having a metal number of at least 80. The high compression ratio implies the disadvantage that the natural gas has to be high-pressure compressed in order to be injected with a suitable overpressure into the combustion chamber at the end of the compression stroke, which requires a noticeable energy consumption of about 5% of the engine's shaft power to the gas compressors.

In order to reduce the energy consumption for high pressure compression of the gas, the engine according to the invention is characterized in that the injection system contains at least liquid injectors for high pressure injection of compressed liquid gas.

It is a prerequisite for injecting liquid gas that the gas comprises propane, butane and / or C5 + -15 hydrocarbons. Pure propane has a metal number of 35, butane a metal number of only 10 and the higher hydrocarbons have substantially lower metal numbers. However, in spite of the expectation of the opposite, it is possible to control in a controlled manner liquid gas with as low as 20 meters in a highly compressed, pressurized engine, it is probably because the gas combustion requires a certain oxygen content. The injected gas evaporates immediately after the injection, but even though the temperature of the combustion chamber is very high, the gas cannot combust until it has been appropriately mixed with the air in the combustion chamber. The decisive factor for combustion is thus the mixture and not the metal itself as it has been assumed so far.

The liquid gas can be compressed to very high 30 pressures with very little energy consumption. The compression can either be done independently of the injection itself in a form of common rail system where the injectors are controlled by control oil, or the compression can be done by piston pumps in the same way as is traditionally done with fuel oil on diesel engines, ie the pump's piston 14 DK 173242 B1 is activated and pressurises the liquid gas when the injection is to take place. In the latter case, the gas injector is opened by the rise in pressure of the liquid gas, so the control oil can be dispensed with.

5 Examples of the invention are explained in greater detail with reference to the very schematic drawing, in which fig. 1 is a diagram of a VOC capture plant from crude oil tanks in a ship; FIG. 2 is a diagram of an injection system for gaseous and liquid gas and fuel oil respectively for an internal combustion engine in a tanker; FIG. 3 is a diagram of a liquid gas fuel subsystem for an internal combustion engine; and FIG. 4 is a diagram of a gaseous gas fuel subsystem for an internal combustion engine.

High pressure gas injection engines of the diesel type and with pressurized charge can be medium-speed four-stroke engines or be large two-stroke cross-head 20 engines, which with today's applicant type MC-GI engines can have a power per cylinder in the range of 250-5800 kW at speeds. in the range 75-250 rpm with stroke-to-bore ratio in the range 2.45-4.20 and with volumetric compression ratios of, for example, from 1:14, 1:15, 1:16, 1:17, 1:18 or higher. Volumetric compression ratio means the classic compression ratio which relates to the volume above the piston when it is in its top and bottom dead center positions.

In FIG. 1 shows a crude oil tank 1 in a ship under filling. The ship may, for example, be a crude oil carrier or a shuttle tanker. Through a tank connection 2, crude oil is supplied from a terminal plant onshore or from an offshore plant, such as a loading buoy at a production platform or by an FPSO vessel (Floating 15 DK 173242 B1

Production Storage Offloading vessel). The ship may also be such an FPSO vessel that receives crude oil from a production well on the seabed.

As the tank is filled with crude oil 3, 5 is pressed into the tank of inert gas and the volatile organic compounds 4 (VOC) evaporated from the crude oil through a discharge tube 5 leading to a compressor 6 which, via an intermediate tube 7 with a cooler 8, delivers the VOC to a condenser 9. Condensed gas 10 is drained from the condenser through a conduit 10 to an insulated tank 11, in which the liquid gas, which typically contains propane and higher alkanes, can be stored at atmospheric pressure and a temperature of approx. -42eC. When the liquid gas is to be used as fuel, it is fed via a suction line 12 15 to one in FIG. 3, which compresses the gas to a delivery pressure which can typically be at 400 bar in a common rail system and at 20 bar if the final compression to the injection pressure is done by piston pumps at each cylinder.

20 From the top of the capacitor 9, a tube 14 conducts the non-condensed components methane and ethane to an in FIG. 4 illustrates a multi-stage compressor 15 which compresses the gaseous gas phase to an injection pressure which can typically be about 250 bar, and from this compressor a common rail system distributes the gas to the individual cylinders of the engine.

