Trim system for fuel combustion systems

A method and apparatus for applying exhaust gas analysis to simple combustion control systems wherein the fuel flow and air flow control devices are interconnected with fixed mechanical linkage, or interconnected by a single specific signal, between the fuel flow and air flow control devices. An apparatus and method are disclosed to automatically compensate the air-to-fuel ratio, pre-calibrated on a volume basis, for uncontrolled variations of air or fuel quality such as density, BTU content and the like so that the calibration of the rate of combustion air flow relative to the rate of fuel flow will always be substantially correct even while these flow rates are changing.

BACKGROUND OF THE INVENTION 
1. Field of Invention 
This invention relates to the art of combustion of fuels and specifically 
to methods and apparatuses for optimizing the flow of air and fuel to the 
combustion apparatus to maximize combustion efficiency. 
More specifically, this invention relates to simple combustion control 
systems employing mechanical linkage, or one specific unaltered signal, to 
position the fuel and air control devices to achieve the desired rate of 
energy release and also provide a means of maintaining the desired fuel to 
air ratio at all times despite variations in the qualities of the fuel or 
air. These variations can be caused by changes in density, moisture 
content, BTU value and the like, and by the method of this invention 
effectively overcoming the time lag existing between the formation of the 
fuel and air mixture and the analysis of exhaust gases. 
2. Description of the Related Art 
It is known in the art to adjust the combination of air and fuel being 
supplied to the combustion chamber to maximize the combustion efficiency. 
It is also known in the art to accomplish this through means of a 
mechanical linkage control. It is also known in the art to analyze the 
exhaust gases of the combustion process in order to determine whether or 
not proper combustion is taking place and what adjustments need to be 
made. It is also known in the art to provide a signal from an exhaust gas 
analyzer to drive different control mechanisms, such as valves and 
dampers. 
When fuel is combusted with air, the flow of air and fuel must be 
controlled in a chemically correct relationship to achieve the most 
efficient combustion. A common way of achieving the desired air flow and 
fuel relationship is to interconnect the air flow regulating devices with 
the fuel control devices by means of mechanical linkages or control 
signals in a pre-calibrated manner. The mechanical linkages or control 
signals are pre-calibrated so that, as the rate of combustion is increased 
or decreased in response to the energy release requirements of the end 
user, the air and fuel control devices operate in a manner that provides 
the desired relationship between fuel flow and air flow regardless of the 
rate of combustion or energy release requirement of the combustion 
apparatus. 
One disadvantage of the above-described system is that it is unresponsive 
to day-to-day variations in the atmosphere, fuel, and other factors which 
can affect the combustion equation. For example, variations in fuel 
qualities, and ambient temperatures, and moisture content of the 
combustion air, and the like can alter the chemical correctness of the 
pre-calibrated relationship between air flow and fuel flow. In such cases, 
the combustion process operates less efficiently. 
The above-described changes to the desired chemical relationship between 
air flow and fuel flow are commonly detected by sensors which monitor the 
exhaust gases of the combustion chamber. The sensors can detect the amount 
of residual, unburned oxygen and/or the amounts of carbon monoxide, carbon 
dioxide, or other substances in the products of combustion which exit the 
combustion chamber with the exhaust gases. Such detecting devices have 
been used in connection with various control devices to correct for the 
variations affecting the desired air flow to fuel flow chemistry. Most of 
these systems suffer from a relatively high installed cost and are 
complex. Further, many have inadequate performance and require specialized 
maintenance and the like. 
To avoid the complexity and high installed cost of the prior art devices, 
this invention provides a relatively simple means of compensating for the 
effect of temperature and similar variations on the desired chemically 
correct pre-calibrated relationship between air flow and fuel flow. The 
invention enables the pre-calibrated relationship between fuel flow and 
air flow to be compensated for differences by adding a second moveable 
element to one or more of the prior art flow control devices. 
