Exploring Soot Particle Concentration and Emissivity by Transient Thermocouples Measurements in Laminar Partially Premixed Coflow Flames

Gianluigi De Falco,Andrea D’Anna,Mariano Sirignano,Patrizia Minutolo,Mario Commodo,Giulia Moggia

doi:10.3390/en10020232

Gianluigi De Falco, Andrea D’Anna + Show 4 more

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https://doi.org/10.3390/en10020232

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Abstract

Soot formation in combustion represents a complex phenomenon that strongly depends on several factors such as pressure, temperature, fuel chemical composition, and the extent of premixing. The effect of partial premixing on soot formation is of relevance also for real combustion devices and still needs to be fully understood. An improved version of the thermophoretic particle densitometry (TPD) method has been used in this work with the aim to obtain both quantitative and qualitative information of soot particles generated in a set of laminar partially-premixed coflow flames characterized by different equivalence ratios. To this aim, the transient thermocouple temperature response has been analyzed to infer particle concentration and emissivity. A variety of thermal emissivity values have been measured for flame-formed carbonaceous particles, ranging from 0.4 to 0.5 for the early nucleated soot particles up to the value of 0.95, representing the typical value commonly attributed to mature soot particles, indicating that the correct determination of the thermal emissivity is necessary to accurately evaluate the particle volume fraction. This is particularly true at the early stage of the soot formation, when particle concentration measurement is indeed particularly challenging as in the central region of the diffusion flames. With increasing premixing, an initial increase of particles is detected both in the maximum radial soot volume fraction region and in the central region of the flame, while the further addition of primary air determines the particle volume fraction drop. Finally, a modeling analysis based on a sectional approach has been performed to corroborate the experimental findings.

Highlights

The formation of soot particles from the combustion of conventional and bio-derived fuels is a topic that attracts considerable interest because of the negative impact on human health, air quality, and climate change [1,2,3]
When hydrocarbon molecules are burnt in non-stoichiometric conditions, pyrolytic and oxidative reactions lead to the formation of benzene and larger polycyclic aromatic hydrocarbons (PAHs), which in turn promote the formation of carbonaceous nanoparticles
thermophoretic particle densitometry (TPD) is a method developed by McEnally et al [15] for soot particle volume fraction measurements

Summary

Introduction

The formation of soot particles from the combustion of conventional and bio-derived fuels is a topic that attracts considerable interest because of the negative impact on human health, air quality, and climate change [1,2,3]. For this reason soot formation in combustion has long been investigated and debated over the years. These include physical clustering of pericondensed aromatic hydrocarbons or oligomers of aromatic hydrocarbons (i.e., compounds with high molecular mass characterized by aromatic functionalities linked by aliphatic bonds) through van der Walls’ forces or even the formation of curved fullerenic-like structures [6,7]

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