Experimental and numerical investigation of the hetero-/homogeneous combustion of lean propane/air mixtures over platinum

摘要

The pure heterogeneous and the coupled hetero-/homogeneous combustion of fuel-lean propane/airmixtures over platinum have been investigated at pressures 1 bar ≤p≤7 bar, fuel-to-air equivalence ratios0.23≤Φ≤0.43, and catalytic wall temperatures 723 K ≤Tw ≤1286 K. Experiments were performed in anoptically accessible catalytic channel-flow reactor and involved 1-D Raman measurements of major gasphasespecies concentrations across the reactor boundary layer for the assessment of catalytic fuel conversionand planar laser induced fluorescence (LIF) of the OH radical for the determination of homogeneousignition. Numerical predictions were carried out with a 2-D elliptic CFD code that included a one-step catalyticreaction for the total oxidation of propane on Pt, an elementary C3 gas-phase chemical reactionmechanism, and detailed transport. A global catalytic reaction step valid over the entire pressure–temperature-equivalence ratio parameter range has been established, which revealed a ~p0.75 dependence of thecatalytic reactivity on pressure. The aforementioned global catalytic step was further coupled to a detailedgas-phase reaction mechanism in order to simulate homogeneous ignition characteristics in the channelflowreactor. The predictions reproduced within 10% the measured homogeneous ignition distances at pressuresp≤5 bar, while at p = 7 bar the simulations overpredicted the measurements by 19%. The overallmodel performance suggests that the employed hetero-/homogeneous chemical reaction schemes are suitablefor the design of propane-fueled catalytic microreactors.