Radicals in nascent soot from laminar premixed ethylene and ehtylene-benzene flames by electron paramagnetic resonance spectroscopy

In this work, we present particle size distribution (PSD), electron paramagnetic resonance (EPR) and Raman spectroscopy measurements of soot particles, collected across the inception region, in two ethylene-air premixed laminar flames and two flames obtained by substituting 30% of the ethylene carbon with benzene. The experimental results are used to investigate the effect of aromatic fuel on the nature and role of radicals in particle nucleation and growth. For all the particles sampled, both in pure ethylene flames and in the ethylene/benzene ones, an EPR signal typical of persistent carbon-centered aromatic radicals is measured. The results point out an involvement of pi-radicals during particle nucleation and initial growth process. Under the conditions investigated, our results show that the electron spin density of particles produced by different fuels is mainly related to the amount of H-atoms available in the particles. Moreover, for all the investigated flames, the spin density presents an inverse dependence with the particle size suggesting that particle surface plays an important role in the early steps of the soot formation process. (c) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

This work investigated the effect of aromatic fuel on radicals in particle nucleation and growth by measuring PSD, EPR, and Raman spectroscopy of soot particles in different ethylene and ethylene/benzene flames. The results showed that pi-radicals are involved in the early stages of particle growth and the spin density of particles is mainly related to the amount of H-atoms available. Additionally, the spin density displayed an inverse dependence with particle size, indicating the importance of particle surface in the soot formation process.