Micro-tubular flame-assisted fuel cells running methane, propane and butane: On soot, efficiency and power density

Highlights: • A method for deriving the theoretical maximum electrical efficiency is discussed. • Methane, propane and butane fuels are compared based on equivalent energy input. • Combustion of methane generates higher syngas at lower equivalence ratios (1.2–1.3). • A high power density of ∼328 mW cm⁻² is achieved in methane combustion exhaust. • A high electrical efficiency (>1.2%) is achieved compared to previous work. -- Abstract: A two-stage combustor with 1^st-stage premixed fuel-rich combustion, integrated micro-tubular flame-assisted fuel cell (FFC) and 2^nd-stage, fuel-lean combustion is described. The current state of research in direct flame fuel cells (DFFCs) is assessed and the dilemma of obtaining high power density, high electrical efficiency and no soot is discussed. A method for deriving the maximum theoretical electrical efficiency from a FFC based system is developed. A method for comparing methane, propane and butane in the two-stage combustor with integrated FFC is developed. Methane, propane and butane are tested at different equivalence ratios and flow rates to assess the power density and electrical efficiency. High power density (>300 mW cm⁻²) and high electrical efficiency (>1.2%) are achieved for equivalence ratios below 1.6. Methane is found to achieve higher power density and electrical efficiency at lower equivalence ratios compared to propane and butane. Soot formation is avoided by operating below the critical sooting limit.