FIELD OF THE INVENTION

The present invention relates to a fuel system for marine vessels such as e.g. cargo ships or freighters that is suitable for handling fuel in the form of an oil-in-water emulsion. Such marine vessels typically use a large multi-cylinder self-igniting combustion engine for propulsion .

BACKGROUND OF THE INVENTION

Large ocean going cargo ships are almost exclusively powered by large multi-cylinder internal combustion engines running on heavy fuel oil. Heavy fuel oil is a residual-type fuel oil with a high viscosity. Residual means the material remaining after the more valuable cuts of crude oil have boiled off. The viscosity nature of the oil means that the oil must be heated, usually by a recirculated low pressure steam system, to ensure that the oil has a viscosity low enough so that it can be pumped. Heavy Fuel Oil, (bunker fuel) has a relatively low costs compared to distillate type oil.

However, further cost reductions are desirable and oil- in-water emulsion fuels provide an alternative means of utilizing heavy hydrocarbons (e.g. residual material, or other hydrocarbons with high viscosity, high density, low flowability) as a fuel for energy production. Oil-in- water emulsion fuels utilize water as the diluent, providing the many potential benefits both in terms of price and performance. However, oil-in-water emulsion fuels have very different characteristics from heavy fuel oil. Basically, the oil-in-water emulsion fuels have two separate viscosities in one fluid, the one viscosity being viscosity of the water itself and the other viscosity being the viscosity of the oil itself. The oil in the oil-in-water fuel emulsion is typically a very high viscous low-cost very heavy residual. Due to the high viscosity of the oil component in the oil-in-water fuel emulsion an operation temperature above ambient is desirable. However, the oil-in-water emulsion fuel should not start to boil and therefore the operation temperature is limited to the boiling temperature of the water under the presiding pressure in the system. Further, oil-in- water emulsion fuels are inherently instable and mechanical action on this type of fuel, such as pumping, throttling or similar activity can lead to deterioration of the oil-in-water emulsion fuel and lead to the emulsion breaking up into oil and water. Thus, in comparison with heavy fuel oil that can be heated to temperatures well above the boiling temperature of water and that has practically no restrictions on mechanical handling a fuel system for handling oil-in-water emulsion fuel needs to take account for greater restrictions due to the nature of the fuel.

DISCLOSURE OF THE INVENTION

On the above background it is an object of the present invention to overcome or at least reduce the problems indicated above.

According to a first aspect this object is achieved by a providing fuel system for delivering an oil-in-water emulsion fuel to an internal combustion engine, the fuel system comprising an oil-in-water emulsion fuel tank, a feed conduit, means for heating the oil-in water- emulation fuel in the feed conduit, a diaphragm-type fuel supply pump with an inlet connected to the oil-in-water emulsion fuel tank and an outlet connected to a feed conduit .

By providing a hydraulically operated diaphragm type fuel supply pump it becomes possible to reliably deliver an oil-in-water emulsion fuel to an internal combustion engine. A diaphragm pump is not affected by the properties of the oil-in-water emulsion fuel that provide for little lubrication. Further, the diaphragm pump exposes the oil-in-water emulsion fuel to less mechanical action thereby affecting the stability of the emulsion lesser than other types of positive displacement pumps.

In a first possible implementation form of the first aspect the diaphragm-type fuel supply pump is a hydraulically actuated diaphragm pump

In a second possible implementation form of the first aspect the diaphragm-type fuel supply pump is driven by a variable speed drive.

In a third possible implementation form of the first aspect the fuel system comprises at least two fuel supply pumps in parallel between the fuel tank and the feed conduit.

In a fourth possible implementation form of the first aspect the oil-in-water emulsion fuel tank is a service tank and wherein the service tank is supplied with an oil-in-water emulsion fuel from a bunker tank.

