Abstract:
In a fuel fractionation device for separating a low-boiling fuel fraction from a liquid fuel of an internal-combustion engine, including a vessel which contains the liquid fuel, and in which a reduced pressure is generated by withdrawing the low-boiling fuel fraction in vapor form from the vessel and making it available to the internal combustion engine, the efficiency of the fractionation is improved by utilizing a carrier-gas which is introduced into the liquid fuel, and which is withdrawn from the vessel together with the fuel fraction vapor.

Description:
[0001]    This is a continuation-in-part application of international application PCT/EP00/03893 filed Apr. 29, 2000 and claiming the priority of German application 199 271 77.1 filed Jun. 15, 1999. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The invention relates to a fuel fractionation device for separating a low-boiling fuel fraction from a liquid fuel of an internal-combustion engine in a container, in which a low pressure is generated for evaporating the low boiling fuel fraction.  
           [0003]    The fuels which are currently available for the operation of internal-combustion engines, for example for motor vehicles such as trucks, passenger cars, buses, represent a compromise between, firstly, restrictions on the part of fuel producers, e.g. on account of different crude oil qualities, production methods, costs and energy expenses, and, secondly, in some cases contradictory demands imposed by the internal-combustion engines, such as for example a reliable cold start even at extremely low temperatures, low exhaust and evaporation emissions, low fuel consumption, good antiknock properties even for turbocharged engines, prevention of deposits, avoidance of corrosion, low sulfur content, quiet engine running and high reliability. To enable existing fuels to be better adapted to the requirements of the internal-combustion engines, fuel fractionation devices of the type described above are used.  
           [0004]    DE 197 13 841 C1 has disclosed a fuel fractionation device of this type in which in a fuel vessel, which may be formed either by a fuel tank of a motor vehicle or by an intermediate vessel, a reduced pressure is generated as a result of gas being sucked out. In the known device, this reduced pressure is selected in such a way that the components of the low-boiling fuel fraction, which are to be separated from the liquid fuel contained in the fuel vessel, evaporate out of this fuel. In this case, the extraction of gas or the generation of the reduced pressure is achieved by means of a gas pump. Moreover, with this extraction of gas also the low-boiling fuel fraction in vapor form which is formed in the vessel is withdrawn from the vessel. On the delivery side of the gas pump, the evaporated components are condensed, in order to be able to provide the low-boiling fuel fraction, which has been separated, to the internal-combustion engine in a liquid state. To improve the performance of the fuel fractionation device, in particular the fractionation rate, the suction side of the gas pump can be heated and/or the pressure side of the pump can be cooled.  
           [0005]    The present invention deals with the problem of improving the performance of a fuel fractionation device of the type described in the introduction. It is a particular object to increase the fractionation rate.  
         SUMMARY OF THE INVENTION  
         [0006]    In a fuel fractionation device for separating a low-boiling fuel fraction from a liquid fuel of an internal combustion engine, including a vessel which contains the liquid fuel, and in which a reduced pressure is generated by withdrawing the low-boiling fuel fraction in vapor form from the vessel and making it available to the internal combustion engine, the efficiency of the fractionation is improved by utilizing a carrier-gas which is introduced into the liquid fuel, and which is withdrawn from the vessel together with the fuel fraction vapor.  
           [0007]    The carrier gas rises through the fuel in the form of bubbles and, in the process, is preferentially enriched with the low-boiling fuel components. The mixture collects above the fuel level in the vessel, from where the carrier gas/fuel fraction mixture formed in this way can be moved out of the vessel. Unlike in the prior art, the reduced pressure, which is in this case generated in the vessel by the gas being sucked out, only has to ensure that the gaseous carrier gas/fuel fraction mixture formed in the vessel is sucked out of the vessel. The pressure reduction required to achieve this is considerably lower than the pressure reduction required to evaporate the components of the low-boiling fuel fraction out of the liquid fuel. The pressure source, which is used to generate the reduced pressure and also the vessel construction, can in this way be simplified.  
           [0008]    Preferably, however, the reduced pressure, which is generated in the vessel as a result of the gas being sucked out, is large enough to suck in the carrier gas, so that there is no need for an additional pump. By way of example, the suction requirements are low enough so that they can be satisfied by the vacuum generated in the air intake of the internal-combustion engine. In the process, at least some of the air required for combustion in the internal-combustion engine is sucked in through the vessel. In this case, the carrier gas used is ambient air.  
           [0009]    According to a particularly advantageous embodiment using air as carrier gas, the air/fuel fraction mixture extracted from the vessel can be fed to the internal-combustion engine directly as a combustible air/fuel mixture, since the air, which is enriched with the low-boiling fuel fraction, forms an ignitable gas mixture.  