During the loading of the ship, the condensing system is in continuous operation, but in the subsequent voyage, sufficient intermittent operation of the system will be controlled based on the measurement of the pressure in the tank 1, so that, for example, the condensation system is started when the gases in the tank are started. 1 has 0.14 bar overpressure and stops when the gases have 0.05 bar underpressure. Reference is also made to the description in Stat-35 oil, The Norwegian State Oil Company a.s Norwegian patent 16 DK 173242 B1 application no. 393/97, filed simultaneously with the present application.

In FIG. Figure 2 shows an embodiment of a single engine cylinder injection system, in which there is a 5 secondary injector 16 for injecting gaseous gas and a liquid injector 17 for injecting liquid gas and a pilot injector 18 for injecting oil.

The three injectors can be separately mounted in each housing in the associated cylinder cover. It is also possible to assemble two of the injectors in a common housing into a so-called dual-fuel injector. Although the pilot injector can of course be included in such a dual-fuel injector, it is preferable in cases where all three injector types are located on a single cylinder, that the secondary injector 15 16 and the liquid injector 17 be combined in the dual-fuel injector, thereby leading the gases to the same injector housing, which facilitates the encapsulation of the gas-conducting systems. For example, dual-fuel injectors are described in more detail in the applicant's Danish patents 153240 20 and 155757 and in the applicant's W095 / 24551 a gas injection injector is further described. There can be several injectors of each type mounted on the same cylinder to achieve better distribution of the fuel in the cylinder, among other things.

25 In the following, we talk about injecting the gas whether it is liquid or gaseous. By injection it is meant that the gas is either injected and atomized or blown in, and both are carried out at an appropriate overpressure relative to the instantaneous pressure in the combustion chamber.

If fuel oil is needed on the cylinder in question, either as auxiliary fuel or because the gases cannot meet the fuel requirement alone, the oil can be delivered periodically at the desired time in the engine cycle to the pilot injector 18 from a fuel oil source 19, which may have different designs. The fuel oil source may be a conventional fuel pump supplied with oil from a low pressure feed line common to the pumps and having a pump piston driven by a cam on a camshaft. A regulator not shown can normally rotate the pump piston for quantity control of the oil delivered from the pump at high pressure up to, for example, 800 bar. Alternatively, the fuel oil source may be an electronically activated fuel pump which is supplied with oil from a common low pressure feed line and quantity controlled and timed by setting signals from an electronic control unit. A third option is the so-called common rail system, where the fuel oil source comprises a high pressure reservoir for 15 oil connected to an inlet port on an electronically actuated control valve, which further has at least two ports, namely a discharge port for a line 20 leading to the valve 18 oil access. and a gate connected by a drain. The control valve may, from control signals received from an electronic control unit, connect line 20 to either the oil supply port or the drain port.

When the fuel oil source 19, at the time of combustion timing desired for combustion, starts supplying high pressure oil to line 20, the pressure will rapidly rise above the opening pressure of the oil valve 18, after which the oil is injected.

The liquid fuel gas is supplied from a fuel gas source 25 which may be configured in the same 30 ways as the fuel oil source 19. For convenience, only the common rail type embodiment is described, the source 25 comprising the low pressure supply from the tank 11 and the high pressure compression in the compressor 13, from which a piping system 26 parallel joints liquid injectors 35 on the engine. A control valve 27 can, in dependence 18, control signals received from an electronic control unit connect the fuel supply of the injector 17 to the high pressure gas line 26 or to a drain. When the control valve 27 opens for the delivery of liquid gas at 5 at the time of combustion timing required for the combustion cycle, the liquid injector 17 opens for injecting and atomizing the gas into the combustion chamber.

The injection of gaseous gas with the injector 16 can only take place when, at the same combustion, 10 liquid fuel is injected which initiates the combustion. This liquid fuel can be either fuel oil from injector 18 or fuel gas from injector 17. An embodiment is then described in which combustion is initiated with pilot oil, but it should be understood that liquid injector 17 can replace pilot injector 18 in the described safety system.

When the pilot injector 18 opens, the oil pressure simultaneously activates a safety device 21 to enable control oil pressure to be applied to the secondary 20 injector 16. The safety device 21 may, for example, be of a well-known mechanical type with a piston holding a drain port in a control oil line 22 until the fuel oil pressure at exceeding said opening pressure displaces the plunger for closing the drainage port. The drainage port is connected through a conduit 23 to a control oil reservoir 24. Alternatively, the safety device may be of an electronic nature that determines in an electronic control unit whether the fuel oil or liquid fuel gas is injected and uses this information as a condition for activating the secondary injector 16. In this case, the control unit can detect the injection on the basis of a pressure sensor in the conduit 20 or by a position sensor in the valve 18 for sensing the actual valve opening.