In a fifth possible implementation form of the first aspect the fuel supply pump is positioned at least 2 meter, preferably at least 3 meter and even more preferable at least 4 meter under the outlet of the service tank so that gravity assists the oil-in-water emulsion fuel from the service tank to the supply pump.

In a sixth possible implementation form of the first aspect the fuel system further comprises a bunker-to- service tank conduit connecting the bunker tank to the service tank and bunker-to-service tank diaphragm-type supply pump in the bunker-to-service tank conduit.

In a seventh possible implementation form of the first aspect the fuel system further comprises a pressure indicator just upstream and just downstream of the a diaphragm-type fuel supply pump.

According to a second aspect of the invention there is provided a marine vessel comprising a fuel system according to the first aspect. According to a third aspect the object above is achieved by providing a fuel system for delivering an oil-in-water emulsion fuel to an internal combustion engine, the fuel system comprising an oil-in-water emulsion fuel tank, a variable speed fuel supply pump with an inlet fluidly connected to the oil-in-water emulsion fuel tank and an outlet connected to a feed conduit that is connected to a fuel inlet of the internal combustion engine, a return conduit connected to the internal combustion engine for returning excess fuel from the internal combustion engine, the return conduit being fluidly connected to the inlet of the fuel supply pump, means for heating the oil- in water emulation fuel in the feed conduit, means for determining the feed flow rate in the feed conduit, means for determining the return flow rate in the return conduit, and a controller configured to adjust the speed of said variable speed fuel supply pump to obtain a predetermined ratio between the feed flow rate and the return flow rate.

By providing a single stage fuel system with the controller configured to let the feed pump deliver a flow rate with a control excess margin over the consumption of the internal combustion engine is possible to avoid using a two-stage fuel system including a recirculation circuit. This is of particular advantage when using oil in water emulsion fuel, since the emulsion can be broken if it is exposed to repeat mechanical action, as may happen in a recirculation circuit. Thus the fuel system according to the first aspect is particularly useful for delivery oil in water emulsion fuels that are sensitive to being broken up into oil and water.

In a first possible implementation form of the third aspect the controller is configured to adjust the fuel supply pump to obtain a constant circulation factor, preferably a circulation factor between 1,5 and 2,75 and more preferably a circulation factor between 2.0 and 2,5 and most preferably a circulation factor of approx. 2,3.

In a second possible implementation form of the third aspect the fuel supply pump is driven by a variable speed drive . In a third possible implementation form of the third aspect the variable speed drive comprises an electrical drive motor In a fourth possible implementation form of the third aspect the fuel system further comprises a motorized control valve for controlling a restriction in a conduit to the suction side of the fuel supply pump and comprising a motorized control valve for controlling a restriction in a the return conduit, the motorized control valve being connected to and controlled by the electronic control unit. According to a fourth aspect of the invention there is provided a marine vessel comprising a fuel system according to the third aspect.

According to a fifth aspect the object above is achieved by providing a fuel system for delivering an oil-in-water emulsion fuel to an internal combustion engine, the fuel system comprising an oil-in-water emulsion fuel tank, a fuel supply pump with an inlet connected to the oil-in- water emulsion fuel tank and an outlet connected to a feed conduit that is fluidly connected to a fuel inlet of the engine, adjustable means for heating the oil-in-water emulsion fuel in the feed conduit, a temperature sensor for providing a temperature signal, the temperature sensor being arranged to sense the temperature of the oil-in-water emulation fuel in the feed conduit downstream of the controllable means for heating the oil- in-water emulsion fuel, and a control unit in receipt of the temperature signal, the control unit being configured to adjust the means for heating the oil-in-water emulsion fuel in the feed conduit so as to keep the sensed temperature of the oil-in-water emulsion fuel in the feed conduit between 70°C and 90°C. By maintaining providing adjustable means for heating the oil-in-water emulsion fuel in the feed conduit the fuel in the supply conduit at a temperature between 70°C and 90°C the oil-in-water emulsion fuel can be supplied to an internal combustion engine with optimal properties for good combustion.

