Numerical and Experimental Investigation of Laminar One-Dimensional Counter-Flow Flames Using Product Gas From Pyrolysis and Gasification of Woody Biomass

Abstract

Further advances in the utilization of biomass-based gaseous fuels in combustion systems require a deeper understanding of the combustion chemistry behind, as well as of the coupling of the chemistry with physical phenomena such as turbulence. The former is investigated in the present study combining both experiments with numerical simulations of different types of laminar non-premixed flames (sooting and non-sooting) in a counter-flow setup. The focus is put on synthetic gas mixtures, resembling, to different extents, typical compositions of the product gas obtained in biomass gasification consisting of CH₄ (reference) and CH₄ mixed with CO₂, N₂, O₂, and/or H₂, always. The oxidizer in all cases is air. A wide range of air-fuel ratios is considered. The influence of the product gas composition on the flame behaviour and flame structure with respect to the changes of the species profiles and peak temperatures with changing flow velocities is discussed. Laser-based spectroscopy techniques, in particular laser-induced Rayleigh scattering and laser-induced fluorescence (LIF), are applied as diagnostic tools. The former can provide an accurate understanding of temperature distributions, while the latter helps to identify the flame front through the tracking of intermediate species, such as CH₂O (formaldehyde). Additionally, CH* chemiluminescence contributes to localize the flame front. Lastly, the influence of the N₂-shroud flow velocities and diameters, as well as resulting buoyancy effects due to a raise in temperature, are taken into account. In correspondence to these experiments, the flames are numerically simulated by an in-house time-dependent implicit Fortran code.