Abstract: A device for burning fuel with air is provided with means for causing partly recirculation of the combustion gases prior to their exit via a preheater. The degree of recirculation may be governed by a parallel path having controllable flow resistance and in which no recirculation occurs.

Abstract: Apparatus for recirculating combustion exhaust gases to the burner region of a Stirling cycle hot-gas engine to lower combustion temperature and reduct NO.sub.x formation includes a first wall separating the exhaust gas stream from the inlet air stream, a second wall separating the exhaust gas stream from the burner region, and low flow resistance ejectors formed in the first and second walls for admitting the inlet air to the burner region and for entraining and mixing with the inlet air portion of the exhaust gas stream. In a preferred embodiment the ejectors are arranged around the periphery of a cylindrical burner region and oriented to admit the air/exhaust gas mixture tangentially to promote mixing. In another preferred embodiment a single annular ejector surrounds and feeds the air/exhaust gas mixture to a cylindrical burner region. The annular ejector includes an annular plate with radially-directed flow passages to provide an even distribution of the air/exhaust gas mixture to the burner region.

Abstract: Fuel is burned in two chambers, the first with excessive air to produce combustion gases containing oxygen and the second using cooled combustion gases from the first to constitute the oxidizing medium. Preferably the proportions of fuel in the two chambers are equal and the combustion gases are cooled to about 800.degree. C.