Method and system for preheating fuel

A method and system for preheating internal combustion engine fuel to an optimum temperature before introducing the fuel into the carburetion system. It has been found that an engine fuel such as gasoline will have an optimum temperature at the point of carburetion for maximum combustion efficiency. A heat exchanger extracts heat from hot engine coolant to add heat to the fuel. A thermostatic switch and solenoid valve controls coolant flow to maintain the optimum temperature. Thermal insulation is provided around the fuel supply system and the heat exchanger to prevent engine heat from causing the fuel temperature to exceed the optimum temperature.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a gasoline preheater for internal 
combustion engines, and more particularly to a method and system for 
preheating gasoline to an optimum temperature for most efficient 
vaporization and combustion. 
2. Description of the Prior Art 
It has been well known in the prior art to preheat gasoline before 
introduction of the fuel into the carburetor. It is also well known to 
utilize the heat of the engine coolant to perform this function. A typical 
U.S. Pat. which discloses this concept is No. 4,083,340 issued to Furr, et 
al. Furr notes a number of earlier patents which also dealt with this 
problem. Furr teaches the use of a superheater having a chamber through 
which the gasoline passes on its way from the storage tank to the 
carburetor with a copper coil disposed within the chamber through which 
heated coolant from the radiator of the engine is passed. An orifice is 
included in the line carrying the hot liquid coolant which is calibrated 
to provide a desired flow of coolant to heat the fuel to a preselected 
temperature. Although Furr states that the calibrated orifice can be 
changed to select the desired gasoline temperature, he states that the 
superheater increased the gasoline mileage on automobiles tested when the 
temperatures were maintained at any selected temperature from 100.degree. 
to 225.degree. F. but notes that the best results depend on the 
composition of the gasoline being used. He found that about 140.degree. F. 
was optimum in his tests. 
I have investigated the use of preheaters for improving the performance of 
gasoline engines and have found that the temperature of the fuel is quite 
critical with present day gasoline compositions. One problem which 
apparently has not been forseen by Furr or by any of the other prior 
workers in this field is that the ambient air temperature, the load on the 
engine, the location of the fuel pump and fuel lines in relation to the 
exhaust manifold, the amount of cooling air from the engine fan, and 
similar factors often control the minimum temperature of the fuel. For 
example, if the device of Furr were used in a high performance engine 
operating under heavy loads in hot weather and a desired temperature of 
140.degree. F. was required, it is quite possible for the fuel to be at a 
higher temperature from the engine heat as well as the ambient air 
temperature. Therefore, the superheater of Furr would be useless. 
Another problem with the Furr-type device is that the selected fuel 
temperature is not easily controlled. For example, I have found 
experimentally that present day fuel compositions produce optimum fuel 
economy when the fuel in the carburetor float chamber is about 120.degree. 
F. Thus, it is apparent that the gasoline producers vary their volatile 
components from time to time. To change the Furr superheater temperature, 
it would be necessary to disassemble the device and to replace the 
calibrated orifice. The use of the calibrated orifice also assumes that 
the coolant temperature is constant and the flow of that coolant is 
constant, a situation that would seldom, if ever, be realized in a 
practical automobile. 
Thus, there is a need for a gasoline preheater which can accurately control 
the temperature of the fuel as it flows into the carburetor, which is 
easily adjustable to suit the composition of the fuel being used, which 
will not be influenced by engine and ambient heat, and which provides a 
means for accurately maintaining the correct temperature. 
