Particle emission characteristics of a gas turbine with a double annular combustor

The total climate, air quality and health impact of aircraft black carbon (BC) emissions depends on quantity (mass and number concentration), as well as morphology (fractal dimension and surface area) of emitted BC aggregates. This study examines multiple BC emission metrics from a gas turbine with a double annular combustor, CFM56-5B4-2P. As a part of the SAMPLE III.2 campaign, concurrent measurements of particle mobility, particle mass, particle number concentration and mass concentration, as well as collection of transmission electron microscopy (TEM) samples, allowed for characterization of the BC emissions. Mass- and number-based emission indices were strongly influenced by thrust setting during pilot combustion and ranged from <1 to 208 mg/kg-fuel and 3×1012 to 3×1016 particles/kg-fuel, respectively. Mobility measurements indicated that mean diameters ranged from 7-44 nm with a strong dependence on thrust during pilot-only combustion. Using aggregation and sintering theory with empirical effective density relationships, a power law relationship between primary particle diameter and mobility diameter is presented. Mean primary particle diameter ranged from 6-19 nm, however, laser induced incandescence (LII) and mass-mobility calculated primary particle diameters demonstrated opposite trends with thrust setting. Similarly, mass-mobility-calculated aggregate mass specific surface area and LII-measured surface area were not in agreement, indicating both methods need further development and validation before use as quantitative indicators of primary particle diameter and mass-specific surface area.The authors express their gratitude to a number of people and organizations in helping to plan, conduct, finance and provide instruments for this measurement campaign. The 537 European Aviation Safety Agency (EASA) funded the SAMPLE III SC02 campaign (EASA.2010.FC.10, Specific Contract No: SC02). The Federal Office of Civil Aviation, Switzerland (FOCA) was critical in for providing additional financial support and arranging facilities which made this study possible. We also thank the SR Technics test bed staff, including Frithjof Siegerist, for operating the engines and enabling access to the test facility. We thank AVL, Cambustion, Grimm & TSI supplying both instruments and expertise.This is the author accepted manuscript. The final version is available from Taylor & Francis via http://dx.doi.org/10.1080/02786826.2015.107845

Improved sizing of soot primary particles using mass-mobility measurements

The properties and impacts of aggregated aerosol particles (i.e., soot, metal oxide fumes) depend on their morphology, as characterized by fractal dimension, prefactor, and primary particle diameter. The morphology may be measured directly by time-consuming ex situ microscopy or rapid but indirect in situ methods. Previously, it was found that particle mass and mobility measurements could be used for the estimation of the primary particle diameter of zirconia aggregates, using plausible assumptions related to the fractal structure (specifically, prefactor kα and exponent Dα). Since the formation and growth of zirconia aggregates are different from carbon soot, here we compare primary particle diameters measured directly from transmission electron microscopy analysis of soot particles with the diameters estimated from mass-mobility measurements. Performing extensive measurements on soot emissions from two reciprocating engines over a range of operating conditions, we found that there are no universal values of kα and Dα that can be used for all conditions. However, new optimized values of kα and Dα are estimated here for soot particles. The variation of the primary particle diameter with particle size is also taken into consideration and is shown to be essential to obtain physically realistic results. Using optimized values of kα and Dα, the average primary particle sizing error is reduced for all soot types. This suggests that with some calibration, in situ sizing of the primary particle diameter, using mass and mobility measurements, can provide useful accuracy