In a first possible implementation form of the fifth aspect the control unit being configured to adjust the means for heating the oil-in-water emulsion fuel in the feed conduit so as to keep the sensed temperature of the oil-in-water emulsion fuel in the feed conduit between 75 °C and 85 °C. In a second possible implementation form of the fifth aspect the adjustable means for heating the oil-in-water emulsion fuel in the feed conduit is provided with electric heating means. In a third possible implementation form the fuel system of the fifth aspect the adjustable means for heating the oil-in-water emulsion fuel in the feed conduit is provided with heating means operated on hot water. In a fourth possible implementation form of the fifth aspect the feed conduit is provided with a temperature sensor and wherein the electronic control unit is in receipt of a signal from the temperature sensor in the feed conduit.

According to a sixth aspect of the invention there is provided a marine vessel comprising a fuel system according to the fifth aspect. According to a seventh aspect the object above is achieved by providing a fuel system for delivering an oil-in-water emulsion fuel to an internal combustion engine, the fuel system comprising an oil-in-water emulsion fuel tank, a source of hot water, a fuel supply pump with an inlet connected to the oil-in-water emulsion fuel tank and an outlet connected to a feed conduit that is fluidly connected to a fuel inlet of the engine, and a water-to-fuel water heat exchanger in the feed conduit for heating the oil-in-water emulsion fuel using hot water from the source of hot water.

By providing the fuel system with a water-two-fuel heat exchanger, it becomes possible to heat the oil-in-water emulsion fuel with hot water as opposed to steamer interested. This has the inherent advantage that the heating medium cannot heat the oil-in-water emulsion fuel to temperatures above the boiling point of the water in the fuel.

In a first possible implementation form of the seventh aspect the source of hot water is configured to use waste heat from the internal combustion engine, such as cooling water from the internal combustion engine.

In a second possible implementation form of the seventh aspect the source of hot water includes a steam-to-water heat exchanger. In a third possible implementation form of the seventh aspect the fuel system further comprising a hot water circulation pump connected to a hot water supply line leading to the fuel to water to fuel heat exchanger and a return line from the water-to-fuel heat exchanger to the hot water recirculation pump.

In a fourth possible implementation form of the seventh aspect the hot water circulation pump is driven by variable speed drive and further comprising a controller configured to maintain the temperature of the water delivered to the water-to-fuel heat exchanger at a predetermined set point by adjusting the speed of the hot water circulation of pump with the variable speed drive.

According to an eighth aspect of the invention there is provided a marine vessel comprising a fuel system according to the seventh aspect.

According to a ninth aspect the object above is achieved by providing a fuel system for delivering an oil-in-water emulsion fuel to an internal combustion engine, the fuel system comprising an oil-in-water emulsion fuel tank, a fuel supply pump with an inlet and an outlet, the inlet of the fuel supply pump being connected to the oil-in- water emulsion fuel tank and to a return conduit, the outlet of the fuel supply pump being connected to a feed conduit that is fluidly connected to a fuel inlet port of the engine, means for heating the oil-in-water emulsion fuel in the feed conduit for heating the oil-in-water emulsion fuel passing through the feed conduit, the return conduit being fluidly connected at one end to a fuel return port the internal combustion engine for returning excess oil-in-water emulsion fuel from the internal combustion engine, the return conduit being at another end connected to the inlet of the fuel supply pump and connected to the oil-in-water emulsion fuel tank, and a valve arrangement for controlling the portion of the return fuel that flows back to the service tank.

By providing the valve arrangement for controlling the portion of return fuel that flows back to the service tank it becomes possible to selectively operate to heat up the fuel in the system quickly when this is needed, e.g. during engine start up or to use the maximum volume including the service tank to minimize deterioration of the emulsion due to mechanical action.

In a first possible implementation form of the ninth aspect the fuel system further comprises a first control valve between the return conduit and the inlet of the fuel supply pump.

