Radiative properties of numerically generated fractal soot aggregates : the importance of configuration averaging

The radiative properties of numerically generated fractal soot aggregates were studied using the numerically accurate generalized multisphere Mie-solution method. The fractal aggregates investigated in this study contain 10\u2013600 primary particles of 30 nm in diameter. These fractal aggregates were numerically generated using a combination of the particle-cluster and cluster-cluster aggregation algorithms with fractal parameters representing flame-generated soot. Ten different realizations were obtained for a given aggregate size measured by the number of primary particles. The wavelength considered is 532 nm, and the corresponding size parameter of primary particle is 0.177. Attention is paid to the effect of different realizations of a fractal aggregate with identical fractal dimension, prefactor, primary particle diameter, and the number of primary particles on its orientation-averaged radiative properties. Most properties of practical interest exhibit relatively small variation with aggregate realization. However, other scattering properties, especially the vertical-horizontal differential scattering cross section, are very sensitive to the variation in geometrical configuration of primary particles. Orientationaveraged radiative properties of a single aggregate realization are not always sufficient to represent the properties of random-oriented ensemble of fractal aggregates.Peer reviewed: YesNRC publication: Ye

A critique of laser-induced incandescence for the measurement of soot

The health and environmental risks due to airborne nanoparticles are important issues facing the citizens and governments of the industrialized countries. To assess and mitigate these risks, increasingly stringent regulations are being enacted to reduce the particulate emissions from the combustion of hydrocarbon fuels, which primarily consist of soot. Improvements to the understanding of the formation of soot nanoparticles and their impact on the health and the environment are required. This necessitates advances in the state of quantitative measurement of soot. Laser-induced incandescence (LII) is an optical diagnostic technique for the measurement of concentration and primary particle diameter of soot with high selectivity. Limitations with conventional LII were identified and a significantly enhanced technique, autocompensating LII (AC-LII), was developed employing time- resolved two-colour pyrometry, low fluence, and an absolute intensity calibration to address these limitations. AC-LII was shown to measure the soot particle temperature and automatically compensate for variations in the measurement environment that affected the peak soot particle temperature. With low fluence, AC-LII was shown to avoid soot sublimation, which impacted the measurements of concentration and size with high fluences. AC-LII was applied to flames and to combustion-generated emissions. At low ambient temperatures it was discovered that the measured concentration varied with fluence. To mitigate this issue, it was recommended that AC-LII be performed at a moderate fluence near the sublimation threshold. In order to assess the impact of distributions of the soot primary particle diameter and of aggregate size, analysis coupling experiments with a state-of-the-art numerical model of the heat transfer was performed. The results showed that AC-LII signal evaluation should begin immediately after an initial anomalous cooling period but before distribution effects become dominant. The sensitivity of AC-LII was optimized and applied to measure atmospheric black carbon concentrations. Comparison to other instruments demonstrated that AC-LII has significant advantages for the measurement of soot, and represents a major advancementin techniques for nanoparticle characterization.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Interlaboratory comparison of particle filtration efficiency testing equipment

This work presents the results of two interlaboratory comparisons of particle filtration efficiency measurements performed by a network of laboratories across Canada and Australia. Testing across multiple layers of a common verification material demonstrates a constant size-resolved quality factor when layering uncharged materials. Size-resolved filtration curves also match expectations, with increasingly size-dependent curves and a predictable increase in the PFE. Candidate reference materials with controlled material properties were also tested across multiple laboratories. Each set of materials sharing a common charge level show specific trends with the material basis weight. Respirators showed more consistency between the laboratories than the other filters. However, across a majority of the tests, dark uncertainties, which are otherwise unexplained variability between laboratories, are significant. This leaves room to improve the test method by developing improved verification procedures and additional reference materials.Comment: 14 pages, 8 figure

A critical evaluation of the thermal accommodation coefficient of soot determined by the laser-induced incandescence technique

Peer reviewed: YesNRC publication: Ye

Experimental investigation of oxygen addition to fuel on soot formation in laminar coflow diffusion flames of ethylene and propane

Peer reviewed: YesNRC publication: Ye

Effects of gas and soot radiation on soot formation in a coflow laminar ethylene diffusion flame

A computational study of soot formation in an undilute axisymmetric laminar ethylene-air coflow jet diffusion flame at atmospheric pressure was conducted using a detailed gas-phase reaction mechanism and complex thermal and transport properties. A simple two-equation soot model was employed to predict soot formation, growth, and oxidation with interactions between the soot chemistry and the gas-phase chemistry taken into account. Both the optically thin model and the discrete-ordinates method coupled with a statistical narrow-band correlated-K based wide band model for radiative properties of CO, CO\u2082, H\u2082O, and soot were employed in the calculation of radiation heat transfer to evaluate the adequacy of using the optically thin model. Several calculations were performed with and without radiative transfer of radiating gases and/or soot to investigate their respective effects on the computed soot field and flame structure. Radiative heat transfer by both radiating gases and soot were found to be important in this relatively heavily sooting flame studied. Results of the optically thin radiation model are in good agreement with those obtained using the wide band model except for the flame temperature near the flame tip.)Peer reviewed: YesNRC publication: Ye

Assessment of a laser-induced incandescence sensor for real-time particulate emissions measurement

NRC publication: Ye

On-board, time-resolved diesel particulate measurements by laser-induced incandescence

NRC publication: Ye

Influence of Pressure on Soot Formation in Laminar Diffusion Flames of Methane-Air up to 40 bar

Peer reviewed: YesNRC publication: Ye