In the illustrated embodiment, the secondary injector 16 can be actuated to open position by applying control oil pressure at the gas valve connection to the conduit 22. The injector may further have a connection 28 for blocking oil and a connection 29 leading to a high pressure. gas well. The barrier oil pressure, for example, is 40 bar higher than the gas pressure in the connection 29. Alternatively, the injector 16 can be kept closed by the control oil pressure and opened upon removal thereof, thereby eliminating the need for barrier oil. This is further described in WO95 / 24551.

An electronically actuated control valve 30 has an inlet port connected to a line 31 with high pressure oil supplied from a pump 32 which is fed through a 15 line 33 from the reservoir 24. The control valve 30 further has at least two ports, namely an outlet port for the line 22 and a drainage port connected to the reservoir 24. The control valve may connect, from control signals received from an electronic control unit 34, the conduit 22 to either the oil pressure conduit 31 or the drainage port. The control valve may, for example, be a solenoid valve, an electronically controlled hydraulic valve or a solenoid valve with so-called magnetic locking, which can give very short switching times.

25 The electronic control unit 34 is well known in the known manner for the instantaneous rotational position of the engine crankshaft, and controls the three injectors 16-18 to inject the combination of fuels most desirable for that combustion.

An example of the gas systems in a crude oil carrier with a propulsion engine according to the invention will now be described in more detail with reference to FIG. 3 showing the liquid gas system; and FIG. 4 with the gaseous gas system. In the drawing 35 only two cylinders 35 are shown, but the engine has, of course, 20 more. Bleed valves 36, 36 'can discharge the gas cylinder systems of gas through a common drain line 37 if necessary. A vent valve 38 can empty the branch line 26 if the engine is not to be operated on liquid gas for a period of 5 years. The entire feed line 26 can be emptied of liquid gas by closing a main valve 39 and opening to the drain valves and to a feed valve 40 connected to an inert gas source 41. In a very similar way, a vent valve 38 '(FIG.

4) emptying a high-pressure gas reservoir 42, the volume of which can contain gaseous gas for, for example, 20 injection processes, and a shut-off valve 43 can close the gas supply if the pressure drop at an injection is so large that the secondary injector must not be properly closed. after the end of the injection. The entire conduit 29 can be flushed clean with inert gas by closing a main valve 44 and opening a shut-off valve 45 in a drain line 46, while opening the valve 40 'to the inert gas source 41.

The gas-carrying elements in the engine room are surrounded by a jacket 47 which, at the outlet of the drain line 37, is supplied with ventilation air as shown by the arrow 48, at least one fan 49 sucking air out of the jacket 47 as the feed line passes into the engine room. Gas detectors 50 are located at appropriate locations in the system for monitoring any gas leaks.

The liquid gas may be heated to, for example, 45 ° C in a unit 51 prior to introduction into the engine compartment to avoid any ice formation within the casings 30 47.

The gaseous gas supplied via conduit 14 is compressed into the generally designated compressor at least in a low pressure compressor 15a which compresses the gas to about 25 bar, and in a high pressure compressor 15b which delivers the gas at a pressure of 21 DK 173242 B1, for example, 250 bar to line 29 which is inserted into the engine room. The drive motors for the compressors are located in a gas-tight enclosure, and both this and the compressor room are ventilated by each fan.

The discharge pressure from the high-pressure compressor 15b may vary with the composition of the gaseous mixture being compressed. The pressure may be lower, such as 175 bar when the content of inert gases is high, and higher when the gas mixture is mainly of combustible gas. It is mentioned above that the pressure can be controlled by means of the engine's electronic control unit based on pressure measurements at combustion course and associated calculation of the energy development during combustion, which when compared with the duration of the injection gives a measure of the gas mixture content of inert gas. Combustion data can therefore be used periodically in a feed-back control to adjust the high-pressure compressor's discharge pressure during subsequent engine operation. It will often be the case that a ship with crude oil tanks sails between fixed destinations and fills the crude oil tanks with crude oil of uniform quality. This allows for the initial filling to record how the inert gas content of the gas mixture varies during and during the period after refueling. This data can then be used for subsequent refills as an empirical basis for regulating the compressor discharge pressure in a feed-forward control.

