Blue Flame Retention Gun Burners And Heat Exchanger Systems

Abstract

Blue flame retention gun burners and heat exchanger process and apparatus for burning liquid hydrocarbon fuel to produce a stable blue flame with low nitric oxide and low particulate (Bachrach) emissions. A major portion of the combustion air is passed in a vigorous jet action directed through a vitiation zone positioned upstream from a fuel injection region leading into a combustion chamber. The vigorous jet action creates a reduced pressure in entering the vitiation zone causing a portion of the gaseous products of combustion from the combustion chamber to be recirculated into this zone in which the combustion air is vitiated and chemically altered before encountering the fuel spray. During recirculation the combustion products therein undergo useful heat exchange so that they are cooled below 800.degree.F. before entering the vitiation zone. A minor portion of the combustion air is utilized to cool the fuel nozzle and then enters the fuel injection region as a plurality of diverging jets aimed toward the combustion chamber. An efficient stable blue flame is produced with relatively low excess oxygen and involving diffuse combustion without allowing localized hot zones which would cause augmented NO formation and without ignition or starting transient instabilities. Many conventional air and oil handling components may be directly utilized in the practice of this invention, such as fuel pumps, blowers, motors, and fuel atomizing nozzles.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a blue-flame retention gun burner and heat exchanger process and apparatus for burning liquid hydrocarbon fuel to produce a stable blue flame with low pollutant emission levels. This invention also enables unusually efficient heat exchange systems to be achieved.

Process and apparatus embodying the present invention provide almost all of the features and advantages of the embodiments of the earlier invention disclosed and claimed in my U.S. Pat. No. 3,545,902, issued Dec. 8, 1970, and entitled "Blue-Flame Gun Burner Process and Apparatus for Liquid Hydrocarbon Fuel", and in addition, process and apparatus embodying the present invention provide numerous other important features and advantages, as will be explained.

SUMMARY OF THE PRIOR ART

Conventional gun-type burners which have been in use prior to said earlier invention and prior to the present invention produce yellow or yellowish-orange flames which are noisy, are characterized by incomplete combustion, and often deposit soot in the flue or chimney or discharge particulate matter into the atmosphere. Also, any cool areas within the firebox tend to quench the yellow flame, stopping further combustion in localized regions and leading to the precipitation of unburned carbon on the cooler areas of the heat exchange surfaces of the firebox. These carbon deposits impede heat transfer and reduce efficiency.

Such yellow flame prior art burners have localized regions of high temperature combustion such that they tend to produce undesirably large amounts of oxides of nitrogen and particulate emissions.

SUMMARY OF FEATURES AND ADVANTAGES OF THE PRESENT INVENTION IN COMMON WITH THE EARLIER INVENTION

Among the advantages of the process and apparatus of the present invention in common with my earlier invention are those resulting from the fact that they enable liquid hydrocarbon fuel, such as fuel oil, to be burned with a quiet, stable blue flame in which substantially complete combustion occurs. The firebox and heat exchange surfaces remain cleaner than with conventional yellow-flame gun burners, improved heat transfer occurs, and reduced maintenance and down time are achieved. The blue flame produced by utilizing this invention to burn fuel oil has characteristics similar to those which are present in conventional gas burners. Accordingly, this invention opens up the possibility of utilizing fuel oil in various installations which have heretofore been limited to gas burners.

The invention provides a compact, inexpensive burner unit adapted to be used in a wide variety of new installations as well as being adapted for use as an improvement replacement unit for existing yellow-flame gun burner installations.

A listing of the features and advantages of the process and apparatus embodying the present invention in common with my earlier invention includes the following:

1. The process and apparatus are versatile for use in many different applications and environments including many of those which have heretofore been limited to gas burners.

2. A clean blue flame is produced, contributing to substantially reduced air pollution.

3. The noise level of the blue flame is lower than that for yellow-flame combustion. Moreover, the burner starts without a loud pressure pulse or bang because there is no substantial pressure build-up during transient starting conditions.

4. The process and apparatus are reliable in operation.

5. The burner unit is easy to service. It is so compact and light weight that it can quickly and conveniently be replaced by another burner unit so that the original can be returned to the maintenance plant, thus providing centralized servicing using interchangeable, compact burner units.

6. The apparatus and systems shown are simple, reliable and low in cost.

7. A multi-fuel burning capability is provided by the process and apparatus. Fuel oil, kerosene or gasoline may be used while providing substantially the same blue flame characteristics, thereby being convenient for mobile home applications, garages, remote locations where fuel availability is limited, etc.

8. The present invention enables fuel oil and other liquid hydrocarbon fuels to be utilized as efficiently and economically as the earlier invention.

DISTINCTIONS, FEATURES AND ADVANTAGES OF THE PRESENT INVENTION RELATIVE TO THE EARLIER INVENTION AND OTHER PRIOR ART

In accordance with the present invention, the following distinctions, features and advantages are among those which are provided relative to the earlier invention and other prior art:

1. The cooled recirculated gaseous products of combustion are thoroughly intermixed with a major portion of the combustion air in a zone for vitiation and chemical alteration of the air located upstream from the fuel spray means, so that most of the combustion air is vitiated and intermixed with chemically altering constituents before it arrives in the vicinity of the fuel spray.

2. This zone for vitiation and chemical alteration of the major portion of the combustion air has a substantially annular configuration surrounding an axial cylindrical flow path through which a minor proportion of the combustion air is passed to cool the fuel spray means.

3. The fuel is injected into a downstream fuel injection region located downstream from said annular zone for vitiation and chemical alternation of the combustion air.

4. Only a minor proportion of the combustion air is non-vitiated and not chemically altered and it is segregated and carefully controlled by passage along a central air flow path so as to be introduced near the beginning of the fuel spray pattern. Thus, this non-vitiated and unaltered air cools the fuel spray means, and it is injected into the vitiated and chemically altered air in a manner to assist in retention of the blue flame near the entrance to combustion chamber. It also aids in establishing ignition quickly and reliably when the electrodes are energized.

5. All of the combustion air and fuel can be passed through the downstream fuel injection region. There is no need for introduction of additional air to provide complete combustion. By virtue of the fact that all of the combustion air and fuel can be passed through this region, a wide adjustment range, or tolerance, is achieved so that the blue-flame combustion continues to occur even though the burner firing rate is adjusted over a wide range. Moreover, all the oxidant is efficiently utilized for combustion and for momentum interchange with recirculated products of combustion. Thus, there is no need for any substantial amounts of excess air to assure that complete combustion occurs.

6. By virtue of the vitiation and chemical alteration of the combustion air, the blue-flame combustion is achieved at a relatively low flame temperature. As a result of this controlled flame temperature and the small amount of excess air achieved, the oxides of nitrogen (NO.sub.x) and particulate pollution emission levels are very low, as compared with a conventional yellow-flame gun burner, as shown by the graphs discussed hereinafter.

7. By virtue of the fact that all of the combustion air and fuel can be passed through the downstream fuel injection region, the components in the barrel of a burner embodying this invention can be made readily removable.

8. Impingement of the fuel spray upon the cylindrical member defining the downstream fuel injection region is avoided. Even though the spray pattern has a relatively wide conical angle, for example 60.degree., it does not impinge directly upon this member and thus avoids the problems which are otherwise encountered when unburned fuel collects upon cold wall surfaces during the start-up and warm-up phases of burner operation.

9. The downstream fuel injection region can open directly into the combustion chamber without passing through a subsequent confining shell member. This free flow directly into the combustion chamber reduces the back pressure occurring at the mouth of the fuel injection region and hence minimizes any tendency for flash back of flame into this region.

10. The burner can be adjusted conveniently while it is in operation so that the operator can directly observe the results of the adjustments as they are being made, thus leading to quick, convenient and proper (not hit or miss) adjustment in actual installed usage. The burner firing rate can be accurately matched to the requirements of the associated heat exchanger.

11. The burner of the present invention can utilize conventional air and oil handling accessory components which are readily available, such as fuel pumps, electric motors, blower wheels, and fuel oil atomizing nozzles.

12. The air metering function is provided downstream from the blower. The blower intake can remain unimpeded, i.e. unthrottled, at all times. This arrangement means that the full blower output pressure is available at all times. This full blower pressure is applied directly to adjustable air-metering orifices thus generating vigorous jets of air issuing from the orifices and directed into the air vitiation and chemical alteration zone. These multiple vigorous jets create a region of reduced pressure at the breech of this zone. Thus, there is achieved a vigorous recirculation of gaseous products of combustion through a low pressure drop path leading into this zone. As a consequence, the burner is stable in operation in spite of changes in the flue pressure, for example, as can occur when a strong puffy wind is blowing over or across the discharge end of the chimney or flue pipe.