The prior art flow control devices work on the principle of an established 
known relationship between the position of a moveable element or 
interconnected moveable elements designed to increase or decrease port 
area within the device through which the fluid can pass. By increasing the 
port area within the device, the rate of fluid flow can be increased. This 
relationship is commonly known as the "flow characteristic" of the flow 
control device. 
It is known that the molecular content of the fluid flowing through the 
device increases or decreases with variations in temperature, solution, 
mixture strength, and other variations in the fluid's quality. 
Consequently, when the control device is used in a pre-calibrated manner 
to deliver a desired chemically correct rate of flow, the flow 
characteristic of the flow control device must be altered to compensate 
for the effect of the temperature difference or other variation in fluid 
quality. This invention provides a means for such flow control device to 
also have the capability to compensate for variations in temperature, 
fluid qualities, etc. This invention correctly adjusts the pre-calibration 
between the rate of combustion air flow control device and the rate of 
fuel flow control device to compensate for uncontrolled variations in air 
or fuel quality so that at any and all air and fuel rates of flow the 
pre-calibrated relationship between the air and fuel control devices will 
be substantially correct before, during and after rate of flow changes. 
The method of this invention largely overcomes the detrimental effect of 
the time lag existing between the point of fuel and air mixture formation 
and the exhaust gas analysis relating to that specific mixture This 
invention further provides a fail safe mechanism which permits the 
combustion process to proceed safely without interruption should faults 
occur in the exhaust gas analyzer, controller, or motion generation means 
for positioning the compensating second moveable element. 
SUMMARY OF THE INVENTION 
To avoid the limitations and disadvantages of present devices and methods, 
an object of this invention is to automatically, or manually, during 
on-line operation, compensate the pre-calibration existing between the 
combustion air control means and the fuel control means for variations in 
air and or fuel quality which tend to render the original pre-calibration 
inefficient for combustion purposes. 
A further object of this invention is to achieve this compensating action 
so that before, during and after changes in fuel and air flow rates the 
desired efficient air to fuel ratio will be maintained despite variations 
in air and/or fuel quality. 
A further object of this invention is a fail-safe means such that the 
combustion process can continue at a safe level of excess air without 
interruption should a fault occur in the exhaust gas analyzer, the 
controller responsive to the exhaust gas analyzer or the motion generation 
means for positioning the second moveable element which carries out the 
compensating function. 
A further object of this invention is a significant reduction in installed 
cost due to the simplicity of the invention to facilitate more widespread 
use. 
These and other objects of the invention are provided by the addition of a 
second moveable element to the prior art rate of flow control device for 
either the fuel flow or the combustion air flow. 
This invention comprises one or more rate of fuel flow control means. The 
first of these fuel flow control means is a rate of combustion air flow 
control device comprising a first moveable element whose motion is 
connected by fixed mechanical linkage to the controlling element of the 
rate of fuel flow control means, or connected by a specific unaltered 
signal to the controlling element of the rate of fuel flow control means. 
The combustion air flow control device comprises a port through whose port 
area the combustion air must flow. The first moveable element of the air 
flow control device controls the combustion air flow rate through the port 
by moving among a variety of positions to expose more or less of the 
available port area and establishing a specific relationship between first 
moveable element travel position and resultant fluid volume flow. This 
combustion air flow control device also comprises a second moveable 
element designed to increase or decrease the port area available to the 
action of the first moveable element at all of its possible travel 
positions, thereby altering the specific relationship established between 
the first moveable element travel position and the rate of volume flow 
through the rate of combustion air flow control device and thereby 
providing a means of applying correction to that specific relationship to 
compensate for variations in air or fuel quality. 
This invention further comprises an analyzer to determine the composition 
of the exhaust gases of combustion, and a controller for comparing the 
composition of the exhaust gases to a desired value or set of values, and 
sending out a corrective control signal. In addition, a motion generator 
means responsive to the controller and connected to suitably position the 
second moveable element, means to detect faults in the exhaust gas 
analyzer, the controller, and the motion generator means of positioning 
the second moveable element of the fuel or the air rate of flow control 
device. 