The capacitance and charge of agglomerated nanoparticles during sintering

University of Minnesota Ph.D. dissertation. December 2017. Major: Mechanical Engineering. Advisor: David Pui. 1 computer file (PDF); xi, 123 pages.This thesis consists of two parts: unipolar diffusion charging of nanoparticles and its application on the method development of surface-area measurements. The electrical capacitance of aerosol particles indicates their potential diffusion charging level, which is important for their classification by electrical mobility, precipitation (removal or collection) in electrical fields, and morphology characterization. A minimum potential energy method was used to calculate the electrical capacitance for agglomerates composed of equally sized spherical primary particles (PPs). By discretizing the particle surface using finite spherical elements, as net charge only resides on the surface of an isolated conductor, this method was extended to calculate the capacitance of arbitrarily shaped particles. Based on the capacitance, the charge of these particles was obtained by diffusion charging theory. In addition, the dynamics of capacitance and mean charge of agglomerate during sintering or coalescence (at constant particle volume) to aggregates and finally to compact structures was computed and found in agreement with sparse experimental data. Particle morphology strongly affects the capacitance and mean charge of fractal-like particles. For example, both decreased by 60% upon full coalescence or sintering of an agglomerate consisting initially of 128 PPs. Although geometric surface area (GSA) of nanoparticles has received much attention in many fields (drug delivery, catalysts, inhalation exposure, toxicity, etc.), no appropriate instruments and methods for online measurements of GSA are readily available. Therefore, this study intends to develop a Geometric Surface Area Monitor (GSAM) to measure the GSA of spherical as well as model agglomerate/aggregate nanoparticles in nearly real-time. The GSAM has two versions: 1. The GSAM (I) consists of several existing techniques in series, including inertial impaction, unipolar charging, electrostatic precipitation, and electrical current measurement. The GSAM (I) was first evaluated and calibrated by measuring the GSA of monodisperse nanoparticles. Spherical, aggregate, and agglomerate nanoparticles were tested in the calibration. It was found that the measured electrical current was proportional to the surface area concentration. The calibration curves obtained from the measurements of monodisperse particles was then applied for polydisperse spherical particles and compared the measured GSA with that determined by the well-known scanning mobility particle sizer (SMPS) where the GSAM (I) had less than 10% of deviation compared with SMPS. 2. In the GSAM (II), the commercialized nanoparticle surface area monitor was used and slightly modified. The instrument responses under two different conditions were combined in a weighted sum (WS) fashion to correlate with the aerosol GSA concentration. We present the GSA concentration results and comparisons with well-known SMPS data in both laboratory testing and field measurement. For the laboratory testing, the two methods have a good agreement with a Pearson correlation coefficient of 0.9961; for the field measurements including the indoor and outdoor samplings, both methods agree well with each other. In addition, the new WS method is more stable in the clean indoor air and suitable for outdoor environmental sampling with a slight overestimation (125% of SMPS). These three studies below comprise parts of the main body of this dissertation and have been published. Chapter 2: Cao, L. N. Y., Wang, J., Fissan, H., Pratsinis, S. E., Eggersdorfer, M. L., & Pui, D. Y. H. (2015). The capacitance and charge of agglomerated nanoparticles during sintering. Journal of Aerosol Science, 83(0), 1-11. doi: http://dx.doi.org/10.1016/j.jaerosci.2015.01.002 Chapter 3: Cao, L. N. Y., Chen, S.-C., Fissan, H., Asbach, C., & Pui, D. Y. H. (2017). Development of a geometric surface area monitor (GSAM) for aerosol nanoparticles. Journal of Aerosol Science, 114, 118-129. doi: https://doi.org/10.1016/j.jaerosci.2017.09.013 Chapter 4: Cao, L. N. Y. & Pui, D. Y. H. A novel weighted sum method to measure particle geometric surface area in real-time, Journal of Aerosol Science, doi: https://doi.org/10.1016/j.jaerosci.2017.12.00

Controlled oxidation of iron nanoparticles in chemical vapour synthesis

In the present study, iron oxide nanoparticles (primary particle size of 80-90 nm) with controlled oxidation state were prepared via an atmospheric pressure chemical vapour synthesis (APCVS) method. Iron pentacarbonyl [Fe(CO)5], a precursor material, was thermally decomposed to iron in the APCVS reactor. Subsequently, the iron was oxidized with controlled amount of oxygen in the reactor to produce nearly pure magnetite or haematite particles depending on the oxygen concentration. Size, morphology and crystal structure of the synthesized nanoparticles were studied with scanning mobility particle sizer (SMPS), transmission electron microscopy (TEM) and X-ray diffraction (XRD). In addition, thermodynamic equilibrium calculations and computational fluid dynamics model were used to predict the oxidation state of the iron oxides and the reaction conditions during mixing. Aggregates of crystalline particles were formed, determined as magnetite at the oxygen volumetric fraction of 0.1 % and haematite at volumetric fraction of 0.5 %, according to the XRD. The geometric mean electrical mobility diameter of the aggregates increased from 110 to 155 nm when the volumetric fraction of oxygen increased from 0.1 to 0.5 %, determined using the SMPS. The aggregates were highly sintered based on TEM analyses. As a conclusion, APCVS method can be used to produce nearly pure crystalline magnetite or haematite nanoparticles with controlled oxidation in a continuous one-stage gas-phase proces