Arrangement for water separation at a fuel tank

Technical field

The invention relates to a device for water separation for a fuel tank connected to an engine in a vehicle, according to the preamble of claim 1.

The invention relates also to a fuel tank according to claim 8 comprising the device, and a vehicle according to claim 9 comprising such a fuel tank.

Background

Fuel supply from a fuel tank to an engine in a vehicle currently involves problems with being able to apply and use the fuel in the tank for safe operation of the engine, because the fuel contains a certain amount of water. To ensure reliable operation of the engine, the water, which arises from condensation, is separated from the fuel, e.g. by means of a filter. The water from, for example, this filter accumulates in the tank and may in time represent a significant amount. This amount of water has to be removed from the tank at regular intervals, e.g. during servicing of the vehicle.

There are fuel tanks in which there is an ancillary space which receives all return fuel from the engine, i.e. fuel mixed with water. The ancillary space occupies a small proportion of the fuel tank. Fuel from the lower portion of the ancillary space is drawn off to the engine. Being of higher density than fuel, water will stratify nearest to the bottom of the ancillary space, with the result that after a time the fuel supply from the ancillary space to the engine will contain a high concentration of water. When such is the case, the engine is supplied with more water than fuel, which may lead to the engine coming to a halt.

Another problem with previously known solutions is that the siphon action which occurs upon switching off of the engine may lead to such small fuel volumes in the ancillary space that reliable operation of the engine cannot be assured until the ancillary space has filled up again. When the engine switches off, the siphon action will lead to equalisation between the levels in the fuel tank and the ancillary space, which means that the level in the ancillary space will be low (thus constituting a small volume) if the level in the fuel tank is low. This is disadvantageous in that the ancillary space needs to be as full as possible in order to be able to supply the engine continuously with fuel.

There is therefore a need for a device which separates water from fuel in an effective manner and ensures that the engine is reliably supplied with fuel.

Summary of the invention

The object of the present invention is to eliminate the above problems. This object is achieved by the fact that the line intended to supply fuel/water leads into a separate container which is situated in the ancillary space and which has its upper end always situated higher than an intended highest possible fuel level in the ancillary space.

The line to the ancillary space is intended for return fuel from the engine and for water from a water-separating filter. This mixture of fuel/water thus occurs in the container, and when the container is full the fuel will overflow the edge/aperture of the container and reach the ancillary space from which the engine is supplied with fuel, while the water, owing to its higher density, separates from the fuel and remains in the container.

This is a simple and inexpensive solution for water separation which involves no moving parts. Long service life and good functionality can thus be assured.

The ancillary space may be situated in the tank, in which case it will be partly separated from the fuel tank by a wall or the like. This version involves few additional parts in cases where existing tank walls are used in the configuration of the ancillary space.

The ancillary space may alternatively be situated outside the tank and take the form of a separate tank, which may be advantageous if available space is limited and it is undesirable to reduce the volume of the tank. The ancillary space may therefore be situated at any suitable location.

In an embodiment of the invention, the line intended to supply fuel/water from the engine is also intended, by means of a venturi tube, to draw fuel/water through a line from the fuel tank in order to deliver the contents of the lines to the container, with the result that fuel from the tank is drawn to the ancillary space without involving a pump device. This version provides an operationally reliable solution with no moving parts.

According to another embodiment of the invention, two lines are so arranged that they lead into the container, one of them being the line intended to supply fuel/water from the engine and the other a line intended to supply fuel/water from the fuel tank, the line from the tank being provided with a pump unit. This alternative configuration may be advantageous if the venturi tube does not provide sufficient fuel supply to the ancillary space, since the pump unit can be dimensioned on the basis of the engine's expected fuel requirement.

According to a further embodiment of the invention, a filter is provided in the container to ensure that water is separated from fuel which runs from the container to the ancillary space when the container is full, which may be advantageous with a view to improving the water separation in that it takes a certain time for water and fuel to stratify in the container, particularly in cases where there are powerful movements of the vehicle.

When the engine switches off and a line connects the container to the fuel tank, the level of fuel/water in the container drains to the same level as the level in the fuel tank, with the result that fuel/water and, above all, water present in the bottom of the container, accumulates in the fuel tank. This draining is entirely self-supporting and takes place by siphon action when the level in the container is higher than the level in the fuel tank. The siphon action thus has a positive effect and entails no risk of causing low levels of fuel in the ancillary space such as occur in previously known solutions in which the fuel tank and the ancillary space are connected together.

Brief description of the drawings

The invention is explained in more detail below with reference to the drawings, in which:

Figure 1 depicts a device for water separation for a fuel tank according to an embodiment of the invention when the engine is in operation,

Figure 2 depicts a device for water separation for a fuel tank according to an embodiment of the invention when the engine is switched off, and

Figure 3 depicts a device for water separation for a fuel tank according to a second embodiment of the invention.

Figure 4 depicts a venturi tube forming part of one of the embodiments of the invention.

