An Experimental Study on Combustion of an Ultralean-Fuel and Air Mixture by Heat Recirculation

Abstract

An experimental study was carried out on the excess enthalpy burning of an ultralean-methane/air mixture using a heat- recirculating burner. The flame-stability limit, the gas temperatures and the chemical composition of the burnt gas were examined, while the flame behavior was carefully observed. The conclusions obtained were as follows : (1) Almost completely burnt gases are produced with a negligibly small amount of nitrogen oxide. (2) If the combustion of the mixture is incomplete in the combustion chamber and the residual of the mixture burns secondarily in the hot part of the heat exchanger downstream of the combustion chamber, the temperatures of both the preheated mixture and the flame drop. (3) The flame blows off prior to the approach to the proper limit of flammability for the preheated mixture, and flame stabilization in the combustion chamber is important since the mixture at the blowoff limit is still flammable.