US2285866A

US2285866A - Combustion device for and method of measuring flame characteristics of gases

Info

Publication number: US2285866A
Application number: US260707A
Authority: US
Inventors: Mathew G Markle
Original assignee: Individual
Current assignee: Individual
Priority date: 1939-03-09
Filing date: 1939-03-09
Publication date: 1942-06-09
Anticipated expiration: 1959-06-09

Description

MARKLE FoR AND METHOD OF MEASURING FLAME CHARACTERISTICS OF GASES 2 Sheets-Sheet l .26 6k: 55 5 thi I o 0 xi! M m MVP 5 mm /.fl .7 J 0 W a J 6J w/ w a z 0 50 W I y I iwrfiaw fl/af/kaw (YT/$7 7776 June 1942 M. G. MARKLE 4 2,235,866

COMBUSTION DEVICE FOR AND METHOD OF MEASURING FLAME CHARACTERISTICS OF GASES Filed March 9, 1959 2 Sheets-Sheet 2 Patented June 9, 1942 UNITED STATES PATENT OFFICE COMBUSTION DEVICE FOR AND METHOD OF MEASURING FLAME CHARACTERISTICS OF GASES 7 Claims.

The present invention relates to measuring instruments and is particularly concerned with devices for and method of measuring and controlling the quantity or quality of factors affecting the flame produced by burning a gas or a mixture of gases.

Most appliances using gas as a source of heat include a burner in Which gas from a supply main is delivered to the burner by a controlling orifice or the like, primary air being admitted and mixed with the gas just before it is burned. Ordinarily, the primary air, supplying oxygen for the combustion of the gas, is drawn into the burner by the aspirating effect of the inflowing gas and the amount of air aspirated is controlled by a sleeve or other suitable means. Each customers appliances of this nature are therefore adjusted according to the type or characteristics of the gas normally supplied, and, once adjusted, the burner will operate satisfactorily so long as the quality, composition, etc., of the gas do not vary to any great extent.

The characteristics of the flame produced by burning a gas or a mixture of gases, are generally dependent upon its specific gravity, B. t. u. content and composition. That is to say, these factors usually control the flame velocity, total heat value and proportion of radiant heat in the flame, and if the flame is stable, the rate of combustion at the flame front is equal to the rate of flow of gas from the burner. As will be obvious, gases of various kinds have various flame speeds and similarly, different gases may have different total heat values but the same flame speed, or the same total heat values and different proportions of radiant heat in the flame.

Various kinds of types of gas are supplied by the utilities serving various localities, some companies furnishing a high B. t. u. gas, around 1000 B. t. u. and other companies furnishing 10w B. t. u. gas, around 500 to 600 B. t. u. Generally, the companies that furnish a gas having a heating value of around 800 B. t. u. provide a mixture of natural gas, reformed natural gas, and manufactured or coke oven gas, depending on the season and other conditions. Straight natural gas has a heat value of about 1000 B. t. u., and the reformed natural gas and manufactured or coke oven gas each may have a heat value of about 555 B. t. u. The heat value of a gas and its burning characteristics depend upon the various constituents in the gas mixture, and these, in turn, depend to a large extent on the composition of the coal, the heat treatment, and other operations during manufacture. During certain seasons, for operating reasons, it may be necessary to provide a supply of make-up gas, usually in the form of carbureted water gas, at about 800 B. t. u., which is mixed with the ordinary 800 B. t. u. gas mixture. It may also be necessary, as when an emergency arises such as a failure of the supply of natural gas, or for other operating reasons, to supply additional quantities of carburetted water gas. However, the amount of carburetted water gas that can be added without affecting the quality of the gas is limited, because carburetted water gas mixed with the usual type of gas, even though both have the same heating value, produces a different burning gas and when the percentage of carbureted water gas at 800 B. t. u. added to the normal 800 B. t. u. gas exceeds a definite point, there is some danger that the operation of customers appliances will be affected.

