METHOD AND APPARATUS FOR REGENERATIVE HEATING OF DIESEL FUEL

Abstract: A method and apparatus for heating and filtering diesel fuel in which incoming diesel fuel is passed in a heat-­ exchange relationship with already heated and filtered diesel fuel, is further heated by either an electric heater (16) or by other means, is passed through a filter (24), and then is passed in a regenerative heat-exchange relationship with the incoming diesel fuel.

Description: Description Method And Apparatus For Regenerative Heating Of Diesel Fuel This invention relates to the filtering and regenerative heating of diesel fuel as it passes from a fuel tank (or other fuel source) to a diesel engine. If diesel fuel becomes too cold, higher molecular weight hydrocarbons therein can solidify, causing "clouding" of the fuel. These solids can block the pores of a fuel filter through which the fuel is pumped, causing the engine to lose power (or stop) or preventing the engine from starting. In order to prevent this, various methods have been proposed for heating diesel fuel before it reaches the filter. For disclosure of such methods, reference may be made, for example, to U.S. Patents Nos. 2,669,299, 3,564,199, 3,935,901, 3,989,019, 4,091,265, 4,372,279, 4,398,084 and 4,406,785 and copending and commonly-assigned U.S. patent applications Serial Nos. 382,259, 423,589 and 474,390. The known systems for the electrical heating of diesel fuel suffer from the disadvantage that the output of the heater must be sufficient to heat all the diesel fuel passing through the fuel system from its storage temperature to a temperature above its cloud point. This is a particularly serious disadvantage when the heater is powered by the electrical system of a vehicle, which has only a limited amount of total power available. Typically, a heater having a power output of 100-150 watts is needed for a car or light truck, with proportionately larger power outputs needed for fuel systems handling larger fuel throughputs, e.g., 450-600 watts for a large truck. Equally important is the fact that the heater may continue to draw power at this rate for a considerable time, so that even if thetvehicle batteries can provide the necessary power initially, they cannot continue to do so. We have now realized that the outgoing diesel fuel (i.e., the fuel which has been filtered) need not be maintained above its cloud point after it has been filtered and that is is therefore possible to reduce the thermal output needed from the heater by passing the outgoing heated and filtered fuel in a regenerative heat-exchange relationship with the incoming fuel to preheat the incoming fuel. This creates a type of regenerative cycle in which low-grade heat that is not necessary after filtering and that would be lost is used to improve thermal efficiency. The present invention makes possible substantial reductions in the power output required of the heater under steady-state conditions, in order to produce a particular increase in the temperature of the fuel as it is filtered, for example a reduction of the power output to less than 25% of that required without any transfer of heat from the outgoing fuel to the incoming fuel as will be seen in the table disclosed later herein. The purpose of the instant invention is to provide a method and apparatus for heating and filtering diesel fuel. To accomplish this purpose, incoming diesel fuel is passed in heat-exchange relationship with already heated and filtered fuel, the heat of the filtered fuel working in a regenerative fashion to reduce the amount of heat and therefor power required to heat the diesel fuel before filtering. In one aspect, the present invention provides a method of filtering diesel fuel as it is pumped from a fuel source in which the fuel is at a temperature below its cloud point, which method comprises: (1) preheating incoming diesel fuel by passing it in a heat-exchange relationship with outgoing, filtered fuel; (2) further heating the incoming diesel fuel by means of an electrical heater; (3) filtering heated diesel fuel from step (2); and (4) passing filtered diesel fuel from step (3) in a regenerative heat-exchange relationship with the incoming fuel, to raise the temperature of the incoming fuel before it is heated in step (2) while maintaining the incoming fuel and the fuel from step (2) physically separate from each other. In another aspect, the invention provides apparatus for heating diesel fuel as it is pumped from a fuel source in which the fuel is at a temperature below its cloud point, which apparatus comprises: (1) an electric heater to heat fuel, said heater connectable to a fuel filter; (2) heat-exchange means connected to the heater, said means having a heat-exchange member therein which is positioned so that incoming fuel pumped from a fuel source going to the heater passes on one side of the member and outgoing filtered fuel emerging from a fuel filter passes on the other side of the member, so that heat is transferred from outgoing fuel to incoming fuel before the incoming fuel enters the heater. Any type of electric heater can be used in this invention. It is preferable, however, to use a self-regulating heater,- e.g. a heater comprising a PTC conductive polymer heating element such as an elongate strip heater comprising parallel wire electrodes embedded in a sheet or strip of conductive polymer comprising a cross-linked fluoropolymer having carbon black dispersed therein. The heater can be placed so that it is directly contacted by the diesel fuel outside a heating chamber, but is preferably placed inside the heating chamber, especially when a self-regulating