Kinetics of nascent soot oxidation by molecular oxygen in a flow reactor

Abstract

Oxidation kinetics of soot is typically measured with well aged soot as substrates. Recent studies show that nascent soot can have structures and surface composition drastically different from mature, graphitized soot. In the present study, the kinetics of nascent soot oxidation by molecular oxygen was observed at temperatures of 950, 1000 and 1050K for molecular oxygen concentrations ranging from 1000 to 7800ppm at ambient pressure in a coupled burner-stabilized stagnation flame burner and laminar aerosol flow reactor. The reactant particles, 10–20nm in diameter, were freshly synthesized from premixed flames of ethylene, n-heptane, and toluene and introduced into the flow reactor continuously. The kinetics of particle oxidation was measured through electric mobility measurement of particle size distributions before and after oxidation. It was found that the specific oxidation rate is has a first-order dependency on gas-phase O2 concentration over the range of O2 concentration studied. The rate measured is an order of magnitude larger than that predicted by the classical Nagle Strickland-Constable (NSC) correlation. The result suggests that the surface of nascent soot is considerably more reactive towards oxidation than graphite or graphitized soot.