For example, changing the characteristics, such as specific gravity or composition of the gas mixture, may produce a different burning gas, and, if the characteristics should be changed so that the radiant heat emitted or flame velocity or both, is increased, the burners of the customers appliances may strike back, or, if the flame velocity is decreased, the flame may lift off the port of the burner. Usually, the amount of carbureted water gas required is not all added at one time; instead, auxiliary stations are provided at several points in the system and equipped to add a quantity of gas as may be required for the conditions in the particular 10- cality served by the station or in an emergency, as when the normal supply of natural gas is deficient or fails. The effect of adding substantial amounts or carburetted gas, as where necessary to supplement the normal or base gas, is to increase the flame velocity or possibly change other characteristics of the gas supplied to the customer, and to compensate for such additions it may be necessary to adjust the flame velocity of the gas mixture by adding a substance which will retard the flame velocity, in order to supply a gas to the customer which has its flame velocity adjusted so as to operate satisfactorily in the customers appliances. Under other conditions it may be desired to add an accelerant.

It was therefore recognized that some accurate and dependable way of securing a measurement or indication, preferably continuous, of those changes in a gas mixture that effect its flame or characteristics in burning would be desirable, whereby appropriate adjustments may be made by the operating unit so as to maintain a supply of gas in the customers lines which will not vary in those characteristics which affect burning to an extent sufficient to interfere with the proper operation of the customers appliances.

In solving the problem of securing a continuous measurement or indication of the type, composition, characteristics, etc., of the gas supplied to the customer, it was found that apparatus capable of measuring, for example, only the heating value of the gas, apparatus for measuring its specific gravity, or other apparatus responsive only to a single factor or characteristic of the gas would not be satisfactory. For example, the ordinarily skilled operator of a gas plant can produce a gas having substantially constant heating value and also substantially constant specific gravity, yet the particular composition of the gas may be such that its flame characteristics Would be considerably different than another gas of slightly difierent composition but giving the same heating value, or specific gravity, or both. In these cases, therefore, devices responsive to only a single factor, such as specific gravity or heating value, would not respond to a change in the composition of the gas affecting its burning characteristics, and hence such devices would not be useful in detecting changes in the gas supplied to 'a customer that might be such that the burners of the customers appliances would strike back or otherwise operate inefficiently, if at all.

I have discovered that with any given burner operating with any given gas, a given point on the burner itself will reach a definite temperature and that, with other conditions remaining constant, a change in the type of gas burned will cause a definite temperature change at the aforesaid given point on the burner. As presently understood, I believe that this correspondence of temperature change at some point 'on the burner to changes in the gas burned is due to the fact that the temperature of the given point on the burner is responsive to any of the characteristics of the gas that affects its burning qualities. For example, if the characteristics of a gas mixture should change so that there would be an increase in the flame velocity of the gas, assuming such other factors as temperature, pressure, and the like remain the same, the increase in the flame velocity of the'gas mixture would result in the flame front occupying a position closer to the burner, therefore the given point on the latter would reach a higher temperature than would otherwise be the'case. Further, a change in the composition of the gas, which would produce an increase in the amount of radiant heat emitted by the gas flame would, likewise, result in a temperature rise at the given point on the burner, since the burner is subjected to the radiant heat rays from the gas flame. Such a change in the radiant heat may be produced by a change in the total heat value of the gas, or by change in the type of gas, since two gases having the same total heat value may emit different proportions of the total heat as radiant heat. Thus, either kind of change would result in a change in the temperature of the given point on the burner,

, With the above in mind, the object and general nature of this invention is the provision of a method of and means for measuring any change in the proportion of a gas mixture that aifects theburning characteristics of the gas. Preferably, a continuous measurement is produced so as to afford the operating department an opportunity to make any necessary adjustment in the plant and correct the gas mixture being supplied before the customers appliances are affected. Also, it is a feature of this invention to provide an arrangement wherein such adjustments may be made automatically, if desired.

More specifically, it is a feature of this invention to provide a test or control burner, which is supplied with a continuous sample of the gas that is furnished to the customers and provided with means for measuring the temperature at the tip or other convenient fixed location on the burner, and it is a further feature of this invention to provide a compensated temperature measurement, preferably by means of two thermocouples differentially connected, one arranged to respond to the temperature of the tip of the burner and the other disposed in the gas mixture supplied to the burner, whereby variations in the room temperature, the temperature of the primary air supplied to the burner or the temperature of the gas will be eliminated in the final reading or control produced by the device.

