Pilot burner apparatus

Pilot burner apparatus is provided which has improved flame stability and other characteristics. The pilot burner is comprised of a hollow body member having a combustible gas inlet nozzle portion at one end connected to a sleeve portion which forms an outlet at the other end. A heat retaining member is disposed within the sleeve portion adjacent the outlet end thereof. Upon short duration combustion disturbances, flame stability is maintained by the burner.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to pilot burner apparatus, and more 
particularly, but not by way of limitation, to pilot burner apparatus of 
the type used to ignite combustible materials emitted from one or more 
other burners in flares, heaters and other similar apparatus. 
2. Description of the Prior Art 
A great variety of pilot burner designs and apparatus have been developed 
and used over the years. Generally, a pilot burner functions to provide a 
continuous pilot flame adjacent one or more main burners for igniting 
combustible materials periodically emitted from the main burners. Examples 
of applications of pilot burners in association with main burners are 
domestic and industrial heaters, boilers, dryers, etc. In addition, a 
variety of emergency and/or waste disposal flare apparatus for burning 
combustible materials are utilized in industry which include pilot 
burners. 
In the above mentioned and other applications for pilot burners, it is 
desirable that the pilot burners have maximum flame stability in a variety 
of environmental conditions, i.e., that the burners be capable of 
maintaining a pilot flame in various forms and quantities of draft, at 
varying inlet combustible gas pressures, when exposed to draft or winds 
from various directions and other similar conditions. In addition, it is 
desirable that a pilot burner have the ability to maintain flame stability 
upon short duration combustion disturbances. The term "combustion 
disturbance" is used herein to mean any of a number of circumstances 
causing flame instability and a possible flame outage such as a 
combustible gas flow interruption, the flame being blown away from the 
pilot by wind, snuffed by wind or a momentary increase in external 
pressure, pulled away from the burner by momentary decreases in external 
pressure, etc. 
By the present invention, pilot burner apparatus is provided having 
improved operational stability and other characteristics including the 
ability to maintain flame stability during and after short-term combustion 
disturbances. 
SUMMARY OF THE INVENTION 
The present invention provides a pilot burner comprised of a hollow body 
member having a combustible gas inlet nozzle portion at one end connected 
to a sleeve portion which forms an outlet at the other end. A heat 
retaining member is disposed within the sleeve portion of the body member 
adjacent the outlet end thereof whereby during the combustion of a 
combustible gas at the burner, the heat retaining member is heated and 
upon short duration combustion disturbances, flame stability is maintained 
by the burner. 
It is, therefore, a general object of the present invention to provide a 
pilot burner apparatus. 
A further object of the present invention is the provision of pilot burner 
apparatus having improved flame stability and other characteristics. 
Another object of the present invention is the provision of pilot burner 
apparatus having the ability to re-ignite combustible gas flowing 
therethrough after short duration combustion disturbances. 
Other and further objects, features and advantages of the present invention 
will be readily apparent to those skilled in the art upon a reading of the 
description of preferred embodiments which follows when taken in 
conjunction with the accompanying drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring now to the drawings, and particularly to FIG. 1, a typical pilot 
burner assembly, generally designated by the numeral 10, and a main burner 
12 are illustrated schematically. The pilot burner assembly 10 is 
positioned with respect to the main burner 12 such that a pilot flame is 
continuously maintained in a position whereby upon the emission of 
combustible materials from the main burner 12, the ignition thereof is 
effected by the pilot burner flame. 
The pilot burner assembly 10 is comprised of a pilot burner of the present 
invention 14 which is positioned adjacent the main burner 12. The pilot 
burner 14 is connected by a conduit 15 to a conventional fuel-air mixer 
apparatus 17. While various fuel-air mixer apparatus have been developed, 
the most commonly used are of the Venturi type which inspirate air into 
the fuel as a result of fuel flow through the mixer. A conduit 19 connects 
the fuel-air mixer 17 to a source of pressurized fuel. When desired, the 
assembly 10 also includes a shut-off valve 21 disposed in the conduit 19 
which is maintained in the open position only so long as a flame exists at 
the pilot burner 14 as determined by a conventional flame sensing device 
23 operably connected to the valve 21. 
