AU2006200438A1 - Multi fuel system - Google Patents

Description

3782-2.doc -1- Multi fuel system (.i Field of Invention SThis invention relates to multi-fuel systems for internal combustion engines and more particularly to systems that store multiple fuels within a single tank or in tanks that are in fluid 00 S 5 communication with each other. The invention has particular use with automobiles, trucks and Sbusses but is not limited to that use.

Background Duel fuel systems exist for automobiles, but they utilise separate tanks for the two fuels.

Typically a duel fuel automobile will use conventional petrol fuel and another fuel, such as liquefied petroleum gas (LPG) or compressed natural gas (CNG). The two fuels are stored in separate tanks. Thus the vehicle will have the petrol tank of a conventional petrol only vehicle and an additional tank to store the second fuel. To provide a reasonable range using either fuel, both tanks need to be relatively large. It goes against conventional wisdom and the present designs to attempt to store more than one type of fuel in one tank especially if the fuels have different phases (gas and liquid).

Because the majority of vehicles sold are single fuel vehicles, they are not designed to accommodate additional fuel tanks. As such, any additional fuel tank(s) are usually placed in the boot (trunk), reducing the volume available to the user and increasing the mass of the vehicle. In addition fuels such as LPG and CNG need to be stored in pressure tanks. Pressure tanks are typically cylindrical or toroidal, cannot easily be made to any shape and so have a lower volumetric efficiency (usable volume/occupied volume) than tanks for liquid fuels stored at atmospheric pressure.

CNG is the cheapest fuel, but it cannot be liquefied under a pressure that is convenient for normal use: 3 tanks of 70 litres have been used to give a total of 210 litres and give a 500 km range by the Ford Company in the late 1990's. This was not successful in the market, most likely due to the extensive space taken up by these 3 tanks. LPG is not quite as cheap but is still much cheaper than petrol, and it converts to a liquid at low enough pressure to give almost 3782-2.doc the same range as a petrol tank of the same size. LPG driven cars are marketed successfully and widely used, especially as taxis. Unless the cars are dedicated to LPG they have 2 tanks, one for LPG and one for petrol, and a dual fuel system in the engine. This normally leads to the need to have the spare wheel in the normal storage compartment making the setup less attractive for the user of the car.

00 Summary of the Invention C In an attempt to overcome at least some of the disadvantages of the prior art, the invention, in one broad form, provides a fuel storage system for a fuel burning device including: at least one tank for storing at least two fuels; the or each tank having at least two outlets for the fuels stored in said tank; at least one valve for opening and closing the or each said at least one outlet, and a control system for selectively opening and closing said valves to selectively supply at least one of said fuels to said fuel burning device.

In another broad form the invention provides a fuel storage system for a fuel burning device, the system storing at least two fuels in at least one first tank and selectively supplying at least one of said fuels to the fuel burning device, the system capable of storing a maximum volume for each fuel, the sum of the maximum amounts being greater than the capacity of the system.

The at least two fuels may be in physical contact with each other within at least one single tank.

The at least one single tank may be divided into at least two physically separate partitions of variable volume and a first fuel is located in a first partition and a second fuel is located in a second partition. A movable barrier may define a wall between adjacent partitions. At least a portion of the barrier may be flexible and the volume of said adjacent partitions may be varied by flexing of said portion.

At least one barrier may be movable within a tank and the volume of partitions adjacent a barrier may be varied by movement of said barrier within the tank. At least one barrier may be 3782-2.doc I-3movable within the tank and may include a flexible portion and the volume of partitions adjacent a barrier may be varied by one or both of movement of said barrier within the tank and flexing of said flexible portion.

The fuel storage system may include at least one second tank for storing at least one fuel. The 00 5 at least one second tank is preferably in fluid communication with at least one first tank, tc, whereby one or more fuels may be transferred between the first and second tanks.

C The fuel storage system may include a control system for controlling supply of fuel to the fuel Sburning device The fuels are selected from at least two of three groups comprising: a first group of fuels that are liquid at ambient temperature and pressure; a second group of fuels that are gaseous at ambient temperature and ambient pressure but liquid at ambient temperature and above ambient pressure, and a third group of fuels that are gaseous at ambient temperature and above ambient pressure.

The control system may be configured to supply fuel from the third group in preference to a fuel from the first and second groups. The control system may be configured to supply fuel from the second group in preference to fuel from the first group.

The fuel storage system may include means to measure the temperature and pressure of the stored fuels and the pressure or temperature or both may be used to determine the switch from one fuel to another.

Preferably when fuels from the second and third groups are stored, the fuel from the third group is used until the pressure and temperature of said fuel from the second group falls to near its boiling point.

The system may include reduction means to reduce the pressure or temperature or both of fuel 3782-2.doc I-4from the second and third groups before supply to said fuel burning device.

The system may include liquid separating means to separate any liquid component that condenses after said pressure/temperature reduction and return means to return said liquid component to said storage. The return means may also return a portion of said cooled gas to 00 5 said storage.

C€3 At least one fuel may be selected from a group including petrol, diesel, Bio-diesel, ethanol, Smethanol, LPG, CNG, ethane, ethylene, hydrogen, carbon monoxide, synthesis gas, C1 to hydrocarbons, alcohols and aldehydes.

