Characterizing Premixed Syngas Combustion and Flame Dynamics in Micro Scales

Abstract

Syngas can potentially replace most of conventional fuels, due to its lower emission rates in the case of lean combustion with acceptable energy densities, and can be used in small-scale combustion-related devices. However, with various constituents having various burning characteristics, syngas combustion at micro scales can be more complicated than that of conventional gaseous fuels. It is therefore highly important to understand syngas combustion characteristics. In this work, premixed syngas combustion in a horizontal, two-dimensional microchannel of length 20 mm and width 2 mm is simulated with detailed chemistry, with axisymmetric boundary condition on the lower wall of the computational domain and a fixed temperature gradient on the upper wall to account for the conjugate heat transfer. The simulations are run with varying inlet velocities ranging from 0.1 m/s to 3.0 m/s. The flame shape and dynamics were similar for all the cases, however, not all cases resulted in a stable flame. Two different types of results, i.e., (i) stable flame and (ii) flames with repetitive ignition and extinction (FRIE) are observed. The ignition, extinction, and FRIE events have been characterized in various cases. In addition, the FRIE phenomenon is analyzed by investigating the FRIE periods (the time intervals between the two consecutive ignitions). Similar to the ignition delays, the FRIE periods are found to be dependent on the inlet velocity. The loci of ignition and of a stabilized flame (in stable cases) are found to be further away from the inlet as the inlet velocity increases.