Slotted Burner for Gas Fireplace

1. Field of the Invention

This invention relates to gas-fired fireplaces and other hearth products and provides a method and apparatus for achieving a yellow, aesthetically-pleasing and realistic flame which closely simulates a wood-burning flame, and which produces low carbon monoxide emissions.

2. Description of Prior Art

Gas fireplaces are becoming increasingly popular in both new home construction and in retrofitting wood-burning fireplaces in existing homes. Popularity of gas fireplaces over traditional wood-burning fireplaces is driven by several factors. Some states and localities have introduced legislation limiting wood-burning fireplaces because of the pollutants generated by burning wood. Wood can also be relatively expensive in some localities, and consumers often merely do not want the inconvenience of storing and transporting wood for a fireplace.

Traditionally, however, gas-fired fireplaces, for example those using natural gas or propane, have not been successful at simulating the appearance of a natural wood-burning flame. Because the velocity and flow rate of gas used in such gas-fired fireplaces remains relatively stable, flames generated by the gas also remain relatively stable and unchanging in appearance, unlike the flickering and rapidly changing flame associated with a wood-burning fire.

Attempts have been made to simulate the appearance of wood-burning fires with gas-fired burners.

U.S. Pat. No. 5,092,313 discloses a gas log fireplace which achieves a high heat output and highly efficient combustion. The fireplace includes a plurality of vertical gas ports and a fibbed heat exchanger positioned above a firebox which enhances heat transfer into the surrounding environment.

U.S. Pat. No. 4,886,445 teaches a gas burning artificial log assembly which includes a burner pan and a burner manifold which form adjustable elongated exit slots that are aligned parallel to artificial logs.

U.S. Pat. No. 4,838,240 discloses a gas burner assembly which includes a gas distribution tile having a plurality of vertical holes which form a honeycomb-like pattern.

U.S. Pat. No. 5,000,162 discloses a gas burner system having decorative gas logs. The burner system includes a plurality of nozzles for producing flames between the logs.

U.S. Pat. No. 4,883,043 discloses a gas-fired fireplace assembly having a plurality of nozzles positioned between artificial logs. The '043 patent indicates that the nozzles are capable of generating yellow flames which simulate a wood-burning fire.

U.S. Pat. No. 4,930,490 discloses a gas log apparatus which includes a ported chamber. The ports are rectangular, and are formed at the apex of a v-shaped ridge. The ports have sharply angled comers. The sharp vertices provide turbulence which the '490 patent indicates produces a ragged yellow and luminous flame.

U.S. Pat. No. 5,081,981 discloses a gas fireplace burner assembly which includes a burner tube that provides a plurality of separate yellow flames of different heights and widths between artificial logs of the assembly.

U.S. Pat. No. 5,320,520 discloses a gas burner assembly for simulating a wood-burning fire. The assembly includes two v-shaped grooves having a plurality of slots in the apex of the groove. Fuel is discharged through the slots and a flow of secondary air is directed into the flames to enhance flickering to simulate a wood-burning fire.

U.S. Pat. No. 5,139,011 discloses an unvented gas-fired heater assembly. A duct assembly directs heated air from the heater assembly into a room.

U.S. Pat. Nos. 4,971,031 and 3,382,861 disclose gas-fired burners which include a plurality of slotted ports through which a combustible gas flows.

It is one object of this invention to provide a method of combustion which achieves a gas-fired yellow flickering flame which simulates the appearance of a natural wood-burning flame.

It is another object of this invention to provide a method of combustion which achieves a flame having a natural wood-burning appearance and produces relatively low carbon monoxide.

It is yet another object of this invention to provide a gas burner which can be used alone or can be integral with a simulated log to produce a flame having a natural wood-burning appearance.

These and other objects of this invention are achieved with a method which includes, according to one preferred embodiment of this invention, introducing a fuel, such as natural gas or propane, into a burner manifold having at least one elongated port at a rate of about 5,000 BTUH to about 30,000 BTUH per square inch of port area. The at least one elongated port has a length-to-width aspect ratio greater than about 10 to 1. According to one preferred embodiment of this invention, the length-to-width aspect ratio exceeds about 100 to 1. From about 0 to about 30 percent by volume of primary air is introduced into the burner manifold. The flame achieved with the method according to this invention produces relatively little carbon monoxide (less than 200 ppm corrected to 0% O.sub.2 in the flue gas), and a yellow flickering flame which realistically simulates a wood-burning flame.

According to another preferred embodiment of this invention, the gaseous fuel is introduced into a burner manifold having a plurality of elongated ports. The elongated ports form at least two parallel rows of elongated ports, and the rows are spaced about one inch from each other. The elongated ports of one row can be in a staggered relationship with the elongated ports of an adjacent row. The multiple rows and relatively close proximity of one row to an adjacent row achieves a novel gas-fired three-dimensional flame appearance which contributes to an overall natural wood-burning appearance.

The gas burner according to this invention can be constructed as a nondecorative manifold whose appearance is hidden by simulated wood logs, or can be constructed as an integral part of a simulated wood log.