The various other aspects, objects and advantages of the present invention will, in part, be pointed out and will, in part, become apparent from the following description when considered in conjunction with the accompanying drawings, in which:

FIG. 1 is a side elevational sectional view of a presently preferred embodiment of the present invention for burning liquid hydrocarbon fuel. FIG. 1 shows a blue-flame retention gun burner and an associated heat exchanger system embodying and for practising the process of the present invention;

FIG. 2 is a cross-sectional view of the burner taken along the line 2--2 of FIG. 1 looking toward the right;

FIG. 3 is a top plan sectional view taken along the line 3--3 in FIG. 1;

FIG. 4 is an enlargement of portions of FIG. 1 for purposes of more fully illustrating and explaining the process and apparatus embodying the present invention;

FIG. 5 is a cross-sectional view of the burner taken along the line 5--5 in FIG. 1 looking toward the left;

FIG. 6 is a perspective view of a fixed member of an adjustable air-metering baffle arrangement;

FIG. 7 is an exploded perspective view of an adjustable (rotatable) air-metering baffle member and fuel nozzle support and air flow tube, together with the electrode support having an arm which serves for adjusting the rotatable metering member;

FIG. 8 is a side elevational sectional view of a modified liquid hydrocarbon fuel burner having similarities to that shown in FIG. 1 and associated with a heat exchanger and fluid heater system as shown in FIG. 1;

FIG. 9 is an enlarged cross sectional view taken along the line 9--9 in FIG. 8;

FIG. 10 is an exploded perspective view of a protion of the burner of FIG. 8, showing axially an adjustable air-metering assembly and the fuel nozzle support and air 1 tube, together with the electrode assembly;

FIG. 11 is a side elevational sectional view of a burner embodying the invention associated with a different heat exchanger and fluid heater system from that shown in FIG. 1 or 8;

FIG. 12 is an exploded perspective view of parts of the heat exchanger system seen in FIG. 11;

FIG. 13 is a side elevational sectional view of a burner embodying the invention associated with a different heat exchanger and fluid heater system from that shown in FIG. 1, 8 or 11; and

FIGS. 14 and 15 are copies of graphs which show the results of evaluation tests comparing an oil burner embodying the present invention with a conventional yellow flame gun burner of the prior art to show the reduced pollution and increased possible efficiency provided by the combustion of liquid hydrocarbon fuel using a burner embodying the present invention.

As shown in FIG. 1, a blue-flame retention gun burner and heat exchanger system embodying the present invention include a burner, generally indicated at 10, having an overall gun shape with the gun barrel aimed into a heat exchanger 12 associated with a conventional residential or industrial water heater 14. The water heater 14 may serve to provide hot water or it may serve as a boiler to provide steam. This invention may be employed to advantage regardless of whether hot water or steam is being produced or whether the heater 14 is a hot air furnace, and it is to be understood that the term "fluid heater" is intended to include heaters for heating any one or more of the fluids water, steam and air, or other heat exchange fluids.

The burner 10 includes a housing assembly 16 which is removably attached as by bolts to a mounting flange 18 on an adapter section 20 extending out from the water heater. In effect, the adapter section 20 defines the barrel of the gun-shaped burner. This adapter section 20 with a mounting flange 18 can be secured into the conventional circular opening 22 in the fluid heater 14 into which was previously inserted the muzzle of a conventional yellow-flame gun burner. Thus, the burner of the present invention enables convenient conversion to be made in such a water heater from sooty yellow-flame combustion to blue-flame combustion. The burner housing assembly 16 can be quickly and conveniently detached from the mounting 18, so that the working parts of the burner can be serviced or replaced.

The housing assembly 16 includes a lower housing section 24 on one side of which is mounted an electric motor 26 (FIG. 2) with a blower wheel 28 attached to the motor shaft 30 and being located within the lower housing section 24. On the other side of the lower housing section 24 from the motor is mounted a fuel delivery unit 32, including a fuel pump which is driven by the motor shaft 30.

It is an advantage of the present invention that a conventional motor 26, conventional blower wheel 28, and conventional fuel delivery unit 32 can be employed, if desired. This delivery unit supplies liquid hydrocarbon fuel, for example such as No. 2 fuel oil or kerosene, or gasoline, to the burner 1, the liquid fuel being supplied through a fuel line 34 (FIG. 2). The fuel may be pumped or gravity fed through the line 34 to the delivery unit 32.

A fuel feed control screw 36 can be adjusted by a screw driver to control the fuel delivery pressure and hence flow rate through a flexible metal line 38, such as a soft copper tube, into a rigid pipe 40 (FIG. 2) extending transversely across the burner housing. Near the center of the transverse pipe 40 is a Tee connection 42 to an axial fuel line 44 (FIG. 1) which extends forward to fuel spray means 46, shown as a conventional high pressure spray nozzle producing a suitable conical fuel spray pattern, for example having an included angle of 60.degree., as shown. The fuel delivery unit 32 delivers fuel under high pressure, for example in the range from 80 pounds per square inch (p.s.i.) to 300 p.s.i., and the finely atomized spray 48 is produce solely by the pressurized fuel issuing through the nozzle 46.

For conveniently removing the fuel spray nozzle and ignition electrode assembly, as will be explained in detail further below, the transverse fuel pipe 40 removably seats in notches 49 (FIG. 1) in the upper edges of the upper section of the housing assembly 16, and a detachable coupling 39 (FIG. 3) may be included between the lines 38 and 40.

The housing assembly 16 includes an upper housing section 50 which is detachably secured to the lower housing section 24 by means of a skirt which overlaps the upper edge of the lower housing section, as shown. An ignition tranaformer 52 is mounted upon a lid 54 which is hinged at 56 to the upper housing section. For securing the burner to the mounting 18, there is a similar mounting flange 58 on the projecting front portion of the upper housing section 50.

As can be seen in FIG. 2, the upper housing section 50 has a generally rectangular cross section and forms a conduit for pressurized air generated by the blower wheel 28. Air is admitted to the interior of the centrifugal blower wheel 28 through unobstructed (unthrottled) air intake means 60 in the side of the lower housing 24 near the fuel delivery unit 32. The blower wheel is partially encompassed by a generally spiral-shaped scroll 62 located within the lower housing and arranged to discharge the pressurized air through the blower outlet 64 into the upper housing 50.

By virtue of the fact that the blower inlet ports are unthrottled, the full output pressure from the blower 28 is available at all times during normal operation in a plenum chamber 66 defined by the upper housing. There may be a gasket not shown, at the joint between the lid 54 and the upper housing 50 and also a gasket, not shown, at the joint between the lower and upper housing sections 24 and 50. These gaskets prevent loss of air pressure from the plenum chamber 66.

In order to meter the feeding of combustion air from the plenum chamber 66, there is a fixed baffle 68 (FIG. 1; please see also FIG. 7) having a generally cup-shape and nesting within the outer end of the tubular adapter section 20 near the mounting flange 18. In the end wall 70 of this fixed metering baffle 68 there are a plurality of orifices 72 arranged in an arc concentric about a larger central opening 74. An arcuate clearance slot 76 also extends part way about the central opening. The cylindrical side wall 78 of the fixed baffle 68 has a diameter to fit snuggly within the tube section 20. A flange 80 on this metering baffle is sized to match with the mounting flange 18, as seen in FIG. 1. In the preferred embodiment, as shown, this fixed baffle member is stamped from sheet metal with the respective openings 72, 74 and 76 being punched out during the stamping operation. As can be seen from FIG. 1, the interior, i.e. upstream side, of the baffle 68 communicates with and forms an extension of the plenum chamber 66 such that pressurized air fills the interior of the baffle 68.

Associated with this fixed baffle 68 is an adjustable (rotatable) baffle member 82 which is securely mounted upon a support tube 84 (see also FIG. 7) to project radially therefrom near the mid-point of the support tube 84. There are a plurality of orifices 86 in the adjustable baffle which are spaced to align with the companion orifices 72 in the fixed baffle member. The support tube 84 extends forward through the central opening 74 (see also FIG. 4) in the fixed baffle such that the support tube is concentric about the axis of the tubular adapter section 20.

As shown in FIG. 4, at the forward end of the support tube 84, there is secured an inwardly extending ring 88 with a sleeve 90 fastened to the ring such that the sleeve 90 is concentric within the support tube 84. This sleeve 90 is sized to fit snuggly about the fuel nozzle (but loose enough to permit the nozzle to slide within the sleeve) and thus serves to support the nozzle 46 and its fuel line 44 concentrically with respect to, i.e. axially within, the main mounting tube 20.

In order to press the rotatable baffle 82 firmly against the end wall 70 of the fixed baffle and to hold the support tube 84 in place, there is a compression spring 92 which is positioned about the rear portion of the nozzle fuel line 44. The back end of this spring seats against a spring retention boss 94 (see also FIG. 3) mounted upon the nozzle fuel line 44 near the Tee connection 42. Because the transverse pipe 40 is seated down in the notches 49, the Tee connection, the nozzle fuel line 44, and retention boss 94 are held in place and cannot be moved in an axial direction with respect to the fixed baffle. The front end of the spring 92 presses forward against a seat 95 (FIG. 4) on an electrode support member 96 (FIG. 7) which has a socket 97 (FIG. 4) embracing the back end of the support tube 84. The electrode support 96 is keyed at 93 to the tube 84 for reasons as will be explained later. This electrode mounting member 96 is preferably formed as a die cast metal unit, for example, of aluminum. This member 96 serves to apply the forward acting spring force to the support tube 84 and hence presses the rotatable baffle 82 forward against the fixed baffle 68. A hole 98 (FIGS. 4 and 7) in the electrode support member receives the nozzle fuel line 44 in a sliding fit and serves to hold this line concentric within the support tube 84.

From the foregoing description, it will be appreciated that the fuel nozzle 46 is supported by the sleeve 90 in the front end of the support tube 84, and the nozzle fuel line 44 is supported by the cross pipe 40 seating in the notches 49. Moreover, the movable baffle 82 is spring-biased against the fixed baffle 68. Thus, this advantageous arrangement avoids any requirement for precise fitting or positioning of the nozzle 46, nozzle fuel line 44, support tube 84, movable baffle 82, and electrode support member 96. For example, if either the support tube or nozzle fuel line happen to be slightly too long or too short relative to each other, or relative to the distance between the notches 49 and the end wall 70 of the fixed baffle, such tolerance variations are accommodated by the spring 92 and by the nozzle sliding slightly forward or backward within its support sleeve 90 and by the nozzle fuel line 44 sliding within the hole 98. Consequently, none of these dimensions is critical and mass production techniques can be used to fabricate these various components.

