Rangetop burner grate for uniform heating during simmer operation

Simmer performance in gas ranges is improved by providing a burner grate with a flame impingement ring centered over the gas burner. The burner grate includes a base and a plurality of fingers attached to the base. The flame impingement ring is attached to all or some of the fingers. The flame impingement ring is sized so that simmer flames from the gas burner will impinge thereon. Thus, the flames are directed away from direct impingement on the cooking utensil, and some heat from the flames is absorbed by the grate. The flame impingement ring can have many cross-sectional configurations including curved, circular, oval or straight.

BACKGROUND OF THE INVENTION 
This invention relates generally to gas ranges and more particularly to a 
burner grate for improving burner simmer performance. 
Household gas ranges typically have a number of gas burners located on the 
cooktop. A burner grate is situated over each burner for supporting a 
cooking utensil such as a pot or pan above the burner. The gas burners 
typically comprise a cylindrical burner head having a plurality of ports 
formed therein. A fuel-air mixture is discharged through the ports to 
produce the flame. 
Adequate simmer performance is an important criterion in gas range burner 
design. Simmer performance is usually defined in terms of the minimum 
stable input rate of the burner; that is, the lowest input rate at which 
the burner is able to support a stable flame. However, the minimum stable 
input rate is not necessarily a good indication of simmer performance. 
This is evidenced by FIG. 1 which shows the local heat flux distribution 
across a typical cooking utensil (nine inch diameter) for five different 
input rates. In each instance, a sharp peak in flux occurs at the point 
where the flame impinges on the cooking utensil. As expected, heat fluxes 
are higher for the greater input rates of 8800 and 4800 BTU/hr. The peak 
heat flux for the input rate of 2500 BTU/hr is approximately 9000 
BTU/hr/ft.sup.2 and occurs about 1.5 inches from the centerline. Reducing 
the input rate to 1500 BTU/hr, which is considered a simmer setting, 
results in only a slight reduction in the peak heat flux. Consequently, 
simmer performance is not significantly improved by this reduction in 
input rate. The local heat flux does begin to drop significantly as the 
input rate approaches 1000 BTU/hr, but most conventional gas burners are 
unable to support a stable flame at input rates this low. 
Accordingly, there is a need for a means to improve the simmer performance 
of rangetop gas burners. 
SUMMARY OF THE INVENTION 
The above-mentioned needs are met by the present invention which provides a 
burner grate comprising a base having a center point, a plurality of 
fingers attached to the base, and a flame impingement ring attached to all 
or some of the fingers. The flame impingement ring is sized so that simmer 
flames from a gas burner will impinge thereon. Generally, the flame 
impingement ring will have an inside diameter which is substantially equal 
to the diameter of the gas burner. The flame impingement ring can have 
many cross-sectional configurations including curved, circular, oval or 
straight. The presence of the flame impingement ring directs simmer flames 
away from direct impingement on a cooking utensil so that there is a more 
uniform distribution of heat flux and simmer performance is improved. The 
flame impingement ring also absorbs heat from the flames and conducts the 
heat throughout the grate. 
Other objects and advantages of the present invention will become apparent 
upon reading the following detailed description and the appended claims 
with reference to the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to the drawings wherein identical reference numerals denote the 
same elements throughout the various views, FIG. 2 shows a burner grate 10 
in accordance with the present invention. The grate 10 comprises a base 12 
and a plurality of utensil-supporting fingers 14. The base 12 is a 
rectangular frame-like member designed to rest on the cooktop of a gas 
range so as to be centered around a gas burner. It should be noted that 
the base 12 is not limited to a rectangular shape; other shapes, such as 
circular, are equally possible. The fingers 14 are attached at one end to 
the top surface of the base 12 and extend radially inward to the center 
point of the base 12. The fingers 14 are thus arranged in a common plane 
above the base 12 so as to be able to support a cooking utensil over a gas 
burner when the grate 10 is positioned on the rangetop. 