A fail safe spring or counterweight responsive to fault detection devices 
positions the second moveable element of the rate of flow control device 
to a position that provides additional excess air for safe combustion 
during fault conditions The control system requires the second moveable 
element to be comprised in either the fuel flow or the air flow control 
device For fail safe action with the fuel flow device, the action would be 
to reduce the fuel rate of flow relative to air flow. When using the air 
flow device for compensation, the fail safe device would increase the air 
flow. In either case, a safe margin of excess air is established so that 
the combustion process need not be interrupted due to faults in the 
exhaust gas analyzer, controller, or second moveable element actuator. The 
fail safe means comprises a means of decoupling, such as a clutch, or 
freewheeling or overriding of the actuator which positions the second 
moveable element. For example, when using a stepper motor as an actuator, 
it is merely necessary to disconnect electric power to allow the spring or 
counterweight to override the stepper motor and position the second 
moveable element to the desired safety position. 
Either the fuel flow control device or the air flow control flow control 
device must be equipped with a means to precalibrate the relationship 
between its first moveable element travel position and the resulting 
controlled flow. Because the movement of this first moveable element is 
mechanically or otherwise unalterably linked to the flow control actuating 
means of the other component of the fuel and air mixture, this 
precalibration of at least one of the flow control devices sets up an 
initial desired air to fuel ratio which can be compensated for variations 
in fuel or air quality as required.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Before proceeding with the description of the preferred embodiment, 
reference will first be made to FIG. 1 which illustrates a typical prior 
art arrangement commonly used on burners and other combustion apparatus to 
maintain a predetermined air to fuel flow rate ratio. The system of FIG. 1 
is commonly known as a jack shaft system. 
There is shown in FIG. 1 combustion apparatus designed generally as 30. Two 
flow control devices, designated 21, 22, provide for a flow or air and 
fuel to the combustion apparatus 30. Flow control 21 is a damper 
regulating air flow from a fan designated as 20. Flow control device 22 is 
a fuel flow control device having means to regulate the flow of natural 
gas or other fuel to the combustion chamber of apparatus 30. A jack shaft 
10 is mounted on suitable bearings 11 and is adapted to be rotated by 
means of actuator 12. Actuator 12 is connected to jack shaft 10 by means 
of linkage 14. A plurality of linkages 16, 18 interconnect jack shaft 10 
the flow control devices 21, 22. Linkages 16, 18 are made up of levers 13, 
15 fixed to the jack shaft 10 and links 17, 19. The actuator 12 is 
controlled electrically or pneumatically by means of circuit 24 responsive 
to a suitable controlling apparatus for regulating the desired rate of 
energy release generally designated 26. 
It should be appreciated from the study of FIG. 1 that rotation of the 
output shaft 28 of actuator 12 produces rotation of jack shaft 10 with 
associated control of flow devices, 21, 22 through respective linkages 16, 
18. When the combustion apparatus 30 is originally calibrated, a burner 
service technician carefully determines a linkage and fuel calibration 
which, at any load, places the damper 21 in the correct position relative 
to the fuel valve 22 such that the proper air flow-fuel flow ratio for 
that firing rate is attained. 
However, operating conditions change, making it desirable to recalibrate 
the control system of the combustion apparatus 30. For example, changes in 
air temperature and relative humidity will effect the amount of oxygen 
delivered to the burner for a given damper 21 position. The amount of 
oxygen delivered to the burner for any position of the jack shaft can 
change as much as 19% or more in practice due to the factors previously 
mentioned. Similarly, changes in fuel heating value, viscosity, and 
specific gravity will produce changes in the combustion equation, as will 
the point of origin of the fuel being burned. Obviously, the original 
calibration is correct for the conditions existing when the service 
technician calibrated the combustion apparatus, but changing conditions as 
described above require that the original calibration be altered to 
compensate for the effect of these changing conditions A simple, 
inexpensive, yet effective means of providing such compensation will now 
be explained with reference to FIGS. 2-7. 