           [0010]    Alternatively, the gas may also be sucked out by means of a special gas pump, so that it is also possible to compress the carrier gas/fuel fraction mixture on the delivery side of the gas pump.  
           [0011]    Instead of an open circuit, in which the air used as carrier gas is fed to the internal combustion engine for combustion together with the fuel fraction which has been separated off in the form of an air/fuel fraction mixture, in which case the carrier gas is consumed, it is also possible to form a closed circuit, in which, after the carrier gas/fuel fraction mixture has been sucked out, the fuel fraction is separated from the carrier gas and is used again. In this case, the fuel fraction, which is separated out of the mixture is held ready in a special reservoir, preferably collected in the liquid state, and is fed into the internal-combustion engine when required. The carrier gas may either be introduced back into the fuel in the vessel or, in particular if air is used as carrier gas, can be discharged the environment.  
           [0012]    In accordance with a particularly advantageous embodiment of the fuel fractionation device according to the invention, the vessel into which the carrier gas is introduced and from which the carrier gas/fuel fraction mixture is sucked out may be formed by a fuel tank in which the fuel for the internal-combustion engine is stored. In the case of a vehicle, this is the vehicle&#39;s fuel tank for supplying fuel to the internal-combustion engine may be employed for that purpose.  
           [0013]    The invention will become more readily apparent from the following description of a preferred embodiment on the basis of the accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 shows a circuit diagram of a fuel fractionation device according to the invention, and  
         [0015]    [0015]FIG. 2 shoes a fuel fractionation device according to the invention with a similar circuit. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0016]    In accordance with FIG. 1, a fuel fractionation device according to the invention comprises a vessel  1 , which contains fuel  2 , for example diesel fuel or gasoline, and is preferably formed by a fuel tank of an internal-combustion engine (not shown). If the fuel fractionation device is installed on board a motor vehicle, the vessel  1  is preferably formed by the vehicle&#39;s fuel tank, which stores the fuel for the internal-combustion engine of the vehicle. It is also possible for the vessel  1  to be formed by a container, which is separate from the fuel tank of the internal-combustion engine, and to be supplied with fuel  2  from the fuel tank.  
         [0017]    The fuel fractionation device according to the invention is equipped with a carrier-gas supply  7  including a gas distributor  4 , which is arranged in the interior of the vessel or fuel tank  1 , in the vicinity of a base  3  of the fuel tank  1 , or is integrated in this base  3 . The gas distributor  4  is arranged sufficiently low in the fuel tank  1  for it to be submerged in the fuel  2  at the levels which customarily occur that is below a fuel level  5 . The gas distributor  4 , which can also be referred to as a swirler, is internally hollow and has a plurality of gas outlet openings  6 .  
         [0018]    The gas outlet openings  6  form the exit side of the gas distributor  4 , which on its entry side is connected to a gas feed line  8 , in which a valve  9  is arranged. The gas feed line  8  is in communication, via an activated carbon filter  10 , at  11  with a carrier-gas reservoir or with a carrier-gas source, which is preferably formed by the environment. In that case, the carrier gas is formed by ambient air. Above the fuel level  5 , the fuel tank  1  contains a gas-collection space  12 , to which a suction line  13  is connected.  
         [0019]    The fuel fractionation device according to the invention also has a gas pump  14 , which has a suction side connected to the suction line  13  and a supply side, by a pressure line  17 , via a non-return valve  15  to a separator  16 . The separator  16  separates the carrier gas and the fuel fraction and may, for example, be equipped with a cyclone and/or include a selective membrane.  
         [0020]    In the pressure line  17  there is a heat exchanger  18  through which a heat-transfer medium can flow, as symbolically indicated by an arrow  42 . Between separator  16  and heat exchanger  18 , a pressure-relief line  19  is connected to the pressure line  17 , and this line  19  is connected to the suction line  13  via a pressure-relief valve  20 .  
         [0021]    The separator  16  is arranged in a housing  21  which, in its interior, also includes a reservoir  22  for a low-boiling fuel fraction  23  which has been separated out of the fuel  3 . In addition, a level sensor  24 , which monitors the level of the fuel fraction  23 , is arranged in the reservoir  22 . The reservoir  22  is connected to the tank  1  by means of a first connection  25 , via a fuel return line  26  in which a valve  27  is arranged. By means of a second connection  28  the fuel fraction  23  stored in the reservoir  22  is supplied to the internal-combustion engine via a fuel feed line  29  in which a valve  30  is arranged. By way of example, the fuel fraction  23  is fed to a fuel manifold of a fuel injection device or is fed directly to an injection valve of this fuel injection device.  