The system may be configured for use with CNG and LPG. The system may be configured for use with petrol or diesel and either LPG or CNG. The system may be configured for use with petrol or diesel and both LPG and CNG. The system may be configured for use with LPG, CNG and Hydrogen. The system may be configured for use with LPG, Hydrogen and/or Carbon monoxide.

When the fuel burning device, such as an internal combustion engine, includes a starter motor, the system may be configured so that activation of the starter motor or similar start activity allows delivery of gas fuel to the fuel burning device.

When used with LPG and CNG, by combining these 2 fuels (CNG and LPG) as per this invention, with for instance 2 tanks of 50 litres, it will more easily fit in a normal car than, say, tanks providing 210 litres capacity for CNG only and still deliver most of the savings that can be obtained with CNG while getting around the problem with a limited range. The driver can then choose the most appropriate strategy knowing what trip has been planned and how easy or convenient it is to refuel with CNG.

In addition, the use of a single tank reduces the mass of the vehicle compared to a conventional two tank duel fuel system.

When used with LPG and CNG this system will eliminate the main disadvantage of CNG: that very large tank storage is needed to give longer range. While still keeping most of the main 3782-2.doc 0 advantage of CNG: lower price and better supply safety long term.

c.l d0 Brief Description of the Drawings Figure I is schematic diagram of a fuel system according to a first embodiment of the invention.

00 Figure 2 is schematic diagram of a fuel system according to a second embodiment of the C€3 invention.

00 Figure 3 is schematic diagram of a fuel system according to a third embodiment of the invention.

Figure 4 is schematic diagram of a fuel system according to a fourth embodiment of the invention.

Figure 5 is schematic diagram of a first system according to the embodiment of figure 1.

Figure 6 is schematic diagram of a second system according to the embodiment of figure 1.

Figure 7 is schematic diagram of a fuel system according to a seventh embodiment of the invention.

Figure 8 is schematic diagram of a fuel system according to an eighth embodiment of the invention.

Figure 9 is schematic diagram of a fuel system according to a ninth embodiment of the invention.

Figure 10 is schematic diagram of a fuel system according to a tenth embodiment of the invention.

Figure 91 is schematic diagram of a fuel system according to an eleventh embodiment of the invention.

Figure 12 is schematic diagram of a fuel system according to a twelfth embodiment of the invention.

3782-2.doc N-6- 0 0 Detailed Description of Preferred and other Embodiments Referring to figure 1 there is shown part of a fuel storage and supply system 10 for an internal C, combustion engine, such as for an automobile. The fuel supply 10 includes a tank 12 designed to store both a liquid fuel 14 and a gaseous fuel 16, such as petrol or LPG and a gas, such as 00 5 CNG or Hydrogen, respectively.

The tank has a liquid fuel line 18 for the petrol and a gas fuel line 20 for the CNG that feed to a Vfuel mixing and regulation part 22 of the vehicle. The mixing and regulation part 22, which may 0 o include pressure regulation, evaporation, mixing or direct injection into the engine and the engine design are not part of the invention and so are not shown in detail.

The liquid fuel line 18 has a pickup point 24 at the base of the tank or is simply a bottom outlet and the gas fuel line 20 has a pickup point 26 at the top of the tank. The two fuel lines 18 and are provided with valves 28 and 30 that are operable to control supply of the fuels to the mixing and regulation part 22. The valves 28, 30 are preferably electrically operable and are preferably controlled by the engine management system 32 of the vehicle.

The engine management system 32 may be programmed to default to use the gas fuel 16 before the liquid fuel 14. Accordingly, the liquid fuel valve 28 is normally shut and the gas fuel valve 30 is normally open, so only gas fuel is supplied to the mixing and regulation part 22.

When the amount of gas in the tank falls below a threshold the gas fuel valve 30 is closed and the liquid fuel valve 28 is opened, so liquid fuel is supplied to the mixing and regulation part 22.

The system also preferably includes a pressure sensor 34 and a safety vent 36. These are not essential but are good engineering practice. The pressure sensor 34 may provide an input to the engine management system 32 so that amount of gas remaining in the tank may be calculated.

The pressure input 34 is also useful for controlling any pressure regulation within the mixing and regulation part 22 of the system.

The tank of this embodiment does not have a barrier between the two fuels and, accordingly the tank 12 may be filled 100% with either the liquid fuel 14 or the gaseous fuel 16. Liquid fuels are normally more expensive per unit of energy than gaseous fuels but for a given volume 3782-2.doc I-7- 0 Sprovide more energy. Thus, if the user is only travelling short distances, the tank may be filled with only a small proportion of liquid fuel (or none at all) and the gaseous fuel used predominantly with more frequent refuelling. Conversely, if long distance travel is required or othe gas fuel is not available, the tank may be filed substantially or totally with the liquid fuel, with a corresponding increase in range and reduction in refuelling frequency. Obviously either of the

O

fuels may be used if the other is not available.

