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Measurement of soot with organic coatings by laser-induced incandescence

University of British Columbia

Time-Resolved Laser-Induced Incandescence (TR-LII) uses a high-energy laser pulse to detect airborne soot particles. When a laser pulse encounters a light-absorbing particle, the energy will be absorbed, resulting in an increase in temperature. If the temperature is high enough, incandescence can be used to quantity of the soot mass (EC). TR-LII tracks the incandescent light as the particle cools, providing information on the particle structure. It is a common in LII research to assume that the soot aggregate particles contain only Elemental Carbon (EC) and if these soot aggregate particles are internally mixed with Organic Carbon (OC), the intense energy from the laser beam evaporates the OC instantly. Unfortunately, these assumptions are inaccurate because the existence of OC will alter the structure and heat transfer properties of the aggregate. The existence of OC also has an effect on the energy absorption by the soot particulates. An experiment was conducted using India ink particles as a soot surrogate and Oleyl Alcohol as a model OC coating. The experiment’s objective is to study the effect of coating (OC) on the LII detection. The coating increased the peak temperature, but the apparent primary particle diameter decreased when more coating was introduced, whereas the main output variable (volume fraction) showed a mixed response. Up until a thickness of 40 nm, the apparent volume fraction value was declining, but for a thicker coating condition, the value was increasing. Another experiment was conducted to study the effect of the coating on the particulate distribution downstream of the laser heating in the LII detecting chamber. The soot fragmentation phenomenon was found to occur in the LII system and the existence of coating has an effect on the soot fragmentation phenomenon. Compared to uncoated particle, which produces small fragments (<40 nm), a coated particle produces additional quantity of middle size fragments (60 to 100 nm) but fewer of small size fragments. Overall, the present project shows that the existence of the coating cannot be ignored for an LII system especially in a condition where heavy coating are expected and a high accuracy is needed.

Text

2012-01-18

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/40129

Mechanical Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/