US3324921A - Wick type burner - Google Patents

Description

June 33, 1%67 ax ET'AL WICK TYPE BURNER Filed Feb.

United States Patent F 3,324,921 WECK TYPE BURNER Leonard J. Fox and (Iharles H. Terwilliger, .ln, Lima, Ghio, assignors to Westinghouse Electric Corporation, Pittsburgh, Pin, a corporation of Pennsylvania Filed Feb. 11, 1965, Ser. No. 431,835 2 Claims. (Cl. 1584) The present invention relates to burners, and more particularly to wick type burners for use in various applications such as in energy conversion devices or thermoelectric generators and the like.

Generally, it is desirable that a burner be structurally organized in a manner which provides for durable operation with a minimum requirement for maintenance. For utility purposes, a burner preferably should have the following among other basic properties:

(1) comparatively good burning efliciency in terms of B.t.u.s per unit volume of combustion space.

(2) Flame stability.

(3) comparatively low operating noise.

(4) Adaptability for using a wide range of grades of fuel.

The burning process should result in substantially complete burning of the fuel vapor so that carbonization and associated maintenance problems are minimized while burning efficiency is promoted. If the fuel for the burner is liquid, quality of the vaporization of the fuel and quality of the mixing of the resulting fuel vapor with the oxidant are determinants which if suitably controlled promote achievement of the preferred basic burner properties.

In accordance with the broad principles of the present invention, a burner comprises a combustion chamber and a ceramic wick through which fuel flows for combustion in the chamber. An oxidant or air also flows through the wick so that a fuel-oxidant mixture is emitted from the wick. If the fuel is liquid, fuel vaporization occurs in the Wick so that the emitted mixture is gaseous. Preferably, a secondary flow of oxidant or air is also provided externally along the wick to produce the desired total oxidant flow through the burner with burning occurring along the fuel emitting surface of the wick and within the volume of the combustion chamber. Heat feedback from the flame at the wick fuel emitting surface efficiently promotes fuel vaporization within the wick itself.

The burner operates cleanly since substantially complete burning of the fuel can be achieved with little or no carbonization. Because of the temperature profile which can be achieved along the fuel flow path, leaded gasoline can even be employed over relatively long periods of time substantially without the operational problems normally caused by lead deposits. Flame stability is excellent, operating noise is relatively low, and burning efficiency is markedly improved. Heat produced by the burning process can be carried by the combustion products for transfer to an energy conversion device such as a thermoelectric generator or to any of a variety of other devices for whatever purpose desired.

It is, therefore, an object of the invention to provide a novel burner which operates with improved burning efficiency.

Another object of the invention is to provide a novel burner which operates with a low noise level and a stable flame and which requires comparatively little maintenance.

A further object of the invention is to provide a novel burner in which substantially complete burning of the fuel is achieved with little carbonization.

It is an additional object of the invention to provide a novel burner in which leaded gasoline can be used sub- Patented June 13, 1967 stantially without the annoying problems normally caused by lead deposits.

Another object of the invention is to provide a novel burner in which the vaporization and oxidant mixing of a liquid fuel is accomplished so well that the liquid fuel is burned with the facility with which gaseous fuel is burned in an ordinary burner.

It is a further object of the invention to provide a novel burner which can be readily started without primary or secondary air preheat.

Another object of the invention is to provide a novel liquid fuel burner which can be readily started without preheating the liquid fuel and without supplying the liquid fuel at high pressure through an atomizing spray nozzle.

An additional object of the invention is to provide a novel burner in which gaseous fuels and a wide range of grades of liquid fuel can be used and in which a wide range of fuel-oxidant mixture ratios can be accommodated in the burning process.

These and other objects of the invention will become more apparent upon consideration of the following detailed description along with the attached drawing, in which:

FIGURE 1 shows a vertical section of a burner constructed in accordance with the principles of the invention along with a portion of a thermoelectric generator with which the burner is associated for heat transfer purposes; and

FIG. 2 shows a section taken along the reference line lI-lI of FIG. 1.

More specifically, there is shown in FIG. 1 a burner 19 associated with a thermoelectric generator 12 which is only partly shown. The principal purpose of the burner 10 in this exemplary application is to produce heat for maintaining a high temperature along the inner surface of a hot cylindrical core 14 of the thermoelectric generator 12. A cold plate (not shown) of the thermoelectric generator 12 is suitably maintained at a low temperature and direct energy conversion from heat to electricity is achieved in accordance with theory well known in the thermoelectric art.

The burner It) comprises a combustion chamber 16 formed in this instance by means of a generally cylindrical combustion tube 18 which in turn is preferably formed from a metallic material such as heat resistant stainless steel. At the base of the combustion tube 18, an outwardly extending flange 20 can be provided to secure the tube 18 in relation to the generator hot core 14-.