0 Because there is no barrier between the liquid and gaseous fuels, some of the lighter (Ni Ohydrocarbons of the liquid fuel will evaporate into the gas fuel. As the gas pressure changes the C components of the liquid fuel in the gas will change and so the composition of the gas fuel delivered will also change with time and usage of the gas fuel. Accordingly, so will the caloric value of both the fuels. To a large extent this caloric value can be predicted from pressure and temperature in the tank. In addition, most engine management systems can automatically adjust the fuel delivery system so as to run optimally. Most modem engine management system utilise oxygen measurement in the exhaust, for a so-called closed loop air/fuel ratio correction system.

As such the system tends to be self regulating. In addition, the engine management system may be programmed with basic parameters for operation with each of the fuels.

The evaporation of liquid fuel components may particularly happen if the liquid fuel consists of several chemical components and the temperature and pressure in the tank is lower than the boiling point of some of the components. The lower boiling components will then boil off, leaving more of the less volatile components in the liquid fuel. This will affect the properties of the liquid fuel in a combustion engine and in many cases may lower the Octane number, potentially causing knocking. However, most modem engine management systems include knock sensors so as to avoid knocking with low octane fuels, with the system automatically adjusting parameters to avoid knocking.

The tank 12 has a single fuel inlet 38 for both the liquid fuel and the gas fuel. It will be appreciated that any gas fuel 16 in the tank is at higher than atmospheric pressure. Accordingly the liquid fuel needs to be injected into the tank 12 at a pressure higher than atmospheric unless all gas fuel is used. This may be achieved by using a special pressurised supply line.

3782-2.doc I-8- 0 0 Alternatively the vehicle may include a small receiving tank at atmospheric pressure and a pump (not shown) that pumps the liquid fuel at high pressure into the main tank 12.

Figure 2 shows a system 52 for storage of two fuels (gas and liquid types). The system 52 has an internal membrane 54 that divides the tank into two physically separate partitions 56 and 58.

00 5 Separate fuels may be stored in each partition 56, 58, such as a liquid fuel 60 and a gas fuel 62. The membrane 54 is flexible and elastic and so the volume of each partition may change, 0 depending on the amount of fuel in both partitions. The membrane 54 may be a suitable (Ni Opolymer that is not degraded by the fuels used.

Because the tank is separated into physically separate partition, each volume has its own fuel inlet, 64 and 66 respectively. Fuel supply lines 68 and 70 with valves 72 and 74 supply fuel as per the figure 1 embodiment and are controlled by the engine management system in a similar manner.

Because the liquid fuel is physically separate from the gas fuel, neither the gas nor the liquid fuels will change composition, so the octane number or any other property of the fuel will not change any more significantly than in single fuel systems.

Figure 3 shows a system 100 having a tank 102. The tank 102 is also divided into two physically separate volumes 106 and 108 by a membrane 104. The system operates similarly to the figure 2 embodiment with fuel delivered via fuel lines 120, 124 and valves 122 and 116.

Fuel is input into the partitions via lines 112 and 118. However, in this embodiment the membrane is relatively stiff and is movable along the length of the tank to provide for variable volumes, depending on the amount of fuel in each volume. The membrane 104 is provided with a peripheral seal 110 to prevent fuel in one volume leaking into the other.

Because the liquid fuel is relatively incompressible, the amount of liquid fuel will determine the position of the movable membrane. When the engine is running on gas the membrane will not move and the gas pressure will slowly reduce. When using liquid fuel the pressure of the gas in the gas fuel partition 108 will push the membrane to reduce the volume of the liquid fuel partition 106.

3782-2.doc I-9- The movement of the membrane 104 along the tank will be limited by the positioning of the fuel inlets 112, 118 and fuel outlets 116, 120, depending on their position in the tank. To increase the range of movement the inlets and outlets may be placed in the end walls of the tank.

Figure 4 shows a system 130 having a tank 132 divided into two partitions 134, 136 by a 00 5 separator 150. The separator 150 combines the features of the embodiments of figures 2 and 3. Accordingly the separator 150 has portion formed of a flexible/elastic membrane 154 and a peripheral seal 152 that allows the separator 150 to move along the length of the tank. Fuel is input into the tank via lines 138, 144 and is output via lines 140, 146 and valves 142, 148. This C' will allow a higher proportion of the tank volume to be available to the gas fuel or to the liquid fuel than the figure 2 or 3 embodiments.

Figure 5 shows a fuel delivery system 160 using a tank 162 according to the embodiment of figure 1 and configured for use with LPG 161 and CNG 163. The tank 162 must meet CNG standards in terms of withstanding pressure.

LPG 161 is fed to an evaporator/regulator 168 via LPG line 164 and CNG 163 is fed via CNG line 156. The fuel is then fed to mixer 170 and subsequently to the engine (not shown).

The fuel lines 164 and 156 are controlled by LPG feed valve 172 and CNG feed valve 174, respectively, under the control of the engine management system 180.

The pressure in the tank 162 is measured by a pressure transducer 176 whilst the temperature is measured by a temperature transducer 178. Signals corresponding to the measured pressure and temperature may be fed to the engine management system 180.