In operation of the pilot burner assembly 10, a constant flow of 
pressurized fuel from a source thereof passes through the shut-off valve 
21 and the conduit 19 into and through the fuel-air mixer 17. While 
flowing through the fuel-air mixer 17, air is inspirated into the fuel 
stream and mixed therewith and the resulting fuel-air mixture flows by way 
of the conduit 15 through the pilot burner 14 where it is combusted. As a 
result of the combustion, a pilot flame is produced at the pilot burner 14 
adjacent the main burner 12. 
The flame sensing device 23 maintains the shut-off valve 21 in the open 
position only so long as a pilot flame exists at the burner 14. In the 
event combustion is terminated and the flame is extinguished, the flame 
sensing device 23 shuts off the flow of fuel and air to the pilot burner 
by causing the shut-off valve 21 to close. In addition, the control signal 
from the flame sensing device 23 can be used to actuate a main burner 
combustible material shut-off. As long as the pilot burner assembly 10 
produces a flame at the pilot burner 14, combustible material such as a 
fuel or a combustible waste emitted from the main burner 12 is ignited by 
the pilot flame and combusted. 
The pilot burner 14, flame sensing device 23 and main burner or burners 12 
may be disposed within a heater or other similar structure wherein the 
draft (intake of atmospheric air) is induced naturally or wherein one or 
more blowers are used for inducing the draft (forced draft). In a flare 
application, the pilot burner assembly 10 and one or more main burners 12 
can be disposed within an enclosure such as in a stack or they can be 
disposed in the open, either at ground level or at an elevated level. 
Referring now to FIGS. 2-6, a presently preferred form of the pilot burner 
14 is illustrated. The pilot burner 14 is comprised of a hollow body 
member 16 having a combustible gas inlet nozzle portion 18 at one end 
connected to a sleeve portion 20 which forms an outlet 22 at the other 
end. The combustible gas inlet nozzle portion 18 of the body member 16 can 
take various forms, but in a preferred form the portion 18 includes a 
centrally disposed threaded bore 24 and a hexagonal shaped exterior 
whereby it can be conveniently threaded to a conduit. The nozzle portion 
18 also includes an internal wall 26 which forms a central discharge 
orifice 28 positioned within and concentrically to the sleeve portion 20 
of the body member 16. In the form of the pilot burner illustrated in 
FIGS. 2-6, with respect to the longitudinal axis of the body member 16, 
the wall 26 extends radially inwardly a short distance, then 
longitudinally towards the discharge end 22 of the member 16 a short 
distance and then radially inwardly again whereby a cylindrical nozzle, 
generally designated by the numeral 25, is formed interiorly of the sleeve 
portion 20. The nozzle 25 and the interior of the sleeve portion 20 form 
an annular space 27 therebetween. 
A first plurality of spaced apart discharge apertures 30 are disposed in 
the first radially inwardly extending portion of the nozzle 25. The 
apertures 30 extend from the interior of the nozzle 25 to the annulus 27. 
A second plurality of spaced apart discharge apertures 32 are disposed in 
the longitudinal portion of the wall 26 and extend from the interior 
thereof to the annulus 27. As best shown in FIGS. 3 and 4, the apertures 
30 and 32 are positioned around the interior of the nozzle 25 in spaced 
relationship to each other. In addition, the axes of the apertures 30 and 
32 converge. Finally, a plurality of spaced apart slots 34 are formed in 
the second radially inwardly extending portion of the wall 26. The slots 
34 extend from the centrally disposed discharge orifice 28 radially 
outwardly to the discharge apertures 32. 
The sleeve portion 20 of the body member 16 includes a plurality of spaced 
apart ports 36 positioned around the sleeve portion 20 in a plane 
perpendicular to the longitudinal axis thereof. 
