WO2005114116A1

WO2005114116A1 - Method and device for measuring the volume of air space in a container

Info

Publication number: WO2005114116A1
Application number: PCT/GB2005/002023
Authority: WO
Inventors: John Dennis Lane; Joseph Luis Esparza; David James Nicholson
Original assignee: John Dennis Lane; Joseph Luis Esparza; David James Nicholson
Priority date: 2004-05-22
Filing date: 2005-05-23
Publication date: 2005-12-01
Also published as: WO2005114113A2; WO2005114113A3; GB0411490D0; GB2414810A; GB0510435D0

Abstract

A meter (1), for determining a volume of a liquid, such as fuel, present in a tank of known volume, comprises a pressurising pump (2) connectable via a measurement unit (3) and a flexible pressure hose (4) to a fitting (5) capable of forming a gas-tight seal with an opening of a fuel tank filler pipe, or the like. The measurement unit (3) contains a valve (8) which in a first position (9) connects the pump (2) to the hose (4), fitting (5) and fuel tank, and in a second position (10) connects the hose (4), fitting (5) and fuel tank to a calibrated restrictor (11) leading to open air. The measurement unit (3) also contains a pressure transducer (12) to measure the pressure within the hose (4), and an electronic control unit, linked to the transducer (12), that controls the valve (8). The fuel tank is pumped up to a preselected pressure, above ambient, at which point the valve (8) is operated to connect it to the restrictor (11), so that pressurised air in the tank is released at a substantially constant rate therethrough. A timer measures how long the pressure in the hose (4) and tank takes to fall between two preselected values, from which an air volume in the tank is calculated, and hence a fuel volume.

Description

METHOD AND DEVICE FOR MEASURING THE VOLUME OF AIR SPACE IN A CONTAINER

The present invention relates to a device to determine a volume of fluid present in a tank or other container. More particularly, but not exclusively, it relates to a device to determine a volume of fuel present in a vehicle fuel tank, for example so as to compare volumes present before and after use, and to a method of use of such a device.

When a car, van or other vehicle is hired out, it is common for a hire agreement to specify that the vehicle should be returned with the same volume of fuel in its fuel tank as was present when it was driven away. Should there be a deficit, the hirer is liable to pay for the vehicle to be refuelled to the initial level.

However, in practice, it is difficult to assess exactly how much fuel is present in a vehicle fuel tank, using only the vehicle's dashboard fuel gauge, which is usually connected to a float sensor within the tank. The gauge can normally be read to no better than the nearest eighth of a tank-full, which will typically represent five to ten litres of fuel. It is thus possible to return a vehicle with significantly less fuel in its tank, without this being clearly indicated by its fuel gauge. Furthermore, in borderline situations, considerations such as good customer relations will often militate against arguing with a customer over whether a fuel gauge needle is nearer to three-eighths of a tank or a quarter of a tank, for example.

It is estimated that such shortfall causes loss to vehicle hirers of around £250,000 per year in the United Kingdom alone. This could be extrapolated to an annual loss for the entire vehicle hire market of approximately £80 million. There is hence a need for a precise and unequivocal means of measuring how much fuel is present in a vehicle's tank, before and after use.

Such means should, however, preferably not involve modification to the vehicles themselves, on grounds of cost and inconvenience. It should be quick and easy to use, and must be safe for use in the presence of highly inflammable fuel vapours.

Conventional liquid level sensors would not be appropriate, since they would be significantly affected by the exact attitude of the vehicle to the horizontal when the measurements are taken. In any case, it is difficult to access the fuel itself from outside the tank. However, an approach that appears to have received little attention is to measure the volume of the air above the fuel in the tank. In practice, the volume of air above the fuel will include the volume of a filler pipe leading from a filler cap or the like to the fuel tank, so the term "tank" hereinafter should be understood also to comprise such piping.

Vehicle fuel tanks will be produced to a standard size for any given model. Thus, the volume of fuel in the tank plus the volume of air above it will be a constant (strictly speaking, only true at a constant temperature, but such considerations can be allowed for mathematically, or by calibrating at a range of temperatures). In principle, a change of air volume in the tank will indicate a change in fuel volume, and measuring air volume has the advantage that a direct connection with this volume can be established through an existing, unmodified filler cap.

While a particular problem to be addressed is the measurement of fuel volumes within vehicle fuel tanks, as discussed above, there will be many other applications in which quick and accurate measurements of liquid volumes within substantially rigid containers will be required. A device suitable for measuring fuel volumes may well also be applicable to other such measurement needs.