In the preferred configuration, the system uses CNG by default, so long as the pressure and temperature will result in most of the LPG remaining liquid. In this state the CNG feed valve 174 is open and the LPG feed valve 172 is shut. If the combination of the temperature and pressure in the tank 162 is under the boiling point of the LPG then the CNG feed valve 174 closes and the LPG feed valve 172 opens to feed the liquid LPG to the evaporator 168. This is done to prevent boiling off too much of the lighter components of the LPG.

The evaporator/pressure regulator 168 is preferably capable of reducing the pressure of the 3782-2.doc D- 1- 01 CNG and also evaporating the liquid LPG. This also provides the ability to use the last amount of LPG from the tank 162, as LPG tends to evaporate in the bottom of the tank just before the tank is out of fuel. Alternatively, a separate regulator for CNG and a separate evaporator for SLPG may be used.

00 5 LPG has a lower octane number than CNG but it is a relatively trivial matter to programme the engine management system to compensate for this as both have higher octane numbers than C petrol.

SIt is possible to have a switch on the dashboard that forces the use of LPG if the driver desires.

In this situation the LPG valve 172 remains open and the CNG valve 174 remains shut irrespective of the pressure in the tank. It is also possible to simply stop filling up with CNG and the system will automatically use the LPG once substantially all the CNG has been used.

The tank can then be filled with CNG alone, LPG alone or a mixture of both.

It is advisable, but not critical, to have about 10 litres of LPG in the tank at all times. Thus, if all the CNG is used the vehicle will be able to travel approximately 70 km to, hopefully, bring it to a place where CNG fuel can again be obtained.

A headspace of 20 is typically needed for the safe storage of LPG. This is because the tank might break if it is totally filed with liquid and the temperature rises. This thermal expansion of the LPG can bring the tank outside the pressure design criteria. This 20 heat space can conveniently be taken up by the CNG and add to the fuel economy and range.

To ensure that the tank does not blow back in an LPG fuel stand a non-return valve 182 on the LPG inlet nozzle is recommended.

With the configuration of figure 5 the tank 162 can only be filled from a conventional LPG stand if the tank pressure is below the LPG supply pressure. This only occurs when all or substantially all of the CNG has been used. This can however be changed if the LPG stands are changed to deliver LPG at a higher pressure. It will also be possible to equip the LPG inlet with a small tank and a pump to inject in LPG at a higher pressure even when CNG is still in the tank.

3782-2.doc -11-

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The LPG stands may also be modified to incorporate CNG-LPG in the same nozzle.

(.i There will be some evaporation of the lighter components of the liquid fuel into the gas phase.

This will then give some change of the composition of the liquid fuel. The fuel system is recommended to manage this; either by changing to liquid fuel or by how often liquid fuel is put 00 5 into the system.

e¢3 Natural gas can be compressed from the main city gas systems; this can either be as a small O home unit or at centres like taxi stands or any petrol station that chooses to do so. On Scentralized stations it should be possible to negotiate a deal with the gas supplier to take the gas from the main high-pressure line, so less pressurization has to be done by the stations.

The following table provides examples of different possible choices that can be made by a driver when fuelling a vehicle having two 50 litre tanks that may be used for with CNG LPG.

The approximate ranges are for a Ford Falcon in city driving and are for example only.

The costs are based on an LPG cost of $0.44 per litre and a CNG cost of 2/3 of the cost of LPG by weight.

Litre LPG Litre CNG Total range Range on Average fuel cost, $/100 km CNG part 0 100 240 240 4.10 90 285 215 4.70 56 44 500 105 5.80 20 608 48 6.10 Notice that the maximum total possible range is 608 km; significantly greater than the 450 km for a conventional petrol Ford Falcon, both in city traffic. The values used here are approximate and the accuracy of this estimate is not critical to the validity of the invention.

Figure 6 shows a fuel delivery system 200 using a tank 202 according to the embodiment of figure 1 and configured for use with petrol 204 and CNG 206. The tank 202 must meet CNG standards in terms of withstanding pressure.

3782-2.doc I- 12- 0 0 Petrol 204 is fed via petrol line 208 and pump 212 to fuel injectors 210 whilst CNG 206 is fed via CNG line 214 under its own pressure to an evaporator/regulator 216. Supply of the two fuels is controlled by petrol feed valve 218 and CNG feed valve 220 under the management of oengine management system 222.

00 5 The pressure in the tank 202 measured by a pressure transducer 224 whilst the temperature is Smeasured by a temperature transducer 226. Signals corresponding to the measured pressure 0 and temperature are fed to the engine management system 222.

o In the preferred configuration, the system uses CNG 206 by default, so long as the pressure 224 of the CNG 206 is sufficient. In this state the CNG feed valve 220 is open and the petrol feed valve 218 is shut. If the pressure drops below a preset or calculated value then the CNG feed valve 220 closes and the petrol feed valve 218 opens so as to supply petrol to the engine.

Conventional teaching is that starting the system on petrol gives a faster and safer start.

Accordingly, when the engine temperature is below a threshold the system may automatically starts on petrol and then automatically switches to CNG once the engine temperature passes a threshold. At this point the petrol feed valve 218 closes and the CNG feed valve 220 opens. In practice, the CNG feed valve 220 may open shortly before the petrol feed valve 218 closes and the engine may be run on a mixture of both fuels for a short period.

