GB2209796A

GB2209796A - I.C. engine fuel supply

Info

Publication number: GB2209796A
Application number: GB8721755A
Authority: GB
Inventors: Thomas Tsoi-Hei Ma
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1987-09-16
Filing date: 1987-09-16
Publication date: 1989-05-24
Also published as: GB8721755D0

Abstract

Fractioning apparatus 14, 16, 20, 22 connected to the fuel tank 10 separates the fuel into fractions of different quality which are stored in reservoirs 14, 22, connected by separate lines 26, 28 to the engine. The reservoir 14 is heated by the exhaust gases via the heat pipe 16. Valves 30, 32 in the lines 26, 28 control the quality of fuel suppled to the engine in dependence upon engine operating conditions and/or the level in the reservoirs 14, 22. A computer may control a fuel injection system, the fuel quality supplied and spark ignition timing. <IMAGE>

Description

FUEL SUPPLY The present invention relates to fuel supply for an internal combustion.

According to the present invention, there is provided a fuel supply for an internal combustion which comprises a fuel tank, fractioning means connected to the fuel tank for separating fuel into fractions of different quality, reservoirs for separately storing the respective fuel fractions, and separate fuel supply lines connecting the respective reservoirs to the internal combustion engine.

Hitherto, engines have been calibrated to run using a particular grade of fuel. However, if the same grade of fuel is to be used at all times, the selection of the grade is a matter of compromise. Under certain operating conditions a low grade of fuel, that is a low octane fuel with low anti-knock rating, is adequate, whereas under other conditions a higher grade of fuel is to be preferred for its improved knock rating or volatility.

In the present invention, the fuel is separated into different fractions and the quality of the fuel burnt by the engine can be varied to suit the prevailing operating conditions.

Preferably, the fractioning means makes use of waste heat available in the engine exhaust or cooling system to evaporate a lighter fraction of the fuel, which lighter fraction is condensed and stored separately from the remaining heavier fraction. The fact that waste heat is used to fraction the fuel means that the engine does not need to do increased work in order to benefit from the availability of fuels of different grades.

In the preferred embodiment of the invention, heat is transferred from the exhaust system to the fractioning means by means of a heat pipe. Heat pipes are known per se and include a medium which evaporates at one end, and condenses at the other. By selection of the medium within the heat pipe, it is possible to predetermine the boiling point of the lighter fraction.

The fuel supply lines leading from the respective reservoirs conveniently include valves. The valves may be on-off valves or proportional valves to permit the fuel quality to be varied at will.

In an internal combustion engine fitted with a computer controlled fuel injection system, a plurality of fuelling maps may be stored in memory and used for engine calibration depending on which of grade of fuel is selected.

When one reservoir is selected in preference to the other, the other will fill up and the size of the reservoir determines the maximum duration that the engine can run using only one of the two fractions.

The reservoirs are therefore preferably substantial to permit prolonged periods of use using one or other of the two fractions. If desired, level sensing means in the reservoirs may be used to control the grade of fuel selected to prevent over-filling of any reservoir. The engine may for example be forced to use an intermediate grade of fuel until the fuel level drops in the overfull reservoir.

The invention can permit an engine to perform as though fuelled by a higher grade of fuel for limited periods of time and can thus allow the engine to be calibrated to run under certain conditions using a higher octane fuel than is available in the tank. The remaining fraction which is of lower grade can be used under low engine load conditions when de-rating of the engine performance does not have a noticeable affect.

The invention will now be described further, by way of example, with reference to the accompanying drawing which is a block diagram of a fuel supply in accordance with the invention.

Fuel in a fuel tank 10 is pumped by means of a pump 12 to a reservoir 14. A heat pipe 16 extends between the reservoir 14 and the exhaust system 18 of the engine and serves to raise the temperature within the reservoir 14 to a level determined by the heat transfer medium within the heat pipe 16. The heating of the fuel in the reservoir 14 acts to boil off the lighter fuel fraction and the vapours condense in a condenser 20 and collect in a second reservoir 22. The condenser may either be water cooled or air cooled. In this way, the heavier fuel fraction remains in the reservoir 14 while the lighter fraction collects in the reservoir 22.

Both reservoirs 14 and 22 are connected to the fuel metering system 24, which may be a fuel injection system of a carburettor, by way of respective lines 26 and 28 each of which includes a valve 30 and 32. If the valves 30 and 32 are on/off valves then fuel is supplied from one or other of the two reservoirs but it is alternatively possible to use proportional valves so as to enable the fuel fractions to be mixed in any desired ratio to vary the fuel grade continuously.

By incorporating the fuel fractioning means, constituted by the reservoirs 14 and 22, the heat pipe 16 and the condenser 20, into the fuel line leading to the engine, it possible to vary the grade of fuel burnt by the engine while the engine is running. Of course, the average grade burnt by the engine must still correspond to the grade in the fuel tank 10. In other words, higher grade fuel than in the tank 10 can be burnt at some times but lower grade fuel than in the tank must then be burnt at other times.

If one or other of the two fractions is not burnt, then it collects in its reservoir and this can only continue until the respective reservoir is full. The reservoirs can be quite large to permit long periods of operation on either grade of fuel and it is possible to store such large quantities of fractioned fuel within a partitioned fuel tank. Nevertheless, once the unused reservoir is full steps must be taken to revert to the other grade of fuel or at least to a mixture corresponding to the grade of fuel in the tank 10. If desired, an additional connection leading directly to the fuel metering system from the tank 10 may be provided for use in the event of one of the reservoirs 14 and 22 becoming full.

As an alternative to monitoring the fuel levels, one may constantly monitor the fuel flow rate and adopt a continuously modified fuelling strategy in order to avoid an excessive build up of either of- the fuel fractions.

The spark timing and mixture strength will clearly depend on the grade of fuel being burnt at any time and it is preferred that the metering system should be a fuel injection system in which the injection quantity is under computer control. Computer control can also be used to vary the spark timing in dependence upon the quality of fuel being burnt. The computer may comprise several fuelling and ignition maps and switching between maps may be effected at the same time as switching between reservoirs.

Claims

CLAIM8

1. A fuel supply for an internal combustion which comprises a fuel tank, fractioning means connected to the fuel tank for separating fuel into fractions of different quality, reservoirs for separately storing the respective fuel fractions, and separate fuel supply lines connecting the respective reservoirs to the internal combustion engine.

2. A fuel supply as claimed in claim 1, wherein the fractioning means makes use of waste heat available in the engine exhaust or cooling system to evaporate a lighter fraction of the fuel, which lighter fraction is condensed and stored separately from the remaining heavier fraction.

3. A fuel supply as claimed in claim 2, wherein heat is transferred from the exhaust system to the fractioning means by means of a heat pipe.

4. A fuel supply as claimed in any preceding claim, wherein the fuel supply lines leading from the respective reservoirs include valves.

5. A fuel supply as claimed in claim 4, wherein the valves are on-off valves, the engine fuel metering system being connected selectively to only one reservoir at any one time.

6. A fuel supply as claimed in claim 4, wherein the valves are proportional valves so as to permit the fuel quality to be varied at will.

7. A fuel supply as claimed in any preceding claim, wherein level sensing means are provided in the reservoirs.

8. A fuel supply constructed arranged and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.