These and other objects and advantages of the present invention will be apparent to those skilled in the art after a consideration of the following detailed description, taken in conjunction with the accompanying drawings illustrating the preferred structural embodiments of my invention.

In the drawings:

Figure l is a View, somewhat diagrammatic, showing one form of the present invention, including a test or control burner and a thermocouple circuit for indicating the difference between the temperature of the burner tip and the temperature of the gas-air stream flowing to the tip;

Figure 2 is a curve showing the uniformity in burner temperature corresponding to a given change in the type of gas burned;

Figure 3' is a diagrammatic view, somewhat similar to that shown in Figure 1, showing an arrangement for performing certain control operations in response to the aforesaid temperature difference; and

Figures 4 to 9, inclusive, disclose modified forms of furnace which maybe employed in carrying out the principles of this invention.

Referring now more particularly to Figure l, the reference numeral I indicates a gas burner, such as an ordinary Bunsen burner, having a base 2, an inlet 3 for the gas to be adjusted or controlled, a gas orifice 4, an inlet 5 for primary air, a burner tube 6, and a tip 1. The burner tube 6 includes a metal sleeve 9 fixed at its lower end to the base 2 and securely connected at its upper end to a sleeve ll] of insulation, the upper end of which receives the burner tip 1, which is preferably of metal or other material of desirable heat absorption qualities.

Secured to the tip I is a thermocouple l5, and disposed within the tube 6 is a second thermocouple H5. The thermocouples I5 and I6 are connected differentially, that is, the polarity of one thermocouple is opposed to the polarity of the other thermocouple. The thermocouples I5 and I6 are connected serially, by leads I9, 20, and 2! the two latter leads being connected in the usual manner to an indicating galvanometer 22. The instrument 22 indicates any flow of current by virtue of one thermocouple being at a higher temperature than the other, and the purpose of arranging the thermocouples l5 and I6 differentially, as mentioned above, is to eliminate any variations in readings due to changes in the temperature of the surrounding air or in the temperature of the gas mixture supplied to the inlet 3. An adjustable sleeve 25 provided with openings 26 adapted to register with the openings is capable of controlling the flow of primary air into the burner tube 6.

In operation, the gas mixture under test is supplied at a constant pressure to the inlet 3. The gas issues through the orifice 4 and passes upwardly through the tube 6, drawing in quantitles of primary air by an aspirating action, the amount of primary air is capable of being adjusted by turning the adjusting sleeve 25 which is provided with the openings 26 that, for maximum air supply, register with the inlet openings 5. As well understood, the gas from the orifice 4 and primary air through the openings 5, 2S produce a combustible mixture which, when ignited, burns with a characteristic flame at the tip 1 of the burner. Seconda y air is supplied to the flame from the zone surrounding the burner. When the sleeve 25 is adjusted properly to supply the right amount of air, the flame produced at the tip will have a characteristic shape which includes an inner cone or flame front 29 and a main flame body 38.

The temperature at the tip I will be registered on the instrument 22, and the thermocouple I6, which responds to the temperature of the gasair stream flowing toward the flame front 29, will eliminate any variation due to a change in temperature of the surrounding air or the temperature of the gas supplied through the inlet 3, which would otherwise be reflected in an indicated change of temperature at the instrument 22. about four volumes of air to one volume of gas, and it will therefore be recognized that a temperature change in the primary air would have a marked effect upon the temperature at the tip I, first because an increase or decrease in the temperature of the primary air would affect the temperature of the flame tip, and second because an increase or decrease in the temperature of the primary air would affect directly the temperature of the tip 1, since the primary air, together with the incoming gas with which it is mixed, sweeps over the inner surface of the tip and cools the latter more or less, depending upon the temperature difference. Therefore, providing the two thermocouples and connecting them differentially, as described above, eliminates any variations due to a change in temperature of the surrounding air or the gas itself. Thus, the instrument 22 will indicate a temperature change when the characteristic of the flame produced by the burning of the mixture varies in such a way that the height or shape of the flame changes, or as the heat value or the proportion of radiant heat of the flame varies.