When the engine is a highly compressed diesel engine, it can also be supplied with liquid gas in the form of LPG or a 30 LPG mixture which can be refined, fractionated or otherwise pre-treated to a more stable composition than liquid gas produced by condensation of VOC. The highly compressed diesel engine according to the invention can be a four-stroke engine which can, for example, have a maximum speed of 700 22 B1 rpm. It is preferred that the engine is a two-stroke cross-main engine having a cylinder bore of at least 200 mm, suitably at least 250 mm, and a maximum speed of 250 rpm. The motor can have a mean pressure of at least 5 16 bar and can be pressurized to at least 3 bar absolutely at full load. The mean pressure can also be higher, such as 17 or 18 bar or greater, as can the pressure charge may also be higher. As a fuel, the engine can also be supplied with compressed liquid gas with as low a metal number 10 as a maximum of 15, but of course can also use higher metal fuel.

It may be appropriate to operate the high compressive engine using dual-fuel fuel systems using liquid gas and fuel oil 15 either separately or together. The oil may optionally be used as auxiliary pilot fuel.

The liquid gas is injected at a pressure greater than the pressure in the combustion chamber. The injection pressure is usually located in the range of 20 200-1200 bar, typically 350-900 bar. At the injection, the fuel is atomized in clouds of fine liquid droplets which immediately evaporate, after which a mixture with the other gases in the combustion chamber takes place. Liquid gas injection takes place over one or more 25 periods, which may begin immediately before the piston reaches the peak dead-end at the end of the compression stroke, for example from 6 ° KV before TDC, but otherwise is in the expansion stroke. The gas can burn when appropriately mixed with oxygen-containing air.

Each liquid gas injector liquid injector 17 is connected to the associated gas supply line 26 which, from a suitable external gas source, may be of the above type on a crude oil carrier or may be connected to a fixed line network if the engine is stationary electric power producing. The conduit 26 23 DK 173242 B1 carries the liquid gas to the liquid injector and is surrounded by the sheath 47. The fan 49 maintains an air flow in the space between the inside of the sheath and the outside of the conduit. It is preferred that the ventilation air is preheated by the freely available waste heat prior to the insertion between jacket and conduit.

This can be done, for example, by heating the air in a heat exchanger with the engine cooling water. The hot air can be fed into the jacket countercurrent with the flowing gas.

10 This can be done, for example, by the air supply being near the engine, but it is possible that there should be two fans. The heating causes no ice formation in or on the pipes in the event of leaks and full or partial discharge of the gas to the atmosphere. In such emptying, a pressure relief for atmospheric pressure will first occur. Thereafter, the liquid gas will evaporate by shock boiling within the conduits thereby cooling. The hot ventilation air counteracts a complete cooling of the gas-carrying system. The gas conducting lines can also be emptied controlled without significant amounts of gas boiling in the lines by displacing the liquid gas with another fluid which is applied to the gas conducting lines with a suitable overpressure, for example fuel oil or a gas such as inert gas.

If the engine is a marine engine, the liquid gas can be stored in a tank which is pressurized and / or cooled.

Claims (21)