heater is used. The heater can be powered from any power source, but when the invention is used on a diesel-engined vehicle, as is preferred, it is preferably connected to the electrical system of the vehicle. Specific heaters are disclosed in U.S. Patents Nos. 3,564,199, 3,935,901, 3,989,019, 4,091,265, 4,177,376, 4,304,987, 4,372,260, 4,372,279 and 4,406,785 which are incorporated herein by reference. The heat exchange between the incoming and outgoing fuel can be effected wholly or partly before the incoming fuel is heated by the heater. However, it is more efficient, i.e. uses less electrical power by recovering waste heat, to heat the incoming fuel by heat exchange with the outgoing fuel prior to heating by the heater. It is within the scope of the invention to perform these functions within the same chamber or plenum as long as the net heat transfer is from the already heated, filtered fuel to the incoming fuel. Attention is now directed to the drawings. Figure 1 discloses apparatus shown generally at 10 for heating and filtering diesel fuel as it is pumped from a fuel source in which the fuel may be at a temperature below its cloud point. The apparatus comprises a housing shown generally at 12 for heating diesel fuel before it is filtered, and a filter 14. The apparatus utilizes an electrical heater 16 or the like having means 18 for connecting the heater to a power supply (not shown). The housing comprises a heatexchange means in the form of a heat-exchange chamber 22 and a heating chamber 24, the electrical heater 16 being within the heating chamber 24. The heat-exchange chamber 22 contains a heat-exchange member 26 which comprises a thermally conductive continuous double spiral partitions which maintains incoming fuel physically separate from outgoing heated and filtered fuel. Heat exchangers with double spiral partitions are also referred to as dual spiral plate heat exchangers. The device 20 for heating diesel fuel before it is filtered and for transferring heat from the filtered diesel fuel to the diesel fuel to be heated and then filtered, is removably securable between a fuel manifold shown generally at 28 and a fuel filter 14. As seen in Fig. 1, the apparatus is removably secured by pipe threads 30 or the like, and is sealed with respect to the manifold by gasket means 32. The fuel filter 14 is likewise secured to the apparatus by threads (not shown) and a gasket or by other equivalent means. Incoming fuel to be heated and filtered is introduced into the apparatus at an inlet shown generally at 34 and exited at an outlet shown generally at 36. Heatexchange chamber 22 has at least a first entry port 38 for the entry of filtered diesel fuel from the fuel filter 14 when the housing is secured to the fuel filter 14, and at least a first exit port 40 corresponding to the device and apparatus exit 36 for the exit of fuel to the fuel manifold 28 when the housing is secured to the fuel manifold. The first entry port 38 and the first exit port 40 define a first passage therebetween on one side of the heat-exchange member 26. The heat-exchange member has a second entry port 42 corresponding to the apparatus inlet 34 for entry of diesel fuel from the fuel manifold 28, and has a second exit port 44 for the exit of fuel to the heater chamber 24 having heater element 16. The second entry port 42 and the second exit port 44 define a second passage on the other side of said heat-exchange member 26. Heat from the first passage is capable of being thermally transferred to said second passage through said heatexchange member 26 to warm the incoming fuel before it passes into the heating chamber 24 and before it then passes into the filter 14. Separation of first and second passages can be more clearly seen in Fig. 2 wherein the second passage terminating at second exit port 44 is traced in phantom line for purpose of illustration. Figs. 2 and 3 are sectional views taken with respect to Fig. 1. By a comparison of these figures it can be seen, for example in Fig. 3, that fuel entering via inlet 34 and second entry port 42 at the top of the device will be kept separate by heat-exchange member 26 from exiting fuel as it travels around the spiral path, eventually to exit through second exit port 44 (also shown in phantom in Fig. 3) into the heater section 16. Likewise it can be seen that fuel returning from filter 14 through center core 46 will re-enter the heatexchange section through first entry port 38 and proceed through the spiral pathway to exit at first exit port 40. It is understood that the heat-exchange member 26 completely separates the two first and second fuel passages as described above from each other. The unique spiral configuration provides an extremely large surface area of contact in a compact cylindrical envelope. Fig. 4 is a schematic view of the instant invention wherein incoming diesel fuel 48 is passed through a heat exchanger 50 in heat-exchange relationship with outgoing filtered fuel and is preheated and then proceeds to heater 52 for further heating such as by means of an electrical heater before being passed through filter 54. The heated and now filtered fuel passes from the filter 54 in regenerative heat-exchange relationship back through the heat exchanger 50 by a separate and distinct path for use in the engine 56. The apparatus of the instant invention is shown contained within the dashed line 58. It is within the scope of the invention to use other types of heat exchangers such as a tube and shell heat-exchanger, double-pipe heat-exchangers and parallel plate heat-exchangers. Heater 52 may be any one of a number of heating devices which are