In a second possible implementation form of the ninth aspect the fuel system further comprises a second control valve between the return conduit and the oil-in-water emulsion fuel tank (30) .

In a third possible implementation form the of the ninth aspect the fuel system further comprising a temperature sensor configured for sensing the temperature of the oil- in-water emulsion fuel in the feed conduit at a position downstream of the supply pump and a controller operatively connected to the temperature sensor and the controller further being configured to direct a smaller portion of the return flow of oil-in-water emulsion fuel in the return conduit to the inlet of the fuel supply pump if the temperature measured by the temperature sensor is below a first given threshold. In a fourth possible implementation form of the ninth aspect the controller is further configured to direct a larger portion return flow of oil-in-water emulsion fuel in the return conduit to the oil-in-water emulsion fuel tank if the temperature measured by the temperature sensor is above a second given threshold.

In a fifth possible implementation form of the ninth aspect the controller is further configured to control the valve arrangement to direct a portion of the return flow of oil-in-water emulsion fuel in the return conduit to the oil-in-water emulsion fuel tank and to direct the remaining portion of the return flow of oil-in-water emulsion fuel in the return conduit to the inlet of the fuel supply pump if the temperature measured by the temperature sensor is above the first given threshold and below the second given threshold.

In a sixth possible implementation form of the ninth aspect the controller is operatively connected to the first control valve and to the second control valve.

In a seventh possible implementation form of the ninth aspect the first control valve is a motorized valve with a variable restriction and wherein the second control valve is a motorized valve with a variable restriction.

According to a tenth aspect of the invention there is provided a marine vessel comprising a fuel system according to the ninth aspect.

Further objects, features, advantages and properties of the fuel system, large ocean going cargo ship and method according to the invention will become apparent from the detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following detailed portion of the present description, the invention will be explained in more detail with reference to the exemplary embodiments shown in the drawings, in which

Fig. 1 is a side view of a marine vessel according to an example embodiment,

Fig. 2 is a diagrammatic representation of an embodiment of a fuel system for the marine vessel of Fig. 1,

Fig. 3 is a diagrammatic representation of another embodiment of a fuel system for the marine vessel of Fig. 1,

Figure 4 is a perspective view of a diaphragm fuel supply pump, and

Figure 5 is a partial cross-sectional view of the diaphragm supply pump shown in Figure 4.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Fig. 1 shows a side view of a marine vessel 1 that uses a fuel system according to an example embodiment. In this embodiment the marine vessel 1 is a container ship. However, the marine vessel 1 could just as well be a general cargo vessel, a tanker, a dry-bulk carrier, a multipurpose vessel, a reefer ship or any other large ocean going type of cargo ship. The marine vessel 1 has a hull 2 and one or more engine rooms 3 provided inside the hull 2. The large ocean going cargo ship 1 is powered by one or more large self- igniting internal combustion engines 4, i.e. four-stroke or two-stroke self-igniting preferably turbocharged internal combustion engines 4 located in an engine room 3. The large self-igniting internal combustion engine (s) 4 are operated on an oil-in-water emulsion fuel for most of the time, and can be operated on marine oil if needed. The large self-igniting internal combustion engine (s) 4 drive (s) the propellers ( s ) and there are one or more auxiliary engines (generator sets) that provide electrical power and heat for various consumers aboard the marine vessel 1.

The hull 2 also contains a fuel system that is described in greater detail below and the fuel system includes at least one bunker tank 6 for storing an oil-in-water emulsion fuel therein.

The large ocean going cargo ship 1 also has one or more funnels 7 and a bridge 8. Containers are shown on the deck in container bays filled with rows of containers in a plurality of tiers. Containers can also be stowed inside cargo space in the hull 2.