Moreover, any relative changes in dimensions due to differential thermal expansions of the various components are readily accommodated by these structural arrangements, as described above.

In operation, as shown in FIG. 4, the pressurized air in the plenum chamber 66 is divided into two portions, a minor portion 99 of this air flows into the support tube 84 through a plurality of small apertures 100 located behind the baffle member 82. A major proportion at 101 of the pressurized air flows forward through the metering orifices 72 and thus forms a plurality of concentrically spaced vigorous air jets 102 which are directed forward into an annular air vitiation and chemical alteration zone 104 that encircles the support tube 84 in front of the baffle 68. The minor portion 99 of this combustion air flow is preferably less than approximately 15 percent of the major portion 101 of the total combustion air flow. Preferably, the two air flows 99 and 101 comprise the total combustion air being supplied to the combustion chamber 106 associated with the heat exchanger 12 (FIG. 1).

In order to adjust the major air flow 101 through the metering orifices while the burner is in operation, there is an arm 108 which extends rearwardly from the electrode support member 96. Adjusting means in the form of a knurled headed machine screw 110 (FIGS. 2, 3, and 7) is screwed through a threaded opening in the wall of the upper housing 50. The end of this adjusting screw 110 bears against one side of the arm 108. A lock nut 112 holds the adjusted position. A plunger 114 extends through an opening in the opposite wall of the upper housing 50 and bears against the opposite side of the arm 108. This plunger 114 has an enlargement 115 (FIG. 7) on its inner end, and a compression spring 116 encircling the shank of this plunger presses against the enlargement 115, so as to urge the plunger 114 against the arm 108. By turning the screw 110, the electrode support 96 is turned, and because it is keyed to the support tube 84, the tube 84 is rotated together with the adjustable baffle. Thus, the position of the orifices 86 (FIG. 7) relative to the fixed orifices 72 is conveniently adjusted to increase or decrease the amount of combustion air flowing through the air metering assembly 68, 82 into the annular air vitiation zone 104. The resulting air jets 102 are vigorous because the full output pressure of the blower is applied to the plenum chamber 66 to drive the air through the orifices in the metering baffle assembly.

By virtue of the fact that the full output pressure of the blower is available in the plenum chamber 66 for producing the jets 102, any fluctuation in pressure in the combustion chamber 106 has an insignificant effect on these jets. Accordingly, sudden downdrafts in the chimney or flue on windy days causing fluctuations in the pressure in the combustion chamber 106 do not adversely affect the burner operation.

A pair of ignition electrode rods 118 extend through ceramic insulating sleeves 120 which are clamped in mounting notches 122 of the support member 96 by a clamp bar 124 secured by a screw 126. The rear ends of these electrode rods 118 are bent up to form resilient contacts 128 which are engaged by the respective high voltage terminals 130 (FIG. 1) of transformer 52, when the lid 54 is closed. The resilience of the contacts 128 and their sliding engagement with the high voltage terminals 130 permits the support member 96 to be rotatably adjusted in position without breaking contact with these terminals 130.

The electrode rods 118 extend forward through a pair of orifices 86 (FIG. 7) in the rotatable baffle 82 and through the arcuate slot 76 in the fixed baffle member 68. The arcuate slot 76 provides clearance so that the support member 96 can be rotatably adjusted to adjust the amount of combustion air flowing through the orifices 72. In this illustrative embodyment five of the orifices 72 are arranged for adjustable damper action by the orifices 86.

Three of the orifices 86, including two through which the electrode rods 118 extend, are aligned with the arcuate slot 76, and the combustion air through these three orifices is not adjustable so that they always provide three vigorous air jets 102. Accordingly, this arrangement provides air metering from full blower capacity down to approximately three-eighths of blower capacity. The fuel feed rate is matched to the amount of combustion air by adjusting the fuel pressure adjustment screw 36 and/or by removing the nozzle 46 and replacing with a nozzle having a different size of nozzle tip orifice.

At their front ends the electrode rods 118 are bent toward each other and radially inwardly to form converging electrode tips 132, as seen most clearly in FIGS. 3 and 7, and the ignition spark forms between these electrode tips. In FIG. 4 the electrodes 118 are omitted in order to illustrate the operation more clearly. The location of the ignition spark is shown by the plus sign within a small circle.

As shown in FIG. 4, a minor proportion 99 of the pressurized air in the plenum volume 66 flows into the nozzle support tube 84. This atmospheric (non-vitiated) air 99 flows forward in the space surrounding the fuel line 44 within the tube 84, thus serving to cool the fuel line 44 and also to cool the nozzle. This cooling air 99 enters the space around the nozzle support sleeve 90 and issues through a plurality of small holes 133 drilled in the nose ring 88. This nose ring 88 is preferably sloped backwardly in the direction radially out from the tip of the nozzle so that the air jets 135 of non-vitiated air preferably diverge in a downstream direction. These jets 135 of non-vitiated air aid in establishing ignition and also aid is providing retention of a stable blue flame in the combustion chamber 106 beyond the mouth 136 of the fuel injection region 105. It is possible to have the small holes 133 aimed directly downstream so that the air jets 135 travel parallel to each other downstream, but the resulting blue flame tends to be more localized along the axis of the cylindrical combustion chamber 106. By diverging the jets 135 as shown in FIG. 4 a more diffuse and uniform blue flame is obtained which more nearly fills the chamber 106, providing better heat transfer action and more stable combustion over a larger range of firing rates.

Within the adapter tube 20 is located a concentric sleeve 134 of metal which encircles the front portion of the tube 84 to define the annular air vitiation zone 104 and also to define a portion of a recirculation path, as will be explained further below. This fluid mixing sleeve 134 extends downstream beyond the fuel nozzle 46 to define a downstream fuel injection region 105 into which the fuel spray pattern 48 is projected. Preferably the sleeve 134 has a relatively large diameter and a relatively short over-all length such that its length to diameter ratio is no more than 2 to 1. Also, preferably the fuel injection region 105 has a relatively large diameter relative to its length L such that the fuel spray pattern 48 misses the lip 136 at the mouth of the sleeve 134. The length L of the fuel injection region 105 is measured in an axial direction from the end of the fuel nozzle 46 to the lip 136. In this illustration embodiment the diameter of the fuel injection region 105 is greater than the length L.

Attached to the sleeve 134 at its mouth 136 is a radial flange or disc 138 of metal whose front surface facing the combustion chamber 106 is covered by a refractory insulation layer 137. This insulation layer 137 is in the form of a flat ring retained in place by a metal shoulder ring 141 secured to the flange 138 around the mouth 136. This disc 138 serves as a deflecting baffle for causing the combustion products to recirculate over heat exchanger surfaces of the fluid heater 14 from which insulation has been removed, as will be explained. The disc 138 and sleeve 134 serve to define a low pressure drop recirculation path 139 and 140 for gaseous combustion products which are recirculated back into the annular air vitiation zone 104. These recirculating combustion products are indicated by the successive arrows 142-1, 142-2 and 142-3.

It is noted that the recirculation path 139 and 140 includes an annular portion 139 extending radially inwardly between the disc baffle 138 and the exposed metal wall 144 of the water jack 146 of the fluid heater. Then there is the cylindrical portion 140 of the recirculation path which resides between the sleve 136 and the tube 20 which fits snuggly into the burner port 148 of the fluid heater 14.

As shown in FIG. 1, there is insulation 150 of low density refractory lining the water-backed heat exchanger 12 surrounding the combustion chamber 106. The back of the combustion chamber 106 is covered by a removable back panel 152 which has an insulation coating. This removable back panel 152 is spaced away from the main water jacket of the heater 14 to define a back passage 154 for the hot combustion gases to flow up and into a plurality of "fire" tube heat exchanger elements 156 extending forward through the top of the water jacket 146 of the heater 14. The combustion gases are collected in a flue box 158 and pass up through a flue duct 160 which may be connected into a chimney or may lead directly out of doors without using a chimney.

The back panel 152, fire tube elements 156, flue box 152 and flue duct 160 can be conventional elements as used with conventional yellow flame gun burners today.

When incorporating the present invention in an existing fluid heater 14, the insulation 150 is scraped away and removed from the heater wall 144 and near by surfaces 151 of the combustion chamber 106 in the vicinity of the recirculation path 139 and 140 before the sleeve 134 and deflector disc 138 are installed. The fluid mixing sleeve 134, baffle disc 138, and facing insulation 137, together with the spacer fins 162 can conveniently be supplied in kit form for field installation in existing fluid heaters 14. When incorporating the present invention in a new fluid heater 14, the insulation 150 is omitted from those surfaces of the heater as shown in FIGS. 1 and 4.

The way in which the baffle disc 138 and sleeve 134 are installed is to remove the back panel 152, and then the sleeve 134 is inserted into the burner port 148 by reaching inward through the now opened back of the combustion chamber. There are a plurality of thin L-shaped spacer fins 162 which are secured to the water jacket wall 144. Three or four of these spacer fins 162 are usually sufficient to make a reliable installation. The baffle disc 138 is secured to these spacer fins 162 by sheet metal screws or pop rivets or the like, and then the insulation facing ring 137 is fitted into place around the shoulder ring 141. After this installation has been made, the back panel 152 is reattached. There is a small clearance between the portions of the spacer fins 162 within the burner port 148 and this port itself such that the forward end of the adapter tube 20 can be slid and attached into the burner port 148 without interference from the previously installed spacer fins 162.

Although the fluid heater 14 is described as having a water jacket 146, it will be understood that this description is for illustrative purposes. The heater 14 can be supplied with any suitable heat exchange fluid within the jacket spaces 146 such as water, steam or air, as may be desired for any given installation.

