An experimental and numerical investigation of premixed syngas combustion dynamics in mesoscale channels with controlled wall temperature profiles

Abstract

The dynamics in H2/CO/O2/N2 premixed combustion was investigated experimentally and numerically in a 7-mm height mesoscale channel at atmospheric pressure, fuel–lean equivalence ratios 0.25–0.42, volumetric CO:H2 ratios 1:1 to 20:1, and wall temperatures 550–1320K. Experiments were performed in an optically-accessible channel-flow reactor and involved high-speed (up to 1kHz) planar laser induced fluorescence (LIF) of the OH radical and thermocouple measurements of the upper and lower channel wall temperatures. Simulations were carried out with a transient 2-D code, which included an elementary syngas reaction mechanism and detailed species transport. Demarcation of the experimentally-observed parameter space separating stationary and oscillatory combustion modes indicated that the former were favored at the higher wall temperatures and higher CO:H2 volumetric ratios, while the latter predominately appeared at the lower wall temperatures and lower CO:H2 ratios. The numerical model reproduced very well all stationary combustion modes, which included V-shaped and asymmetric (upper or lower) modes, in terms of flame shapes and flame anchoring positions. Simulations of the oscillatory flames, which appeared in the form of ignition/extinction events of varying spatial extents, were very sensitive to the specific boundary conditions and reproduced qualitatively the flame topology, the ignition sequence (including the periodic reversion from upper-asymmetric to lower-asymmetric flame propagation), and the range of measured oscillation frequencies. Predicted emissions in the stationary modes ranged from 25 to 94ppm-mass for CO and from 0.1 to 0.3ppm-mass for H2, while in the oscillatory modes incomplete combustion of both CO and H2 was attested during their oscillation period.