Catalytic combustion of selected hydrocarbon fuels on platinum: Reactivity and hetero–homogeneous interactions

This paper addresses the interactions between homogeneous and heterogeneous reactions for different hydrocarbons namely, compressed natural gas (CNG), liquefied petroleum gas (LPG), butane and dimethyl ether (DME) over platinum. Experiments are performed to study the effects of varying the temperature of the incoming mixture (Tjet), its equivalence ratio (Ø) and the Reynolds number (Re), on the reactivity limits. Computational fluid dynamic (CFD) calculations using detailed chemical kinetics for both the platinum surface and gas phase are completed for a range of methane–air mixtures to resolve the impact of varying Tjet, Ø and Re on the compositional structure of the flow. Comparison between numerical and experimental results is performed where relevant.For flameless conditions (defined by the presence of reactions on the plate without a gaseous flame), it is found for all fuels studied here that the temperature of the platinum plate, resulting from reactions with the co-flowing fuel–air mixture, increases with increasing Tjet and Re. However, with CNG, the temperature of the plate peaks near stoichiometry while for LPG, butane and DME the peak occurred at richer mixtures of Ø ≈ 1.5. The reactive limits for CNG, propane and DME are found to broaden significantly. Numerical simulations show very good agreement with the measured plate temperature at different equivalence ratios. The computed compositional structure confirms the existence of a flame inhibition effect due to the presence of the catalyst and shows interesting trends of some species at different Re, Tjet and Ø. Gas and surface chemistries seem to affect a few species such as CO, CO2, H2, and H2O depending on the conditions of the co-flowing mixture. Minor species such as CH3, CH2O, O, HCO, and OH are largely controlled by gas-phase chemistry.