In operation, as shown in FIG. 4, the multiple vigorous jets 102 with their high velocity flow entering the breech of the annular air vitiation zone 104 create a low pressure in the region 164 near the multiple orifices 72. This low pressure region 164 causes the gaseous products of combustion 142-1 near the rim of the deflecting disc 138 to be drawn inward and then back through the recirculation path 139, 140 as indicated by the successive arrows 142-1, 142-2 and 142-3. These recirculating gases 142 pass in effective heat exchange relationship with the exposed metal walls 151 and 144 both of which are backed by water, and in heat exchange with the mounting tube 20. Such an effective cooling action is obtained that the recirculated gases 142-3 at the breech of the sleeve 134 are at a temperature below 800.degree.F.

The multiple vigorous jets 102 are highly effective in providing momentum interchange with the recirculating gases 142-3, thus causing a large recirculation of combustion gases to occur and propelling these recirculated gases forward through the annular air vitiation zone 104. A thorough intermixing occurs between the combustion air in the eight jets 102 and the recirculant gases 142-3. In this way the combustion air becomes vitiated and its composition is chemically altered by intermixture with the cooled recirculated gases.

It is noted that this vitiation and chemical alteration of the major portion of the combustion air is carried out in the annular zone 104 before the vitiated air reaches the downstream fuel injection region 105. The vitiated air and fuel spray 48 are brought into intimate intermixture in the region 105. Because the major proportion, namely approximately 80 to 90 percent of the combustion air has been vitiated before it reaches the vicinity of the fuel, there is very little opportunity for this burner 10 to lapse into yellow flame combustion due to puffy wind conditions at the flue outlet or in spite of adjustment over a wide range of firing rates.

The non-vitiated air jets 135 produce an eddying flow 166 near the nose ring 88 which serves to pull a mist of fine fuel droplets from the spray pattern 48 into the vicinity of the ignition spark, thus aiding in establishing prompt ignition of the fuel. The flame front quickly moves downstream, and the flame becomes established in the combustion chamber downstream from the mouth 136 of the fuel injection region 105.

There is an abrupt increase in cross sectional area of the flow path downstream from the mouth 136, such that a backward eddying vortex 168 of the blue flame occurs in the combustion chamber 106 near the insulated face 137 of the baffle disc 138. This backward eddying vortex 168 extends around the mouth 136 and serves a flame retention function to stabilize and hold the blue flame in the combustion chamber 106. It will be seen that the diverging non-vitiated air jets 135 are preferable aimed so that they just clear the lip 136 and thus pass close to the flame stabilizing vortex 168. In this way there is provided a very slight oxygen enrichment associated with the stabilizing vortex 168, which I have found to be of advantage in retention of the blue flame and in diffusing the blue flame throughout much of the volume of the combustion chamber 106. The air jets 135 preferable diverge at an included angle from 30.degree. to 60.degree., and these diverging jets also cause the fuel spray to diffuse advantageously into substantially the entire cross section of the vitiated air stream issuing from the burner mouth 136.

MODIFIED EMBODIMENT OF THE INVENTION

In illustrating the modified burner 10A shown in FIGS. 8, 9 and 10, corresponding reference numbers will be used for parts performing functions corresponding to those in the burner 10. In general, the burner 10A is similar to the burner 10, except that the air metering assembly is operated by an axial movement instead of a rotary motion. Accordingly, only the differences will be described.

The fixed baffle member 68 has a cup section with an inturned lip 170 which engages and retains the periphery of a fixed circular metering baffle wall 70 (FIG. 10). This circular wall member 70 is secured to the upstream end of the fuel nozzle support tube and air cooling conduit 84 and contains eight stationary orifices 72.

In order to adjust the amount of combustion air flowing through the fixed orifices 72, there are a plurality of longitudinally movable tapered cylindrical damper valve plugs 172 each of which is inserted into a respective one of the orifices 72. As seen in FIGS. 9 and 10, two of these tapered damper plugs are formed by the insulating sleeves 120 which surround the electrode rods 118 that extend through two of the orifices 72. The six damper plugs 172 are fastened to the perimeter of the support member 96. The two electrode insulating sleeves 120 are held clamped in position by encircling bands 174 attached to opposite ends of a clamp bar 124. A clamp screw 126 is threaded through a screw hold in the uppermost plug 172 and presses against the clamp bar 124. When the screw 126 is loosened, the electrodes 118 can be adjusted longitudinally and rotatably by moving the insulating sleeves 120 with respect to their mounting saddles 122 on the support member 96 for positioning the electrode tips 132 as desired.

For simultaneously moving all of the damper plugs 172 and insulating sleeves 120 longitudinally, the support member 96 is slidable along the nozzle fuel line 44. A compression spring 176 seats against a busing 178 secured to the fuel line, and this spring presses forward against the slidable support member 96 to urge it forward with respect to the fuel line. As adjusting rod 180 is secured to the support member 96 and extends back through a hole in a mounting block element 182. This adjusting rod 180 and also the fuel line 44 are slidable through the mounting element 182. By tightening a nut 184 the user moves the support member 96 and all of the valve plugs rearwardly in unison against the action of spring 176, thus increasing the amount of combustion air issuing in the multiple air jets 102, and vice versa to decrease the combustion air flow.

The full blower air pressure is available in the plenum 66, so that the air jets 102 are vigorous and effective in creating a low pressure region 164 (FIG. 8) near the multiple orifices 72. In addition, the tapered valve plugs 172, 120 with their forwardly projecting pintle sections 186 are effective in reducing the amount of the major combustion air flow 101 while retaining symmetrical energetic jets 102. These multiple vigorous jets 102 achieve a large momentum interchange with the gaseous products that have been recirculated through the recirculation path 189, 140, thereby effectively vitiating the air in the annular air vitiation zone 104 before the downstream fuel injection region 105 is reached. The recirculant in the path 139, 140 is cooled to a temperature below 800.degree.F by the exposed metal wall section 151 and 144 of the fluid heater 14.

A minor proportion 99 of the combustion air flows forward through the support tube and air duct 84 so as to cool the nozzle 46. This air 99 issues through multiple small holes 133 (FIG. 10) in the nose ring 88. These holes 133 preferably diverge outwardly in a downstream direction at an included angle in the range from 30.degree. to 60.degree. to create a plurality of non-vitiated diverging air jets 135 directed to miss the lip of the sleeve 134 near the annular vortex 168, thereby providing a stable and generally diffuse blue flame in the combustion chamber 106.

In order to further increase the proportionate amount of recirculant being pumped into the annular zone 104, the tube 134 can be flared out at its breech, as shown in FIG. 8. This same flaring of the breech of the tube 134 can be incorporated in the burner 10 of FIGS. 1 - 7, for the same reasons.

For accurately aligning and centering the tapered valve plugs 172, 120 with the orifices 72, three or more centering vanes or flutes 188 can be provided on the forward end of one or more of the valve plugs. These flutes 188 define a uniform outside diameter and are sized to slide freely in the orifice 72 to serve as centering guides.

The resilient leaf spring electrode contacts 128 remain in engagement with cooperating leaf spring extensions of the transformer terminals 130 in spite of the fact that the whole vane plug assembly is longitudinally adjustable in position.

The spring 92 between the mounting element 182 and the bushing 178 urges the fuel line forwardly, thus pressing the nozzle means 46 against the inside of the nose ring 88. The resulting forward pressure on the front end of the tube 84 holds the priphery of the baffle member 70 firmly seated against the retainer lip 170.

Advantageously, the whole air metering and electrode assembly shown in FIG. 10 can be removed from the burner 10A in the field for inspection or servicing and can be reinserted into the burner 10A without altering the original adjustment of the damper elements. The lid 54 is swung up and open in a forward direction about the hinge 56. The mounting element 182 is moved forward against the action of spring 92 to clear the wall of the housing so that the projecting fuel line 44 and adjusting rod 180 can be lifted up from a notch 49 in the housing wall. Then the whole assembly of FIG. 10 can be removed in a rearward and upward direction to withdraw the baffle member 70 from engagement with the fixed member 68.

The springs 92 and 176 accommodate tolerance variations and differential expansions of the various parts so that they can be readily mass produced. This axially adjustable air metering damper assembly as shown in FIG. 10 has the advantage that it is capable of being embodied with only minor alterations in various blue flame retention gun burners having different designs but embodying the present invention as described in connection with the burners 10 and 10A.

FURTHER EMBODIMENT OF THE INVENTION

FIGS. 11 and 12 show the burner 10 or 10A associated with a different fluid heater 14A from the fluid heaters shown in FIGS. 1, 4 and 8. This fluid heater 14A is shown as being a domestic oil-fired water heater with a water feed line 190 extending into the bottom of a heat exchange water tank 146 and a hot water supply line 192 from the top of the tank. The shape of the hot water storage tank 146 is typical of many conventional water heaters and includes a bare metal bottom surface 151.

The combustion chamber 105 is defined by a low density high temperature insulation material 150 which may be supported in a metal pan 196. A glass fiber insulation material 198 or similar insulation surrounds the combustion chamber 106 for heat insulation and sound deadening purposes. A metal deflector panel 200 extends as a shelf around the top of the combustion chamber.

The hot gaseous products of combustion rise up into a head space 194 in heat exchange relationship with the exposed concave surface 151 and are deflected downwardly. The deflector panel 200 re-directs the hot gases up into an annular heat exchange passage 202 surrounding the tank 146 and communicating with the flue duct 160. An outer insulated casing 204 surrounds the heat exchange passage 202.

As seen most clearly in FIG. 11, there is a hollow member 206 of generally annular configuration which surrounds the breech end of the mixing tube 134 so as to define an annular recirculation chamber 140 for the cooled combustion gases. The annular member 206 includes an upstanding duct portion 208 which provides a recirculation flow passage 139 interconnecting the recirculation chamber 140 with the head space 194 above the combustion chamber 106. A recess 210 in the shelf panel 200 received the duct section 208.