With reference to FIG. 2, the principle of operation of a prior art V-port 
control valve is schematically represented. Triangle 34, encompassed 
between points 35, 36, 37 represents the available port area. Rectangle 
42, encompassed 38, 39, 40, 41, represents a first moveable element 42 
with a leading edge 70. The leading edge 70 extends between points 38 and 
39 can travel from a closed position to an open position. In FIGS. 2 and 
5, "t" represents the travel of the leading edge 70 of the first moveable 
element 42 travels up to the point where it is coincident with a line 
designated 43. In this closed position, no portion of the available port 
area (i.e. the area of triangle 34) is exposed to allow fluid to pass 
through the flow control device. 
The open position is reached when the leading edge 70 is coincident with 
line 44. At this position, all of the available port area is exposed to 
allow maximum flow rate of fluid through the control device. 
With reference to FIG. 3, there is disclosed a graph depicting a typical 
relationship between the rate of fluid flow and the travel position of the 
first moveable element 42 for this prior art V-port configuration. 
FIG. 4 is a graph depicting various typical relationships between rate of 
fluid flow through the flow control device and the travel position of the 
first moveable element 42 in various configurations of prior art flow 
control devices. 
FIG. 5 schematically shows a means of fluid flow control of the invention. 
With reference to FIG. 5 (and comparing FIG. 5 with FIG. 2) the total 
available port area 34, that area of the triangle encompassed between 
points 35, 36, 37, has been enlarged by the addition of a triangular port 
area 60, encompassed by points 35, 37, and 45. This second triangular port 
area 60 is shown in FIG. 5 with horizontal shading to assist the reader in 
his understanding. 
With continuing reference to FIG. 5 there is provided a second moveable 
element 46, encompassed between points 35, 47, and 48. This second 
moveable element 46 is shown in FIG. 5 with vertical shading to assist the 
reader in his understanding. The second moveable element 46 is pivoted at 
point 35 and is located behind the V-port area opening 34, in relationship 
to the first moveable element 42, which is positioned in front of V-port 
opening 34 in FIG. 5. 
In practice, the relative locations of the first and second moveable 
elements 42, 46 to the port area 34 and to each other can be whatever is 
expedient to the equipment designer, providing that their interaction 
achieves the desired control action of compensation. Pivoted second 
moveable element 46 can be positioned so that its leading edge 62, the 
line between points 35 and 47, can be moved to coincide with line 64 
between end points 35 and 49. This position is called the "normal" port 
area position. The second moveable element 46 can also be positioned so 
that its leading edge 62 is coincident with line 66, between end points 35 
and 50, which is called the "minimum total available port are position." 
The second moveable element 46 can be positioned so that its leading edge 
62 can be coincident with any line that can be drawn between point 35 and 
any point on the segment represented by the arc between points 47 and 50. 
With reference to FIG. 6, there is disclosed a graph depicting the 
relationship between the rate of fluid volume flow and the travel position 
of the first moveable element 42 of FIG. 5 at three typical positions of 
the second moveable element 46. At the normal position, the total port 
area available to the action of the first moveable element 42 is the 
triangular area 34 encompassed by points 35, 36 and 37 of FIG. 5. This is 
the same port area depicted in FIG. 2. Consequently, the rate of fluid 
flow to travel relationship at the normal position of the second moveable 
element 46, as depicted in the graph in FIG. 6, is generally the same as 
shown in the graph in FIG. 3 for the prior art V-port valve. 
By positioning the leading edge 62 of the second moveable element 46 of 
FIG. 5 so that it is coincident with a line between end points 35 and 47, 
the total port area available to the flow control action of the first 
moveable element 42 is increased to provide a larger volume flow at every 
position of the first moveable element 42 throughout its available travel. 
This increased port area compensates for a condition requiring an 
increased volume flow. This newly increased relationship between rate of 
fluid volume and flow and first moveable element travel is depicted on the 
graph shown in FIG. 6 relating to a port area increased by a correction 
factor. 