capable of raising the temperature of the fuel placed in contact with the heater. An example is the coiled PTC heater disclosed in commonly-assigned U.S. Patent Application Serial Nos. 474,390, filed March 11, 1983, and 606,033, filed May 1, 1984, which are incorporated by reference herein. Other types of heaters may be used such as electrical resistance wires, barium titanate PTC resistors, mineral insulated cable and self-regulating heaters as described in U.S. Patent No. 4,177,376 referred to earlier. It is also within the scope of the invention to utilize other heating sources (other than electricallygenerated heating sources), as for example heat exchangers utilizing engine coolant, engine oil, exhaust gas, hot return fuel or devices mounted directly on the engine. A device as shown in Fig. 1 and functioning per the diagram of Dig. 4 was connected to a variable flow rate diesel fuel pump and reservoir system and a source of direct current electrical power. The results obtained are shown in the Table below. It can be seen that in the case of a 0.5 gallon-perminute flow rate a reduction of the power output to 24% of that necessary to product an equivalent fuel temperature rise at the filter inlet without any transfer of heat from the outgoing fuel to the incoming fuel was achieved by the regenerative heat exchanger. In the case of a higher fuel flow rate of 0.68 gallons-perminute a reduction of power output to 17% of that necessary to produce an equivalent temperature rise at the fuel filter inlet without any transfer of heat from the outgoing fuel to the incoming fuel was achieved by the regenerative heat exchanger. TABLE EQUIVALENT % TOTAL %TOTAL %IMPROVEMENT HEATER FLOW FUEL TOTAL HEATER EXCHANGER FROM FROM OVER HEATER ACTUAL WATTS FOR RATE INLET #T # T # T EXCHANGER HEATER ALONE HEATER SAME EFFECT GPM OF OF OF OF Volts Amps Watts 0.5 9 45 10.8 34.2 76% 24% 318% 14 14.7 205.8 860 0.68 18 32 5.5 26.5 83% 17% 482% 14 16 224 1300 The apparatus can be configured so that the heatexchange chamber and the heating chamber are integral. Such an integral unit and the fuel filter can be removably securable to each other and in turn removably securable to a fuel manifold. In practice, this invention can be used either with spin-on filters or replaceable element filters. In an integral heater and heat-exchange unit, a cavity for a replaceable filter element with appropriate fuel passages may be included. In a preferred embodiment, the heating chamber and the heat-exchange chamber form part of an integral unit which can be secured between the fuel manifold and the filter of a conventional vehicle fuel system, so that the integral unit can be retrofitted to the conventional system with little difficulty. In another embodiment of this. invention, a water separator may also be incorporated into the apparatus either anywhere prior to the filter, as part of the filter, or anywhere after the filter The above description and attached drawing are given by way of illustration to set forth the preferred method of the present invention. Other methods and modifications thereof may be envisioned that fall within the scope of the following claims.

Claims: WHAT IS CLAIMED IS: 1. Apparatus for heating diesel fuel as it is pumped from a fuel source in which the fuel is at a temperature below its cloud point, which apparatus comprises: (1) an electric heater to heat fuel, said heater connectable to a fuel filter; (2) heat-exchange means connected to the heater, said means having a heat-exchange member therein which is positioned so that incoming fuel pumped from a fuel source going to the heater passes on one side of the member and outgoing filtered fuel emerging from a fuel filter passes on the other side of the member, so that heat is transferred from outgoing fuel to incoming fuel before the incoming fuel enters the heater. 2. Apparatus according to Claim 1 wherein the heater is a self-regulating heater. 3. Apparatus according to Claim 1 further including a fuel filter connected to said heater and said heatexchange means. 4. Apparatus according to Claim 3 wherein the heater, heat-exchange means and fuel filter are enclosed within a common housing. 5. Apparatus according to Claim 3 further including a water separator operatively connected to the fuel filter to separate water from the fuel. 6. Apparatus according to Claim 5 wherein the heater, heat-exchange means, the fuel filter and the water separator are enclosed within a common housing. 7. A method of filtering diesel fuel as it is pumped from a fuel source in which the fuel is at a temperature below its cloud point, which method comprises: (1) preheating incoming diesel fuel by passing it in a heat-exchange relationship with outgoing, filtered fuel; (2) further heating the incoming diesel fuel by means of an electrical heater; (3) filtering heated diesel fuel from step (2); and (4) passing filtered diesel fuel from step (3) in a regenerative heat-exchange relationship with the incoming fuel, to raise the temperature of the incoming fuel before it is heated in step (2) while maintaining the incoming fuel and the fuel from step (2) physically separate from each other. 8. A method according to Claim 7 including the step of separating water from the diesel fuel. 9. A method according to Claim 7 wherein the heating step is done in a thermally-controlled manner by a self-limiting heater element wherein the heater comprises a PTC conductive polymer heating element.

Inventors: LEARY, DAVID F., OLDS, RICHARD N.
Applicants: RAYCHEM CORPORATION (A DELAWARE CORPORATION)
Application year: 1985
Main classification: F02M31
IPC codes: F02M31, F02B3, F02M37