For attachment of the burner mounting flange 58, there are a plurality of bolt studs 212 on the recirculation chamber 206 which extend through bolt holes in a burner bracket mount 214. This bracket 214 includes a burner port 22 for receiving the tubular adapter section 20 (FIG. 10) of the burner which is aligned with a corresponding burner port 22A in the recirculation chamber 206. A port 216 in the wall of the combustion chamber receives the mixing tube 134 which projects through a port 218 in the opposite wall of the mixing chamber from the port 22A.

It is noted that there is an abrupt increase in cross sectional area of the combustion chamber 106 beyond the lip 136 at the mouth of the fuel injection region 105 producing the back eddying annular vortex 168. As discussed above in connection with FIGS. 1, 4 and 8 such a back eddy aids in retention of a stable blue flame in the combustion chamber 106.

A portion of the gaseous products of combustion after undergoing useful heat exchange with the water backed surface 151 of the heat exchanger 12 are drawn down through the recirculation flow passage 139 into the annular region 140. Advantageously, these recirculant gases are drawn from a region near the downturned rim 220 where the products of combustion are being deflected downwardly from the head space 194 toward the shelf panel 200. The recirculant is drawn by the multiple air jets of the burner 10 or 10A from the recirculation region 140 into the air vitiation and chemical alteration zone 104.

ANOTHER EMBODIMENT OF THE INVENTION

FIG. 13 shows the burner 10 or 10A associated with a compact fluid heater 14B which is adapted to be connected with a remote storage tank for the hot fluid (not shown) or connected directly with equipment for utilizing the hot fluid. This fluid heater 14B is shown as a compact water heater with a feed water line 190 connected to a monotube coil section 222 of a heat exchanger 12. The other end of the coil section 222 connects to a hot water supply line 192. This supply line 192 can be connected to a hot water storage tank or directly to utilization equipment for using the hot water or other hot fluid being produced by the fluid heater 14B.

This fluid heater comprises a first elongated cylindrical cup 224 formed of rigid low density thermally resistant insulation material 150 which defines the combustion chamber 106. The sleeve 134 of the burner 10 or 10A extends through a port 216 in the circular end wall 226 of the cylindrical insulation cup 224. There is an abrupt increase in cross sectional area downstream from the lip 136 of the sleeve 134 thus forming the back eddying vortex 168 in the combustion chamber 106.

The first elongated cylindrical insulation cup 224 is supported near its opposite ends by a plurality of radial spacer elements 228 formed of low density thermally resistant insulating material similar to the lining 150 of the combustion chamber. The open end 230 of the first cylindrical cup 224 nests concentrically within a second larger elongated cylindrical cup 232 formed of the same insulation material 150. The first and second cylindrical insulation members 224 and 232 are radially and axially spaced to define a generally annular cylindrical passage 234 communicating with the opposite end of the combustion chamber 106 from the fuel injection region 105. The cylindrical member 234 is supported by a jacket 236 of heat resistant metal, such as stainless steel, secured by brackets 238 to the cylindrical casing 240 of the heater 14B. Preferably the casing 240 is also formed of similar heat resistant metal.

The second elongated cylindrical member 232 and the casing 240 are radially and axially spaced to provide an annular cylindrical space 241 for the coil section 222 communicating with an outlet end chamber 242 connected to the flue duct 160.

At the burner end of the heater the casing is completed by an extending cylindrical mounting section 20 integral with an end cover disc 244. Between the cylindrical mounting section 20 and the sleeve 134 is defined the annular recirculation path portion 140. A radial recirculation path portion 139 is defined between the cover 244 and the end of the first cylindrical cup member 224. The coil section 222 is shaped to fit into the recirculation path protions 139 and 140. Thus, useful heat exchange between the recirculated gases and a fluid-cooled heat sink occurs such that these recirculated gases are cooled to a temperature below 800.degree. F. before they enter the air vitiation and chemical alteration zone 104.

Advantageously, the combustion products can diffuse and slow down while passing through the annular passage 234 which has a relatively large total cross sectional area. Thus, there is a substantial differential in pressure occurring between a point at the juncture of passages 234 and 139 and the low pressure region 164 near the multiple vigorous air jets aimed into the zone 104. The recirculation path 139 and 140 is a low pressure drop path because it is short and has a relatively large cross sectional area; and so a highly effective recirculation of cooled combustion products is produced through the path 139,140.

DISCUSSION OF GRAPHS

FIG. 14 graphs the effect of excess air on the amount of emissions of nitric oxide (NO) and carbon monoxide (CO) for a conventional commercially available fuel oil burner with a flame retention head firing into a commercial outdoor water heater and also for a burner embodying the present invention firing into the same water heater. The conventional outdoor water heater was modified by scraping off the insulation near the burner inlet port 22, as shown in FIG. 4 at 144 and 151. Both the conventional burner and the burner of the present invention were tested in this water heater after the insulation had been scraped off. (This modification reduced the NO emissions for the conventional burner below that which occurred when the insulation was present at 144 and 151, and thus this modification did not adversely affect the performance of the conventional burner.) Both the conventional burner and the burner of the present invention were fired at a rate of 0.75 to 0.80 gallon of No. 2 fuel oil per hour utilizing conventional high pressure fuel atomizing nozzles.

The excess air is plotted as the independent variable along the horizontal axis, being expressed as a percentage above a stoichiometric ratio of air to fuel. For example, 10 percent excess air means that the amount of air being fed through the burner exceeds a stoichiometric ratio by ten percent, and so forth.

The values plotted along the vertical axis in FIG. 14 are grams of NO or CO produced per kilogram of fuel which was burned under steady state operating conditions. This fuel was conventional No. 2 fuel oil purchased commercially.

The values plotted in FIG. 14 are averages compiled during a series of tests. In any given instance the data actually measured was within approximately plus or minus 10 percent from the curves shown in FIG. 14. It is to be noted that the shape of the NO curve 252 in FIG. 14 is not typical of all conventional burners, but the emission data for NO lying above 0.07 grams of NO per Kg of fuel is typical of all conventional flame retention head burners, in the range of excess air shown in FIG. 14, as shown by David P. Howekamp and Mark H. Hooper in Paper No. APCA No. 70-45 presented at the annual meeting of the Air Pollution Control Association, in St. Louis, Mo. on June 14 to 19, 1970, entitled Effects of Combustion Improving Devices on Air Pollutant Emission From Residential Oil-Fired Furnaces.

FIG. 15 graphs the dependence of smoke emissions and furnace efficiencies on the amount of excess air under steady state operating conditions. The smoke emissions are plotted along the vertical axis at the left in terms of Bachrach Number. The furnace efficiencies are plotted along the vertical axis at the right.

Taking into account the shape of the smoke emissions curve 250 (FIG. 15) for the conventional burner, it is seen that the least smoky range of operation (for operation of the conventional burner in this particular water heater) is from approximately 20 percent to approximately 60 percent excess air. Over this range from approximately 20 percent to approximately 60 percent excess air the furnace efficiencies for the conventional burner as shown by curve 251 ranged from approximately 75 percent to approximately 66 percent.

As shown by the curve 252 (FIG. 14) over this same range from approximately 20 percent to approximately 60 percent excess air the NO emissions from the conventional burner ranged from approximately 1.18 to approximately 0.07 grams per kilogram of fuel burned. Over this same range of excess air as shown by the curve 253 (FIG. 14) the CO emissions from the conventional burner remained almost constant at approximately 0.24 grams per Kg of fuel burned.

Taking into account the shape of the smoke emissions curve 254 for the burner embodying the invention, it is seen that the least smoky range of operation is from approximately 10% excess air up to approximately 15 percent excess air or more, if desired. However, considering the shape of the efficiency curve 255 for the burner embodying the present invention, it is seen that higher efficiencies are obtained by remaining in the range from approximately 10 percent to approximately 15 percent excess air, and over this range as shown by the curve 255 the furnace efficiencies range from approximately 79 percent to approximately 77 percent.

Over this same range from approximately 10 percent to approximately 15 percent excess air, as shown by the curve 256 (FIG. 14), the NO emissions from the burner of the present invention remained almost constant at approximately 0.32 grams per Kg of fuel burned. Over this same range the CO emissions as shown by the curve 257 ranged from approximately 0.26 to approximately 0.25 grams per Kg of fuel burned.

The actual comparison is somewhat more favorable to the burner of the present invention than appears from a glance at these curves, because of the somewhat greater efficiency obtained with the burner of the present invention. By virtue of the fact that in the range from approximately 10 percent to approximately 15 percent excess air the burner of the present invention provides furnace efficiencies from approximately 79 percent to approximately 77 percent a lesser consumption of fuel is required to produce the same effective heating than with a conventional burner operating at furnace efficiencies from approximately 75 percent to approximately 66 percent in the excess air range from approximately 20 percent to approximately 60 percent. Accordingly, the amount of emissions caused by the burner of the present invention in actual use would be reduced in proportion to this reduction in fuel consumption resulting from the increased efficiency.

The burner embodying the invention which was tested to produce the graphs of FIGS. 14 and 15 was similar to that shown in FIGS. 1 - 8, except that the air jet orifices 72 were fixed in size by drilling in the baffle member 68. There was no means provided to adjust the size of these orifices 72, and so I arranged to drill several different baffle members with different sized orifices and selected the best one for the tests. Since the time when these tests were run, I conceived and developed the adjustable orifice mechanisms as shown and described in the drawings. I intend to include a burner having orifices 72 of fixed size in certain of the following claims.