SUMMARY OF THE INVENTION 
The preheater system of my invention includes a heat exchanger having a 
chamber through which the engine coolant is circulated by tapping off from 
the automobile heater supply and return lines. A solenoid valve is 
installed in a feed line to the chamber and is controlled by a sensitive 
precision thermostat having a bulb immersed in the chamber. The coolant 
inlet line into the chamber is in the form of a J-tube such that the 
incoming coolant is directed at the temperature thermostat bulb to cause 
it to quickly sense variations in coolant temperature such as will 
normally occur in an operating engine. The solenoid valve is preferably 
installed in the outlet coolant line from the chamber with the solenoid 
operated from the thermostatic switch. Therefore, the flow of coolant is 
cut off when the desired temperature is reached but is quickly restarted 
when the coolant in the chamber drops below the preselected temperature. A 
helical metal heat exchange tube, preferably copper, is disposed within 
the coolant chamber and connected between the engine fuel pump and the 
carburetor fuel inlet. Therefore, all fuel from the tank flows through the 
helical coil on its way to the carburetor. Sufficient surface area of the 
helical coil is provided to ensure that the fuel flowing through the coil 
is at essentially the same temperature as the coolant in the chamber for 
the maximum fuel flow rate. 
As noted above, a preheat system will not operate properly if the 
temperature in the engine compartment of the automobile is higher than the 
selected fuel temperature since such circumstance can heat the gasoline in 
the fuel pump and the fuel lines to the carburetor, as well as in the 
carburetor float chamber. Advantageously, I insulate all of these 
components, preferably with a foam-type insulation to prevent the heat in 
the engine compartment from affecting the fuel as it flows from the tank 
to the carburetor. 
It is a principal object of my invention to provide a system for preheating 
the fuel to the carburetor of an internal combustion engine to an optimum 
temperature for maximum efficiency of the engine. 
It is another object of my invention to provide a preheat system which is 
easily adjustable to suit the fuel being used by the engine. 
It is yet another object of my invention to provide a fuel preheat system 
having means to prevent excessive heating of the fuel from ambient 
temperature conditions around the engine. 
It is still another object of my invention to provide a fuel preheat system 
for an automobile engine using a reservoir into which hot engine coolant 
is directed having a heat exchange coil immersed therein through which the 
fuel flows from the fuel pump to the carburetor. 
It is a further object of the invention to control the flow of coolant into 
the reservoir by means of a solenoid valve controlled by an adjustable 
thermostat having its temperature sensitive element immersed in the 
coolant in the reservoir. 
It is still a further object of my invention to provide a fuel preheat 
system for gasoline engines which will permit accurate control of the 
temperature of the fuel in the carburetor float chamber at a temperature 
which will produce optimum efficiency of the engine and thereby decrease 
the fuel consumption of the automobile. 
These and other objects and advantages of my invention will become apparent 
from the following detailed description when read in conjunction with the 
drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring first to FIG. 1, the results of a typical experiment using a test 
vehicle in which the temperature of the fuel in the carburetor float 
chamber can be varied over a wide range. The graph plots the fuel 
temperature versus miles per gallon. These results were obtained from 
tests utilizing a 1977 Cadillac coupe de ville having a 425 CID engine. 
Two persons were in the automobile during the test with the air 
conditioning equipment operating. The test runs were made in Florida in 
March, 1982 with an average outside temperature of about 85.degree. F. at 
a speed of 55 mph. A Prince mileage computer was installed on the vehicle 
and was previously calibrated. 
As may be noted from the graph of FIG. 1, a sharp increase in miles per 
gallon was obtained between 115.degree. and 120.degree. F. with the 
optimum mileage of 25 miles to the gallon obtained at approximately 
117.degree. F. The efficiency of the engine decreased rapidly above 
120.degree. F. dropping to about 9 miles per gallon at 140.degree. F. The 
fuel temperature was controlled during the test by means of the fuel 
preheat system of my invention to be described in more detail below. 
Without the system of the invention installed, this vehicle averages a 
fuel consumption of about 17 miles per gallon at 55 miles per hour under 
the conditions of the above described tests. 
As may be understood from the graph of FIG. 1, there exists an optimum fuel 
temperature with respect to fuel economy and that such point falls within 
a narrow range of temperatures. Of particular importance is that excessive 
fuel temperatures result in a decrease of efficiency indicating that a 
practical system must be able to prevent engine heat and ambient air 
temperatures from fortuitously raising the fuel temperature much above the 
optimum value. 