It is hence an object of the present invention to produce a device to determine the volume of liquid present in a container by measuring the volume of gas in the container, and provide a method for determining such volumes and changes in such volumes, using said apparatus.

According to a first aspect of the present invention, there is provided a device to measure a volume of liquid held within a container comprising means to connect the device to the container, means to alter the gas pressure within the container, gas flow restrictor means, valve means to connect the container either to the pressure altering means or to the restrictor means, means to measure pressure within the container, and means to time a period taken for the pressure within the container to change from a first predetermined value to a second predetermined value while the container is connected to the restrictor means.

Preferably, the device is provided with display means to indicate said period. Alternatively or additionally, the device may be provided with memory means adapted to record said period for future reference, or for subsequent transmission to a separate computing device.

Advantageously, said display means may comprise numeric or alphanumeric display means.

Optionally, said display means comprises a liquid crystal display.

Preferably, the device is provided with electronic control means.

Advantageously, said electronic control means is adapted to operate the valve means.

The electronic control means may be adapted to operate the valve means so as to connect the container to the restrictor means when the pressure in the container has been altered to a third preselected value, further than said first and second values from ambient pressure.

The gas flow restrictor means preferably comprises calibrated orifice means through which gas may flow at a substantially constant rate.

The device may be provided with means to convert said period to a liquid volume within a particular container.

Said conversion means may comprise a set of graphs or tables of said periods against gas volume and/or liquid volume for particular preselected containers. Alternatively or additionally, the device may be provided with memory means containing data to enable conversion of said periods to gas volumes and/or liquid volumes for particular preselected containers, and the electronic control means is adapted to perform said conversion.

The device may then be provided with display means adapted to indicate a calculated volume.

The pressure-altering means preferably comprises pump means.

Advantageously, the pump means is manually- or pedally-operable.

The pump means may be adapted to raise the pressure within the container above ambient pressure.

Alternatively, the pump means may be adapted to reduce the pressure within the container below ambient pressure.

The pressure-altering means may alternatively comprise a source of gas under pressure, such as a compressed-air line or a reservoir vessel containing gas under pressure.

The device may be provided with pressure release means adapted to operate at a pressure differential within the container below that which might damage the container. The connecting means may be adapted to form a gas-tight connection with a range of different container apertures, for example fuel tank filler pipe openings of different models of vehicle.

According to a second aspect of the present invention, there is provided a method for measuring a volume of liquid held within a container comprising the steps of providing a device as described in the first aspect above, connecting it to an aperture of the container, connecting the pressurising means to the container and raising the pressure therein to above a first predetermined value, connecting the container to the gas flow restrictor means so as to allow gas from the container to exit therethrough, timing the period taken for the pressure within the container to fall from said first predetermined value to a second predetermined value, and calculating from said period a gas volume and hence a liquid volume within the container.

Preferably, the method further comprises the steps of subsequently measuring an altered liquid volume within the container as described above and calculating a change in liquid volume between said measurements.

An embodiment of the present invention will now be more particularly described by way of example and with reference to the accompanying drawing, in which:

Figure 1 is a frontal elevation of a fuel volume meter embodying the present invention. Referring now to the figure, a fuel volume meter 1 comprises a pressuring pump 2 connected to a measurement unit 3, which is in turn linked by means of a flexible pressure hose 4 to a tank connector fitting 5. The tank connector fitting 5 is shaped to form a gas-tight seal with an external opening of a fuel filler pipe leading to a fuel tank of a vehicle. (Where a wide range of different sizes of and/or shapes of openings may be encountered, it may be necessary to provide alternative, exchangeable fittings 5).

The pressurising pump 2 is here a manually-operable stirrup pump, with a reciprocally vertically-moveable pump handle 6 and a stirrup base 7 into which a user may insert a foot in order to stabilize the meter 1 during pumping. Other embodiments may use foot-operated pumps, or even (at the expense of portability) an existing or dedicated compressed-air supply, via a suitable regulator. It would even be possible to use a regulated compressed gas cylinder, for example to provide a source of inert gas for use in connection with extremely flammable fuels or other liquids.