Fig. 2 is a diagrammatic representation of a fuel system according to an exemplary embodiment and of a large self- igniting internal combustion engine 4 that is supplied with oil-in- water emulsion fuel by the fuel system. The fuel system includes a bunkering manifold 9 on the port side and on the star board side of the marine vessel 1. The bunkering manifolds 9 are connected via pipeline that includes a handful of the operating butterfly valve 10 to one or more bunker tanks 6.

In an embodiment the bunker tanks 6 are heated, for example using a heating coil, such as an electric heating coil or heating coil operated by warm water. Oil-in-water emulsion fuel is stored in the bunker tank 6. The oil-in- water emulsion fuel is in an embodiment kept at a temperature of approximately 20 to 30°C in the bunker tank 6. A bunker tank to service tank feed line 26 serves to transport the oil-in-water emulsion fuel from the bunker tank 6 to the one or more service tanks 30.

A pumping station including at least two supply pumps 22 in parallel is provided in the bunker tank to service tank feed line 26. In an embodiment the supply pumps 22 are hydraulically operated diaphragm pumps. Each of the supply pumps 22 is driven by electric drive motor (not shown) . In an embodiment a pressure indicator PI is provided just upstream and just downstream of the supply pumps 22. In an embodiment the service tanks 30 are provided with a heating coil, such as for example an electric heating coil or a hot-water heating coil in order to keep the oil-in-water emulsion fuel stored in the service tank 30 at a temperature between 30° and 40°C.

A supply line 36 connects the service tanks 30 to a pumping station that includes at least two supply pumps 52 arranged in parallel. The supply pumps 52 are hydraulically operated diaphragm pumps that will be described in greater detail further below. The supply pumps 52 are driven by an electronic drive 51 that includes an electric drive motor that is powered by a variable drive so as to allow the supply pumps 52 to be operated a variable speed. In the drawing only a single drive 51 is shown, it is however understood that each of the supply pumps 52 is driven by an electric drive 51. The supply pumps 52 are flexible mounted and pulse damped by pulse damper 56 in order to facilitate measuring the flow rate of the fuel delivered by the supply pumps 52.

That fuel system also includes a marine oil tank 40 for storing marine oil. The marine oil tank 40 is connected to the pumping station with the fuel supply pumps 52 via supply line 42.

A switchover valve 38 has one inlet port connected to the fuel supply line 36 and has one inlet port connected to the fuel supply line 42. An outlet port of the switchover valve 38 is connected to the pumping station with the fuel supply pumps 52. The position of the switchover valve 38 determines whether the pumps receive oil-in- water emulsion fuel from the service tanks 30 or marine oil from the marine oil tank 40. The fuel system is configured for normal operation with oil-in-water fuel emulsion but can be operated with marine oil if necessary, e.g. for flushing the fuel system with marine oil if a large overall job is needed or for longtime standstill (several months) . A similar switchover valve 48 is provided for ensuring that return fuel from the large self-igniting internal combustion engine 4 is returned to the appropriate tank, i.e. service tank 30 or marine oil tank 40, respectively.

A pressure indicator PI is provided just downstream and just upstream of each of the fuel supply pumps 52. The fuel supply pumps 52 are arranged several meters below the outlet of the service tanks 30 in order to let gravity assist in transporting the oil-in-water emulsion fuel from the service tanks 30 to the inlet of the fuel supply pumps 52. The difference in the height between the outlet of the service tanks 30 and the inlet of the supply pumps 52 is preferably at least 2 meter, more preferable at least 3 meter and even more preferable at least 4 meter. A feed conduit 55 connects the outlet of the fuel supply pumps 52 to the fuel inlet port of the internal combustion engine 4. A flow meter 53 is provided downstream of the pumping station. A temperature indicator and control 54 is arranged downstream of the flow meter. The feed conduit 55 passes at least one (preferably at least two) water-to-fuel heat exchanger 60. The water-to-fuel heat exchanger 60 is operated with hot water and the amount of heat transferred to the fuel is controlled by adjusting the flow rate and temperature of the hot water that is delivered to the water-to-fuel heat exchanger 60. The water-two-fuel heat exchanger 60 can be a plate heat exchanger or a tube heat exchanger. Hot water for the water-to-fuel heat exchangers 60 can be provided using waste heat from the engine, such as jacket cooling water, or as shown in Fig. 2 by heating the water with a steam-to-water heat exchanger 70. The hot water is circulated by hot-water circulation pumps 94 using a hot- water supply line 78 and a hot-water return line 77. An expansion vessel 90 is connected to the hot-water return line.