A system with a total capacity of about 70 litres in a large standard car will allow the spare wheel to be in its normal space and still provide an acceptable range. Such a capacity may be provided by 3 tanks of about 23 litres each or a single toroidal (donut) tank.

Figure 7 shows a fuel delivery system 230 using a tank 232 according to the embodiment of figure 1 and configured for use with petrol and LPG. The tank 232 must meet LPG standards in terms of withstanding pressure.

Petrol 234 is fed via petrol line 236 to fuel injectors 238 whilst LPG 240 is fed via LPG line 241 to an evaporator/regulator 242. Supply of the two fuels is controlled by petrol feed valve 244 and LPG feed valve 246.

3782-2.doc I-13- The pressure in the tank is measured by a pressure transducer 248 whilst the temperature is measured by a temperature transducer 250. Signals corresponding to the measured pressure and temperature are fed to the engine management system 252.

In the preferred configuration, the system uses LPG 240 by default, so long as the pressure of 00 5 the LPG is sufficient. In this state the LPG feed valve 246 is open and the petrol feed valve 244 tc, is shut. If the pressure drops below a preset or calculated value then the petrol feed valve 244 CI opens and petrol is fed to the engine. The LPG valve may stay open while petrol is being delivered. This will allow all of the LPG to be used up down to atmospheric pressure. The CI petrol will then only be used as a supplement as the LPG pressure fades away and in the end the petrol will be the only fuel used.

A system configured for use with CNG and diesel or CNG and Ethanol or Hydrogen and LPG or Hydrogen and Petrol will have a similar configuration.

The system 230 may also be used with three or more different types of fuel, such as a fuel liquid at normal pressures and temperatures (petrol, ethanol), a fuel liquid at pressure (LPG) and a gaseous fuel (CNG, Hydrogen or Carbon monoxide).

In use, by default the system will use the gaseous fuel first. As an example, if the system is used with CNG, LPG and Petrol: the CNG will be fed via the gas line 241 to the evaporator 242 and mixer 254. When substantially all of the CNG has been used the pressure in the tank 232 will have dropped and LPG components will start to boil off. Thus more volatile components mostly propane will be fed through the gas line 241 and to the mixer 254. Once the pressure is even lower the rest of the liquid, comprising mostly of petrol components with some Butane from the LPG, can be fed through liquid feed line 236 and to the injectors 238.

Figure 8 shows a fuel supply system 260 using the tank 262 of figure 1 for use with a liquid fuel 264 and a gaseous fuel 266. The system may be used with LPG and CNG and/or Hydrogen.

It is possible to cool the gas down as much as possible and bring heavier components back as condensate to the tank. Accordingly, the system includes a gas feed line 268 and a condensate/gas return line 270. The gas is first cooled by expanded low pressure gas, by heat 3782-2.doc I-14exchanging the expanded gas with the gas fed from the tank. The cooled feed gas is then as a gas/liquid mixture fed to a separator and any liquid and, optionally, some cooled gas is fed back to the tank 262 via line 270. The gas from the separator then enters the regulator where it Sexpands and cools incoming gas. The gas or liquid returned to the tank 262 will cool the tank, leading to less loss of propane from the LPG. If the temperature of the tank becomes too low 00 c and the gas pressure falls then the system may switch to liquid fuel via liquid feed line 276.

When the pressure is low the rest of the liquid, comprising mostly of LPG, can be fed through liquid feed line 276.

Figure 9 shows a system 280 that provides additional condensing and separation of liquid components from the feed gas.

The tank 282 feeds gas 283 via gas feed line 284 to a heat exchanger 288 where the gas is cooled. This may cause some of the gas to condense. The cooled mixture passes along line 290 to separator 292 where liquid is separated and returned to the tank 282 via pump 302 and return line 286. The cooled gas passes from the separator 292 to regulator 294 and its pressure is reduced to an operating pressure. This results in further cooling and condensing of liquid components and so the mixture passes through a second separator 298. Liquid components are separated and returned to the tank 282 via pump 300 and line 286. The gaseous components pass through heat exchanger 288 and the optional gas heater 306 to the engine.

This configuration ensures that the more volatile components are used first and that most LPG components that are carried with the CNG are returned to the tank 282. Once the CNG gas been substantially all used, the system switches to using the LPG and this is supplied to the engine via liquid feed line 304.

Figure 10 shows a system 310 with 2 or more tanks prioritised for different fuels. One tank 312 may be prioritised for CNG or Hydrogen and the other tank 314 for LPG. The system can be managed so the carry- over of the liquid fuel into the engine gas feed is minimised, while giving the maximum flexibility in fuel choice.

3782-2.doc The two tanks 312 and 314 are interconnected by transfer line 320. Fluid communication is controlled by valves 322 and 324. If desired, only one valve is necessary, although the safety regulations for gas tanks may require two valves. The end 326 of the transfer line is located at Sthe base of tank 312 or is simply a bottom outlet whilst the other end 328 is located close to the top of the other tank 314, preferably some distance from the top, so tank 314 can not be 00 Cc overfilled with liquid.