Positioned within the sleeve portion 20 and terminating adjacent the outlet 
22 thereof is a heat retaining member 38. In the form illustrated in FIGS. 
3 and 6, the heat retaining member 38 is a helical coil formed of an 
elongated metallic material, the ends of which are rigidly attached, such 
as by welding, to the sides of the sleeve 20. In this form, the heat 
retaining member 38 is preferably a heat resistant metal alloy capable of 
withstanding prolonged heating such as an alloy of nickel and chromium. 
However, other suitable metals or ceramic materials can also be used. 
Operation of the Pilot Burner 14 
In operation of the pilot burner 14, a fuel-air mixture enters the interior 
of the nozzle portion 18 from a conduit threadedly connected thereto. The 
fuel-air mixture is driven by pressure differential through the discharge 
apertures 30 and 32, the discharge slots 34 and the discharge orifice 28, 
all in the nozzle 25. The portion of the fuel-air mixture flowing through 
the discharge orifice 28 forms a jet which flows longitudinally through 
the sleeve portion 20 and out of the sleeve portion 20 by way of the 
outlet 22 as the fuel-air mixture burns. The fuel-air mixture flowing 
through the discharge apertures 30 and 32 form jets which collide with 
each other and with the interior wall of the sleeve portion 20 within the 
annulus 27 as the fuel-air mixture begins to burn. The collisions bring 
about a reduction in the velocity of the jets and improve the stability of 
the flame produced by the pilot burner 14. The discharge slots 34 act to 
transfer the burning to the main jet produced by the discharge orifice 28. 
Also, portions of the fuel-air mixture adjacent the internal walls of the 
sleeve portion 20 may flow through the ports 36 therein and be combusted 
outside the sleeve portion 20. The ports 36 act to help equalize pressure 
between the interior of the sleeve 20 and the external environmental 
surrounding the sleeve 20. 
As indicated above, the fuel-air mixture flowing through the body member 16 
of the pilot burner 14 is partially combusted within the sleeve portion 20 
and partially combusted outside the sleeve portion 20 whereby an elongated 
flame extends from within the sleeve portion 20 a distance beyond the 
outlet 22 thereof. The combustion that takes place within the sleeve 
portion 20 of the pilot burner 14 continuously heats the member 38 
disposed therein. In the event of short duration combustion disturbances, 
the heat retaining member 38 remains hot and re-ignites or otherwise 
stabilizes the flame produced from the fuel-air mixture. 
Referring now to FIGS. 7-11, an alternate form of the pilot burner of the 
present invention is illustrated and generally designated by the numeral 
40. The structure and operation of the pilot burner 40 is similar to the 
structure and operation of the pilot burner 14 except that the heat 
retaining member of the pilot burner 40 is removable. Also, the pilot 
burner 40 is illustrated with an alternate nozzle discharge orifice and 
aperture arrangement. More specifically, the pilot burner 40 includes a 
hollow body member 42 having a combustible gas inlet nozzle portion 44 at 
one end connected to a sleeve portion 46 which forms an outlet 48 at the 
other end. The nozzle portion 44 of the body member 42 can, and in most 
cases preferably does, include a radially inwardly extending internal wall 
forming an internal nozzle with a central discharge orifice and two sets 
of discharge apertures identical to the nozzle 25 of the pilot burner 14 
described above. However, for purposes of this disclosure, the nozzle 
portion 44 of the pilot burner 40 is illustrated with an optional nozzle 
arrangement which can be utilized in applications where the operating 
environment and/or requirements for the pilot burner are different. 
The nozzle portion 44 of the pilot burner 40 includes a radially inwardly 
extending wall 50 which forms a central discharge orifice 52. A single 
plurality of spaced apart discharge apertures 54 is provided, the 
apertures being spaced around the interior of the wall 50 and extending 
therethrough. 
