US2812015A

US2812015A - Combustion and flame detecting

Info

Publication number: US2812015A
Authority: US
Publication date: 1957-11-05
Anticipated expiration: 1974-11-05

Description

Nov. 5, 1957 c. D. M cRAcKEN COMBUSTION AND FLAME DETECTING APPARATUS Filed April 30, 1954 INVENTOR. CALvm D. MAQLRMKEN ATTORNEY.

United States Patent COMBUSTION AND FLAME DETECTING APPARATUS Calvin D. MacCracken, Tenafly, N. 1., assignor to Jet- Heet, Inc., Englewood, N. J., a corporation of New York Application April 30, 1954, Serial No. 426,860

1 Claim. (Cl. 15828) This invention relates to improvements in combustion devices having flame detecting apparatus, and particularly to flame detecting apparatus of the so-called flame electrode type.

This application is, in part, a continuation of my copending application Serial No. 145,531, filed February 21, 1950, now Patent No. 2,705,530, granted April 5, 1955.

As is well known, ionization of the heated air in a flame or the like makes it possible to pass a rectified electric current through the flame between a pair of electrodes contacted by the flame. In combustion apparatus, this phenomenon has been used for flame detection by mounting an electrode to project into the path of current between the electrode and the chamber wall and through the associated electric circuit is utilized as a control means for maintaining the supply of fuel to the burner. If the flame should be extinguished for any reason, the resulting interruption in electric current flow will cause the control circuit to react in such a fashion as to shut off the supply of fuel.

One of the problems that has been encountered with flame detecting apparatus of this type, especially when operating in an oil flame, is the tendency for carbon to collect on the detecting electrode. After a suflicient period of time, enough carbon may build up to bridge the space between the electrode and its companion element in the electric circuit so that current flows continuously whether or not there is a flame in the area. If the electrode is located in a part of the flame that is hot enough to prevent carbon formation, the temperature is so high that the electrodeis liable to be burned off.

It is, accordingly, among the objects of the present invention to provide an improved combustion device having flame detecting apparatus of the flame electrode type wherein the formation of carbon deposits on the electrode are avoided and yet the electrode is adequately protected against deterioration due to overheating.

In accordance with a preferred embodiment of the invention, the foregoing and other related objects and advantages are obtained in a flame producing and detecting apparatus wherein the flame electrode is mounted in a part of a combustion chamber that is lined with refractory material. The refractory material becomes heated sufiiciently to burn off any carbon on the electrode by radiant heat. In order to prevent overheating, an air space is provided around the flame detecting electrode mounting where the latter passes through the refractory in order to allow cooling air to flow over the electrode.

A more complete understanding of the invention can be had by reference to the following description of illustrative embodiments thereof, when considered in connection with the accompanying drawing, the single figure of which is a section view of a burner apparatus having a flame detector embodying the invention.

"ice

Referring to the drawing, the fuel burner there illustrated comprises an oil burner provided with a liquid fuel nozzle or atomizer 10 of the return-flow type having a supply pipe 12 and a return pipe 14. The atomizer 10 supplies fuel oil in the form of a fine cone-shaped spray. The fuel burner further comprises a pair of

cylindrical sleeves

16, 18 disposed one within the other and held in spaced coaxial relation by a circular, dished-shaped end wall 20 having its outer portion formed into a circular channel 22 which cooperates with the edges of the

sleeves

16, 18 and is secured thereto in any suitable way. The end wall 20 is provided at its center with an opening 24 through which the fuel spray from the atomizer enters the combustion space defined by the inner sleeve 16. Mounted on the end wall 20 is a casing 26 which houses the atomizer.

The inner sleeve 16 of the fuel burner is perforated with a large number of small holes 28, and is also provided with several series of circularly arranged larger holes 30. The purpose of the small holes 28 is to permit air to seep through the inner sleeve 16, thereby providing on its inside surface a layer or cushion of air for the purpose of preventing carbon formation, as is explained in applicants copending application Serial No. 277,185, filed March 18, 1952, now Patent No. 2,692,014, granted October 19, 1954. The larger holes 30 in the inner sleeve admit freely not only the air necessary to support substantially complete combustion of the liquid fuel, but also additional air which dilutes the gaseous products of combustion. An ignition device 32 of any well known form is shown as extending through aligned openings in the

sleeve

16, 18 into the combustion space within the inner sleeve.