Experiments have shown that, with the other factors constant, the various heats at the burner tip I, as registered on the galvanometer are an indication of changes in the gaseous mixture burned by the burner. It was found, also, that with other factors constant, a change in pressure at which gas was supplied to the inlet 3 varied the range over which given changes in the gas mixture were registered at the instrument 22. I found that when the gas mixture was supplied at a pressure equal to three inches of water, the range of temperature change produced by given changes in the gas mixture was much greater than at a pressure equal to five inches of water. It was also noted that with the ordinary Bunsen burner, one not having an insulation section such Ordinarily, a Bunsen burner consumes as H! in Figure 1, only about a 72 range in temperature change was indicated at the tip for gas mixtures varying from approximately 100% regular mixture (i. e., natural gas, reformed natural gas, and coke oven gas, at 800 B. t. u.) to 100% carburetted water gas (800 B. t. u.) Apparently the metal of the burner tube in the ordinary Bunsen burner conducted the heat away from the thermocouple at the tip or flame end of the burner at a rate fast enough to prevent the full effects of the heat at the tip of the burner being registered on the instrument 22, and therefore in order to produce a wider range, the construction shown in Figure 1 was adopted, including the insulating section ID. The function of the insulating section I0 is to prevent this flow of heat away from the tip 1, so that the full effects of the heat gathered by the tip I would be effective to produce an indication at the instrument 22. Incidentally, however, it was found that a tip of approximately half of the height of that indicated in Figure 1 produced a temperature range of approximately 300, but the registrations were quite variable, whereas the registrations produced at the instrument 22 when using the tip I were consistent and uniform throughout the range of changes in gas mixture which produced temperature changes within the 160 range.

Figure 2 shows, 'by way of illustration only, a chart 32 for the burner of Figure 1, indicating the consistent correspondence of tip temperature changes with uniform changes in the gas mixture. The line 33 indicates the different temperatures indicated when the composition of the gas burned varied from regular mixture to 100% carburetted water gas, as mentioned above. For these changes I found that the tip temperatures varied, in the manner indicated in the chart 32, from about 280 to 440. Similar tests on the other types of burners, described below, gave curves quite similar to that shown in Figure 2.

Primarily, it is believed that the underlying principle, whereby the temperature changes registered on the instrument 22 responds quite uniformly to corresponding changes in the characteristics of the gas, is due to the effect of said changes upon the amount of radiant heat from the flame absorbed by the burner tip. The amount of radiant heat that is emitted by a flame varies according to the composition of the gas burned, for with different gases different proportions of the total heat emitted appear as radiant heat, and of course with the same kind of gas, and hence a constant proportion of radiant heat, the amount of radiant heat emitted from any given flame varies as the total heat of that flame. Now the amount of radiant heat absorbed by the burner tip therefore varies as the above two factors, namely, composition of the gas insofar as it affects the proportion of heat emitted as radiant heat, and total heat value of the flame assuming a constant type of gas. Further, however, the amount of radiant heat absorbed by the burner tip varies as a third factor which is flame speed. Assuming a gas having a constant total heat value and a constant radiant heat proportion, it will be seen that an increase in flame velocity of the gas will result in a higher temperature at the burner even though the other factors just mentioned remain the same. That is to say, assuming such a change in the gas supplied that the flame speed of the mixture is increased, the flame 3!] will occupy a position somewhat closer to the tip '1, as indicated in dotted lines in Figure 1, and the temperature of the tip, which is then closer to what might be termed the center of heat, that is, a pointfr'om which it may be considered that all of the heat of the flame originates, will increase an amount approximately proportional to the increase in flame velocity. The amount of radiant heat absorbed by any object, such as the tip I, is proportional to the area of that object and the square of the distance from the radiating source, and since the area of the burner tip is a constant and an increase in the flame velocity will cause the center of heat of the flame to approach closer to the tip I, it therefore follows that with an increase in flame velocity the tip will become hotter and the corresponding increased temperature indication will be registered on the instrument 22.