The measuring unit 3 contains a two-position valve 8. In a first position, represented by solid arrows 9, the valve 8 connects the pressurising pump 2 to the pressure hose 4, and hence to the fuel tank. In a second position, represented by broken arrows 10, the pressurising pump 2 is connected to open air, while the pressure hose 4 and fuel tank are connected to a restrictor 11 comprising a calibrated orifice through which air may exit the meter 1. A pressure transducer 12 measures the air pressure within the pressure hose 4 (and hence within the fuel tank). The measuring unit 3 also contains electronic control apparatus (including a timing circuit), which is adapted to control the valve 8 and to receive data from the pressure transducer 12. The measuring unit 3 is also provided with a display 13, most conveniently a liquid crystal numeric or alphanumeric display, although light emitting diode or analogue displays may also be used. The electronic components are all encapsulated for safety in the presence of highly flammable fuel vapours. The portable meter 1 shown uses a low- voltage dry cell battery as power supply, which is also located within a gas-tight chamber.

To use the meter 1, a filler cap is removed from a fuel filler pipe of a vehicle, and the fitting 5 is securely and sealingly connected to its external opening. The meter 1 is turned on, the valve 8 being in its first position 9. The user pumps the handle 6 of the pressurising pump 2, transferring air through the hose 4 to an interior of the fuel tank.

When the pressure within the fuel tank, the filler pipe and the hose 4 reaches 250 millibars above atmospheric pressure, as indicated by the pressure transducer 12, the electronic control apparatus switches the valve 8 from its first position 9 to its second position 10. The pressurising pump 2 is now connected to the atmosphere, so no more air can be pumped into the fuel tank, which is now linked, via the hose 4, to the restrictor 11. The slightly pressurised air within the fuel tank is now free to bleed out via the calibrated orifice of the restrictor 11, so that the pressure in the fuel tank, etc, begins to fall.

When the pressure transducer 12 registers a first pre-set pressure, for example 200 millibars, the timing circuit begins to run. Air continues to bleed out through the restrictor 11 until a second pre-set pressure is reached, for example 100 millibars, at which point the timing circuit stops. The display 13 indicates an elapsed time between reaching the first and second pre-set pressures, which the user may record. The pressure within the tank is then allowed to return to atmospheric pressure, and the fitting 5 is removed.

In principle, the behaviour of a gas under pressure is governed by the ideal gas equation: PV = nRT

where P is pressure, V is volume, T is temperature, R is the ideal gas constant, and n is the number of moles of gas present. In the course of the above pressurisation and de- pressurisation sequence, V is the free volume of the fuel tank above the fuel (which includes, as defined, the volume of the filler pipe and the hose 4, which will be substantially constant). Over the range of pressure changes envisaged, it may be assumed that the temperature T will not vary appreciably, the volume V will not change and R is an universal constant. Thus, the pressure is in effect directly related to n, the amount of gas present, and a change in pressure, ΔP, is directly related to a change in the amount of gas present, Δn:

ΔP = Δn.RT/V

Hence, the larger the value of V, the greater the value of Δn to give a particular value of ΔP.

The calibrated orifice in the restrictor 11 allows gas to escape at a relatively constant rate (for the overpressure ranges in question), i.e. it allows n to change at a substantially constant rate over time.

Thus, the time t, measured for a specific pressure drop to occur through the restrictor 11 is a measure of the amount of gas that has escaped to produce that pressure drop:

Δn = k.t, where k is a constant .\ΔP = k.t.RT/V or V = k.t.RT/Δ P

Since k and R are constant, and T is effectively constant and ΔP is predetermined, the free volume V above the fuel in the tank is directly proportional to the time t.

In reality, gas behaviour tends to diverge from idea gas behaviour, but in a repeatable fashion. Thus, a graph of V versus t may not be a straight line, but it is possible to produce a reliable calibration curve for any given standard fuel tank by part-filling it with a range of known volumes of liquid, and measuring t in each case.

Thus, one may use the meter 1 on a tank of known type containing an unknown volume of fuel, to obtain an accurate assessment of the free volume within the tank, and hence the volume of fuel.

This procedure may be carried out when a vehicle is hired out, repeated when the vehicle is returned, and any difference calculated. If there is a deficit, the hire company may charge the person who has hired the vehicle for the exact shortfall.

In its basic form, the meter 1 indicates only the time taken for the pressure to drop from a first to a second preset value, leaving the user to read off a fuel volume from a calibration curve for the particular vehicle model being used. However, it is envisaged that the meter could be provided with a memory chip or the like containing the calibration curves for a range of vehicles, and a touch-pad or the like allowing the user to select a particular model. The meter display 13 would then show a calculated fuel volume. Alternatively, the meter could record the time in its memory, and then be connected to a computer, over a standard RS232 connection, USB port or the like, in order to transfer this time data. In this case, the computer could hold the calibration curves in its memory and use them to calculate the fuel volume present. It would store the "as hired" fuel volume of each vehicle, compare it with the "as returned" fuel volume of that vehicle, and calculate any refuelling charges automatically.