Supporting means or a support plate 22 is also provided adjacent the base of the combustion tube 18 for the purpose of supporting a refractory or ceramic wick 24 through which a fuel, selected from a large group of possible fuels, is fed for combustion in the chamber 16. The wick 24 in this case is cylindrically shaped and is preferably formed continuously throughout its volume from a felt-like refractory or ceramic material which is sufliciently soft and porous to allow desired incoming flow of the selected fuel. The porosity in turn depends on the density of the felt wick. Commercially available ceramic felt sold under tradenames such as Cerafelt or Fiberfrax can be obtained in a wide range of densities which provide a spectrum of felt materials ranging from very soft fluff-like properties to relatively hard and rigid fiberboard-like properties. As an illustation, a density of Gait/ft. is suitable for use, but greater or lesser densities are also suitable so long as fuel flow can be maintained through the ceramic felt in a :manner now to be described.

Fuel is fed to the wick 24 by fuel feed means 26 such as a suitably supported hypodermic needle 28 from which a capillary "fuel line 30 is extended to feed liquid fuel under predetermined pressure through an opening 32 in the support plate 22 and through wick surface 34 which is preferably continuous with and disposed generally centrally of bottom wick surface 35. If the fuel is liquid as preferred, the injected fuel is vaporized, as will be described, and transported by absorption to annular fuel emitting surface 36 of the wick 24. The emitting surface 36 is preferably continuous and is preferably about the side periphery of the wick 24 for reasons which will subsequently become more apparent.

To assure side directivity in the fuel flow, a baffle plate 38 is disposed on or secured over the top surface of the wick 24. A solid portion 42 of the baffle plate 38 obstructs fuel emission from the wick top surface, and circumferentially spaced lugs 44 extend radially outwardly from the batfle plate solid portion 42 for purposes subsequently to be considered.

A tubular conduit 46 is provided below the combustion tube 18 for feeding the necessary oxidant or combustion air thereto. The wick support plate 22 is formed as an integral end plate of the conduit tube 46 and the fuel line 30 is connected to the plate 22 through the conduit tube 46. Circumferentially spaced openings 48 are provided about the fuel feed opening 32 in the support plate 22, and a portion (say up to 60% of the total required oxidant) of the incoming oxidant (or air) flow in the conduit 46 is thus channeled as primary air into the felt wick 24.

Preferably, the primary air is fed directly into the material mass of the wick 24 through continuous wick bottom surface portions 50, and the primary air then is dispersed throughout the wick volume to aid in vaporizing liquid fuel fed through the fuel line 30 and to mix with the fuel in providing a fuel-air mixture closely conforming to a predetermined desired ratio. The wick 24 thus operates as a mixer as well as a vaporizer. The rate at which the fuel-air mixture is emitted from the wick fuel emitting surface 36 depends primarily on factors such as the fuel feed rate, the wick porosity, the fuel inlet pressure, the primary air flow rate and pressure and the exposed area of the fuel emitting surface 36.

To start the burner 10, a match or other similar source can be ignited and placed near the wick fuel emitting surface 36. At this time total air flow is preferably low to provide a fuel rich mixture,, but there is no need for air preheat nor for fuel preheat in order to start the burner 10. During the starting period it would be normal for a sooty flame to appear. Shortly, however, the total air flow can be increased to provide a very clean and stable flame.

Preferably, the total amount of required air is provided in part by the primary air flow just described and in part by secondary air flow from the conduit 46 through circumferentially spaced openings 52 in the wick support plate 22 into annular space 54 which is disposed about the wick fuel emitting surface 36 and within the combustion tube 18. Secondary air thus sweeps over the emitted fuel air mixture upwardly into the main combustion chamber space above the baflie plate 38. Burning takes place in the main chamber space and to some extent in the annular space 54 where high flame temperatures are experienced at the intersurface boundary between the wick fuel emitting surface 36 and the annular space 54. Heat is thus fed back into the felt wick 24 to aid in vaporization of liquid fuel, but since the wick 24 is insulative a considerable temperature gradient is established between the fuel emitting surface 36 and the fuel inlet surface 34 of the wick 24. Incoming fuel thus experiences a continuous temperature rise and increasing mixture with primary air as it vaporizes, and, if it is a lead-bearing liquid fuel such as leaded gasoline, substantially no or negligibly little lead deposits from in the critical burner areas, namely neither in the feed line 30 nor in the wick 24.

Since the secondary air flows directly and smoothly substantially wtihout obstruction into the main combustion chamber space, excellent mixing of the secondary air and the emitted fuel-air mixture is achieved so that substantial-1y complete burning of the fuel can be realized. Carbonization in most applications can thus be substantially eliminated and, with readily obtained uniformity in the fuel flow, a clean, quiet and stable flame is produced. The circumferentially spaced baffle lugs 44 are to some extent obstructively positioned in the described flow, but since the lugs 44 are in turbulent flame, carbonizing does not result and the lugs 44 thus can be employed advantageously to aid in stabilizing and retaining the flame in the cavity 54. This minimizes the pulsating nature of the flame front and accordingly the noise which is associated therewith.

