WO1997019265A2

WO1997019265A2 - Fuel pre-heater

Info

Publication number: WO1997019265A2
Application number: PCT/CA1996/000769
Authority: WO
Inventors: Gordon Bridgeman
Original assignee: UNIVERSAL DIESEL PRODUCTS Inc
Current assignee: UNIVERSAL DIESEL PRODUCTS Inc
Priority date: 1995-11-21
Filing date: 1996-11-21
Publication date: 1997-05-29
Anticipated expiration: 1998-05-21
Also published as: WO1997019265A3; AU7614796A; ZA969783B

Abstract

A fuel pre-heater is used for heating the fuel for internal combustion engines, especially diesel engines. The pre-heater has an elongate cylindrical outer container housing (12) an inner S-shaped baffle (36). A fuel tube (32), formed into a coil extends the length of the container, with its inlet (28) and outlet (30) exiting through the ends (16, 18) of the container. Heating medium inlet (24) and outlet nipples (26) for the container are arranged tangentially, at opposite ends of the container and oriented in opposite directions. The heating medium inlet and outlet are connected into the coolant system of the internal combustion engine while the fuel inlet and outlet are connected into the fuel line leading to the fuel injectors or carburator of the engine. The pre-heater produces with its long path and counterflow pattern highly efficient heat transfer from the cooling medium to the fuel. In preferred embodiments, an electric heater (42) may be installed on the container for prestart-up heating. A temperature sensor (46) monitors the fuel outlet temperature and controls a valve (48) in the coolant inlet (24), closing the valve when the fuel has reached the desired temperature.

Description

FUEL PRE-HEATER FIELD OF THE INVENTION

The present invention relates to a heat exchanger for pre¬ heating fuel with a heated liquid. BACKGROUND

Cold ambient temperatures frequently cause problems in the operation of internal combustion engines, especially diesel engines. It is known that pre-heating the fuel for such an engine, before carburetion or injection, is useful in improving operation and engine fuel economy. Various fuel pre-heaters for pre-heating fuel using hot coolant from the engine cooling system have been proposed. These include the heat exchanger disclosed in United States patent 4,858,584 of Gordon Bridgeman, issued August 22, 1989. That heat exchanger comprises: a container with a cylindrical outer wall and closed ends; a tube formed into a helical coil located within the outer wall, with ends of the tube extending through the container to the exterior thereof, adjacent opposite ends of the container; inlet and outlet fittings connected to the cylindrical outer wall, to open in opposite tangential directions into the container adjacent opposite ends thereof; and a baffle extending along the container, from end to end of the container and within the coil.

In this heat exchanger, the baffle is an inner tube, concentric with the outer housing, providing an annular chamber around the coil. This confines the flow of heating fluid to the annular chamber around the coil.

In general, size and weight are restrictive factors in the engine compartments of newer vehicles. It therefore becomes important to reduce these physical parameters and to improve the efficiency of the heat transfer in such a unit. The present invention aims at these and other improvements in such a heat exchanger. SUMMARY

According to one aspect of the present invention, there is provided a fuel pre-heater of the type described in the foregoing characterized in that: the baffle is of substantially S-shaped cross-section across the container.

In preferred embodiments, the spacing between the coil, the baffle and the outer wall is kept to a minimum. Fuel is passed through the coil in counter flow to hot engine coolant passing through the container between the baffle and the outer wall.

A fuel heat exchanger so constructed has a number of significant characteristics. The tangential inlet and outlet for heating medium and the helical fuel tube coil cause the heating medium to flow helically through the annular chamber to provide the maximum length of heat transfer path. This provides the highest possible log mean temperature difference.

The most important factor in heat transfer is the heat transfer surface area and the second most important factor is the method of using that area.

Heat transfer is inhibited when laminar flow exists at the heat transfer surface, as one of the most important factors influencing the amount of heat that can be transmitted through any wall is the film resistance of the fluid at the wall. Film resistance is a function of film thickness, and film thickness is an inverse function of flow rate.

SUBSTITUTE SHEET (RULE 26)

ISA/EP Consequently, the higher the flow rate, the thinner the film and the lower the film resistance.

The S- shaped baffle is close to the surface of the internal coil at two points, along the longitudinal edges of the baffle. This may be about one half the coil to internal tube spacing in the unit of U.S. patent 4,858,584. As a result, the flow rate should in theory double, thereby increasing the Reynolds number and producing more turbulent flow, which in turn reduces the film coefficient. Additional turbulence and hence film reduction will be caused by turbulence created by the non-uniformity of the baffle itself.

In actual practice, the new configuration has been found to heat fuel to an outlet temperature of 186°F (86°C), as compared to the heater of the earlier patent discharging fuel at 1 70°F (77 °C).

