Mounted fuel tank heater
TECHNICAL FIELD 
     This invention relates to a system for preheating fuel for an internal combustion engine in the fuel tank normally provided with a vehicle or other machine powered by such engine. 
     BACKGROUND ART 
     It is well known that preheating the fuel used in an internal combustion engine improves the efficiency of the engine. Further, preheating the fuel typically used in a diesel engine can avoid serious fuel flow problems well known to occur in cold weather environments. 
     Diesel fuel, and in particular the No. 2 fuel oil typically burned by the engines of over-the-road trucks, can congeal or &#34;wax&#34; in the cold weather regularly experienced during the winter months in the northern states of the United States and in Canada. The jelling or waxing of fuel can shut a diesel engine down, necessitating the towing of the vehicle to a repair facility where the fuel tank must be heated to alleviate the problem. The expense of towing and downtime can be substantial. 
     A number of methods and devices have been developed in an attempt to solve the problem of congealing fuel oil in cold weather. One method has been to install a heater in the fuel line. U.S. Pat. No. 3,929,187 discloses a device which utilizes this method. However, this method does not solve the problem of fuel oil congealing within the fuel tank itself before it even gets into the fuel line. Another method is to install a heater in the fuel tank. U.S. Pat. No. 4,237,850 discloses a device which utilizes this second method. The device disclosed in this patent has two primary disadvantages. One, while the fuel can be heated in the tank to a temperature above that at which it &#34;waxes&#34;, it is not necessarily heated to a temperature which will prevent it from congealing in the fuel line in extremely cold weather, because of the volume of fuel which must be heated in the tank which is usually directly exposed to the cold outside air temperatures. Second, the device disclosed in this patent requires an access opening which must be cut/formed into the top of the fuel tank prior to installation of the device. 
     Therefore, it is a principal object of the present invention to provide a system for preheating diesel fuel in the fuel tank to a temperature above that at which the fuel would normally congeal. 
     It is a further object of the present invention to provide a system for preheating the diesel fuel leaving the fuel tank to a temperature which is sufficiently higher than the temperature at which the fuel would normally congeal such that the fuel cannot jell in the fuel line between the fuel tank and the diesel engine to which it is supplied. 
     It is yet another object of the present invention to provide a system for preheating the fuel in the fuel tank of a diesel engine-powered vehicle or machine which includes a heat exchanger which can be installed through and secured in the opening normally provided in such a fuel tank for the installation of a fuel level gauge. 
     DISCLOSURE OF THE INVENTION 
     Other objects and advantages will be accomplished by the present invention which provides a system for preheating fuel for an internal combustion engine in the fuel tank normally provided with the vehicle or other device powered by such engine. The system includes a heat exchanger which is installed in the fuel tank of the vehicle or other device. In the preferred embodiment, the heat exchanger is installed through and secured to the opening normally provided in the fuel tanks of most diesel engine-powered over-the-road trucks for installation of a fuel gauge. Most such trucks are provided with two fuel tanks and the fuel gauge access opening is usually only used for a fuel gauge in one of the tanks. Therefore the unused opening in one of the tanks can be used for installation of the present invention. 
     In the preferred embodiment, the heat exchanger is an elongated substantially cylindrically shaped device made of a thermally conductive material, preferably a corrosion resistant metal. The heat exchanger includes a heated fluid chamber and a fuel tube extending through such chamber. The heated fluid chamber includes an inlet port and an outlet port positioned in a first end portion of the heat exchanger. A divider plate is provided in the heated fluid chamber between the inlet and outlet port which extends from the first end portion of the chamber through all but a small portion of the length of the chamber. The divider plate divides the heated fluid chamber into an inlet section and an outlet section whereby heated fluid from an external source enters through the inlet port and travels through the inlet section toward the second end portion of the chamber where it passes into the outlet section and travels back toward the first end portion where it exits through the outlet port and is returned to the external source for reheating. Heat is transferred through the external walls of the heat exchanger from the heated fluid to the fuel in the fuel tank. 
     As indicated above, a fuel tube is provided which extends through, and is therefore surrounded by the heated fluid chamber. In the preferred embodiment, fuel is drawn into an open fuel inlet end of the tube proximate and external to the second end portion of the heat exchanger and is drawn through the fuel tube where it is further heated by the heated fluid in the above-described chamber which surrounds the fuel tube and exits from the fuel outlet end of the tube which is connected to the fuel line of the vehicle in which the present invention is installed, proximate and external to the first end portion of the heat exchanger. 
     In the preferred embodiment, the external source of heated fluid is the radiator of the vehicle in which the present invention is installed. Fluid communication can be provided between the radiator and the inlet and outlet ports of the above-described heated fluid chamber via flexible hoses similar to those normally used in internal combustion engines to provide fluid communication between the radiator and the engine block. In another embodiment of the present invention, the heated fluid can comprise lubricating oil circulated from the oil pan of the engine with which the system is used. 