From the above-described operation, it will be apparent that the present device will afford an indication of practically any change in a gas which affects its burning characteristics. It is particularly adapted to furnish an indication of the flame speed of the gas, but it is not necessarily limited thereto, since the device is just as responsive to any other change in the gas or the characteristics thereof that affect the total amount of heat, the height or shape of the flame, or the amount of radiant heat emitted by the gas when burned. It is well known that different constituents of the gas give different radiating capacities, although the total heat evolved by any given flame would be the same.

Heretofore, attempts have been made to provide flame analyzers but generally they include some form of temperature responsive device disposed in the flame itself. Where such a device is in the nature of a thermocouple, the latter while furnishing a useful indication of the temperature of the flame at certain points, is responsive only to a negligible degree, if at all, to the radiant heat of the flame, Further, such devices, being in the flame zone itself, interfere with the proper burning of the gas and may corrode or otherwise change so that the heat transfer is affected. Also different portions of the flame are at different temperatures, so that the temperature registered by those flame analyzers having thermocouples or other devices within the flame itself do not furnish a consistent indication which is uniform throughout the range desired.

Another disadvantage of measuring flame temperatures directly is that the temperatures are quite high, sometimes reaching 3060" and due to the small mass of the thermocouple in the flame, it would therefore be greatly affected by drafts, gas and air temperature variations, or the like, since the thermocouple would have practically no residual heat. Further, where such high temperatures are encountered, it would be difficult, if not impossible, to secure uniform temperature variations for relatively small changes in the characteristic of the gas. Also, the thermocouples have a short life where they are maintained at high temperatures in a reducing atmosphere, and the structural changes resulting therefrom would, in addition, affect the thermal response of the thermocouple. However, the present device is adapted as a flame propagation analyzer and it provides a very uniform indication of flame speeds and is not subject to the wide fluctuations to which thermocouples and other ject.

If desired, instead of merely indicating the temperature at the gas burner tip, or the difference between the temperature of the gas mixture before combustion and the temperature of the tip, the present invention contemplates providing means responsive to these temperatures for effecting the desired or required controlling operations automatically. Thus, for example, where it is desired to provide a continuous cent'rol for, say, the amount of decelerant or the amount of carburetted water gas at 800 B. t. u. to be added to the gas supplied to the customer, the burner I would be connected as described above in connection with Figure l, with the gas supply and the other factors, such as temperatur'e, specificgravity, and composition maintained constant, the amount to be added can be nicely controlled by the apparatus shown in Figure 3.

Referring now to Figure 3, it will be seen that the two thermocouples I5' and I6 are connected to the burner I in substantially the same manner described above. However, instead of being connected directly to an indicating galvanometer 22, as in Figure 1, the leads 26a and 2 la extend to a continuously operating recording and controlling potentiometer, indicated in its entirety by the reference nuineral 35. An instrument of this char 'acter is well known to those skilled in the art and is at present available in the open market. Generally, they consist of a galvanometer 36 controlling an indicating hand 31, which indicates temperature, and a recording pen 38 which recor'ds temperature on a continuously moving record strip 39. Through suitable mechanism, the details of which per Se are of no particular concern, changes of temperature between the tip of the burner and the inflowing gas mixture unbalance the galvanometer circuit in the instrument 36, which sets in motion the recording pen 38 and also a shaft 4| which at one end carries a sliding contact 42. The contact 42 engages a slide wire 44, one end of which is connected by a lead 45 to one pole of a standard cell 46 arranged to supply constant voltage, the other end of the slide wire 44 being connected through a lead 41, an adjustable resistance 48 and a lead 49 to the other pole of the standard cell 46. As will be recognized bythose familiar with instruments of different types, the momentary unbalance of the galvanometer circuit, occasioned by temperature change between the thermocouples l5 and I6, results in a'n actuation of the mechanism including the shaft 4| which, rocking the arm 42 along the wire 44, brings the galvanometer back into balance, the corresponding movement of the shaft 4| operating the recording arm 38.