Based on a through-put rate of one imperial gallon (4.5 litres) per hour, the total heat transferred with the new configuration is approximately 666 Btu (7 x 10⁵ joules) per hour as compared to approximately 588 Btu (6.2 x 10⁵ joules) per hour with the internal tube.

This is an increase of 78 Btu (8.23 x 10⁴ joules) per hour, or 1 3 per cent.

In view of this, a diesel engine may be fitted with a smaller unit to accomplish the desired diesel fuel temperature increase. The smaller units are more easily fitted to all engines. There are cost savings for the manufacturer as less steel is required to produce similar results.

Another characteristic of preferred embodiments of the present invention is an electric heater element extending into the container, within the coil, from one end of the container.

The electric heater may be used before start-up, especially in cold weather. According to another aspect of the present invention, a fuel pre-heater comprising a container with a cylindrical outer wall and closed ends and a fuel tube formed into a helical coil located between the outer wall, with the tube having inlet and outlet ends extending through the container to the exterior thereof, adjacent opposite ends of the container is characterized by: temperature sensor means for sensing the temperature of fuel in the fuel tube at the outlet end of the tube; valve means for controlling coolant flow through the coolant inlet and outlet fittings; ^«and valve operating means responsive to temperatures sensed by the temperature sensor means for operating the valve means.

The sensor will detect a fuel outlet temperature that is sufficient that further pre-heating is not required. The valve will then shut off the coolant flow until the outlet temperature drops below that desired. BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, which illustrate an exemplary embodiment of the present invention:

Figure 1 is an isometric view of a fuel heat exchanger according to the present invention;

Figure 2 is a side elevation with the outer wall shown in section of the heat exchanger in Figure 1 ;

Figure 3 is a schematic view of the connections of the heat exchanger to an internal combustion engine;

Figure 4 is an isometric view of the baffle; and

Figure 5 is a cross-section along line 5-5 of Figure 2.

SUBSTITUTE SHEET (RULE 26)

ISA/EP DETAILED DESCRIPTION

Referring to the accompanying drawings, and particularly to Figures 1 and 2, there is illustrated a heat exchanger 10 that is housed within a container 12 defined by a cylindrical outer wall 14 and two circular end walls 16 and 18. The end wall 16 has a clean-out and bleed opening closed by a plug 20. Two mounting brackets 22 of L-shape are mounted on the respective ends of the heat exchanger. The cylindrical outer wall 14 of the container 12 is fitted with tangential inlet and outlet nipples 24 and 26 respectively. The inlet nipple 24 is located adjacent the end 18, while the outlet nipple 26 is located adjacent the end 16. The two nipples project in opposite tangential directions from the container.

A fuel inlet tube 28 projects through the end 16 of the container 12, adjacent the periphery of the wall, while a fuel outlet 30 projects through the end 18, also adjacent the periphery of that wall. The inlet and outlet 28 and 30 are the opposite ends of a fuel tube 32 that is formed into a coil 34 inside the container 12. The coil 34 surrounds an inner baffle 36 that extends between the ends 16 and 18 of the container 12. The baffle has an S-shaped cross-section as seen in Figures 4 and 5. The longitudinal edges 38 and 40 of the S-shaped baffle are directed away from the inlet and outlet 28 and 30.

In use, fuel is supplied to the fuel inlet 28 to flow internally through the helical coil 34 to the fuel outlet 30. A heating medium such as engine coolant, is supplied to the container through the tangential inlet 24. The flow is caused by the helical coil 34 to flow in a swirling path, following the coil to the outlet 26 at the opposite end of the heat exchanger. The close spacing between the baffle and the coil ensures that this flow travels at high velocity in the vicinity of the coil The changing flow cross-section

SUBSTITUTE SHEET (RULE 26) around the baffle produces turbulence that reduces the film coefficient and increases heat transfer.

As illustrated in Figures 1 and 2, an electric heater 42 extends into the container 12 through the end 1 6 associated with the fuel inlet 28 and the coolant outlet 26. This heater is of a conventional type and is shaped into a U extending along an axial slot 44 in the center of the baffle 36. The heater is mains powered to heat the coolant in the pre-heater before starting the engine.

At the opposite end of the heater is a temperature sensor 46 mounted on the fuel outlet 30 to monitor the temperature of the fuel leaving the pre-heater. Also at this end of the pre-heater is a valve 48 mounted on the coolant inlet 24. This is a shut-off valve operated by an electric valve actuator 50. The actuator is connected to the temperature sensor 46 and to an electrical supply from the vehicle through a connector 52 on the end of the heater.

