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Show INTRODUCTION Since the 1970s, public concern over airborne pollutants and their environmental consequences has been driving increasingly strict legislation limiting the permissible levels of toxic emissions. Combustion processes are inherently problematic, producing such pollutants as particulate matter, hydrocarbons, carbon monoxide, sulfur, oxides, and nitrogen oxides to name a few, and as such are a prime contender for environmental regulations. Early laws were focused on reducing the amount of pollutants generated by industry, power plants, and automobiles. As it becomes increasingly difficult and expensive to lower emissions from these sources, emissions from household appliances such as wood burning stoves, two-stroke motors, and water heaters are being scrutinized and regulated. Proposed new legislation will limit nitric oxide, NO, and nitrogen dioxide N02 (know generically as NOx) emissions to below 50 PPM (corrected to 3% oxygen), with the possibility of 25 PPM legislation in the future. As the conventional rack-style burners in current natural gas water heaters utilize rich flames (equivalence ratio ~ > 1.0) with temperatures approaching 2250 K, NOx production is primarily attributed to thermal N Ox generation through the Zeldovich mechanism, with NOx production increasing exponentially with temperature [1]. Once generated, relatively expensive and complex remediation techniques are required to reduce high NOx concentrations to acceptable levels. Since flame temperatures drop with decreasing <1>, one commonly accepted method to reduce NOx emissions is to utilize a lean burning combustion process (<I> < 1.0). With the lower lean flame temperatures (1700-2000 K), total NOx emissions drop due to decreasing thermal NOx generation. Premixing the fuel and air allows for precise control of ~, enabling reductions of NO emissions to 25 PPM or less. The drawback with lean combustion systems is that the flame can be difficult to stabilize. Developed at Lawrence Berkeley National Laboratory (LBNL), the WeakSwirl Burner (WSB) is a new process that solves the problem of lean flame blowoff [2]. Laboratory studies have shown that the operation of WSB is insensitive to small 2 |