According to'the present invention, I make use of this type of instrument by mounting on the shaft 4| a mercury switch indicated in its entirety by reference numeral 66. The switch 6|] includes a tube 6| containing a globule of mercury and having at each end a pair of

constant points

63, 64 and 65, 66. The leads 64 and 65 are connected to a wire 61, and wires 68 and 69 are connected, respectively, to the

contacts

63 and 66. A first relay 1| may be connected between the wires 61 and 68, and a second relay 12 may be connected between the wires 61 and 69.

Thus, when the temperature at the tip of the burner increases, this would indicate that more decelerant would be required, and the resulting unbalance of the galvanometer circuit would cause the shaft 4| to swing in one direction thus closing oneof the pairs of

contacts

63, 64 or 65, 66. This would'actuate one of the relays which is connected to any control apparatus desired, such a valve mechanism, for adding more de-r celerant to the system. Conversely, if the temperature at the tip begins to fall, the resulting unbalance of the galvanometer circuit would result in the shaft 4| turning in the other direction, thereby actuating the other relay which can be connected to close the valve, thus diminishing the amount of decelerant added.

The present arrangement is also admirably adapted to control the composition of the gas by controlling the amount of carbureted water gas to be added to the system to supplement the regular gas mixture as explained above. Since the addition of carbureted water gas to the usual mixture may produce a different burning gas, it is particularly important that the station, adding its make gas to that received from the main plant for distribution, know or have an indication or registration of the amount of carbureted water gas already added to the mixture which is received at the station.

The present invention is admirably adapted for use at such stations since it is a simple matter to connect a line from the gas supply to the inlet 3 of the burner I. Then, after the gas is ignited and the burner temperatures become stabilized, the indications on the galvanometer 22, or the controlling operations effected by the instrument 35, can be used to prevent an inadvertent addition of excessive quantities of make gas by the stations to the gas supply received from the main source. Ordinarily, a Bunsen burner is capable of burning satisfactorily under wider conditions of gas variations than the burners of most appliances, and in operation I arrange the control mechanism of Figure 3, or cause the operation of the usual controls under the guidance of the apparatus shown in Figure 1, so that the temperatures indicated or recorded fall within limits that experience has shown result in a satisfactory gas for distribution to the consumers. For example, when measuring the amount of carburetted gas that has been added, as indicated in the chart of Figure 2, the point a should not be exceeded, since generally no more than around 55% of carburetted water was at 800 B. t. u. should be added to base gas at 800 B. t. u. This may of course vary, depending on conditions an other factors.

The control apparatus shown in Figure 3 may .be used to govern such other factors as gas-air proportioning, pressure and the like. For example, the controlling apparatus shown in Figure 3 may be arranged to control flame height, that is, height of the inner cone. In some industrial installations, such as automatic can forming machines, it is very essential to have the inner cone maintained at a constant height, and by the use of the present invention the potentiometer shaft 4! may be connected to any suitable controlling means, such as through the relays H and 12, to control the gas-air proportion to maintain the height of the inner cone constant. This may be done by connecting the relays H and 12 to some form of motor device for determining the amount of air added. Also, the control apparatus of the present invention can be arranged to control the pressure at which the gas supply is delivered to the customers mains or appliances. Heretofore, relatively elaborate apparatus is required to maintain the pressure constant, but according to the present invention, it would be necessary merely to connect the relays H and 12 to some form of motor valve. Thus, a change in temperature at the burner tip would result in unbalancing the galvanometer circuit momentarily which, as described, would energize or actuate one or the other of the relays to secure a readjustment of the motor valve.

It will be obvious, of course, that forms of controlling means other than that shown in Figure 2 may be incorporated with the test or control burner, and likewise various forms of burners may be employed in carrying out the principles of my invention. For example, in Figure 4 I have shown a more or less conventional Bunsen burner H! having a gas inlet ll and an adjustable sleeve 12 having one or more primary air inlets I3, being substantially the construction indicated in Figure 1. A thermocouple I6 is arranged within the burner tube just above the inlet for the gas and the primary air, and the hot thermocouple I5 is connected to a screen 11 supported in any suitable manner above the end of the burner tube in such a manner that the screen becomes the tip of the burner, since each small opening in the screen has its own flame cone. The thermocouples l5 and I6 are connected difierentially by leads I9, 20, and 2|, either to an indicating galvanometer such as the one indicated at 42 in Figure 1, or a recording or control apparatus such as that shown at 35 in Figure 3.