One other difference between the burner embodying the invention which was tested to produce the graphs of FIGS. 14 and 15 and that shown in FIGS. 1-8 was that the former had a plurality of radial support fins in the zone 104 projecting inward from the sleeve 134 and located intermediate the jets 102. These radial fins defined a plurality of sectors of the annular zone 104 with each of the jets 102 aimed generally along the centerline of these respective sectors of the zone 104. I intend to include a burner having fins in the annular zone 104 in certain of the claims. Tests have also more recently been run on the burner of FIGS. 1-8, and the results of these recent tests were comparable to those which were used to produce FIGS. 14 and 15.

ADDITIONAL DISCUSSION

Although it is among the advantages of the present invention that it enables many conventional air and oil handling components to be directly utilized in the practice of the invention, there are certain instances in which special components may be used. For example, the blower 28 in the burner 10 or 10A may be a high performance blower for supplying pressurized air at a higher pressure than conventional for use with heat exchanger systems 12 requiring high velocity flow of the combustion products therethrough to provide high convective heat transfer rates to the fluid being heated.

Claims

I claim:

1. The process of burning liquid hydrocarbon fuel to produce a stable blue flame with low nitric oxide and low particulate emission level comprising the steps of

a. spraying fine droplets of liquid fuel into a fuel injection region in a direction toward a combustion chamber positioned downstream from said fuel injection region,

b. pressurizing air to provide a source of combustion air,

c. dividing the pressurized combustion air into a minor proportion and a major proportion,

d. feeding the minor proportion of the combustion air into the fuel injection region near said spraying of the fuel,

e. igniting the spray of fuel to produce combustion,

f. feeding the major proportion of the combustion air through a plurality of spaced orifices providing multiple jets of air directed into an air vitiation and chemical alteration zone positioned upstream from said fuel injection region with said jets of air being directed through said zone toward said fuel injection region,

g. arranging said multiple jets of air to create a region of reduced pressure near said multiple orifices relative to the pressure within said combustion chamber, said region of reduced pressure being located at the entrance to the air vitiation and chemical alteration zone,

h. flowing a portion of the gaseous products of combustion being generated in said combustion chamber through a recirculation path extending in heat exchange relationship with a heat exchanger being cooled by fluid for cooling the recirculant gaseous products to a temperature below 800.degree.F.,

i. introducing the cooled recirculant gaseous products into said region of reduced pressure,

j. mixing said cooled recirculant gaseous products with said multiple jets of air in said air vitiation and chemical alteration zone as the major proportion of the combustion air is passing through said zone, and

k. introducing the vitiated air into said fuel injection region for mixing the vitiated and chemically altered air with said fuel spray and with the minor proportion of combustion air in said region for preparation and mixing of the fuel spray with the vitiated air,

whereby the prepared mixture of fuel spray and vitiated air passes from said region into said combustion chamber to burn therein with a stable blue flame providing a low nitric oxide and low particulate emission level.

2. The process of burning liquid hydrocarbon fuel to produce a stable blue flame with low nitric oxide and low particulate emission level as claimed in claim 1, in which:

said minor proportion of the combustion air is fed into the fuel injection region as a plurality of air jets directed outwardly for enhancing radial diffusion of the fuel spray.

3. The process of burning liquid hydrocarbon fuel to produce a stable blue flame with low nitric oxide and low particulate emission level as claimed in claim 2, in which:

there is provided an abrupt increase in cross sectional area of the flow path in passing from the fuel injection region into the combustion chamber creating a back eddying vortex of generally annular configuration in the combustion chamber downstream from the fuel injection region, and

said plurality of air jets fed into the fuel injection region are directed outwardly and aimed generally toward said back eddying vortex to provide a slight oxygen enrichment associated with said back eddying vortex for producing a stable blue flame retention action.

4. The process of burning liquid hydrocarbon fuel to produce a stable blue flame with low nitric oxide and low particulate emission level as claimed in claim 2, in which:

the fine droplets of liquid fuel are sprayed in a pattern diverging downstream in a direction toward the combustion chamber,

said plurality of air jets fed into the fuel injection region are spaced around said diverging pattern of fuel spray and are aimed outwardly in a configuration diverging downstream, and

igniting said spray of fuel at a point intermediate said diverging pattern of fuel spray and said diverging configuration of air jets,

whereby said diverging configruation of air jets pull a mist of fine fuel droplets from the spray pattern into the vicinity of said igniting point to aid in establishing prompt ignition of the fuel.

5. The process of burning liquid hydrocarbon fuel to produce a stable blue flame with low nitric oxide and low particulate emission level as claimed in claim 1, in which:

said air vitiation and chemical alteration zone has an annular configuration,

feeding said major proportion of the combustion air as multiple jets spaced in a generally circular configuration directed into said annular zone,

feeding said minor proportion of the combustion air axially through said annular zone, and

then feeding said minor proportion of the combustion air into the fuel injection region as a plurality of jets positioned about the fuel spray.

6. The process of burning liquid hydrocarbon fuel to produce a stable blue flame with low nitric oxide and low particulate emission level as claimed in claim 5, including the steps of:

dividing the annular air vitiation and chemical alteration zone into a plurality of sectors, and

feeding said major proportion of the combustion air as multiple jets and aiming each of said jets generally along the centerline of a respective one of said sectors.

7. The process of burning liquid hydrocarbon fuel to produce a stable blue flame with low nitric oxide and low particulate emission level as claimed in claim 1, including the steps of:

flowing said portion of the gaseous products of combustion through a recirculation path starting from a position near said back eddying vortex and ending near said region of reduced pressure,

said recirculation path including a portion extending inwardly from a larger diameter and then a cylindrical portion extending back toward said region of reduced pressure, and

cooling the recirculant gaseous products by passing them in heat exchange relationship in said inwardly extending portion.

8. The process of burning liquid hydrocarbon fuel to produce a stable blue flame with low nitric oxide and low particulate level as claimed in claim 1, in which:

said minor proportion and major proportion of the pressurized combustion air constitute substantially all of the air which enters the combustion chamber,

whereby substantially all of the combustion air enters the fuel injection region.

9. The process of burning liquid hydrocarbon fuel to produce a stable blue flame with low nitric oxide and low particulate emission level as claimed in claim 1, including the step of:

preferably providing a fuel injection region having a cylindrical configuration in which its diameter is greater than its length L.

10. The process of burning liquid hydrocarbon fuel to produce a stable blue flame with low nitric oxide and low particulate emission level comprising the steps of

a. spraying fine droplets of liquid fuel into a fuel injection region in a direction toward a combustion chamber positioned downstream from said fuel injection region,

b. pressurizing air in an unthrottled manner to provide a source of combustion air of full pressure,

c. dividing the pressurized combustion air into a minor proportion and a major proportion,

d. feeding the minor proportion of the combustion air into the fuel injection region near said spraying of the fuel,

e. igniting the spray of fuel to produce combustion,

f. applying the full pressure of a major proportion of the pressurized combustion air to a plurality of spaced orifices providing vigorous multiple jets of air directed into an air vitiation and chemical alteration zone positioned upstream from said fuel injection region with said jets of air being directed through said zone toward said fuel injection region,

g. arranging said multiple jets of air to create a region of reduced pressure near said multiple orifices relative to the pressure within said combustion chamber, said region of reduced pressure being located at the entrance to the air vitiation and chemical alteration zone,

h. flowing a portion of the gaseous products of combustion being generated in said combustion chamber through a recirculation path extending in heat exchange relationship with a heat exchanger being cooled by fluid for cooling the recirculant gaseous products to a temperature below 800.degree.F.,

i. introducing the cooled recirculant gaseous products into said region of reduced pressure,

j. mixing said cooled recirculant gaseous products with said multiple jets of air in said air vitiation and chemical alteration zone as the major proportion of the combustion air is passing through said zone, and

k. introducing the vitiated air into said fuel injection region for mixing the vitiated and chemically altered air with said fuel spray and with the minor proportion of combustion air in said region for preparation and mixing of the fuel spray with the vitiated air,

whereby the prepared mixture of fuel spray and vitiated air passes from said region into said combustion chamber to burn therein with a stable blue flame providing a low nitric oxide and low particulate emission level.

11. The process of burning liquid hydrocarbon fuel to produce a stable blue flame with low nitric oxide and low particulate emission level as claimed in claim 10, including the step of:

throttling the flow of the major proportion of the combustion air at said plurality of spaced orifices for regulating the burning process.

12. A blue flame retention burner for burning liquid hydrocarbon fuel to produce a stable blue flame with low nitric oxide and low particulate emission level comprising

a burner housing having air chamber means,

blower means associated with said housing providing combustion air under pressure in said chamber means,

baffle means having orifice means communicating with said chamber means for providing a first flow of air jetting forwardly in front of said baffle means,

an air tube communicating with said chamber means such that combustion air under pressure can pass from said chamber means into said air tube, said air tube extending out in front of said baffle means,

said orifice means being spaced about said air tube for providing said first flow of air jetting forwardly around said air tube,

a fuel line extending forward within said air tube to a fuel spray nozzle for feeding liquid hydrocarbon fuel to said nozzle,

said fuel spray nozzle being located at the forward end of said air tube for spraying a pattern of fuel spray forwardly beyond the end of said air tube,

said air tube having a ring portion at its forward end surrounding said fuel spray nozzle,

said ring portion having opening means therein spaced about said fuel nozzle for forming the combustion air passing through said air tube into a second flow of air jetting about said fuel spray pattern,

said orifice means and said openings being sized such that said first air flow comprises a major proportion of the combustion air and said second air flow comprises a minor proportion of the combustion air, and

ignition means for igniting the fuel in said spray pattern,

whereby:

a. when said air tube and nozzle are inserted into a large sleeve having a forward end directed into a combustion chamber of abruptly larger cross sectional area than said sleeve and said combustion chamber is associated with a fluid cooled heat exchanger, and

b. when said orifice means are positioned to direct said first flow of air jetting forwardly into the annular space within said sleeve surrounding said air tube, and

c. when means are provided defining a recirculation path for gaseous products of combustion extending from said combustion chamber back to the end of said sleeve near said orifice means, and

d. when said recirculation path passes in heat exchange relationship with respect to said heat exchanger so as to cool the recirculated gaseous products of combustion to a temperature below 800.degree.F. before they reach the end of said sleeve near said orifice means,

then a stable blue flame is produced in said combustion chamber downstream from said sleeve with low nitric oxide and low particulate emission level.

