Abstract
The objective of this dissertation is to investigate fundamental aspects of premixed flame structures as well as flame dynamics that arise due to conjugate heat transfer in narrow channels. Laminar premixed combustion simulations in narrow 2D channels show that conjugate heat transfer allows for combustion of mixtures at small scales that are not flammable at normal conditions. To investigate the impact of conjugate heat transfer, preheated 1D cases with premixed H2/Air fuel are simulated for a wide range of operating conditions based on inlet temperature and equivalence ratio. For post-processing, Chemical Explosive Mode Analysis (CEMA, an eigen-analysis technique) is used as a computational diagnostic tool. Classical CEMA is refined to introduce directional information to track dominant promoting and counteracting chemical modes that are linked to specific species and reactions. A major result of this analysis is that flame structures are shown to follow the same trend if they have similar flame temperature, regardless of the inlet conditions. Laminar premixed combustion in narrow channels is known to produce a range of dynamic flame phenomena (stationary/non-stationary and symmetric/asymmetric flames) that depend on operating conditions. Mechanisms that lead to different dynamics are investigated by tracking flame fronts and related metrics for laminar premixed CH4/air and syngas/air flames. Flow re-directions because of local extinctions and corresponding flame edges are found to be the main causes for such dynamics. Synthesized gases (syngas) have been recently considered to be used at small-scale combustion systems because a) they can be produced from cheap heavy fuels such as glycerol and b) they have better combustion characteristics compared to the initial heavy fuel. Therefore, syngas production from glycerol, which is available in high volumes and low costs has been studied. By investigating glycerol reforming processes at a wide range of intermediate temperatures and stoichiometries, optimum operating conditions for producing syngas are explained.
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