Gas broiler

An oven broiler is provided with an elongated stoichiometric burner having two rows of apertures from which emerge free turbulent gas jets entraining the stoichiometric quantity of combustion air before merging on account of the spacing between the apertures being proportional to the aperture diameter, the ratio of the Rankin temperature of gas and air; a curvilinear radiator shield is heated by the combustion products and directs radiation away from the burner, and a second shield is heated by the combustion products flowing off the first shield.

BACKGROUND OF THE INVENTION 
My co-pending patent application Ser. No. 796,424 describes my 
stoichiometric burners and presents an expression for the stoichiometric 
aperture spacing. The stoichiometric spacing equation is exact, provided 
that the temperatures of the air and gaseous fuels are identical. This 
however is not the case in oven broilers. 
The sole purpose of this application is to develop an equation for the 
stoichiometric aperture spacing of burners which will operate in a gas 
broiler whenever the air and gaseous fuel temperatures differ. 
The stoichiometric air-to-fuel gas ratio is the most fundamental parameter 
in determining the stoichiometric aperture spacing. Under the assumption 
that the temperatures of fuel gas and air are equal, I found that a 
stoichiometric burner should be constructed to have a gas fed burner 
chamber with a flat top having a two dimensional array of apertures of 
diameter d.sub.0 wherein the linear spacing between these apertures should 
be given by the equation D.sub.s =2.42Rd.sub.0, wherein R is the 
air-to-gas ratio, representing the relative amount of air entrained by the 
free turbulent gas jets emerging from these apertures before the jets 
merge at some distance from the burner plane. For a specific distance 
D.sub.s, the jets merge when the amount of air that has been entrained is 
such that R is the stoichiometric air-to-gas ratio as needed for complete 
combustion. I found that if the spacing is smaller by just a few 
percentages as compared with the desired value for true stoichiometry, the 
combustion becomes drastically incomplete. I further found that a spacing 
D.sub.s being about 15 percent or more larger than the stoichiometric 
spacing, the air-gas mixture is too diluted for maintaining a temperature 
sufficient for combustion. Thus, the spacing of the aperture should be as 
close as feasible to the stoichiometric spacing, permitting roughly a 
tolerance range from about -1 percent to less than +15 percent. 
The stoichiometric ratio is a volumetric ratio. However, the densities of 
air and gaseous fuels are temperature dependent. The densities of these 
gases are inversely related to their absolute temperatures. In other 
words, the product of the densities and Rankine temperatures of the same 
gas is equal to a constant. The density of air at 70.degree. F. which is 
530.degree. F. on the absolute scale, is 0.075 lbs/ft.sup.3. Thus, the 
arbitrary constant becomes 0.075 .times. 530 = 39.75. 
The density of a specific natural gas is 0.0465 lbs/ft.sup.3 at 530.degree. 
Rankine. Thus, the arbitrary constant for the gaseous fuel is 0.465 
.times. 530.degree. = 24.65. Thus, the densities of air and gaseous fuels 
can be expressed by the following equation, namely: 
EQU .lambda..sub.A = 39.75 T.sub.R and .lambda..sub.G = 24.65 T.sub.R 
where 
.lambda..sub.A and .lambda..sub.G are the densities of air and gaseous 
fuels in units of lbs/ft.sup.3 and T.sub.R is the absolute Rankine 
temperature. 
DESCRIPTION OF THE INVENTION 
In accordance with the present invention, I found therefore that in order 
to maintain stoichiometric conditions, I must modify the spacing of the 
apertures in a two dimensional but elongated array of apertures in a gas 
fed burner chamber of a broiler, because the burner chamber in a broiler 
operates in a strong radiation field which heats the burner surfaces 
therein and also heats the surfaces in the broiler compartment and, 
therefore, the gas, while the air temperature remains low. I found that 
the stoichiometric spacing of the apertures of a two dimensional array of 
apertures in the burner top is given by the equation 
EQU D.sub.s = 2.42 .times. R d.sub.o .times. T.sub.RG /T.sub.RA 
where R is the air-gas ratio, d.sub.o is the aperture diameter, and 
T.sub.RG /T.sub.RA is the Rankine temperature ratio of the gaseous fuel to 
the combustion air temperatures. The permissible deviations from the true 
stoichiometric spacing as given by this equation should also not exceed a 
few percents on the down side, preferably not more than on the up side, 
the deviation should be less than about + 15%. 
In order to control the temperature of the gas, I found that the radiation 
field requires particular design. In the preferred embodiment I use a 
primary and a secondary radiator. The primary radiators used in my earlier 
broilers used V-shaped radiators. The V-shaped radiators, however, 
produced two dark banks on the toasted bread which occurred opposite the 
center of the sides of the V-shaped radiator. 
To solve this problem, I changed the primary radiator to a curvilinear 
surface. The curvilinear primary radiator produced an excellent toast 
test. 
The A.G.A requires a bake test where two cakes must have a uniform color 
and surface texture. My broiler did (without the secondary radiator) not 
produce a satisfactory cake test. The cakes contained pockets of steam 
inside the cakes and the surface of the cakes was not smooth, and the 
edges of the cakes were cracked. The reason why the cakes were 
unsatisfactory was because the cakes were too hot. 
In order to solve this problem, I had the secondary radiator blasted with 
grit and sprayed with a thick coating of aluminum. The purpose of using an 
aluminum coating was to reduce the emissivity to about 0.05 to 0.10. I 
also found that the reflectivity of an aluminum plate is about 90%. Thus, 
this aluminum plate would reflect this quantity of radiation emitted by 
the top surface of the secondary radiator. 
I found that the cake test with these changes produced perfect cakes. I 
also found that the toast test was very satisfactory and the time required 
was 3.15 minutes. The prior art broilers required 6.3 minutes. 
My stoichiometric burner has an aperture array which will produce a uniform 
radiation field. The aperture array is shown in FIGS. 2 and 3. I inserted 
thermacouples in each end of the burner and found that the average gas 
temperature was 1020.degree. R. I then measured the combustion air 
temperature and found that the air temperature was 805.degree. R. 
Thus, the aperture spacing is given by the equation 
EQU D.sub.s = 2.42 .times. 1020/805 .times. 0.016 
EQU so D.sub.s = 2.42 .times. 1.27 .times. 0.016 = 0.492 
My oven-broiler required only 11 minutes to broil 2 spencer steaks which 
were one inch thick and weighed 0.65 pounds each. The steaks were nicely 
browned with charred points and fat frizzled. There was no gray 
appearance. The steaks were juicy and pink inside for medium and were also 
juicy when well done. 
The prior art oven-broiler has no value whatsoever. Its gas consumption was 
6.75 cubic feet. My stoichiometric burner consumed 4.14 cubic feet of 
natural gas, which represented an energy saving of 38.6%.

