An experimental and numerical study of surface chemical interactions in the combustion of propylene over platinum

It is found that the platinum plate temperature peaks at slightly rich propylene/air mixtures (Ф = 1.3) when flameless combustion (defined by the presence of reactions on the plate without a gaseous flame) is observed. While the lean reactivity limits over platinum are lower than those for gaseous propylene/air mixtures, the rich limits are also lower than those of the gas phase alone and a sharp drop in the surface temperature is observed at Ф = 1.4. This sharp transition to extinction may be due to surface contamination by soot precursors. Carbon monoxide (CO), and hydrogen (H2) appear in low quantities at certain flow conditions. Consistent with other fuels, the streamwise profiles of species confirm the presence of two reacting zones along the plate, namely: (i) the leading edge zone where high gradients of species mole fractions are observed and (ii) the trailing zone where the profiles are more flat and stable. Numerical simulations show broad agreement with measurements up to Ф = 1.4 but fail to reproduce the sharp transition to extinction hence overpredicting the rich reactive limits. Major species such as O2, C3H6, and CO2 are in good agreement with the measured mole fractions while some discrepancies are noted for CO and H2. Differential molecular as well as thermal diffusions are found to be significant hence disrupting the atomic balance and leading to leaner mixtures in the vicinity of the plate.