The first tank 312 has a gas fuel outlet 330 controlled by valve 332 whilst the second tank 314 has a liquid fuel outlet 334 controlled by valve 336.

The pressures in the tanks 312 and 314 are measured by pressure transducers 316 and 318, respectively. The pressure signals produced are P 1 and P 2 In use, if the pressure P 1 is above a threshold, usually about 900 kPa, then the engine is run on gas from the first tank 312. Accordingly valve 332 is open and valve 336 is shut.

If the pressure P 1 is below the threshold then the engine is run on liquid fuel from the second tank 314. Accordingly valve 336 is open and valve 332 may be shut.

This is the basic rule that will ensure that gas fuel is mainly used and during use the system defaults to using the gas fuel.

Other system rules: If P 1 is less than a threshold, typically under the critical pressure for the mixture, such as about 9,000 kPa, and P 2 exceeds P 1 then the valves 322 and 324 are opened.

This allows the second tank 314 to feed the first tank 312 with some gas at a pressure where tank 312 is not at critical pressure. This will allow gas fuel to escape the second tank 314 in a way that will minimise the use of liquid fuel from the system.

When running on liquid fuel, if P 1 is below a threshold, such as 900 kPa, and the second tank 314 is less than substantially full, such as 70 and P1 is greater than P2 then valves 322 and 324 are opened. This will allow any liquid fuel in the first tank 312 to go to the second tank 314 so it can be used.

3782-2.doc I-16- If the temperature T 2 of the second tank 314 rises substantially this will result in an increase in pressure P 2 If P 2 exceeds a threshold, in a normal system, the system just vents gas to the environment via safety valve 338. To avoid this loss of fuel and repair of the safety valve 338 Sthe transfer line 320 may be opened at a lower threshold to transfer gas from the second tank to the first tank, if the first tank 312 is at a lower pressure than the second tank 314.

00 Accordingly, If P 2 exceeds a threshold, such as about 20,000 kPa, and P 2 exceeds P 1 then C valves 322 and 324 are opened. This will relieve the pressure in the second tank 314. This may also occur if liquid or cooled gases are fed into the second tank 314 via return line 340. Line C 340 is optional in this system and is only required if the system returns condensate from the cooling and expansion system.

The system also monitors pressures when refuelling to optimise the second tank for liquid fuel storage.

When gas is being supplied to the first tank, if the pressure P 1 is above a threshold, such as about 19,000 kPa, and P 1 exceeds P 2 by a threshold, usually about 500 kPa, then gas is allowed to flow into the second tank 314 via transfer line 320 by opening valves 332 and 324.

This will ensure that second tank 314 only gets gas fuel into it when the first tank 312 is almost full.

When liquid fuel is being supplied to the second tank 314, and the pressure P 1 316 in the first tank 312 is below a threshold, usually about 1000 kPa, and P 1 is also less than P 2 and the second tank 314 is more than a set percentage (such as 70%) full of liquid fuel, then liquid fuel is allowed to flow into the first tank 312 via transfer line 320 by opening valves 322 and 324. If all of these three conditions are not met then the valves 322 334 remain closed and only the second tank receives liquid fuel. This will ensure that the first tank 312 can only receive liquid fuel when it is substantially empty of CNG and the second tank 314 is almost full.

This allows the first tank 312 be used for LPG if that is possible and desired, such as when a long range is needed.

The system will work with or without the condensate feedback system of figure 8 and 9. This 3782-2.doc I-17- 0 Sfeedback may then be through line 340.

c.l 0 Figure 11 shows a system 335 which is a variation of the system of figure 10. The same numerals are used for the same components. This system 335 allows liquid fuel to be filled in at the earliest possible time and minimises the risk of running out of fuel. In addition to this it can at 00 5 particular times accept the liquid fuel at its normal delivery pressure, so no special pump is en needed to force liquid fuel into the tank system.

kD The main physical difference between the systems of figures 10 and 11 is that the transfer line O 320 in figure 11 has a spur line 350 that connects with the gas feed line 330 from the first tank 312. Communication between the gas feed line 330 and transfer line 320 is controlled by valve 352.

If there is no liquid fuel in the system then the prioritisation of gas use has additional rules to those stated in relation to the figure 10 embodiment.

Initially gas from the second tank 314 is used, by opening valves 322 and 352. This allows gas from the second tank 314 to flow directly into the gas feed line 330 via transfer line 320. The valves 324 and 332 are kept closed to prevent gas from the first tank 312 being used or back flowing into the second tank 314.

This occurs until the second tank 314 is at low pressure so there is minimal gas in the second tank. From that time the second tank 314 may then be filled with liquid fuel at its normal delivery pressure for the longer range. It is also possible to fill in more gas fuel into the first tank 312 that will then flow in to the second tank 314 once the pressure 316 is high enough.

Due to the other rules this will also result in use of the gas in the first tank 312 down to a gas pressure of about 19,000 kPa. The system also preferably includes a status flag showing that there is liquid fuel in the second tank 314 because if the pressure in the second tank 314 is above around 10,000 kPa the mixture goes supercritical, so a liquid level can no longer be detected by a conventional device that relies on a liquid/gas boundary to determine liquid level.

