Study on the combustion process of premixed methane flames with CO 2 dilution at elevated pressures

Abstract

The article presents the results of experimental and numerical investigation of turbulent premixed methane flames diluted by carbon dioxide (up to 30%) at atmospheric and elevated pressures (up to 0.5 MPa). The study included the influence of fuel properties and operation parameters on the emission of NO x and CO as well as flame properties. The investigation has been prepared for two combustion system configurations (axisymmetric flames and flames supported by a pilot flame) in a wide range of air/fuel equivalence ratios (φ = 0.42 ÷ 0.85). It has been reported that reduction of NO x emission by CO 2 fuel dilution reached a level of up to 45% in atmospheric conditions and 30% at elevated pressure, decreasing with a drop in the equivalence ratio. The results have shown influence of pressure on NO x composition, where for pressurized tests, NO 2 was doubled compared to atmospheric tests. Carbon monoxide emission rises with CO 2 content in the fuel as a result of thermal dissociation, but this phenomenon is mitigated by a pressure increase. Planar laser induced fluorescence (PLIF) study has shown that flame length decreases with an increase in pressure and CO 2 content in the fuel. Fuel staging increased NO x emission, especially for richer flames (φ > 0.6) at low pressure, while CO increased in the whole range of equivalence ratios.