The above-mentioned and other features and objects of this invention will be better understood from the following detailed description taken in conjunction with the drawings wherein:

FIG. 1 shows a top view of a burner manifold according to one preferred embodiment of this invention;

FIG. 2 shows a front view of the burner manifold shown in FIG. 1;

FIG. 3 shows a side view of the burner manifold shown in FIG. 1;

FIG. 4 is a graph showing the effect of port loading, slot widths and volume percentages of primary air to theoretically required combustion air on carbon monoxide emissions;

FIG. 5 is a graph showing the effect of multiple slots, volume percentages of primary air to theoretically required combustion air, and the distance between slots on carbon monoxide emissions;

FIG. 6 is a graph showing the effect of port loading, volume percentages of primary air to theoretically required combustion air, and the gap between slots on carbon monoxide emissions;

FIG. 7 is a graph showing carbon monoxide emissions associated with certain Froude Numbers;

FIG. 8 shows a burner manifold according to another preferred embodiment of this invention; and

FIG. 9 is a cross-sectional view taken along line 9--9 of FIG. 8.

Although the relevant parameters of the method according to this invention are referred throughout the specification and claims in certain dimensional units such as BTUH and inches, one aspect of this invention can also be described with reference to a nondimensional number commonly referred to as the Froude Number. The Froude Number is identified as ##EQU1## where Fr is the Froude Number, V is the gas/air mixture exit velocity from the slotted ports in feet per second, g is the gravitational constant 32.2 ft/s.sup.2, and L is the hydraulic diameter of the slot in feet. The Froude Number is used to describe the ratio of the kinetic forces (momentum) to the gravity forces (buoyancy). When the Froude Number is equal to 1, the momentum forces in the fuel/air mixture jet are equal to the buoyancy forces. We have discovered that a burner operating under parameters equivalent to a Froude Number between 0.05 and 4.0 achieves a buoyancy controlled yellow flickering flame which closely simulates the appearance of a natural woodburning flame. The different design parameters can be incorporated into the compact form of Froude Number, which is a design criteria for a yellow flame burner.

FIGS. 1-3 show top, front and side views, respectively, of a burner 18 according to one preferred embodiment of this invention. For the sake of clarity, the burner is shown as having a primarily cylindrical shape, however the burner according to this invention could be designed to have other suitable shapes, such as rectangular, or could even be shaped as a simulated wood-burning log.

Rear pipe 20 contains elongated slot 28 and elongated slot 29. According to one preferred embodiment of this invention as shown in FIG. 1, elongated slots 28, 29 are 0.04 inches wide and 15 inches long, for an aspect ratio of 375:1. However, the burner according to this invention can have as small an aspect ratio as about 10:1. Slot widths can range from about 1/64" to about 9/64".

The port loading of burner 18 according to this invention is in the range of about 5,000 BTUH/in.sup.2 to about 30,000 BTUH/in.sup.2. According to one preferred embodiment of this invention the port loading is in the range of about 15,000 BTUH/in.sup.2 to about 25,000 BTUH/in.sup.2. Burner 18 achieves an aesthetically pleasing yellow dancing flame with carbon monoxide emissions below 200 ppm with a volume of primary air between about 0% and about 30% of the total volume of air required for stoichiometric combustion of the fuel.

While conventional gas-fired burners fire a diffusion flame vertically upward, resulting in a substantially uniform flame pattern, the method and apparatus according to this invention operates to produce a buoyancy controlled flame that rises primarily because of temperature rather than because of the momentum of the fuel.

FIG. 4 is a graph with y-axis values of carbon monoxide emissions and x-axis values of port loading in BTUH/in.sup.2 for a burner with a single slot. The length of the slot is 14 inches. FIG. 4 shows various plots representing slot widths from 0.052" to 0.128" with volume percentages of primary air varying from 10% to 33%. FIG. 4 shows how port loading, slot width and the ratio of primary air to fuel affects carbon monoxide emissions.

FIG. 5 is a graph with y-axis values of carbon monoxide emissions and x-axis values of port loading in BTUH/in.sup.2 for a burner having two slots. Each slot is 14" long and 0.042" wide. The graph shows how carbon monoxide emissions are affected by varying the volume percentages of primary air, the gap between the two slots, and the port loading.

FIG. 6 is graph with y-axis values of carbon monoxide emissions and x-axis values of port loading in BTUH/in.sup.2 for a burner having two slots. Each slot is 14" long and 0.099" wide. The graph shows how carbon monoxide emissions are affected by varying the volume percentages of primary air, the gap between the two slots, and the port loading.

FIG. 7 is a graph with y-axis values of carbon monoxide emissions and x-axis values of Froude Numbers.

FIG. 8 shows another preferred embodiment according to this invention. Burner 18 has top face 38 with a plurality of staggered slots 40, 42. Fuel and primary air are fed to burner 18 through nipple 46. A distance 44 between the upper slot row which includes slot 40 and the bottom slot row which includes slot 42 is in the range of about 0.25" to about 1", and is preferably about 0.5". The staggered slots create a novel three-dimensional appearance to the flame which closely simulates the appearance of a natural wood-burning flame.

FIG. 9 is a cross-sectional view taken along line 9--9 of FIG. 8. Although burner 18 has a triangular cross section, it is understood that burner 18 could have any suitable cross section, including round or rectangular. The three dimensional effect achieved by the staggering and spacing of the slots with respect to each other helps achieve the appearance of a natural wood-burning flame.

While in the foregoing specification this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purpose of illustration, it will be apparent to those skilled in the art that the invention is susceptible to additional embodiments and that certain of the details described herein can be varied considerably without departing from the basic principles of the invention.