The construction indicated in Figure 4 has slightly different operating characteristics as compared with the type of burner shown in Figure 1 having the tip I and an insulated sleeve In. In Figure 4, the screen 11 is especially responsive to changes in the flame characteristics and is insulated from the burner tube by an air space indicated at 83.

As mentioned above in connection with Figure 1, some form of insulation is usually provided between the burner tip, that is, that part whose temperature responds to flame conditions which, in turn, is responsive to various characteristics of the gas-air mixture being burned. The insulation is desired in order that there should not be too great a flow of heat from the tip end of the burner to the other portions and particularly from the main body of the tip to the surrounding atmosphere. Figure 5 illustrates a construction in which the conventional Bunsen burner 10 is employed and the thermocouples l5 and I6 connected, respectively, to the tip end of the burner tube and adjacent the lower end as in the previously described constructions. In order to prevent too great a heat loss from the burner tube to the surrounding atmosphere, the construction shown in Figure 5 embodies a sleeve 86 that surrounds the tube 85 and is formed of insulating material of any suitable kind which is satisfactory at the temperature encountered. The insulating sleeve is held in place by a cap screw 81 and extends up to a short distance from the tip end of the tube 85. The amount of the tube exposed determines the portion of the tube that receives heat from the flame and therefore the position of the sleeve determines to some extent the range of temperatures which any given change in the gas will cause. The thermocouples I5 and [6 are connected differentially in the same manner shown in Figures 1 and 3. As will be apparent, the sleeve 86 may be adjusted vertically to vary the area of the burner tip exposed to the heat of the flame.

Under other conditions it may be desirable to provide the test or control burner with means for dissipating heat from the burner tip, rather than insulating means or other mechanism for lessening the heat flow away from the burner tip to which the thermocouple is connected. Figures 6 and 7 illustrate an arrangement of this kind in which the burner carries a screen heat dissipator 90. Preferably the screen 90 is in the form of a sleeve or cylinder having a number of convolutions, the inner portion of which are secured in any suitable manner to the end of the burner tube. While the primary purpose of the sleeve 90 is to dissipate heat from the tip of the burner, it will be observed, particularly from Figure '7, that there is, nevertheless, a fairly substantial area of material exposed to the radiant heat emitted from the flame, and therefore the burner shown in Figures 6 and '7' readily responds to changes in the amount of radiant heat in the flame.

Figure 8 shows a slightly different form of burner but one which, for all practical purposes, is quite similar to the type of burner shown in Figure l. A tip 95 is provided with a flared portion 95 which encircles the upper end of the burner tube 91 and is carried thereby through the medium of small pins 98 or the like. This construction prevents too great a heat flow from the tip 95 down to the burner tube 91. However, the tip sleeve 95 has sufficient area disposed to the flame so as to be responsive to a large degree to the amount of radiant heat emitted by the flame.

Under, other conditions it may be desirable to provide a burner which is especially adapted to respond to radiant heat, and, as shown in Figure 9, to this end I provide the burner 10 with a flat disc or auxiliary ring lfll secured by welding or'the like to the tip end of the burner so as to present a relatively great area to pick up the radiant heat rays emitted by the flame. The thermocouples l5 and l6in the form of the invention shown in Figure 9 are connected in the usual manner. If desired, however, the thermocouple I5 may be secured to the ring l0]. To a certain extent the disc [0| also acts to dissipate heat from the burner tube, and therefore the gas but each has its own' range of temperatures. However it was found in all cases that temperature changes followed a definite well defined curve for changes in gas mixtures, and that the curve shown in Figure 2 is representative of the response of burner temperatures to changes in flame characteristics.