The combustion space defined by the inner sleeve 16 is extended by a cylindrical sleeve 34 of refractory material. The sleeve 34 is fabricated of refractory cement and'may be molded for additional strength on a wire mesh 36 inside a casing 38. The outer diameter of the refractory sleeve 34 is substantially the same as the diameter of the outer sleeve 18, while the inner diameter of the sleeve 36 is slightly greater than that of the inner sleeve 16. The refractory terminates a short distance from the end of the inner sleeve 16, with the gap between inner sleeve 16 and the refractory sleeve 34 being bridged by a metal collar 40 provided by a reduced diameter portion of the casing 38. The collar 40 has the same diameter as the inside diameter of the refractory sleeve, and overlaps the end of the inner sleeve 16. The sleeve 38 is held in place by struck-out portions 42 of the collar 40 which engage the inner sleeve 16, thereby maintaining the collar and the sleeve in accurate coaxial alignment with a small annular space 44 between sleeve and collar.

The fuel burner is located within a casing 46 to which air is supplied under pressure through an inlet 48 from a blower (not shown). This air enters the annular space 50 between the inner and outer sleeves, as indicated by the arrow a. The major portion of the air enters the combustion chamber through the opening 30 in the inner sleeve, while some of the air seeps through the smaller openings 28. By passing through'the annular space 50 between the

sleeves

16, 18, the air absorbs heat from the inner sleeve 16 before passing into the combustion chamber, and also serves to moderate the temperature of the outer sleeve 18. The combustion products flow out of the burner through the refractory sleeve 34.

The novel manner in which a flame electrode is mounted in the combustion chamber will now be described. The flame electrode is shown as comprising a rod 52 of suitable heat-resisting and current-conducting material, such as a compound containing silicon carbide and free silicon. The rod 52 is'mounted in and projects through a sleeve portion 56 from which arms 58 project.

54 f insulating material, such as porcelain. Secured to the porcelain sleeve 54 is a metal spider having a hub These arms 58 are provided with angularly extending ends 60 having perforations through which extend screws 62 which enter threaded holes in a flange 64 which is secured to the outer face of the sleeve casing 38 in any suitable manner, as by spot welding. It will be noted that an annular space 66 is provided between the porcelain sleeve 54 and the wall of the opening in the refractory lining 34 of the combustion chamber. It will also be noted that the opening through the flange 64 is of larger diameter than the diameter of the porcelain sleeve 54. Therefore, air is permitted to flow into the combustion .chamber through the annular space 66, thereby cooling the porcelain sleeve 54 which is, of course, subjected to heating by the flaming gases in the combustion chamber. In this way, cracking and sooting of the porcelain sleeve 54 of the flame electrode is prevented, and the rod 52 of the flame electrode is supported in the path of the flaming gases. Experience has proved that, when the flame, electrode is thus mounted in the wall of the combustion chamber, the flame electrode functions satisfactorily to permit the passage of a rectified electric current (in a control circuit not shown) through the rod 52 and the ionized space within the combustion chamber to any exposed metal part, such as the end of the inner sleeve 16 of the fuel burner. At the same time, the radiant heat of the refractory effectively prevents formation of carbon deposits on the porcelain 54 or on the electrode 52, while the air space provides a cooling air current which prevents burning of the electrode. Also, the air space allows air to flow past the electrode after the burner is shut down but while the blower is still operating. This blows away any air ionized by the refractory, which ionized air otherwise might pass current and give a false indication of flame in the combustion chamber.

I claim:

In a combustion and flame detecting apparatus including a liquid fuel burner of the type comprising a housing to which air is supplied under pressure and which encloses a pair of cylindrical sleeves which are closed at one end and open at the other end, said sleeves being disposed one within the other in spaced coaxial relation, and said burner further including an atomizing nozzle at said closed end of said sleeves for discharging atomized liquid fuel into the inner one of said sleeves, said inner sleeve having side openings therein for admitting said air supply to said housing into'the space inside said inner sleeve, the improvement which comprises the combination with said burner of an open-ended sleeve of refractory material extending through a wall of said housing from the open end of said inner sleeve as a continuation thereof, said refractory sleeve having a side opening therein intermediate the ends thereof and within said housing, a flame electrode, a sleeve of insulating material enclosing a portion of said electrode, said insulating sleeve having smaller cross-sectional dimensions than the corresponding crosssectional dimensions of said opening, said insulating sleeve being supported in said opening and spaced from said refractory material, with said electrode extending into the space inside said refractory sleeve, whereby to expose said electrode to radiant heat from the inner surface of said refractory sleeve to prevent the accumulation of carbon deposits from said electrode and to provide for the flow of cooling air from said housing through the space between said insulating sleeve and said refractory material.

References Cited in the file of this patent UNITED STATES PATENTS 1,899,744 Briesky et a1 Feb. 28, 1933 2,173,115 Hutto Sept. 19, 1939 2,282,551 Yates May 12, 1942, 2,538,952 Yates et al. Jan. 23, 1951 2,541,236 Giuffrida Feb. 13, 1951 2,698,655 Meredith Jan. 4, 1955