FIG. 2 is a schematic diagram of my fuel preheater system as applied to a 
typical automobile engine. Radiator 20 contains the normal engine coolant 
which is circulated through engine block 24 by water pump 22. As is also 
conventional, the heater 26 for the vehicle utilizes a portion of the 
circulating coolant which enters the heater via line 21 and returns via 
line 23. 
In accordance with my invention, I utilize heat exchanger 10 to provide the 
desired fuel temperature. A coolant inlet line 25 is tapped off of the 
heater line 21 and connects to J-tube 16 in heat exchanger 10. Outlet line 
27 from heat exchanger 10 connects to heater return line 23. A valve 19 is 
controlled by solenoid 18 to open or close line 27. With the engine 
operating and solenoid valve 19 open, heated coolant will flow through 
line 25 and J-tube 16 to fill the body of heat exchanger 10 with coolant 
34. This coolant will circulate then from line 25 through line 27 back to 
the engine system. Although the solenoid valve formed by valve 19 and 
solenoid 18 may be any suitable type, I have found that a 12 volt dc 
manufactured by Airmatic Allied, part no. 20385 is well suited for this 
use. 
Also, installed in heat exchanger 10 is a thermostatic control switch 14 
which is adjustable over a range of temperatures. There are various such 
thermostatic switches available commercially. A Fenwal part no. 17100 has 
been found to give excellent results in this application. Thermostatic 
switch 14 is connected in series with solenoid 18 to the battery supply of 
the vehicle. When thermostatic switch 14 is closed, solenoid valve 19 is 
open to permit coolant flow. When the temperature of the coolant 34 in 
heat exchanger 10 reaches the setting of thermostat 14, the switch opens, 
closing solenoid valve 19. This cuts off the flow of coolant. Assume that 
the temperature of coolant 34 drops below the setting of thermostatic 
switch 14; the switch will then close operating solenoid 18 and opening 
solenoid valve 19, permitting coolant flow to start. It will be noted that 
J-tube 16 is disposed such that the initial flow of coolant from line 25 
will strike the bulb of thermostatic switch 14, ensuring a minimum delay 
or lag in sensing of the temperature. 
Also disposed in heat exchanger 10 is helical coil 12 which is preferably 
formed from copper tubing. Helical coil 12 is connected to the outlet of 
fuel pump 32 by line 13 with the opposite end connected to carburetor 30 
by line 15. As may now be noted, fuel from the fuel tank is pumped by fuel 
pump 32 via line 33 through helical coil 12 to carburetor 30. Heat from 
coolant 34 is transferred through the walls of helical coil 12 to raise 
the temperature of the fuel flowing therethrough. The size and length of 
helical coil 12 is selected for the maximum rate of fuel flow to permit 
sufficient heat transfer to maintain the desired fuel temperature. For 
example, a 5/16" by 10' copper tube has been found to be suitable. An 
optional pilot lamp 29 may be connected across solenoid 18 and installed 
in the dashboard of the vehicle to indicate to the operator that the 
preheater system is operating normally. I have found in tests that it is 
normal for the solenoid to open for short periods of about one second or 
so and to then close. 10 to 30 seconds later the solenoid may again open 
for a short period. Of course, the exact cycle would depend upon the 
driving conditions, speed, initial fuel temperature, load, and the like. 
For a typical installation, I have found that a transit time for fuel 
through helical coil 12 to be about 30 seconds which is sufficient to 
obtain the desired heat transfer. 
To maintain the fuel at a optimum temperature which may be in the 
120.degree. F. region, it is necessary to prevent heat in the engine 
compartment from the exhaust manifold and from the block, as well as from 
the ambient air, from heating the fuel in the supply line 33, the fuel 
pump 32, the lines 33 from the fuel pump to the heat exchanger 10, and 
from the heat exchanger 10 to the carburetor 15 from being heated to a 
higher temperature than the optimum value. In some vehicles, heating of 
the fuel can also take place via the carburetor float chamber. To obviate 
this problem, I provide suitable insulation for these portions of the fuel 
system. I have found that expanded plastic or rubber foam jackets may be 
installed around lines 15 and 13 and, if necessary, line 33 and will 
effectively prevent heat transfer into those lines. The same type of 
material may be formed to cover fuel pump 32 and heat exchanger 10 as 
indicated at 35 by the dashed lines. In addition, where necessary, an 
expanded foam cover may be installed around the carburetor 30. Thus, 
insulation 35 permits the temperature of the fuel into the carburetor to 
be completely controlled by heat exchanger 10 and not to be influenced by 
engine and other heat sources. 
