Turbulent flame speed for syngas at gas turbine relevant conditions

Modifications of conventional natural-gas-fired burners for operation with syngas fuels using lean premixed combustion is challenging due to the different physicochemical properties of the two fuels. A key differentiating parameter is the turbulent flame velocity, S-T, commonly expressed as its ratio to the laminar flame speed, S-L. This paper reports an experimental investigation of premixed syngas combustion at gas turbine like conditions, with emphasis on the determination of S-T/S-L derived as global fuel consumption per unit time. Experiments at pressures up to 2.0 MPa, inlet temperatures and velocities up to 773 K and 150 m/s, respectively, and turbulence intensity to laminar flame speed ratios, u'/S-L, exceeding 100 are presented for the first time. Comparisons between different syngas mixtures and methane clearly show much higher S-T/S-L for the former fuel. It is shown that S-T/S-L is strongly dependent on preferential diffusive-thermal (PDT) effects, co-acting with hydrodynamic effects, even for very high u'/S-L. S-T/S-L increases with rising hydrogen content in the fuel mixture and with increasing pressure. A correlation for S-T/S-L valid for all investigated fuel mixtures, including methane, is proposed in terms of turbulence properties (turbulence intensity and integral length scale), combustion properties (laminar flame speed and laminar flame thickness) and operating conditions (pressure and inlet temperature). The correlation captures effects of preferential diffusive-thermal and hydrodynamic instabilities. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.