An electronic control unit 50 receives a signal from temperature indicator and controller 64. The electronic control unit 50 also receives temperature information on the temperature indicator and controller 63 that indicates the temperature of the fuel leaving the water- to-fuel heat exchanger. The electronic control unit 50 uses these temperatures to determine the speed of the circulation pumps 94 and to control the amount of steam delivered to the steam to water heat exchangers 70 with a control valve 68 that is arranged in a steam supply line 78. The hot water temperature as sensed by the temperature indicator in controller 64 has a fixed set point, for example 98°C and the electronic control unit 50 is configured to maintain this fixed set point for the hot-water temperature of the water supply to the water- to-fuel heat exchangers 60. The electronic control unit 50 is configured to keep the in oil-in-water emulsion fuel in the feed conduit 55 at the temperature sensor 63 between approximately 70°C and 90°C, preferably between 75°C and 85°C. This is achieved by the electronic control unit 50 adjusting the speed of the hot-water circulation pumps 94 in response to the signal from the temperature indicator and controller 63 that indicates the temperature of the oil-in-water emulsion fuel downstream of the hot water to fuel heat exchangers 60.

A filter arrangement 80 is provided in the feed conduit 55 downstream of the water-to-fuel heat exchanger 60. The filter 80 arrangement includes a standby manual filter and a Boll automatic filter with magnets, and has a mesh no finer than approximately 150 micron. A pulsation damper 82 is connected to the feed conduit 55 a position just downstream of the filter arrangement 80.

The feed conduit 55 connects to the inlet port of the internal combustion engine 4. An engine pulsation damper 98 is provided just upstream of the fuel inlet port of the internal combustion engine 4. A return conduit 66 is connected to a fuel return port of the internal combustion engine 4. An engine pulsation damper 96 is provided just downstream of the fuel outlet port of the internal combustion engine 4. A flow meter 57 is provided in the fuel return conduit 66 and connected to the control unit 50.

The fuel system is a single stage system using the fuel supply pumps 52 as supply and circulation pumps. The engine control unit 50 determines the difference in flow between the feed conduit 55 and the return conduit 66 on the basis of the signal from flow sensor 53 in the feed conduit and flow sensor 57 in the return conduit and the engine control unit 50 is configured to adapt the speed of the pumps 52 accordingly. Thus, the speed of the pumps 50 is adjusted such by the electronic control unit that it exceeds the consumption of the large internal combustion engine 4 by a given margin that corresponds to a desired amount of recirculating fuel.

In an embodiment one of the supply pumps 52 is running close to maximum speed at all times, also during engine standstill with the electronic control unit 50 configured to ramp up the second and/or third supply pump 52 as demand increases when the large self-igniting internal combustion engine 4 is powered up and an operation.

The two motorized valves 37 and 46 are controlled under command from the electronic control unit 50 to control the return flow to the suction side of the supply pumps 52. The motor operated valves 37 and 46 are motorized valves with a variable restriction. Thus, by adjusting the restriction of each of the valve's the portion of the return fuel that flows to the service tank 30 can be adjusted according to needs. The electronic control unit 50 uses the criterion to maintain the temperature set point (temperature sensor 54) before the water-to-fuel heat exchangers, in an embodiment to approximately 50°C to 60°C. This ensures that the system quickly heats up when started before spilling hot fuel back to the service tanks 30. Once the system is warmed up, this criterion will ensure that the major part of the return fuel flows through the return to service tank line 34 to the service tanks 30. This ensures that it is not the same small volume of water-in-oil emulsion fuel that is recirculated for long period and instead the larger amount of fuel in the service tanks 30 is included in the recirculation. The reason for avoiding a small volume of fuel to be recirculated for longer periods is that the recirculation process can deteriorate the properties of the oil-in- water emulsion fuel and break up the emulsion.