     Fuel is drawn from the fuel tank through the fuel tube of the present invention into the fuel line as described above by the fuel pump of the engine of the vehicle or other device in which the system is installed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a perspective view, partially cut away of a system for preheating fuel for an internal combustion engine in a fuel tank constructed in accordance with various features of the present invention. 
     FIG. 2 illustrates a top view in section of the heat exchanger, taken at 2--2 of FIG. 1, of a system for preheating fuel for an internal combustion engine constructed in accordance with various features of the present invention. 
     FIG. 3 illustrates a front elevation view of an alternate embodiment of a system for preheating fuel for an internal combustion engine in a fuel tank constructed in accordance with various features of the present invention. 
     FIG. 4 illustrates a block diagram of a system for preheating fuel for an internal combustion engine in a fuel tank constructed in accordance with various features of the present invention as illustrated in FIGS. 1 and 2. 
     FIG. 5 illustrates a perspective view, partially cut away, of another embodiment of a system for preheating fuel for an internal combustion engine in accordance with various features of the present invention. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     A system for preheating fuel for an internal combustion engine in the fuel tank normally provided with the vehicle or other device powered by such engine is illustrated generally at 10 in FIG. 1. The system includes a heat exchanger shown generally at 12 in FIG. 1. The heat exchanger 12 is installed through an access opening 14 which is normally provided in fuel tanks for diesel engine-powered over-the-road trucks for installation of a fuel gauge. A portion of such a fuel tank is illustrated at 16 in FIG. 1. The heat exchanger 12 is provided with a flange 18, which is dimensioned and predrilled to match the flange 20 surrounding the opening 14 in the fuel tank 16, proximate a first end portion 22 of the heat exchanger 12. When the system 10 is installed, an appropriate gasket or seal (not shown) is installed between the flange 18 and the flange 20. 
     The heat exchanger 12 comprises a substantially cylindrical vessel having an outer wall 24 which defines an interior heated fluid chamber 26. An inlet port 28 and an outlet port 30 are provided proximate the first end portion 22 of the heat exchanger 12, between the first end portion 22 and the flange 18, through which a heated fluid is supplied from and returned to an external source of the heated fluid. A fuel tube 32 extends axially through the heat exchanger 12 from externally of its second end portion 34 to externally of its first end portion 22. The fuel tube 32 is surrounded by the heated fluid chamber 26 as shown in FIGS. 1 and 2. The heated fluid chamber 26 is divided into an inlet section 36 and an outlet section 38, as illustrated in FIG. 2, by a divider plate 40, comprised of two coplanar plate sections 40A and 40B positioned between the fuel tube 32 and the outer wall 24 of the heat exchanger 12. The divider plate 40 extends from the first end portion 22 of the heat exchanger 12, parallel to the fuel tube 32, for all but a small portion of the length of the heat exchanger 12 where it terminates in a distal end portion 42, such that fluid communication is provided between the inlet section 36 and the outlet section 38 of the heated fluid chamber 26 proximate the second end portion 34 of the heat exchanger. 
     Referring to FIG. 1 and to FIG. 4, which is a block diagram of the system 10, it can be seen that heated fluid enters via an appropriate fitting 44 into the inlet port 28 of the heat exchanger 12, as indicated by the arrows 50A and 50B. The heated fluid travels down through the inlet section 36 of the heated fluid chamber 26 and under the distal end portion 42 of the divider plate 40 into the outlet section 38 of the heated fluid chamber 26, as indicated by the arrows 50B, 50C, and 50D. The heated fluid exits the outlet section 38 of the chamber 26 through the outlet port 30 via an appropriate fitting 46, as indicated by the arrows 50E and 50F. It will be appreciated by those skilled in the art that heat from the heated fluid will be transferred to the fuel in the fuel tank which surrounds the heat exchanger 12, which preferably is constructed of a corrosion resistant metal which has good thermal conductivity. In the preferred embodiment, the heated fluid comprises heated coolant supplied from and returned to the radiator of the vehicle or other device in which the system 10 is installed as illustrated by the block diagram illustrated by FIG. 4. It will be appreciated by those skilled in the art that fluid communication can be provided between the radiator and the inlet and outlet port fittings, 44 and 46 respectively, by hoses, indicated by the reference numerals 52A and 52B in FIG. 4, similar to those typically used between a radiator and the block of an internal combustion engine. 
     Also, as indicated with dashed lines in FIG. 4, the hoses 52A and 52B could be alternately connected to the oil pan of the internal combustion engine for the circulation of lubricating oil as the heated fluid for the heating of the fuel. 