The sleeve portion 46 of the body member 42 includes a plurality of ports 
56 formed therein, which function in the same manner as the ports 36 
described above, and positioned within the sleeve portion 46 is a 
removable heat retaining member 60. The heat retaining member 60 is 
similar to the heat retaining member 38 described above in connection with 
the pilot burner 14 in that it includes a helical coil 62 formed of heat 
resistant metal such as a metal alloy. However, instead of being directly 
attached to the sleeve portion 46 of the body member 42, the coil 62 is 
attached to three elongated spacing members 64 which are in turn slidably 
disposed within the interior of the sleeve portion 46. Enlarged portions 
are provided on the members 64 to prevent the heat retaining member 60 
from being moved inwardly within the sleeve portion 46 too far and for 
facilitating the removal thereof. 
Referring now to FIGS. 12 and 13, yet another form of the pilot burner of 
the present invention is illustrated and generally designated by the 
numeral 70. The pilot burner 70 is similar in structure and operation to 
the pilot burners 14 and 40 described above. More specifically, the pilot 
burner 70 is comprised of a hollow body member 72 having a combustible gas 
inlet nozzle portion 74 at one end connected to a sleeve portion 76 which 
forms an outlet 78 at the other end. The inlet nozzle portion 74 is 
illustrated in the same arrangement as the pilot burner 40, i.e., it 
includes a radially inwardly extending internal wall 75 which forms a 
central discharge orifice 77 and has discharge apertures 79 formed 
therein. The sleeve portion 76 of the body member 72 includes a heat 
retaining member 82 which is removable disposed within the sleeve portion 
76. However, instead of a helical coil formed of elongated heat resistant 
material, the heat retaining member 82 is of an alternate design which 
includes three elongated longitudinally positioned heat resistant heat 
retaining plates 84 formed of a suitable material. The plates 84 are 
connected together at the inner sides thereof and the outer sides are in 
slidable contact with the interior of the sleeve portion 76 so that the 
member 82 is removable. Each of the plates 84 forming the heat retaining 
member 82 can include a plurality of openings 86 formed therein for 
promoting mixing, etc. 
As will be understood by those skilled in the art, the heat retaining 
member utilized with the pilot burner of the present invention can take 
various forms other than those which are presently preferred and 
specifically disclosed herein. Further, the heat retaining member can be 
formed from a variety of materials with those having the properties of 
long life and high heat retention being preferred. 
The pilot burner of the present invention has improved flame stability 
properties over a variety of conditions including over a broad range of 
fuel gas pressures, under back pressures, over a broad range of draft 
conditions, both natural and forced, and under various air supply and wind 
conditions including those at directions transverse to the axis of the 
pilot burner. For example, while the times vary with a variety of factors, 
under simulated low natural draft conditions (0.08 inches of water column) 
and a fuel pressure of 15 psig, a pilot burner of the present invention 
(as illustrated in FIGS. 2-6) with a heat retaining member 38 formed of a 
heat resistant alloy of nickel and chromium re-ignites the fuel mixture 
after fuel mixture flow interruptions of up to six seconds. Under 
simulated forced draft conditions of 0.2 inches water column positive 
pressure and 15 psig fuel pressure, re-ignition is achieved after a fuel 
mixture flow interruption of four seconds. Under a positive pressure of 
0.7 inches water column, the maximum time the fuel mixture flow can be 
interrupted with re-ignition taking place is two seconds with full heat 
retaining member reheating between interruptions. Under 0.7 inches water 
column positive pressure and only a four second reheat time, the maximum 
pilot burner fuel mixture flow interruption time is one second. 
Thus, the present invention is well adapted to carry out the objects and 
attain the ends and advantages mentioned as well as those inherent 
therein. While presently preferred embodiments of the invention have been 
described herein for purposes of disclosure, numerous changes in the 
construction and arrangement of parts can be made by those skilled in the 
art, which changes are encompassed within the spirit of this invention as 
defined by the appended claims.