FIG. 1 shows an elevation of the stoichiometric burner with a burner 
chamber 22 and the gaseous fuel inlet 21. The free turbulent jets 5 
entrain the combustion air, and coalesce in the stoichiometric demarcation 
plane 7. A primary radiator 11 having a curvilinear form and a nose which 
prevents the radiation from excessively heating the top surface of the 
stoichiometric burner is disposed above the burner 22. The radiation from 
the nose of the primary radiator 11 is also very effective in producing 
uniform radiation field in addition to the radiation from the curvilinear 
surface. A secondary radiator 12 is disposed above primary radiator 11 and 
extends farther to both sides. Radiator 12 is grit blasted and then 
sprayed with molten aluminum as mentioned previously. The flat plate 14 
reflects the radiation which is emitted by the secondary radiator 12. 
After ignition, the combustion products 9 impinge on the primary radiator 
11 first and heat it to a red heat. The radiation from this primary 
radiator heats the burner chamber 22 and the gaseous fuel flowing in the 
chamber 22. The combustion products 9 flowing laterally have a much lower 
temperature when they reach the secondary radiator 12. The secondary 
radiator 12 with its much larger area produces a quantity of thermal 
radiation produced by the primary radiator 11 will provide a uniform 
radiation field on the broiler pan 3. The vertical dimensions of the 
assembly are disturbed in that broiler pan 3 is of course spaced farther 
down underneath the burner 22. 
FIG. 2 shows an array of apertures 23 which array produces a uniform 
temperature on the primary radiator 11. This is accomplished by reducing 
the number of apertures in the central region. The linear spacings between 
the apertures 23 of the burner follows the rule outlined above. The array 
shown in FIG. 3 follows the same pattern including the spacing, but the 
number of apertures is reduced. I found this to be advantageous for 
reducing the gas consumption. 
While I have described a preferred embodiment of the invention in 
considerable detail for the purpose of illustration, it should be 
understood that the invention is not restricted to the specific details 
which I have shown.