     Still referring to FIGS. 1 and 4, it can be seen that fuel from the fuel tank enters the fuel tube 32 through the open fuel inlet end 48 of the tube 32, as indicated by the arrow 60A, and exits through the fuel outlet end 54 of the tube 32, proximate and externally of the first end portion 2 of the heat exchanger 12, as indicated by the arrow 60B. The outlet end 54 of the fuel tube 32 communicates with the fuel line, indicated by the line 60 in the block diagram illustrated in FIG. 4, which supplies fuel to the engine. It will be appreciated by those skilled in the art that the fuel entering the fuel line will have been further heated in the fuel tube 32 by the heated fluid in the chamber 26 which surrounds the tube 32. 
     Referring to FIG. 3, an alternate embodiment 10&#39; of the system of the present invention is illustrated. In the system 10&#39;, the heat exchanger 12&#39; comprises a U-shaped tube secured proximate its inlet and outlet openings, 28&#39; and 30&#39;, respectively, to a flange 18&#39; which may be secured to a fuel tank 16 in a manner similar to that described for the system 10 illustrated in FIGS. 1, 2 and 4. 
     Referring now to FIG. 5, another alternate embodiment 10&#34; of the system of the present invention is illustrated. In the system 10&#34;, the heat exchanger 12&#34; comprises an elongated substantially cylindrical vessel having a similar overall external appearance to the heat exchanger 12 of the system 10 illustrated in FIG. 1. However, in this embodiment, there is no fuel tube extending through the heat exchanger 12&#34; as in the system 10; in this system 10&#34;, fuel is drawn from the bottom of the fuel tank in the conventional manner, i.e. fuel line connections in the vehicle or other device in which the system is used are left undisturbed. The heat exchanger 12&#34; defines a heated fluid chamber 26&#34; and includes a heated fluid inlet port 28&#34; coaxially (with the longitudinal axis of the heat exchanger 12&#34;) positioned in the first end portion 22&#34; of the heat exchanger. A heated fluid inlet tube 70 is provided which extends coaxially through the heat exchanger 12&#34; from an inlet end 72, positioned externally of and proximate the first end portion 22&#34; of the heat exchanger 12&#34;, through the inlet port 28&#34;, to an open outlet end 74 positioned within the heated fluid chamber 26&#34;  proximate the second end portion 34&#34; of the heat exchanger, such that heated fluid in the inlet tube 70 flows into the heated fluid chamber 26&#34;, as indicated by the arrows 50&#34;. In this embodiment, heated fluid from an external source (as described above for the system 10) enters the inlet end 72 of the inlet tube 70, flows down through the tube 70 and out of the outlet end 74 into the chamber 26&#34; proximate the second end portion 34&#34; of the heat exchanger 12&#34;, and back toward the first end portion 22&#34; of the heat exchanger where it exits through the outlet port 30&#34;, as indicated by the arrows 50A&#34;, 50&#34; and 50B&#34;. The heat exchanger 12&#34; includes a flange 18&#34; which may be secured to a fuel tank 16 in a manner similar to that described for the system 10 illustrated in FIG. 1. It will be appreciated by those skilled in the art that, because of the flow path of the heated fluid, the greatest heat transfer from the heated fluid to the fuel in the fuel tank will occur near the second end portion 34&#34; of the heat exchanger 12&#34;. Since the heat exchanger is installed through an opening normally provided in the top portion of the fuel tank, the second end portion 34&#34; of the heat exchanger will be positioned near the bottom of the fuel tank from which fuel is drawn into the fuel line. Therefore, heating of the fuel entering the fuel line is enhanced. This embodiment of the present invention also has the advantage of having improved heat transfer characteristics over prior art systems which utilize a U-shaped tube heat exchanger similar to that shown in the system 10&#39; illustrated in FIG. 3. Heat transfer from the heated fluid to the fuel in the fuel tank is increased because of the relatively large surface area provided by the external walls 24 of the heat exchanger 12&#34; as compared to the U-shaped tube devices. 
     In light of the foregoing, it can be seen that a system 10 is provided by the present invention for preheating the fuel for an internal combustion engine in the fuel tank 16 by a heat exchanger 12 installed through an access opening 14 in the fuel tank. Heat from a heated fluid which is supplied to the heat exchanger 12, as indicated by the arrows 50, is transferred to the fuel in the fuel tank 16. The fuel is further heated by the heated fluid as it is drawn through the fuel tube 32 into the fuel line 60. Accordingly, when the system 10 is installed in a vehicle or other device powered by an internal combustion engine, the efficiency of such engine will be improved. In particular, the system 10 will eliminate or minimize the problem of congealing or &#34;waxing&#34; of diesel fuel in a diesel engine-powered vehicle or other device operated in cold weather environments. 
     While a preferred embodiment has been shown and described, it will be understood that it is not intended to limit the invention to such disclosure, but rather it is intended to cover all modifications and alternate constructions falling within the scope of the invention as defined in the appended claims.