Fuel-rich hetero-/homogeneous combustion of C3H8/O2/N2 mixtures over rhodium

Abstract

The catalytic (heterogeneous) and gas-phase (homogeneous) combustion of C3H8/O2/N2 mixtures over rhodium was investigated experimentally and numerically at 5 bar and at fuel rich equivalence ratios φ = 2.0 3.5 relevant to propane Catalytic Partial Oxidation (CPO). In situ spatially resolved Raman measurements of major gas phase species concentrations and Planar Laser Induced Fluorescence (PLIF) of formaldehyde were applied in an optically accessible channel flow reactor to monitor the catalytic and gas phase processes, respectively, while accompanying 2D simulations were carried out with detailed hetero-/homogeneous chemical reaction mechanisms. Due to the high gas phase reactivity of propane, homogeneous chemistry could not be ignored over most of the reactor’s oxidation zone length (upstream zone where the deficient reactant oxygen is not fully consumed). The presence of gas phase chemistry deteriorated the otherwise high catalytic syngas (H2 and CO) selectivities over the oxidation zone. Raman measurements of major gas-phase species concentrations over the restricted oxidation zone length without appreciable gas-phase chemistry showed that the catalytic reaction mechanism slightly underpredicted (overpredicted) the H2 (CO) formation. The same behavior was also attested over the remaining length of the oxidation zone where combined catalytic and gas phase chemistry was present. The production of considerable amounts of H2 at the highest investigated equivalence ratio of 3.5 accelerated the onset of homogeneous ignition and the formation of strong flames. The discrepancies between measured and predicted homogeneous ignition distances were less than 6.8% in all cases, illustrating the validity of the employed hetero-/homogeneous kinetic schemes. Contrary to past methane CPO studies, the contribution of gas phase chemistry and the formation of strong flames in propane CPO was detrimental to syngas production.

Publication
In Proceedings of the Combustion Institute

Related