The computer could be a conventional personal computer or mainframe, or it might usefully be a portable device, such as a PDA (portable digital assistant) or a dedicated handheld computing device.

Many such devices have wireless connectivity, using radio frequency or infra-red beam communications, such as Bluetooth technology (Bluetooth is a registered trade mark). The meter could then be provided with an appropriate data transmission system in place of, or as well as, an RS232 connection or the like.

The meter may also be provided with a printer system, so that a ticket bearing the time and optionally volume data may be printed out, either as a confirmatory hard copy/receipt or as its main data output.

The meter described will be safe in use, as its electrical components are isolated from any fuel vapour mixed with the air above the fuel in the vehicle's tank. Also, the overpressures used, approximately one-quarter of atmospheric pressure at most, will be well within the range of what a vehicle fuel tank is designed to withstand. If safety regulations require, a pressure relief valve, bursting disc, or the like can be provided to release excess pressure if the valve fails to operate at 250mbar as described above.

It should also be noted that while operation of the meter 1 is described above with the fuel tank, etc, being pressurised to a slight overpressure, it is equally possible to evacuate the tank partially, creating an underpressure that sucks air into the tank through the restrictor 11.

A further application for a meter similar to that described above is to check accurately the volume of fuel present in a fuel tank of a racing car, such as a Formula One racing car. At present, the volume of fuel added to the tank is estimated using a flow meter in the fuel delivery hose system and a timer; no direct accurate measurement of the volume present in the tank is available. The mass of fuel carried is of vital importance to the performance of a racing car, but if no safety margin is left, the car could run out of fuel before finishing. An accurate measurement of the volume actually present in the tank would thus be of great assistance.

Another potential application is believed to be in the field of fuel delivery tanker vehicles. It is still common practice for a tanker driver to check the volume present in a tanker trailer or the like by using a dipstick. This cannot be particularly accurate, may expose the driver and his surroundings to noxious, inflammable fuel vapours, and often requires the driver to climb on top of the tanker, risking a potentially fatal fall.

The empty volume of a tanker will be known or measurable, and so a meter similar to that described above would be able to determine the volume of fuel present therein.

Claims

1. A device to measure a volume of liquid held within a container comprising means to connect the device to the container, means to alter the gas pressure within the container, gas flow restrictor means, valve means to connect the container either to the pressure altering means or to the restrictor means, means to measure pressure within the container, and means to time a period taken for the pressure within the container to change from a first predetermined value to a second predetermined value while the container is connected to the restrictor means.

2. A device as claimed in claim 1, provided with display means, optionally numeric or alphanumeric display means, to indicate said period, and optionally provided with memory means adapted to record said period for future reference, or for subsequent transmission to a separate computing device.

3. A device as claimed in any one of the preceding claims, provided with electronic control means, optionally adapted to operate the valve means.

4. A device as claimed in claim 3, wherein the electronic control means is adapted to operate the valve means so as to connect the container to the restrictor means when the pressure in the container has been altered to a third preselected value, further from ambient pressure than said first and second values.

5. A device as claimed in any one of the preceding claims, wherein the gas flow restrictor means comprises calibrated orifice means through which gas may flow at a substantially constant rate.

6. A device as claimed in any one of the preceding claims, provided with means to convert said period to a liquid volume within a particular container.

7. A device as claimed in any one of the preceding claims, wherein the pressure-altering means comprises pump means, optionally manually- or pedally-operated pump means, or a source of gas under pressure, such as a compressed-air line or a reservoir vessel containing gas under pressure.

8. A device as claimed in any one of the preceding claims, provided with pressure release means adapted to operate at a pressure differential within the container below that which might damage the container.

9. A method for measuring a volume of liquid held within a container comprising the steps of providing a device as claimed in any one of the preceding claims, connecting it to an aperture of the container, connecting the pressurising means to the container and raising the pressure therein to above a first predetermined value, connecting the container to the gas flow restrictor means so as to allow gas from the container to exit therethrough, timing the period taken for the pressure within the container to fall from said first predetermined value to a second predetermined value, and calculating from said period a gas volume and hence a liquid volume within the container.

0. A method as claimed in claim 9, further comprising the steps of subsequently measuring an altered liquid volume within the container as described above and calculating a change in liquid volume between said measurements.