         [0022]    By means of a gas return line  31 , in which an adjustable pressure control valve  32  is arranged, the separator  16  is in communication with the environment  11  via the activated carbon filter  10 . The suction line  13  can be connected to the gas return line  31  via a valve  33 . An air intake line  34 , in which a valve  35  may be arranged and which is connected to an air intake (not shown) of the internal-combustion engine, is in communication with the gas feed line  8 .  
         [0023]    To actuate and control the electrical components, there is a control unit  36 , which is connected to the corresponding components via signal and control lines  37 . The signal and control lines  37  are only slightly indicated for the sake of clarity.  
         [0024]    The fuel fractionation device shown in FIG. 1 operates as follows:  
         [0025]    At the beginning of a cold start of the internal-combustion engine, for example as a result of a starter motor being actuated, the gas pump  14  is activated and the valve  9  is opened, while the valve  33  is closed. This position of the valves leads to a reduced pressure being generated in the fuel vessel  1  via the suction line  13 , and this reduced pressure spreads to the carrier-gas feed  7 , so that air can be sucked out of the environment  11  through the activated carbon filter  10 . In the gas distributor  4 , this air passes through its outlet openings  6 , distributed as finely as possible, into the fuel  2 , where it rises through the fuel  2  and is preferentially enriched with low-boiling fuel components before collecting in the gas collection space  12  of the vessel  1 . On account of the gas being sucked out through the suction line  13 , the air/fuel fraction mixture formed in this way is sucked out of the gas collection space  12  by the gas pump  14  and is fed to the separator  16  via the pressure line  17 . In the heat exchanger  18 , the compressed air/fuel fraction mixture is cooled with the result that the fuel fraction is liquefied. According to a particular embodiment, the fuel  2  of the fuel tank  1  can be used as cooling medium, whereby the fuel is heated, which enhances the fractionation of the fuel  2 . The heat exchanger  18  may also be acted on by ambient air or may be connected to a cooling circuit which is already present on the vehicle, for example to the cooling circuit of an air-conditioning system or to an engine cooling circuit.  
         [0026]    In the separator  16 , the liquid fuel fraction is separated from the air. While the fuel fraction  23  enters the reservoir  22 , where it collects, the air is returned to the activated carbon filter  10  through the gas return line  21 .  
         [0027]    During a cold start, the fuel fraction  23 , which serves as starting fuel, is supplied to the internal-combustion engine. The pressure control valve  32  is set to the required injection pressure by the control unit  36 . Since the separator  16  and the reservoir  22  are accommodated in the common housing  21 , which is designed as a pressure vessel, the pressure which is set at the pressure control valve  32  automatically also prevails in the fuel fraction  23 .  
         [0028]    Before the valve  30  is opened in order to feed the fuel fraction  23  to the internal-combustion engine, the valve  27  is opened briefly in order to return any water of condensation which may have collected in the reservoir  22  to the fuel tank  1  from the reservoir  22 .  
         [0029]    When the cold start or a warm-up phase of the internal-combustion engine has ended, the valve  30  closes. The fuel fractionation may be continued in order, for example, to top up the supply of low-boiling fuel fraction  23  in the reservoir  22 . During this fractionation, the compression pressure is regulated at the pressure control valve  32 , for example as a function of the ambient temperature. The compression pressure on the delivery side of the pump  14  is selected in such a way that the partial pressure of the fuel components which remain in the carrier gas is as low as possible after the separation and downstream of the pressure control valve  32 , i.e. the compression pressure is set in such a way that particularly effective condensation and separation can be carried out.  
         [0030]    Downstream of the separator  16 , the carrier gas is fed to the activated carbon filter  10 , from where it can be introduced back into the carrier-gas feed  7 . In the embodiment shown in FIG. 1 a closed circuit is formed for the carrier gas, since the carrier gas, after the fuel fraction has been separated out of it, is available without having been consumed and, in particular, is used a number of times.  
         [0031]    Depending on the state of charge of the activated carbon filter  10 , it is either regenerated or charged. This procedure enables the regeneration of the charged activated carbon filter  10  to take place independently of operation of the internal-combustion engine. Moreover, all the low-boiling components available in the fuel are available for cold starts of the internal-combustion engine, since during the intake of air for blowing the air into the fuel as carrier gas, the activated carbon filter  10  is regenerated. During fractionation operation, the loading of the activated carbon filter  10  can take place by means of a residual proportion of fuel components in the returned quantity of carrier gas. When the fractionation has ended, the valve  33  is opened, so that the loading of the activated carbon filter  10  takes place via the evaporation emissions of the fuel  2  from the fuel tank  1 .  