Fig. 3 diagrammatically illustrates another embodiment the fuel system. The system according to Fig. 3 is very similar to the fuel system of Fig. 2 and the same reference numerals indicate the same components.

However, the fuel system according to Fig. 3 is different in that it is a two-stage system with feed pumps 52 and circulation pumps 59 with a mixing tank 58 therebetween. Preferably, the supply pumps 52 and the circulation pumps 59 are hydraulically operated diaphragm pumps.

The water in fuel emulsion fuel in the feed conduit 55 is heated by a steam to fuel heat exchanger 71. The steam to fuel heat exchanger 71 are provided with steam by a supply line that is adjusted by a control valve 68 in the control electronic control unit (not shown) . Alternatively, the fuel in the supply line 55 can any of the embodiments be heated with electric tracing. Otherwise, the operation of the fuel system according to Fig. 3 is essentially identical to the fuel system of the embodiment according to Fig. 2 is the same set point temperatures for the all in water emulsion fuel.

The fuel pumps 22,52 are in an embodiment rotary- operated, oil-backed/driven diaphragm pumps. There pumps are high-pressure pumps capable of pumping oil-in-water emulsion fuel because it has no sliding pistons or seals to abrade. The diaphragm isolates the pump completely from the fuel, thereby protecting the pump. Such a diaphragm pump is shown in Figs. 4 and 5. Pump 22,52 has a drive shaft 122 rigidly held in the pump housing 124 by a large tapered roller bearing 126 at the rear of the drive shaft 122 and a small bearing (not shown) at the front of the drive shaft 122. Sandwiched between another pair of large bearings 129 is a fixed- angle cam or wobble plate 128. As the drive shaft 122 turns, the wobble plate 128 moves, oscillating forward and back converting axial motion into linear motion.

The three piston assemblies 130 (only one piston assembly is shown) are alternately displaced by the wobble plate 128. Each piston is in an enclosure including a cylinder such that the enclosure is filled with oil. A ball check valve 132 in the bottom of the piston/cylinder assembly 130 functions to allow oil from a reservoir 127 (wobble plate 128 is in the reservoir) to fill the enclosure on the suction stroke. During the output or pumping stroke, the held oil in the enclosure pressurizes the back side of diaphragm 134 and as the wobble plate moves, causes the diaphragm to flex forward to provide the pumping action. Each diaphragm 134 has its own pumping chamber 135 that is associated with an inlet and an outlet check valve assembly 136,137. As the diaphragm 134 retracts, oil-in-water emulsion fuel enters the pump 22,52 through a common inlet and passes through one of the inlet check valves 136. On the output or pumping stroke, the diaphragm 134 forces the oil-in-water emulsion fuel out the discharge check valve 137 and through the manifold common outlet. The diaphragms 134, equally spaced from one another, operate sequentially to provide constant, virtually pulse-free flow of oil-in-water emulsion fuel.

The fuel system of has been described in detail with reference to a single oil-in-water fuel bunker tank, a single oil-in-water fuel day tank and a single purifier but it is understood that there can be a plurality of any of these tanks and purifiers in any desirable combination of numbers. The term "comprising" as used in the claims does not exclude other elements. The term "a" or "an" as used in the claims does not exclude a plurality. Although the present invention has been described in detail for purpose of illustration, it is understood that such detail is solely for that purpose, and variations can be made therein by those skilled in the art without departing from the scope of the invention.