Heterogeneous reaction and homogeneous flame coupled combustion behavior of n-decane in a partially packed catalytic bed combustor

Abstract

The premixed combustion experiments of n-decane were conducted in micro-combustors. The characteristics and mechanism of three combustion modes were studied: homogeneous combustion (HMC), heterogeneous combustion (HTC), and coupled combustion (CC) with both HTC and HMC. The homogeneous flame in CC cases can be established downstream of catalytic bed. The stable combustion range of CC is near the stoichiometric ratio, and the lean/rich limits of equivalence ratio (Φ) are close to the lean limit of the HMC and the rich limit of the HTC respectively. The HTC cases show high CO2 selectivity, and CO2 is the major products even at Φ > 1. The different mechanisms of O2 and n-decane adsorption on the Pt active site have significant effects on the stable limits of HTC. Hot flame in the fire core is followed by warm flame in the HMC cases. When Φ > 0.9, n-decane can’t burn out in so small hot flame that the effect of warm flame becomes obvious, resulting in some combustible species being generated in products. CO becomes the main product instead of CO2 in the HMC cases, when Φ > 1.6. In the CC cases, high n-decane conversion owes to the coupling of homogeneous flame and heterogeneous reaction. The homogeneous flame presents warm flame properties at Φ = 1.3 ~ 1.4, and hot flame properties at Φ = 1. More importantly, compared with HMC and HTC, much longer combustion zone achieved in CC with more even distribution of wall temperature and without obvious hot spots, which is significative to actual applications like the thermo-photovoltaic system.