This invention relates generally to atmospheric gas burners and more particularly to such burners used in domestic cooking appliances.
Atmospheric gas burners are commonly used as surface units in household gas cooking appliances. Conventional gas burners ordinarily comprise a cylindrical head having a number of ports formed around its outer circumference. A mixer tube introduces a mixture of fuel and air into the burner head. The fuel-air mixture is discharged through the ports and ignited to produce a flame. A significant factor in the performance of gas burners in general is a burner's operating range as measured by the turndown ratio (i.e., the ratio of the maximum fuel input rate to the minimum fuel input rate that will support a stable flame). Operating range is particularly important for gas burners used in gas cooking appliances because such burners are often required to operate over a wide range of inputs.
A burner's turndown ratio is limited by the minimum gas velocity at the burner ports that will support a stable flame. When fuel input is reduced for simmer operation, the gas velocity through the ports becomes lower. Eventually, the gas velocity can become so low as to result in no flame at all or a marginal flame that is prone to being extinguished by disturbances in the surroundings, such as room drafts or oven door slams. The problem is particularly evident in the so-called sealed gas burner arrangements, i.e., burner arrangements lacking an opening in the cooktop surface around the base of the burner to prevent spills from entering the area beneath the cooktop, thereby facilitating easier cleaning of the appliance. Generally, the turndown ratio for such burners with one fuel stream is limited to about 13:1.
One known burner that provides an increased turndown ratio is the dual fuel stream burner, which incorporates two separate burner bodies having individual fuel inputs. Such burners have a central burner body, which is much like a smaller version of a standard cylindrical burner head, encircled by a separate annular burner body having a larger diameter. However, the central burner body does not experience as much external air flow because it is completely surrounded by the outer burner body. Thus, less secondary combustion air is available, and the heat output of the burner is reduced. Other drawbacks of such "dual ring" burners are that they are more difficult to clean and are generally more costly than single body burners.
Accordingly, there is a need for a single body atmospheric gas burner that provides increased turndown ratio.