If desired, any of the above described burners may be equipped with a shield surrounding the same with air inlets at the lower end and the shield extending upwardly far enough to inclose the flame and prevent the latter from being affected by drafts or currents of air in the surrounding atmosphere. Such a shield is indicated in Figure 3 by the reference numeral H0 and includes a shell III carried by the base of the burner, or by any other suitable means; and which has one or more inlet openings H2 to pro vide for a flow of air to the .primary air inlets 26. Preferably, the shield extends upwardly beyond the flame, and as will be clear, a shield may be and preferably is provided for each of the burners shown in the other figures.

From the above description it will therefore be apparent that, according to the present invention, simple but accurate means is provided for ascertaining changes in the characteristics of the gas by measuring temperature changes at a given point on the burner, the temperature at which given point varies as follows:

As the flame velocity of the particular gas mixture varies, since an increase in the flame velocity, other factors remaining the same, will cause the flame, in effect, to burn closer to the tip where the temperature measurements are made;

As the heating value of the gas, since the hotter the flame the greater will be the temperature at the tip of the burner, other factors remaining the same; and

As the constituents of the gas, especially those which affect the radiant heat emitted from the flame, which may vary even though the total heat value of the flame might remain constant.

What I claim, therefore, and desire to secure by Letters Patent is:

1. Apparatus for comparing combustion characteristics of different combustible gases and mixtures thereof comprising a burner tube having air and gas inlet means, a pair of differentially connected thermocouples, one being disposed Within the tube adjacent said inlet means and the other being disposed on the tube adjacent its outer end so as to measure the temperature rise of said outer end of said tube due only to the combustion of air and gas by the burner, and a temperature modifying sleeve surrounding said tube between said thermocouples.

2. Apparatus for comparing combustion characteristics of different combustible gases and mixtures thereof comprising a burner tube having air and gas inlet means, a pair of differentially connected thermocouples, one being disposed within the tube adjacent said inlet means and the other being disposed on the tube adjacent its outer end so as to measure the temperature rise of said outer end of said tube due only to the combustion of air and gas by the burner, and a heat insulating sleeve surrounding said burner tube for a substantial portion of its length, a portion of said tube to which said other thermocouple is connected being exposed beyond the outer end of said insulating sleeve.

3. Apparatus for comparing combustion characteristics of different combustible gases and mixtures thereof comprising a burner tube having air and gas inlet means, a pair of differentially connected thermocouples, one being disposed within the tube adjacent said inlet means and the other being disposed on the tube adjacent its outer end so as to measure the temperature rise of said outer end of said tube due only to the combustion of air and gas by the burner, and a sleeve of screen-like material having ex-- tensive superficial area and secured in heat transmitting relation to the outer end of said tube for radiating heat therefrom.

4. Apparatus for comparing combustion characteristics of different combustible gases and mixtures thereof comprising a burner tube having air and gas inlets, a plurality of pins carried at the upper end of said tube, a short sleeve supported on said pins in insulated relation with respect to said tube, and a pair of differentially connected thermocouples, one fixed to said sleeve and the other disposed within said burner tube adjacent said inlets so as to measure the temperature rise of said sleeve due only to the combustion of air and gas by the burner.

5. Apparatus for comparing combustion characteristics of different combustible fluids and mixtures thereof comprising, a burner including a tube through which the combustible fluid flows to a flame at one end, metallic means at the base of the flame eflectively heat insulated from the other end of said tube, and means for measuring the temperature rise of said metallic means due only to heat from said flame.

6. Apparatus for comparing combustion characteristics of difierent combustible fluids and mixtures thereof comprising, a burner including a tube through which the combustible fluid flows to a flame at one end, metallic means at the base of the flame, means effectively heat insulating said metallic means from the other end of said tube so that heat received by said metallic means from said flame is concentrated thereat, and means for measuring the temperature rise of said metallic means due only to heat from said flame.

7. Method of determining where to stop in adding a supplementary combustible gas to a base combustible gas having different combustion characteristics than the supplementary gas for supplying burners adjusted to operate satisfactorily using the base gas which comprises: measuring the diflerence between the temperature of a mixture of the composite gas and air in a burner as it flows to a flame and the temperature of a part of the burner exposed to the heat of the flame.

MATHEW G. MARKLE.