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Abstract

A multilayer matrix burner which has exceptionally low NO.sub.x emissions can be operated over a broad turndown range. The burner is, in effect, a three-dimensional matrix of spaced apart emissive layers. There is a first three-dimensional porous layer which acts to distribute a fuel/air mixture. There is a wider gap (which may be adjustable) between the distributive layer and one or more two-dimensional porous emissive layers. An exemplary emissive layer is a refractory wire screen. Preferably, there are multiple such emissive layers with a narrower gap between successive layers. Preferably, the porosity increases in each successive layer downstream from the preceding layer. This arrangement provides a stable flame wherein most of the combustion occurs adjacent to successive incandescent emissive layers. Preferably the successive layers in the downstream direction have a large open area for transmitting radiant energy from preceding emissive layers. Such high intensity burners, e.g. 1,500,000 BTU/h.multidot.ft.sup.2, may be used in water heaters or boilers or in a thermophotovoltaic apparatus which produces both electric energy and heated water. For a thermophotovoltaic application, the matrix burner preferably has a smaller open area than upstream layers for providing a location of highest temperature on the outermost layer.

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