The prioritisation may also switch to the second tank 314 if the total fuel contents of the tanks 3782-2.doc 18- 0 0 can only drive the car less than a threshold, such as 60 km. This will automatically make space for liquid fuel when the low fuel light comes on. The priority shall be switched back to gas from the first tank 312 when the pressure in the second tank 314 is low. This will be useful when othere is only very little liquid fuel in the second tank 314, such as around 5 litres.

00 5 It is also possible to manually override the normal rules by the press of a button to force the en o prioritisation of using fuel from the second tank 314 even if there is liquid fuel in it. The manual 0 override may be manually deactivated and/or automatically deactivated if either or both of the O tanks are refuelled.

This will allow the driver to make space for more liquid fuel if a long distance drive is unexpectantly coming up at a time when there is not much liquid fuel in the second tank 314 or if the driver knows that gas is not available. Once any gas fuel is used up in the second tank 314 the driver can fill the second tank 314 up with liquid fuel at its normal delivery pressure. Then the system will automatically switch to using gas from the first tank 312. Once the gas in the first tank 312 is used up it will also be possible to fill liquid fuel in that tank too if needed or desired. Another rule may also be applied. If P 2

P

1 a threshold, such as 500 kPa then valve 322 is opened. This allows some gas to go from the second tank 314 to the first tank 312 in the relatively rare cases where there is gas fuel at a greater pressure in the second tank 314 than in the first tank 312. This is most likely to happen if use of liquid fuel is manually forced when the first tank 312 is at a fairly low pressure.

If desired there may be separate pressure displays for the 2 tanks on the dashboard as well as a level indicator for liquid in the second tank 314. This level indicator shall show the last known liquid level if the second tank 314 is at supercritical pressure. There may be a fuel display showing how much fuel is left, preferably in Km range.

The system will work with or without the indicated condensate feedback system of figures 8 and 9 via line 340.

Figure 11 and system 335 can also be used in a different way, with only gas being feed to the engine.

3782-2.doc I- 19- 0 0 This use of the system 335 can be done with all the gas fuels, typically Hydrogen, Carbon monoxide, methane, ethane and then LPG to provide longer range. This however will only be practical if LPG made of mostly Propane is used, as it is in most parts of US. All items on figure 11 are used as explained above, except that outlet 334 and valve 336 is in this case not used to feed an evaporator and then the engine. This outlet 334 is now an optional feature and only used if too many heavier components being Butane and less volatile components build up oin tank 314. In that case they can be dumped through line 334 and valve 336. This use of the system makes a much simpler fuel feeding system for the engine, but the heavier components o will build up in tank 314 if the LPG is not clean enough and contains too much Butane and if the system is used with LPG alone for too long a time. The system with more than one tank will in this case be without a feed of liquid fuel to the engine. The gas fuels will, as earlier explained, be either from valve 332 and tank 312 or valve 322 and tank 314. The rules of supply could be the similar as above in the first example of use of figure 11. Heating of tank 314 may be used to allow better evaporation of heavier components.

Figure 12 shows an electric system 900 that will allow for easier start of the engine than present electric safety systems. Most present systems have most of the components of this system such as: The safety shutoff valve 903 that normally sits on the gas supply line just before the mixer.

The gas/liquid selector switch 901 and the manifold inlet pressure switch 902. These two items work together to prevent gas fuel being delivered to the engine unless the action of the engine running pulls a vacuum in the inlet manifold. Most gas systems have this safety system (shutoff valve) where gas fuel is only delivered when the engine has drawn a vacuum 902 in the inlet manifold. This is to prevent gas delivery if the engine is no longer running even when the key is in and the ignition is on. This is a good safety feature, which can prevent an engine fire to be fed in case of a traffic accident. This safety feature does, however, make it more difficult to start the engine. This is due to the fact that the engine needs to crank a few times on the starter motor before a vacuum is created, so it increases wears of the starter motor. This can be avoided by allowing gas delivery if the gas fuel is selected 901 and the starter motor is activated 904. With this arrangement it will be possible to start earlier, while still keeping the original safety feature as soon as the engine is running and the starter engine is no longer 3782-2.doc O- 20 switched on.

In addition to fuels such as petrol, diesel, ethanol, LPG, CNG, Hydrogen and Carbon monoxide that have a relatively consistent composition, any mixture of hydrocarbons of lengths 1 to 10 carbons may be used with some embodiments of the invention and correctly delivered 00 5 to a spark plug equipped engine. Preferably the pressure switch point is adjusted to e¢3 correspond to the lowest octane number that the engine is designed for. This will allow using an unrefined or low refined head fraction from oil refineries, either from the direct raw oil distilling or from a cracker. The contents of ethylene and propene will lower the octane number, but as that would to some extent be offset by the content of methane and ethane a certain content of these unsaturated hydrocarbons is acceptable.

Natural gas may be used substantially as it comes out of the well with minimal treatment. Only water and particulates need to be removed. Petrol components (Pentane and longer carbohydrates) are also best removed as they may lower the octane number too much. The mixed components can be used in this system, as it will automatically switch to the liquid line when heavier components have built up in the tank after several tank's full of this raw natural gas.