1. Diesel-type combustion engine for combustion of gas compressed to a high pressure suitable for supply to the engine of at least 60 bar, said engine having an injection system with injectors which, at high pressure, inject liquid fuel into the combustion chambers of the cylinders (35), in that the injection system contains at least liquid injectors (17) for high-pressure injection of compressed liquid gas produced by volatile organic compounds evaporated from crude oil tanks (1). An internal combustion engine according to claim 1, characterized in that the injection system comprises 15 secondary injectors (16) for high-pressure injection of gaseous mixtures containing at least partially evaporated gas from petroleum tanks (1) and possibly inert gas which has been filled with the petroleum tanks as explosion-proof air. . Combustion engine according to claim 1 or 2, characterized in that the injection system comprises pilot injectors (18) for injecting inflammable pilot fuel which initiate a combustion process at the injection. Internal combustion engine according to one of claims 1-3, characterized in that a number of the liquid injectors (17) and of the secondary injectors (16) are combined in a corresponding number of dual-fuel injectors capable of injecting both the liquid gas and the gaseous, gaseous mixtures. Internal combustion engine according to one of claims 2-4, characterized in that the injection system periodically activates the secondary injector (16), even when no gaseous fuel is to be injected into the associated cylinder (35). DK 173242 B1 Combustion engine according to one of the preceding claims, characterized in that only some of the cylinders (35) are provided with secondary injectors (16), while others of the cylinders (35) are provided with liquid injectors (17), all of the cylinders. also may optionally have pilot and / or fuel oil injectors (18). Combustion engine according to one of the preceding claims, characterized in that the engine is the main engine of a ship with crude oil tanks (1), such as a shuttle tanker or a crude oil carrier, and evaporated volatile organic compounds from these tanks. , which may have temporally varying ignition characteristics, burn values and / or evaporation rates, constitute a substantial portion of the main engine's fuel consumption. Combustion engine according to claim 7, characterized in that the engine has an electronic control unit (34) which, on the basis of monitoring the instantaneous cylinder pressure, controls at least the injection pressure of the gaseous fuel gas, preferably such that the injection pressure is lower when the gas content of inert gas is greater. A method of fuel supplying a gas-fired diesel-type internal combustion engine 25 which is compressed to a high pressure suitable for supply to the engine of at least 60 bar, which has an injection system with injectors which inject high-pressure fuel into the cylinders (35). combustion chambers, characterized in that, after any temporary storage and compression, the volatile organic compounds evaporated from crude oil tanks 30 (1) are fed to the engine's fuel system and used as fuel in the engine, regardless of the time-varying ignition characteristics, burn values 35 and / or afdampningsmængder. DK 173242 B1 Process according to claim 9, characterized in that the evaporated and compressed compounds comprise both a gaseous and a liquid phase which are substantially separate from each other by the supply to the engine. Method according to claim 10, characterized in that the injection pressure of the gaseous phase is controlled such that the injection pressure is lowered as the content of inert gases in the 10 gaseous phase increases. Method according to claim 10 or 11, characterized in that the temperature of the gaseous phase in the engine's fuel and injection system is kept higher than the temperature which the gaseous phase had after compression to the pressure at which it was delivered to the engine. fuel system. Process according to claim 12, characterized in that the temperature of the gaseous phase in the fuel system is controlled to rise towards the engine. Process according to one of claims 10 - 13, characterized in that said liquid phase and said gaseous phase are both supplied to all the cylinders (35). Process according to one of claims 10 - 14, characterized in that said liquid phase is supplied to some of the cylinders (35), while said gaseous phase is supplied to others of the cylinders (35). 3 0 Process according to one of claims 9 to 15, characterized in that the engine is the main engine of a ship with crude oil tanks (1) from which volatilization of volatile organic constituents takes place and that the engine is supplied only with fuel oil to the extent necessary. as an ignition aid or is required because the current fuel needs of the engine 17 174242 B1 exceed the supply of fuel gas to the engine. Method according to one of claims 9-16, characterized in that the motor is connected to a shaft generator in a shuttle tanker or in a vessel for collecting hydrocarbons from a drilling or production well, and at least part of the steam evaporated by the oil load. volatile organic compounds are combusted in the engine which drives the shaft generator 10 for electric power generation to drive units in the dynamic positioning system of the tanker or vessel. 18. Diesel-type combustion engine for combustion of gas compressed to a high pressure suitable for injection in the cylinders of the engine of at least 15 200 bar, said engine being charged to a charge pressure of at least 3 bar absolute and having a volumetric compression ratio of at least 1: 14 and an average pressure of at least 15 bar and has an injection system with injectors which at high pressure inject liquid fuel into the combustion chambers of the 20 cylinders (35), characterized in that the injection system contains at least liquid injectors (17) for high-pressure compressed liquid gas. An internal combustion engine according to claim 18, characterized in that the engine, which is preferably a two-stroke cross-head motor, has a cylinder bore of at least 200 mm and a speed of at most 700 rpm, suitably a cylinder bore of at least 250 mm and a speed of at most 250 rpm. An internal combustion engine according to claim 18 or 19, characterized in that the compressed liquid gas has a metal number of not more than 15. An internal combustion engine according to one of claims 18 to 20, characterized in that each liquid gas injector for injection of liquid gas is connected to a gas supply line which from the outside gas source feeds the liquid gas to the liquid injector, the gas supply line. is surrounded by a jacket, that a fan maintains an air flow in the space between the inside of the jacket 5 and the outside of the conduit, and that the ventilation air is preheated.