Detailed description of the invention

Figure 1 depicts a device for water separation for a fuel tank 1 connected to an engine 16 in a vehicle. The fuel tank 1 comprises an ancillary space 2 containing a certain amount of fuel 10 and separated from the fuel tank by a wall 3 or the like. The ancillary space 2 may be situated in an outer portion of the fuel tank 1, as depicted in the drawings, e.g. in a corner of the tank, in which case the ancillary space 2 is delineated by walls between it and the interior of the fuel tank 1 and by walls of the fuel tank 1. Other positions of the ancillary space, e.g. in the interior of the tank or outside the tank, are also possible. Where space is limited, the ancillary space 2 may be separate from the fuel tank 1. When the engine 16 is in operation, a line 4 leading into a separate container 7 supplies fuel/water. The container 7 is situated at a suitable location in the ancillary space 2 and fastened therein in a suitable manner and will thus contain a mixture of fuel and water, which water, owing to its higher density, will settle nearest to the bottom of the container, whereas the fuel will settle on top of the water. The upper end 12 of the container 7 is situated higher than a highest possible fuel level 10 in the ancillary space 2 so that the fuel runs down to the ancillary space 2 when the container 7 is full, whereas the water will stay in the container 7. Fuel from which water has separated is led from the ancillary space 2 to the engine 16 via a line 6.

The container 7 has in this embodiment an elongate cylindrical shape, with an open upper end 12. The cross-section of the container 7 in this case is circular, but it may also be, for example, oval or rectangular.

The ancillary space 2 occupies only a small proportion of the fuel tank. How large a proportion of the tank the ancillary space should occupy depends on the expected fuel requirement of the engine 16, e.g. the volume of the ancillary space may be of the order of 10-40% of the whole volume of the fuel tank 1.

In the container 7 there will thus be a mixture of fuel and water, which water, owing to its high density, will be nearest to the bottom of the container 7, as illustrated by ref. 8, whereas the fuel will stratify on top of the water higher up in the container 7. When the level 8 in the container 7 reaches the upper end 12 of the container 7, the fuel will thus overflow the edge 12 and run down into the ancillary space 2 outside the container 7.

In an embodiment of the device, return fuel is supplied from the engine 16 to the container 7 via the line 4. The return fuel may contain a certain amount of water arising from condensation and separated out, e.g. by an undepicted water-separating filter, before the fuel is supplied to the engine 16. The line 4 which supplies fuel/ water is provided with a venturi tube, depicted schematically at 13 in Figure 1 and in more detail in Figure 4. The venturi tube comprises a section 17 with reduced diameter which causes an increase in the flow velocity through the section 17, resulting in a negative pressure and consequent suction in a line 5 which has its one end connected to the section 17 where it joins the line 4 and its other end leading into the fuel tank 1. Fuel/water is thereby drawn from the fuel tank 1 through the line 5 for delivery of the contents of the lines 4, 5 into the container 7.

Fuel is drawn to the engine 16 from the lower portion of the ancillary space 2 via a line 6. There is thus assurance that the inlet to the line 6

will always be below the fuel level 10 even if the ancillary space 2 is not entirely full of fuel. However, the ancillary space needs to be always relatively full of fuel to ensure reliable operation of the engine 16.

When the engine switches off, the fact that the fuel level 11 in the fuel tank 1 is the same as or lower than the level 8 in the container 7 means that the levels will become equal. This is because siphon action between the connected spaces of the container 7 and the fuel tank 1 causes the level 8 of fuel/ water in the container 7 to drop to the same level 1 Ib as the fuel 1 Ia in the fuel tank 1, as depicted in Figure 2. The fact that the line 4 has its outlet situated at the bottom of the container means that water will substantially drain to the fuel tank 1 without causing any problems there, since no fuel is supplied from the fuel tank 1 directly to the engine 16. That space is also considerably larger than the ancillary space 2, so the water concentration in it will be relatively low and cause no problems. A further advantage of this version is that there is no direct connection between the ancillary space 2 and the fuel tank 1 , with the result that the fuel in the ancillary space 2 no longer drains to the fuel tank 1 by siphon action when the engine 16 stops, since the ancillary space 2 will keep the fuel at the higher level so that plenty of fuel is already present at the next start of the engine 16, which was not the case with previous solutions.

Figure 3 depicts a further embodiment of the invention in which a line 15 from the fuel tank 1 is provided with a separate pump unit 14 of a suitable type instead of the previously mentioned venturi tube solution. Both the line 4 which then supplies fuel/water from the engine 16 and the line 15 which connects the fuel tank 1 and the container 7 then deliver fuel/water to the container 7.

A filter may be provided in the container 7 to ensure better separation of water from the fuel which overflows the edge of the container 7 to the ancillary space 2 when the container is full.

The volume of the container 7 will depend on, for example, the volume of the fuel tank 1 , the expected operating time of the vehicle and the magnitude of the flow of fuel and water. However, the volume is preferably such that the container 7 can accommodate the amount of water expected to be separated during an operating cycle of the engine 16. After the engine has switched off, the water in the container 7 drains to the fuel tank 1 via the connection to the fuel tank 1. The container 7 has with advantage the form of an oblong container, e.g. a circular cylinder open at its upper end 12 or a cylinder of oval or angular cross-section. As an alternative to an entirely open upper end, the cylinder may be partly closed at its upper end and only provided with apertures in the form of holes or the like for supplying and leading away fuel/water. Hoses or the like may be connected to the apertures.

In another embodiment of the invention, the container may have an upper end which is partly closed and provided with one or more apertures for leading fuel away to the ancillary space 2. Hoses or the like may also be connected to the apertures to lead the fuel to the ancillary space 2.

Although it is described above on the basis of some exemplifying embodiments, the invention is not limited to them but is defined on the basis of the accompanying claims.