Depending on conditions, the gas going to the mixer or injector may be heated with the engine cooling liquid, especially in order to evaporate any heavier components that might have flashed out during the pressure reduction.

Unless the context clearly requires otherwise, throughout the description and the claims the words 'comprise', 'comprising', and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to".

It will be apparent to those skilled in the art that many obvious modifications and variations may be made to the embodiments described herein without departing from the spirit or scope of the invention.

Claims (4)

1. 3782-2.doc I-21- (N The claims defining the invention are as follows: 1. A fuel storage system for a fuel burning device, the system storing at least two fuels in o at least one first tank and selectively supplying at least one of said fuels to the fuel burning device, the system capable of storing a maximum amount for each fuel, the sum of the 00 Cc 5 maximum amounts being greater than the capacity of the system.
2. 2. A fuel storage system for a fuel burning device including: cxl O at least one tank for storing at least two fuels; the or each tank having at least two outlets for the fuels stored in said tank; at least one valve for opening and closing the or each said at least one outlet, and a control system for selectively opening and closing said valves to selectively supply at least one of said fuels to said fuel burning device.
3. 3. The fuel storage system of claim 1 or claim 2 wherein at least two fuels are in physical contact with each other within at least one single tank.
4. 4. The fuel storage system of claim 1 or claim 2 wherein said at least one single tank is divided into at least two physically separate partitions of variable volume and a first fuel is located in a first partition and a second fuel is located in a second partition. The fuel storage system of claim 4 including a movable barrier defining a wall between adjacent partitions. 6. The fuel storage system of claim 5 wherein at least a portion of the barrier is flexible and the volume of said adjacent partitions is varied by flexing of said portion. 7. The fuel storage system of claim 5 or claim 6 wherein at least one barrier is movable within the tank and the volume of partitions adjacent a barrier may be varied by movement of said barrier within the tank. 3782-2.doc ID-22- 0 8. The fuel storage system of anyone of claims 5 to 7 wherein at least one barrier is movable within the tank and includes a flexible portion and the volume of partitions adjacent a barrier may be varied by one or both of movement of said barrier within the tank and flexing of o said flexible portion. 00 5 9. The fuel storage system of any one of the preceding claims including at least one C€3 second tank for storing at least one fuel. The fuel storage system of claim 9 wherein said at least one second tank is in fluid o communication with said at least one first tank, whereby one or more fuels may be transferred between the first and second tanks. 11. The fuel storage system of any one of the preceding claims including a control system for controlling supply of fuel to the fuel burning device 12. The fuel storage system of any one of the preceding claims wherein said fuels are selected from at least two of three groups comprising: a first group of fuels that are liquid at ambient temperature and pressure; a second group of fuels that are gaseous at ambient temperature and ambient pressure but liquid at ambient temperature and above ambient pressure, and a third group of fuels that are gaseous at ambient temperature and above ambient pressure. 13. The fuel storage system of claim 12, said control system configured to supply fuel from the third group in preference to a fuel from the first and second groups. 14. The fuel storage system of claim 12 or claim 13, said control system configured to supply fuel from the second group in preference to fuel from the first group. The fuel storage system of any one claims 11 to 14 including means to measure the temperature and pressure of the stored fuels and wherein the pressure or temperature or both 3782-2.doc ID-23- 0 0 is used to determine the switch from one fuel to another. c.l 0 16. The fuel storage system of claim 15 wherein, when fuels from the second and third groups are stored, the fuel from the third group is used until the pressure and temperature of said fuel from the second group falls to near its boiling point. 00 M 5 17. The fuel storage system of any one of claims 12 to 16 including reduction means to oreduce the pressure or temperature or both of fuel from the second and third groups before Ssupply to said fuel burning device. S18. The fuel storage system of claim 17 including liquid separating means to separate any liquid component that condenses after said pressure/temperature reduction and return means to return said liquid component to said storage. 19. The fuel storage system of claim 18 wherein said return means also returns a portion of said cooled gas to said storage. The fuel storage system of any one of the preceding claims wherein at least one fuel is selected from a group including petrol, diesel, Bio-diesel, ethanol, methanol, LPG, CNG, ethane, ethylene, hydrogen, carbon monoxide, synthesis gas, CI to C20 hydrocarbons, alcohols and aldehydes. 21. The fuel storage system of any one of the preceding claims configured for use with CNG and LPG. 22. The fuel storage system of any one of the preceding claims configured for use with petrol or diesel and either LPG or CNG. 23. The fuel storage system of any one of the preceding claims configured for use with petrol or diesel and both LPG and CNG. 24. The fuel storage system of any one of the preceding claims configured for use with LPG, CNG and Hydrogen. 3782-2.doc N- 24- 0O 24. The fuel storage system of any one of the preceding claims configured for use with LPG, Hydrogen and/or Carbon monoxide 25 The fuel storage system of any one of the preceding claims wherein the fuel burning device includes a starter motor and activation of the starter motor or similar start activity allows 00 5 delivery of gas fuel to the fuel burning device. 26. A fuel storage system, substantially as herein described with reference to the drawings. 0 Dated 2 February 2006 Henrik Graulund By his Patent Attorneys M A MARTIN ASSOCIATES