A cross sectional view of a preferred embodiment of heat exchanger 10 is 
shown in FIG. 3. A section of schedule 40 PVC pipe having a three inch 
inside diameter and a length of about six inches may be used for body 40. 
A bottom cap 41 is formed from a schedule 80 PVC three inch pipe cap 
suitably cemented to body 40. Similarly, top cap 42 is formed from a 
schedule 80 PVC three inch pipe cap 42 having a plurality of drilled and 
tapped holes therethrough. Standard compression fittings 37, 38, 39, and 
46 are installed in cap 42. The ends of helical coil 12 may be soldered or 
welded into fittings 38 and 39 which serve to suppot helical coil 12 
within the heat exchanger 10. A short length of tubing 36 soldered into 
fitting 37 provides an outlet for the coolant from the chamber of heat 
exchanger 10 while inlet J-tube 16 may be soldered into fitting 46 as 
shown. Alternatively, fittings 37, 38, 39 and 46 may be drilled so that 
the tubes will pass completely through the fittings and directly to the 
fuel elements and coolant connections. A ferrule and compression nut, such 
as nut 44, is used with each tube to seal each fitting. Thermostatic valve 
14 is installed through cap 42 such that its bulb is adjacent the open end 
of J-tube 16 as previously described. Leads 43 from the switch portion of 
thermostatic switch 14 are shown which will connect to the solenoid valve 
circuit. Thermostatic switch 14 includes an adjustment screw 45 having a 
suitable locknut which permits adjustment of the control temperature over 
a wide range. The coolant flow is into fitting 46 as indicated by arrow A 
and flows out of the heat exchanger 10 via fitting 37 as shown by arrow B. 
Also shown in partial view is fuel inlet line 13 connected to fitting 38 
and outlet fuel line 15 connected to fitting 39. The entire heat exchanger 
10 and lines 13 and 15 are encased in a suitable insulating material 35 
such as expanded foam rubber, plastic or the like as described above. Any 
suitable mounting clamps may be provided for heat exchanger 10 for 
mounting in the vehicle engine compartment. 
As may now be recognized, a novel fuel preheat system for maintaining fuel 
for an internal combustion engine at its optimum temperature for most 
efficient combustion has been disclosed. Means are provided to prevent 
engine and ambient heat from raising the fuel temperature above the 
optimum value and a heat exchanger utilizing the hot engine coolant to 
preheat the fuel to the optimum value. The heat exchanger utilizes a 
thermostatic device to control the coolant flow through the heat 
exchanger. Advantageously, the thermostatic device is adjustable. The 
optimum fuel temperature is a function of the fuel composition which may 
differ seasonally and geographically. Thus, the user may experimentally 
determine the optimum temperature by varying the thermostatic device 
setting and noting the setting that produces minimum fuel consumption. 
The method of my invention may be seen to utilize the steps of determining 
the optimum temperature for the composition of fuel being used with 
respect to combustion efficiency, maintaining the fuel from the supply 
tank and fuel pump to the carburetor at a temperature equal to or less 
than the determined optimum temperature, providing a heat exchanger for 
extracting heat from hot engine coolant for maintaining the fuel to the 
carburetor at essentially the optimum temperature, controlling the flow of 
hot coolant through the heat exchanger, and feeding the preheated fuel to 
the carburetor. 
Although a specific embodiment of my system has been disclosed, it will be 
obvious to those of skill in the art to substitute equivalent elements and 
to make various modifications without departing from the spirit and scope 
of my invention.