Thermocouple particle densitometry for quantification and characterization of combustion-formed particulate matter

In this work, thermocouple particle densitometry (TPD) has been demonstrated to be a valid tool for the analysis of combustion-formed carbon nanoparticles. The TPD methods has been successfully used to describe both particle volume fraction and the chemical evolution of carbonaceous nanoparticle in an ethylene/air premixed flame. Scanning mobility particle sizer (SMPS) and Raman spectroscopy have been used in comparison with the TPD analysis and to corroborate the TPD results. As a result, TPD has shown excellent agreement to the SMPS particle volume fraction measurements along the entire flame, starting from the very low values at the inception region. Furthermore, TPD has shown a clear evidence that the two classes of carbon nanoparticles, i.e. the two modes of the particle size distribution, strongly differentiate in terms of their graphitization degree based on the different values of emissivity of the material deposited on the thermocouple. While primary soot particle, i.e. those with diameter 10-20 nm, present emissivity of approximatively 1, thus acting as a black body, nucleated nanoparticles present emissivity values of about 0.5-0.6 indicating that they have a lower graphitization degree, i.e. higher content of organic carbon as compared the grown ones. Finally, Raman scattering, measured directly on the thermocouple previously coved by carbon nanoparticle, supported the TPD analysis. The possible use of TPD as valid, reliable and cost-effective combustion aerosol sensor in hot gas-stream is discussed.