Abstract View
Achieving Sampling Parameter-Independent Measurements of Incipient Soot in Laminar Flames with High-Resolution Differential Mobility Analysis
FARNAZ KHOSRAVI, Francesco Carbone, University of Connecticut
Abstract Number: 56
Working Group: Combustion
Abstract
The detailed analysis of the transition from the gas to the particle phase that occurs in flames and causes soot formation and emissions is one of the major challenges faced by the combustion community. This study investigates the size distribution function (SDF) and charge-state of the nanometer-sized products of one premixed and one diffusion, ethylene-fueled, laminar flames experimentally. A sampling orifice drilled in a horizontal tube probe under small constant suction pressure extracts the samples to be analyzed, including incipient soot, from the flames while the nitrogen dilution flow enforces them to a Half-Mini High-Resolution Differential Mobility Analyzer (DMA). We investigate the effects of the nominal DMA resolution, the sampling orifice diameter (i.e., the dilution ratio, DR), and the transport time (Δt) to the DMA inlet separately. We implemented several flow patterns to bring the sample at the entrance of DMA to control Δt independently of all other parameters and reduce its values down to 30 ms. The results determine the conditions under which one can measure the shape of the sample SDFs independently of the sampling and analysis parameters. Increasingly larger values of DR/Δt are necessary to avoid distortions of the SDF shape as the sample ages in the flames when the sampling orifice positioning is further downstream. On the other hand, changes in DR may affect the measured total number concentrations even when they do not affect the SDF shape. We are performing additional experiments to try to rationalize this peculiar finding.