         [0032]    When there is no fractionation in progress, the activated carbon filter  10  can also be regenerated by briefly opening the valve  35 , so that the internal-combustion engine sucks in at least some of its intake air through the activated carbon filter  10 .  
         [0033]    To end the fractionation, the gas pump  14  is switched off, the valve  9  is closed and the valve  33  is opened.  
         [0034]    [0034]FIG. 2 shows another embodiment of the fuel fractionation device according to the invention, in which identical components are denoted by identical reference numerals.  
         [0035]    In accordance with FIG. 2, in this variant there is a controllable gas pump  14 ′ in order to suck out the gas in order to generate a reduced pressure in the vessel  1 . On its delivery side, this gas pump  14 ′ is connected to at least one injection valve  38 , by means of which the air/fuel fraction mixture which has been sucked out of the gas collection space  12  of the vessel  1  is supplied to the internal-combustion engine or individual combustion chambers or induction regions of these fuel chambers. A fuel sensor  39 , which senses the content or concentration of the fuel fraction in the air/fuel fraction mixture and transmits a correlated signal value to the control unit  36  via a corresponding line  37 , is arranged in the pressure line  17 . The delivery side of the gas pump  14 ′ is in communication, via a return line  40  which is connected to the pressure line  17  and in which an adjustable pressure control valve  41  is arranged, with the gas feed line  8  upstream of the valve  9 , so that the delivery side of the gas pump  14 ′ is connected to the environment  11  via the activated carbon filter  10 .  
         [0036]    At the beginning of a cold start and a warm-up phase of the internal-combustion engine, the gas pump  14 ′ is switched on, the valve  33  is closed and the valve  9  is opened. As a result, a reduced pressure is formed on the suction side of the gas pump  14 ′ and spreads via the suction line  13  into the gas collection space  12  of the vessel  1 . Moreover, the reduced pressure causes air to be sucked in from the environment  11  through the activated carbon filter  10  and through the carrier-gas feed  7  into the fuel  2 . The carrier gas or air, which has been sucked in, is discharged in finely distributed form into the fuel  2  in the gas distributor  4  and removes the low-boiling components from the fuel  2 . The air/fuel fraction mixture, which collects in the gas collection space  12 , is conveyed via the suction line  13  to the delivery side of the gas pump  14 ′. The suction capacity or the delivery capacity of the gas pump  14 ′ is regulated as a function of the engine speed, the engine load and as a function of the fuel concentration measured at the sensor  39 . The pressure at which the air/fuel fraction mixture is available at the valves  38  of the internal-combustion engine is set at the pressure control valve  41 . This pressure regulation takes place as a function of the ambient temperature in order, for example, to prevent condensation of fuel in the pressure line  17 . Air/fuel fraction mixture which is not used flows across the pressure control valve  41  and is introduced into the gas feed line  8 , where, when the fractionation is active, it is once again introduced into the fuel  2  through the gas distributor  4 .  
         [0037]    The valves  38  are controlled as a function of the engine speed, the engine load, the fuel concentration in the air/fuel fraction mixture and the pressure set on the delivery side of the gas pump  14 ′.  
         [0038]    After the cold start or the warm-up phase has ended, the gas pump  14 ′ is switched off, the valve  9  is closed and the valve  33  is opened. When the fractionation is inactive, the activated carbon filter  10  takes up the evaporation emissions of the fuel  2  in the tank  1 . The activated carbon filter  10  can be regenerated in the customary way via the air intake line  34  as a result of the induction operation of the internal-combustion engine. Preferably, however, regeneration takes place during fractionation operation, in which the ambient air is sucked through the activated carbon filter  10  with a corresponding regeneration action.  
         [0039]    The embodiment of the fuel fractionation device which is illustrated in FIG. 2 and forms part of a fuel supply installation of the internal-combustion engine, unlike the embodiment illustrated in FIG. 1 takes place without a reservoir for the low-boiling fuel fraction. By means of the carrier-gas feed  7  which is proposed in accordance with the invention, it is possible for an ignitable air/fuel fraction mixture, which is particularly suitable for starting and warming up an internal-combustion engine to be produced in sufficient quantities in an “on-line” fashion.  
         [0040]    Since in this embodiment the air used as carrier gas is consumed, so that new air has to be constantly sucked in from the environment  11  for fractionation, the circuit is in this case open.