13. A blue flame retention burner for burning liquid hydrocarbon fuel to produce a stable blue flame with low nitric oxide and low particulate emission level as claimed in claim 12 in which:

said opening means in said ring portion at the forward end of said air tube are arranged to direct said second flow of air as a plurality of air jets aimed outwardly around said fuel spray pattern.

14. A blue flame retention burner for burning liquid hydrocarbon fuel to produce a stable blue flame with low nitric oxide and low particulate emission level as claimed in claim 13, in which:

said openings direct said plurality of air jets outwardly around said fuel spray pattern to diverge at an included angle from 30.degree. to 60.degree..

15. A blue flame retention burner for burning liquid hydrocarbon fuel to produce a stable blue flame with low nitric oxide and low particulate emission level as claimed in claim 12 in which:

said housing means has untrhrottled openings associated with said blower means for allowing unobstructed entry of air to said blower means to provide full blower output pressure in said chamber means.

16. A blue flame retention burner for burning liquid hydrocarbon fuel to produce a stable blue flame with low nitric oxide and low particulate emission level, as claimed in claim 12 in which:

said orifice means include a plurality of orifices in said baffle means,

adjustable air metering means associated with said orifices for metering the first flow of combustion air jetting forwardly in front of said baffle means,

and adjustment means for adjusting said metering means relative to said orifices.

17. A blue flame retention burner for burning liquid hydrocarbon fuel to produce a stable blue flame with low nitric oxide and low particulate emission level, as claimed in claim 16, in which:

said adjustable air metering means are rotatably adjustable, and

said adjustment means serve to turn said adjustable air metering means relative to said baffle means.

18. A blue flame retention burner for burning liquid hydrocarbon fuel to produce a blue flame with low nitric oxide and low particulate emission level, as claimed in claim 16, in which:

said adjustable air metering means are longitudinally adjustable relative to said baffle means, and

said adjustment means serve to move said adjustable air metering means longitudinally.

19. A blue flame retention burner for burning liquid hydrocarbon fuel to produce a stable blue flame with low nitric oxide and low particulate emission level as claimed in claim 12 in which:

said baffle means include a fixed baffle having a plurality of orifices therein forming first air jets,

a rotatable metering baffle member positioned adjacent to said fixed baffle having a plurality of companion orifices spaced to align with the orifices in the fixed baffle, and

control means for turning said rotatable baffle member relative to said fixed baffle member for metering the combustion air passing through said orifices to said first air jets.

20. A blue flame retention burner for burning liquid hydrocarbon fuel to produce a stable blue flame with low nitric oxide and low particulate emission level as claimed in claim 19, in which:

said control means include a control arm for turning said rotatable metering baffle member, and

an adjusting element extending through said housing for moving said control arm.

21. A blue flame retention burner for burning liquid hydrocarbon fuel to produce a stable blue flame with low nitric oxide and low particulate emission level as claimed in claim 19, in which:

said fixed baffle has a central opening,

said air tube extends forwardly through said central opening and is rotatable in said central opening,

said rotatable metering baffle member is secured to said air tube and is positioned behind said fixed baffle, and

spring means removabley urge said rotatable baffle member forward against said fixed baffle member.

22. A blue flame retention burner for burning liquid hydrocarbon fuel to produce a stable blue flame with low nitric oxide and low particulate emission level as claimed in claim 21, in which:

said ignition means include an electrode support associated with said air tube, said electrode support being positioned behind said rotatable baffle member with electrode means mounted on said electrode support and extending forward through said rotatable baffle member and through said fixed baffle to a position near said fuel spray pattern,

said rotatable baffle member and said fixed baffle have openings therein for accommodating the forward extension of said electrode means and for accommodating the rotatable adjustment of said rotatable baffle member, and

said rotatable baffle member, said air tube, said electrode support and said electrode means are removable together as an assembly from said housing.

23. A blue flame retention burner for burning liquid hydrocarbon fuel to produce a stable blue flame with low nitric oxide and low particulate emission level as claimed in claim 21, in which,

said fuel line is removably held in said housing,

said spring means surrounds said fuel line while urging said rotatable baffle member forward,

whereby removal of said fuel line from said housing releases the spring force for enabling removal of said rotatable baffle and said air tube together with said fuel line and nozzle.

24. A blue flame retention burner for burning liquid hydrocarbon fuel to produce a stable blue flame with low nitric oxide and low particulate emission level, as claimed in claim 18, in which:

said adjustable air metering means include a plurality of tapered valve plugs adapted to extend into respective orifices in said baffle means,

a support member for supporting said valve plugs in spaced parallel relationship adapted to be aligned with the respective orifices, and

said support member being moved by said adjustment means.

25. A blue flame retention burner for burning liquid hydrocarbon fuel to produce a blue flame with low nitric oxide and low particulate emission level, as claimed in claim 24, in which:

spring means urge said fuel nozzle forward against said ring portion of said air tube,

said air tube is connected to said baffle means,

means are provided for retaining said baffle means in position against the forward thrust of said spring means, and

said fuel line, nozzle, air tube, baffle means, support member and valve bodies are removable.

26. A blue flame retention burner for burning liquid hydrocarbon fuel to produce a stable blue flame with low nitric oxide and low particulate emission level, as claimed in claim 24, in which:

said ignition means include a pair of electrodes mounted on said support member and extending forward through a pair of said orifices.

27. A blue flame retention burner adapted to operate with a combustion chamber associated with a fluid heater including a fluid-cooled heat exchanger to burn liquid hydrocarbon fuel to produce a stable blue flame with low nitric oxide and low particulate emission level, said burner comprising:

a cylindrical sleeve having a rear end which defines a breech and a front end which defines a mouth, said cylindrical sleeve defining a fuel injection region adjacent to said mouth,

fuel nozzle means positioned within said sleeve and a fuel line for feeding liquid fuel to said nozzle means, said nozzle means being directed to form a fuel spray in said fuel injection region with said fuel spray travelling forward toward said mouth,

a burner housing having air chamber means,

a blower means associated with said housing providing combustion air under pressure in said chamber means,

an air tube communicating with said chamber means and extending through the breech of said cylindrical sleeve into said sleeve for conducting air from said chamber means to the vicinity of said fuel nozzle means for cooling said nozzle means,

said cylindrical sleeve being larger diameter than said air tube defining an annular zone within said sleeve and surrounding said air tube and communicating with said fuel injection region,

orifice means positioned near to the breech of said cylindrical sleeve communicating with said chamber means and providing a jetting flow of combustion air directed into and through said annular zone toward said fuel injection region, and

ignition means for igniting said fuel spray,

said burner being adapted to operate with said mouth of said cylindrical sleeve being directed into a combustion chamber having a larger cross sectional area than said mouth associated with a fluid heater including a fluid-cooled heat exchanger and with means defining a recirculation path for conducting a portion of the gaseous products of combustion formed in said combustion chamber back to the breech of said cylindrical sleeve with said recirculation path passing in heat exchange relationship with said fluid-cooled heat exchanger for cooling the recirculated gases before they reach the breech of said cylindrical sleeve,

whereby a stable blue flame is produceable in said combustion chamber downstream from said mouth of said cylindrical sleeve, such blue flame having low nitric oxide and low particulate emission level.

28. A blue flame retention burner adapted to operate with a combustion chamber associated with a fluid heater including a fluid-cooled heat exchanger to burn liquid hydrocarbon fuel to produce a stable blue flame with low nitric oxide and low particulate emission level, as claimed in claim 27, in which:

said air tube has a forward portion surrounding said fuel nozzle means with opening means in said forward portion for discharging the combustion air which has cooled said nozzle means as jetting air issuing from said air tube into said fuel injection region about said fuel spray, and

said opening means and said orifice means are sized for discharging a minor proportion of the combustion air as said jetting air issuing into said fuel injection region.

29. A blue flame retention burner adapted to operate with a combustion chamber associated with a fluid heater including a fluid-cooled heat exchanger to burn liquid hydrocarbon fuel to produce a stable blue flame with low nitric oxide and low particulate emission level, as claimed in claim 27, in which:

the breech of said cylindrical sleeve is flared out.

30. A blue flame retention burner adapted to operate with a combustion chamber associated with a fluid heater including a fluid-cooled heat exchanger to burn liquid hydrocarbon fuel to produce a stable blue flame with low nitric oxide and low particulate emission level, as claimed in claim 27, in which:

said cylindrical sleeve has a relatively large diameter and a short over-all length with a length to diameter ratio no more than 2 to 1.

31. A blue flame retention burner adapted to operate with a combustion chamber associated with a fluid heater including a fluid-cooled heat exchanger to burn liquid hydrocarbon fuel to produce a stable blue flame with low nitric oxide and low particulate emission level as claimed in claim 27, in which:

adjustable air metering means are associated with said orifice means for adjustably throttling the flow of combustion air through said orifice means, and

control means are provided for adjusting said air metering means.