In some cases, it may be desirable to eliminate secondary air flow and to provide a fuel-air premix. In such case, the baflle plate 38 and the annular space 54 can be eliminated (not shown) with fuel and the total air flow being mixed in the felt wick 24 as it flows generally upward for emission from the top wick surface. In this modiflcation, burning occurs along the top wick emitting surface to provide the advantages of heat feedback described in connection with the burner 10.

A wide range of fuels can be used in the burner 10 and a wide range of burner thermal capacities can be obtained (say from 3000 B.t.u./hr. or less to 100,000 B.t.u./hr. or more). Gaseous as well as liquid fuels such as leaded gasoline, JP-3, JP4, kerosene and light diesel fuels can be used. The lower grade fuels can he used, even though they have poorer vaporability, primarily because of the excellent vaporizing conditions achieved within the felt wick 24. In fact, ]P4 which is a high grade kerosene, can be burned with a very blue flame, much the same as a gaseous fuel, even though no atomizing equipment is employed.

Further, because of the excellent fuel vaporization and mixing achieved, liquid fuels can be burned with combustiOn rates as high as one million B.t.u./hr./ft. of combustion space. This exceeds by a very favorable margin combustion rates commonly achieved in industrial furnaces, namely 100,000 to 200,000 B.t.u./hr./ft. of combustion space. As one practical advantage of the high combustion rate of the burner 10, the combustion chamber can be comparatively reduced in size where compactness in the burner is desired.

The combustion products can be used as desired. In the present case, a cylindrical member 56 is disposed with an open face 58 thereof in the downward direction and with wall 60 disposed between the combustion cham- 'ber wall 18 and the thermoelectric generator core 14. The cylindrical member 56 can be supported in this position by spokes 62 or the like secured to the combustion chamber wall 18. A double pass arrangement through channels 64 and 66 is thus provided for exhausting the combustion products while transferring heat to the thermoelectric generator core 14. In this example, then, the exhaust gaseous temperature in the channel 66 and the hot core temperature tends to be uniform along the height of the burner 10 because of heat transfer from incoming gas in the channel 64 to outgoing gas in the channel 66 through the cylindrical member wall 60.

The following data is given as an example of a typical burner constructed in accordance with the principles of the invention:

The foregoing description has been set forth only to illustrate the principles of the invention, Accordingly, it is desired that the invention be not limited by the embodiment described, but, rather, that it be accorded an interpretation consistent with the scope and spirit of its broad principles,

What is claimed is:

1. A burner comprising a combustion chamber, a support plate adjacent one end of the combustion chamber, a porous ceramic wick supported on the support plate, the support plate having a central opening, means for feeding fuel through said opening to an adjacent surface of the wick, the support plate also having a plurality of other openings, means for directing air to flow through said other openings into the Wick, a baffle plate spaced from the support plate and covering another surface of the wick, the wick having a lateral surface extending between the support plate and the baffle plate and exposed to the combustion chamber, whereby fuel and air are mixed in the wick and emitted from said lateral surface, and means for directing additional air to flow over the lateral surface of the wick.

2. A burner as defined in claim 1 in which the bafile air.

References Cited UNITED STATES PATENTS 3/1966 Brown 158-96 5/1940 Brace 158 10/1945 Hess 158- 7/1948 Trimble et al. 15896 3/1959 Downs 158- 1/1961 Downs 158- 1/1963 Woollen 263- 8/1964 Hottenroth et a1. 158-96 FOREIGN PATENTS 5/ 1964 Canada.

FREDERICK KETTERER, Primary Examiner.

Claims (1)

1. A BURNER COMPRISING A COMBUSTION CHAMBER, A SUPPORT PLATE ADJACENT ONE END OF THE COMBUSTION CHAMBER, A POROUS CERAMIC WICK SUPPORTED ON THE SUPPORT PLATE, THE SUPPORT PLATE HAVING A CENTRAL OPENING, MEANS FOR FEEDING FUEL THROUGH SAID OPENING TO AN ADJACENT SURFACE OF THE WICK, THE SUPPORT PLATE ALSO HAVING A PLURALITY OF OTHER OPENINGS, MEANS FOR DIRECTING AIR TO FLOW PLATE THROUGH SAID OTHER OPENINGS INTO THE WICK, A BAFFLE PLATE SPACED FROM THE SUPPORT PLATE AND COVERING ANOTHER SURFACE OF THE WICK, THE WICK, HAVING A LATERAL SURFACE EXTENDING BETWEEN THE SUPPORT PLATE AND THE BAFFLE PLATE AND EXPOSED TO THE COMBUSTION CHAMBER, WHEREBY FUEL AND AIR ARE MIXED IN THE WICK AND EMITTED FROM SAID LATERAL SURFACE, AND MEANS FOR DIRECTING ADDITIONAL AIR TO FLOW OVER THE LATERAL SURFACE OF THE WICK.

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