The temperature sensor 46 monitors the outlet fuel temperature and, when it reaches a sufficient level that further heating is not required, the sensor closes the electric circuit to the actuator 50, causing it to shut off the valve 48 and the coolant supply to the pre-heater. If the fuel temperature drops sufficiently, the sensor will open once again, allowing the valve 46 to re-open and supply hot coolant to the pre-heater.

Figure 3 illustrates the use of the heat exchanger in connection with an internal combustion engine 53. The engine has a coolant pump 54 that pumps the engine coolant from the radiator 56 through a line 58 to the low water jacket 60 of the engine 53. A line 62 allows hot engine coolant to flow from the high water jacket 64 to the top of the radiator 56 when the engine thermostat is in the open position. A hot coolant line 68 leads from

SUBSTITUTE SHEET (RULE 26) the high water jacket 64 of the engine 53 to the heating medium inlet 24 of the heat exchanger 10. A second coolant return line 70 leads from the outlet 26 of the heat exchanger 10 to the suction side of the water pump 54.. A fuel tank 72 is connected to a fuel line 74 leading to the fuel inlet 28 of the heat exchanger 10, while a further fuel line 76 leads the heated fuel from the heat exchanger 10 to a fuel filter 78. From the fuel filter 78 a fuel line 80 leads the heated fuel to a schematically illustrated fuel atomizing device 82 of the engine 53 which, for a diesel engine, is a set of fuel injectors. The heat exchanger 10 may also be installed after the fuel filter 78 and before the atomizing device 82. A return line 84 from the atomizing device to the fuel tank 72 supplies excess warm fuel to the fuel tank to prevent gelling in gold weather.

In the foregoing, a single embodiment of the present invention has been described. It is to be understood, however, that other embodiments are possible within the scope of the invention, and that the invention is to be considered limited solely by the scope of the appended claims.

SUBSTITUTE SHEET (RULE 26)

ISA/EP

Claims

1 . A fuel pre-heater comprising: a container with a cylindrical outer wall and closed ends; a tube formed into a helical coil located within the outer wall, with ends of the tube extending through the container to the exterior thereof, adjacent opposite ends of the container; inlet and outlet fittings connected to the cylindrical outer wall, to open in opposite tangential directions into the container adjacent opposite ends thereof; and a baffle extending along the container, from end to end of the container and within the coil, characterized in that: the baffle is of substantially S-shaped cross-section across the container.

2. A pre-heater according to Claim 1 wherein the coil is located substantially midway between the outer wall and longitudinal side edge of the baffle.

3. A pre-heater according to Claim 1 wherein the ends of the coil project through the ends of the container.

4. A pre-heater according to Claim 1 wherein the coil is wound to intercept fluid flowing tangentially into the inlet fitting and to direct the flow into a helical path leading towards the outlet.

5. A pre-heater according to Claim 1 including an electric heater element extending into the container, within the coil, from one end of the container.

6. A pre-heater according to Claim 5 wherein the heater element extends into the container through an end of the container adjacent an inlet end of the tube.

7. A pre-heater according to Claim 1 wherein the ends of tube are inlet and outlet ends respectively and including temperature sensor means for sensing the temperature of liquid in the tube at the outlet end of the tube, valve means for controlling fluid flow through the inlet and outlet fittings and valve operating means responsive to temperatures sensed by the temperature sensor means for operating the valve means.

8. A pre-heater according to Claim 7 wherein the valve means is a shut-off valve and the valve operating means comprise means for shutting off the valve means in response to the sensing by the temperature sensor means of a temperature greater than a preset temperature.

9. A fuel pre-heater according to any preceeding Claim, characterized by: an electric heater element extending into the container, within the coil, from one end of the container.

10. A pre-heater according to Claim 9 wherein the heater element extends into the container through an end of the container adjacent an inlet end of the tube.

1 1 . A fuel pre-heater according to any preceeding Claim and including: temperature sensor means for sensing the temperature of fuel in the fuel tube at the outlet end of the tube; valve means for controlling coolant flow through the coolant inlet and outlet fittings; and valve operating means responsive to temperatures sensed by the temperature sensor means for operating the valve means.

12. A fuel pre-heater comprising: a container with a cylindrical outer wall and closed ends; a fuel tube formed into a helical coil located between the outer wall, with the tube having inlet and outlet ends extending through the container to the exterior thereof, adjacent opposite ends of the container; temperature sensor means for sensing the temperature of fuel in the fuel tube at the outlet end of the tube; valve means for controlling coolant flow through the coolant inlet and outlet fittings; and valve operating means responsive to temperatures sensed by the temperature sensor means for operating the valve means.

13. A pre-heater according to Claim 1 1 or 12 wherein the valve means is a shut-off valve and the valve operating means comprise means for shutting off the valve means in response to the sensing by the temperature sensor means of a temperature greater than a preset temperature.