32. A blue flame retention burner adapted to operate with a combustion chamber associated with a fluid heater including a fluid-cooled heat exchanger to burn liquid hydrocarbon fuel to produce a stable blue flame with low nitric oxide and low particulate emission level as claimed in claim 27, in which:

means are provided to divide said annular zone within said cylindrical sleeve and surrounding said air tube into a plurality of sectors, and

said orifice means include a plurality of orifices, each of said orifices being positioned generally in alignment with the centerline of a respective one of said sectors for directing jets of combustion air generally along the centerlines of the respective sectors.

33. A method of converting an existing oil-fired fluid heater having a fluid-cooled heat exchanger with an insulation-lined combustion chamber and a burner port extending into the combustion chamber and with a conventional yellow flame oil burner associated with said burner port, into: a liquid hydrocarbon fueled fluid heater capable of operating with a stable blue flame having low nitric oxide and low particulate emission level comprising the steps of

removing the conventional burner from said burner port,

removing some of the insulation lining from the combustion chamber to expose a metal wall of the fluid-cooled heat exchanger in a region adjacent to the burner port,

inserting a cylindrical sleeve into the burner port and positioning a deflecting baffle in the combustion chamber extending around the mouth of said sleeve,

said sleeve and baffle being positioned such that said baffle is spaced from the exposed metal wall of the fluid-cooled heat exchanger near said burner port for defining a portion of a recirculation path communicating with the combustion chamber and extending inwardly toward said sleeve and such that said sleeve is spaced within said burner port to define a cylindrical portion of the recirculation path extending out to the opposite end of said sleeve from the mouth thereof, and

positioning a blue flame retention burner in cooperative relationship with said sleeve, said burner including a burner housing having air chamber means, blower means associated with said housing providing combustion air under pressure in said chamber means, baffle means having orifice means communicating with said chamber means for providing a first flow of air jetting forwardly in front of said baffle means, an air tube communicating with said chamber means such that combustion air under pressure can pass from said chamber means into said air tube, said air tube extending out in front of said baffle means, said orifice means being spaced about said air tube for providing said first flow of air jetting forwardly around said air tube, a fuel line extending forward within said air tube to a fuel spray nozzle for feeding liquid hydrocarbon fuel to said nozzle, said fuel spray nozzle being located at the forward end of said air tube for spraying a pattern of fuel spray forwardly beyond the end of said air tube, said air tube having a ring portion at its forward end surrounding said fuel spray nozzle, said ring portion having opening means therein spaced about said fuel nozzle for forming the combustion air passing through said air tube into a second flow of air jetting about said fuel spray pattern, said orifice means and said opening means being sized such that said first air flow comprises a major proportion of the combustion air and said second air flow comprises a minor proportion of the combustion air, and ignition means for igniting the fuel in said spray pattern, and

positioning said burner with said air tube and nozzle inserted into said opposite end of said sleeve with said nozzle and said opening means being located intermediate said opposite end and said forward end of said sleeve and said orifice means positioned to direct said first flow of air jetting forwardly into the annular space within said sleeve surrounding said air tube,

whereby a stable blue flame is produced in said combustion chamber downstream from said sleeve with low nitric oxide and low particulate emission level.

34. The method of converting an oil-fired fluid heater as claimed in claim 33 including the step of

providing an insulation layer on said deflecting baffle positioned around the mouth of said sleeve and facing toward the combustion chamber.

35. A method of converting an existing oil-fired water heater having a hot water storage tank with a concave bottom surface defining a head space and an annular heat exchange passage surrounding the tank and a combustion chamber beneath said head space and with a burner port extending into the combustion chamber and with a conventional yellow flame oil burner associated with said burner port, into: a liquid hydrocarbon fueled water heater capable of operating with a stable blue flame having low nitric oxide and low particulate emission level comprising the steps of

removing the conventional burner from said burner port,

inserting a cylindrical sleeve into the burner port,

surrounding the outer end of said sleeve with a hollow member of generally annular configuration including an upstanding duct extending up toward said head space for providing a recirculation path for gaseous products of combustion after they have come into heat exchange relationship with said concave bottom surface, and

positioning a blue flame retention burner in cooperative relationship with said sleeve, said burner including a burner housing having air chamber means, blower means associated with said housing providing combustion air under pressure in said chamber means, baffle means having orifice means communicating with said chamber means for providing a first flow of air jetting forwardly in front of said baffle means, an air tube communicating with said chamber means such that combustion air under pressure can pass from said chamber means into said air tube, said air tube extending out in front of said baffle means, said orifice means being spaced about said air tube for providing said first flow of air jetting forwardly around said air tube, a fuel line extending forward within said air tube to a fuel spray nozzle for feeding liquid hydrocarbon fuel to said nozzle, said fuel spray nozzle being located at the forward end of said air tube for spraying a pattern of fuel spray forwardly beyond the end of said air tube, said air tube having a ring portion at its forward end surrounding said fuel spray nozzle, said ring portion having opening means therein spaced about said fuel nozzle for forming the combustion air passing through said air tube into a second flow of air jetting about said fuel spray pattern, said orifice means and said opening means being sized such that said first air flow comprises a major proportion of the combustion air and said second air flow comprises a minor proportion of the combustion air, and ignition means for igniting the fuel in said spray pattern, and

positioning said burner with said air tube and nozzle inserted into the outer end of said sleeve with said nozzle and said opening means being located intermediate said outer end and the end of said sleeve toward said combustion chamber, with said orifice means positioned to direct said first flow of air jetting forwardly into the annular space within said sleeve surrounding said air tube,

whereby a stable blue flame is produced in said combustion chamber downstream from said sleeve with low nitric oxide and low particulate emission level.

36. A blue flame retention burner and fluid-cooled heat exchanger system adapted to burn liquid hydrocarbon fuel to produce a stable blue flame with low nitric oxide and low particulate emission level comprising:

a cylindrical sleeve having a rear end which defines a breech and a front end which defines a mouth, said cylindrical sleeve defining a fuel injection region adjacent to said mouth, said mouth being directed into a combustion chamber defined by a fluid-cooled heat exchanger,

fuel nozzle means positioned within said sleeve and a fuel line for feeding liquid fuel to said nozzle means, said nozzle means being directed to form a fuel spray in said fuel injection region with said fuel spray travelling forward toward said mouth,

a burner housing having air chamber means,

a blower means associated with said housing providing combustion air under pressure in said chamber means,

in air tube communicating with said chamber means and extending through the breech of said cylindrical sleeve into said sleeve for conducting air from said chamber means to the vicinity of said fuel nozzle means for cooling said nozzle means,

said cylindrical sleeve being larger diameter than said air tube defining an annular zone within said sleeve and surrounding said air tube and communicating with said fuel injection region,

orifice means positioned near to the breech of said cylindrical sleeve communicating with said chamber means and providing a jetting flow of combustion air directed into and through said annular zone toward said fuel injection region, and

ignition means for igniting said fuel spray,

said combustion chamber having a larger cross sectional area than said mouth, and

means defining a recirculation path for conducting a portion of the gaseous products of combustion formed in said combustion chamber back to the breech of said cylindrical sleeve with said recirculation path passing in heat exchange relationship with said fluid-cooled heat exchanger for cooling the recirculated gases before they reach the breech of said cylindrical sleeve,

whereby a stable blue flame is produced in said combustion chamber downstream from said mouth of said cylindrical sleeve, such blue flame having low nitric oxide and low particulate emission level.

37. A blue flame retention burner and fluid-cooled heat exchanger system as claimed in claim 36, in which:

said means defining the recirculation path includes a deflection baffle extending out about the mouth of said sleeve and positioned in spaced relationship with a surface of said fluid-cooled heat exchanger to define a portion of the recirculation path behind said baffle near said surface and includes support means spacing said sleeve from the heat exchanger to provide a cylindrical space about said sleeve defining a second portion of the recirculation path communicating with the portion thereof behind said baffle.

38. A blue flame retention burner and fluid-cooled heat exchanger system as claimed in claim 36 in which:

said means defining the recirculation path includes a hollow member of generally annular configuration surrounding the breech of said sleeve,

said hollow member having a duct associated therewith extending to a position near the heat exchanger for recirculating a portion of the gaseous products of combustion after they have passed in heat exchange relationship with the heat exchanger.

39. A blue flame retention burner and fluid-cooled heat exchanger system as claimed in claim 36, in which:

said fluid-cooled heat exchanger includes a first elongated cylindrical member of thermally resistant insulation defining the combustion chamber,

said mouth of said sleeve extending through a port in an end wall of said member with said combustion chamber being of larger cross sectional area than said mouth,

a second larger elongated cylindrical member of insulation material positioned around said first member, said first and second members being radially and axially spaced to define a generally annular cylindrical passage communicating with the opposite end of said combustion chamber from the mouth of said sleeve,

a casing, preferably of heat resistant metal, positioned around said second member, said casing and second member being radially and axially spaced to define a generally annular space communicating with said annular passage,

a coil section positioned in said annular space adapted for fluid flow through said coil section to be heated,

said means defining the recirculation path providing communication between the breech of said sleeve and a point near said coil section.

40. A blue flame retention burner and fluid-cooled heat exchanger system as claimed in claim 39 in which:

said point is located near the juncture of said annular passage and said annular space, and

said coil section is shaped to extend into said recirculation path.

41. A sleeve and deflector baffle assembly for use in the burner port and combustion chamber of a blue flame retention burner and fluid-cooled heat exchanger system comprising:

a sleeve having smaller diameter than said burner port,

a deflector baffle extending out around one end of said sleeve

a layer of insulation on said deflector baffle on the side thereof facing away from said sleeve, and

support means for mounting said sleeve concentrically within said burner port with said deflector baffle spaced away from the wall of the combustion chamber near the burner port.