Similarly, by positioning the leading edge 62 of this second moveable 
element 46 to be coincident with the line between end points 35, 50, the 
total port area available to the flow control action of the first moveable 
element 42 is decreased to provide a lesser volume flow at every position 
of the first moveable element 42 throughout its available travel. This 
lower volume flow compensates for a condition requiring a reduced volume 
flow. Again, this newly decreased relationship between rate of fluid 
volume flow and first moveable element 42 travel is depicted in the graph 
in FIG. 6 relating to a port area decreased by a correction factor. 
In summary, with second moveable element 46 having its leading edge 62 
coincident with a line between end points 35 and 49, a position called the 
normal position, no correction factor is applied to the relationship 
between the rate of volume flow and travel position of the first moveable 
element 42 as depicted in the graph in FIG. 5. As the leading edge 62 of 
the second moveable element 46 is positioned away from the normal 
position, and toward a position coincident with a line between end points 
35 and 47, any desired increasing correction factor can be applied to the 
normal relationship between rate of fluid volume flow and the travel 
position of a first moveable element 42 as depicted in the graph in FIG. 
5. Similarly, as the leading edge 62 of second moveable element 46 is 
positioned away from the normal position, and toward a position coincident 
with the line between end points 35 and 50, any desired decreasing 
correction factor can be applied to the normal relationship between rate 
of fluid volume flow and the travel position of first moveable element 42, 
as depicted in the graph in FIG. 5. 
With reference to FIG. 7, a schematic representation of the invention 
applied to a combustion process is shown. A sensor 25, sends a signal to a 
controller 76, capable of detecting that a correction to the normal 
calibration is required. The sensor 25 can be an analyzer for oxygen, 
carbon dioxide, combustibles, a calorimeter for a heating value, a 
temperature or pressure sensor, or any other device able to measure a 
parameter describing the combustion process. When the controller 76 
receives the signal from the sensor 25, the controller 76 puts out a 
suitable corrective action signal to an actuator 78. The actuator 78 
positions the second moveable element 46, of a flow control device. The 
controller 76 and its actuator 78 are designed so that, should corrective 
action to increase the flow characteristic be required, the leading edge 
62 of the second moveable element 46 will be moved in a direction 
approaching coincidence with the line between end points 35 and 47 until 
the controller 76 senses that sufficient corrective action has been 
applied. Similarly, should decreasing flow corrective action be required, 
the controller 76 and its actuator 78 will move the leading edge 62 of the 
second moveable element 46 in a direction toward a line coincident with a 
line between end points 35 and 50. 
Preferably, this system should be designed to include fault detection 
techniques designed to free the motion of the second moveable element 
actuator 78 in order to permit a spring 80 or other means to position the 
second moveable element 46 to a desired safe position. 
The flow control device of this invention having a first moveable element 
42 and a second moveable element 46 may be applied to either a fuel flow 
control device or a combustion air flow control device or both as desired. 
Although the preferred embodiment is based on the motion of a pivotal 
segment acting as the second moveable element 46, many other 
configurations can be made of a flow control device having a first 
moveable element establishing a relationship between its travel position 
and the rate of fluid volume flow through the control device, and also 
incorporating a second moveable element capable of altering the rate of 
volume flow relationship between the first moveable element and its travel 
position. 
For example, with reference to FIG. 8, the basic port area could be 
rectangular in shape as incorporated by a valve assembly utilizing 
concentric cylinders. In such an embodiment, cylindrical element 88, 
containing one or more rectangular ports rotates about cylindrical element 
86 which contains a similar port or ports such that the effective port 
area is varied. In this same configuration, element 90 could be designated 
as the compensating second moveable element, and element 88 as the first 
moveable element controlling basic rate of flow. Furthermore, element 88 
could be held stationary and element 86 caused to rotate. 