A flame impingement ring 16 is fixed to the distal ends of the fingers 14 
so that the center point of the ring 16 is vertically, or axially, aligned 
with the center point of the base 12. As shown in FIG. 2, the ring 16 is 
supported by all of the fingers 14. In this way heat absorbed by the ring 
16 can be conducted to each finger. Alternate configurations are possible. 
For example, the ring 16 could be supported by only the four fingers 
extending from the midpoints of the sides of the base 12, not the fingers 
extending from the corners of the base. The base 12, fingers 14 and ring 
16 are preferably integrally formed to ensure good thermal conduction 
throughout the grate 10, although the ring 16 can also be separately 
attached to all or some of the fingers 14 in a conventional manner such as 
welding as long as there is good thermal conduction. The flame impingement 
ring 16 is preferably made of the same material as the rest of the grate 
10. Suitable materials include cast iron or aluminum or other materials 
with a high thermal conductivity. 
FIG. 3 shows the burner grate 10 situated over a gas burner 18 of a gas 
range. The grate 10 rests on the cooktop 20 of the range in order to 
support a cooking utensil 22 above the gas burner 18. The flame 
impingement ring 16 is centered over the gas burner 18 when the grate 10 
is properly positioned on the cooktop 20. The ring 16 is sized so that 
simmer flames from the gas burner 18 will impinge on the ring. 
Specifically, the inside diameter of the ring 16 is substantially equal to 
or slightly less than the diameter of the gas burner 18, and the outside 
diameter of the ring 16 extends slightly beyond the point where simmer 
flames extend. The ring 16 curves inward and downward so as to be concave 
with respect to the cooktop 20 of the range. The inner rim of the ring 16 
is thus closer to the gas burner 18 than the outer rim. 
When the burner 18 operates at normal input rates (i.e., above simmer), the 
flames (shown in dotted lines) pass beyond the flame impingement ring 16 
and burner performance is unaffected. During simmer operation however, the 
flames (shown in solid lines) are smaller and consequently impinge on the 
ring 16. The simmer flames are thus redirected by the ring 16 away from 
direct impingement on the cooking utensil 22, thereby eliminating the hot 
spot that exists with conventional burner grates as is evident in FIG. 1. 
The result is a more uniform heat flux distribution and better simmer 
performance for a given input rate. In addition, the ring 16 will absorb 
heat from the flames impinging thereon, and this heat will be conducted to 
the fingers 14 and the base 12. Thus, the total heat input to the utensil 
22 will be reduced for a given input rate, further improving simmer 
performance. 
The better simmer performance achieved by the present invention is shown 
graphically in FIGS. 4 and 5. FIG. 4 shows the heat flux distribution that 
occurs with a gas burner operating at an input rate of 1499 BTU/hr with a 
conventional grate. FIG. 5 shows the local heat flux distribution that 
results when using the same burner with the grate 10 of the present 
invention and at an input rate of 1510 BTU/hr. As can be seen, the peak 
heat flux in FIG. 5 is significantly less than that of FIG. 4 and is 
closer to the center. Also, the total heat into the utensil, which is the 
area under the curve, is reduced by the present invention because thermal 
conduction through the grate 10 removes energy from the system, as 
described above. The total heat into the utensil is 1260 BTU/hr in FIG. 4 
and 967 BTU/hr in FIG. 5. 
The flame impingement ring 16 is not limited to the curved cross-sectional 
configuration of FIG. 3; other configurations are possible. For instance, 
FIG. 6 shows a flame impingement ring 116 having a circular 
cross-sectional configuration, and FIG. 7 shows a flame impingement ring 
216 having an oval cross-sectional configuration. These embodiments 
present large thermal masses for absorbing heat. FIG. 8 shows a flame 
impingement ring 316 which is straight in cross-section and angled 
downward with respect to the fingers 14, thereby having a frustoconical 
shape. This ring 316 will tend to distribute simmer flames farther away 
from the center of the cooking utensil. 
The foregoing has described a burner grate which improves the simmer 
performance of a gas range. While specific embodiments of the present 
invention have been described, it will be apparent to those skilled in the 
art that various modifications thereto can be made without departing from 
the spirit and scope of the invention as defined in the appended claims.