A further embodiment is shown in FIG. 9A-9D, that of a circular motion 
valve 170. The valve 170 comprises an assembly on a common shaft (not 
shown). The assembly comprises four plates 172, 174, 176, 178. One of the 
plates is an inlet plate 172, a second plate is the port area plate 174, a 
third is the holding plate 176, and finally the outlet plate 178. The four 
plates 172, 174, 176, 178 have a suitable fluid sealing means to be 
described below. 
The inlet plate 172 of FIG. 9A comprises a fluid inlet fitting 140, a fluid 
inlet cavity 144, a hole 146 for receiving common assembly shaft, and a 
hole 142 for receiving the second moveable element positioning means. 
The port area plate 174 in FIG. 9B comprises a port area 148 and shaft 
holes 142' and 146'. 
The holding plate 176 in FIG. 9C contains a second moveable element 150. A 
motion generator means 152 can selectively position the second moveable 
element 150. The plate 174 also has holes 142" and 146". 
The outlet plate 178 is shown in FIG. 9D and comprises a fluid outlet 
fitting 156, a fluid outlet cavity 158, and a leading edge 160 of said 
outlet cavity 158. The outlet plate 178 also comprises means to be rotated 
relative to the second moveable holding plate sub-assembly, and thereby 
comprising the first moveable element 172 with leading edge 160. Leading 
edge 160 is effective to expose more or less of port 148 whose effective 
area is compensated by the position of the second moveable element 150. 
With reference to FIG. 10, a still further modification of the invention is 
shown. The basic port area is shown as being rectangular in shape, with 
the leading edge 100 of a second moveable element 102 moving at right 
angles to the movement of a first moveable element 104. 
Applications of the schematic arrangement of FIG. 5 are shown FIGS. 11-15 
and 16-20. In FIG. 11 control valve 110 is shown. The port 112 (FIG. 14) 
is triangular and its available area is limited by the position of the 
first moveable element 42 and the second moveable element 46. The movement 
of the first moveable element 42 is controlled by linkage 116. The 
movement of the second movable element 46 is controlled by linkage 117 
(FIG. 12) or some suitable means of transmission which is typically 
attached to an actuator. The actuator receives signals from the controller 
76. (see FIG. 7) 
With reference to FIGS. 16-20 a valve 120 is disclosed. The port area 122 
(FIG. 16) is triangular in shape. A first moveable element 42 moves along 
an axis of the control valve 120 via linkage 124. A second moveable 
element 46 comprises a triangular shaped plate whose position is adjusted 
by actuator 130. Actuator 130, as shown in FIG. 16, is a stepping motor, 
alternate means may be employed to activate element 46. The fail safe 
spring designated 80 in FIG. 16 and FIG. 12 could be designed for tension 
or compression action as required. 
With reference to FIGS. 21-27, an alternate embodiment of a circular valve 
180 is disclosed. With reference to FIG. 21, a front housing 182 is 
disclosed. The front housing has a handle 186 rotatably attached to a 
shaft 190 which runs through the center of the valve 180. 
With reference to FIG. 22, a back housing 194 is shown. Note that the back 
housing also features a handle 196. 
With reference to FIG. 1-27, and especially FIGS. 23-27, the workings of 
this embodiment of a circular valve is described. With special reference 
to FIG. 23, note that movement of handle 196 causes rotation of eccentric 
200, thereby causing movement of second moveable element 202. Likewise, 
movement of handle 186 causes movement of the first moveable element. 
With reference to FIG. 27, the valve 180 has an inlet 208 and an outlet 
210. The valve is comprises of a front housing 182, a first plate 184, a 
second plate 206, and a back housing 194. The first plate 184 contains the 
first moveable element while the second plate 206 contains the second 
moveable element. As described previously, rotation of handle 186 causes 
movement of the first moveable element while rotation of handle 196 causes 
movement of the second moveable element. 
The invention has been described with reference to the preferred 
embodiment. Obviously, modifications and alternations will occur to others 
upon a reading and understanding of this specification. It is intended to 
include all such modifications and alterations insofar as they come within 
the scope of the appended claims or the equivalence thereof.