Hsi-Wu Wong

Microphysical Modeling of Ground-Level Aircraft-Emitted Aerosol Formation: Roles of Sulfur-Containing Species

Particulate matter emissions from aircraft engines have received increased attention due to their impacts on climate, health, and regional air quality. However, understanding of particulate matter formation from aircraft emissions at ground level is still limited. In this work, a detailed, one-dimensional model consisting of plume chemistry, wake dilution, and aerosol microphysics was developed to study sulfur-containing aerosol formation in near-field aircraft plumes at ground level. Parametric studies of ambient conditions and engine operating parameters were performed following the centerline plume trajectories up to 1 km downstream. The sampling system used in a recent experimental measurement campaign (NASA APEX-1) was also investigated. Our results show that binary homogeneous nucleation of H 2 SO 4 -H 2 O is sensitive to ambient conditions, and heterogeneous condensation on soot is dependent on engine power. The results also suggest that at certain atmospheric conditions the observations from the experimental sampling system at moderate (e.g., 30 m) downstream locations may not represent the particle evolution further downstream. A comparison with experimental data provided a limited initial assessment of the model. This assessment suggests that the important physics are being captured, and the model may be used to interpret experimental results and help guide future directions of field measurements.

Effects of additives and secondary phases on the sintering behavior of zinc oxide-based varistors

AbstractThe influence of additives and secondary phases on the sintering behavior of zinc oxide-based varistors has been investigated in thisstudy. Addition of Bi 2 O 3 and Sb 2 O 3 to ZnO results in rapid shrinkage of the specimens at around 10008C. This rapid shrinkage is attributedto the reaction between the pyrochlore phase and ZnO. This reaction has been verified by investigating the system of ZnO and a synthesizedpyrochlore phase ZnBi 1.5 Sb 1.5 O 7 . This pyrochlore phase has a cubic symmetry, with a lattice parameter a o ‹10.4438 A˚ . ZnBi 1.5 Sb 1.5 O 7 isfound to react with ZnO at 10008C to lead to the formation of Bi 2 O 3 , which accelerates the sintering rate of ZnO through a liquid-phasesintering mechanism. On the other hand, the spinel phase a-Zn 7 Sb 2 O 12 hinders the sintering process as well as the grain growth of ZnO.# 2000 Elsevier Science S.A. All rights reserved. Keywords: Zinc oxide; Pyrochlore phase; Sintering; Microstructure 1. IntroductionZinc oxide has been widely used to fabricate varistorssince 1970s because of its excellent non-ohmic property [1].Varistors are important protection devices against voltagesurges in solid-state devices and electrical power generationsystems [2]. To improve the electrical characteristics ofvaristors, considerable research efforts have been devotedto study the effects of adding small amounts of variousadditives to ZnO [3–7]. The most commonly used additivesare Bi

Impact of aviation on climate: FAA’s Aviation Climate Change Research Initiative (ACCRI) Phase II

AbstractUnder the Federal Aviation Administration’s (FAA) Aviation Climate Change Research Initiative (ACCRI), non-CO2 climatic impacts of commercial aviation are assessed for current (2006) and for future (2050) baseline and mitigation scenarios. The effects of the non-CO2 aircraft emissions are examined using a number of advanced climate and atmospheric chemistry transport models. Radiative forcing (RF) estimates for individual forcing effects are provided as a range for comparison against those published in the literature. Preliminary results for selected RF components for 2050 scenarios indicate that a 2% increase in fuel efficiency and a decrease in NOx emissions due to advanced aircraft technologies and operational procedures, as well as the introduction of renewable alternative fuels, will significantly decrease future aviation climate impacts. In particular, the use of renewable fuels will further decrease RF associated with sulfate aerosol and black carbon. While this focused ACCRI program effort...

Measurement of pyrolysis products from phenolic polymer thermal decomposition

Batch pyrolysis of phenolic polymer was performed using a step-wise heating procedure in a 50 K increment from room temperature up to 1250 K. A phenolic-polymer sample of 50 mg was loaded in a reactor assembly speci cally designed and built for this study. The mass loss was measured after each 50 K step and the production of gas-phase species was quanti ed using gas-chromatography techniques. The overall mass loss reached about 35%. Water was found to be the dominant product below 800 K. Yields of permanent gases such as hydrogen, methane, carbon monoxide, and carbon dioxide increased with temperature up to 900 K and then decreased at higher temperatures. The yields of light hydrocarbons, such as C2 to C4 hydrocarbons, increased with reaction temperature up to 1000 K and dropped subsequently. Yields of aromatic products, including benzene, toluene, and xylene, were signi cant between 700 and 850 K. The quantitative molar production of species versus temperature is made available for the development of detailed phenolicpolymer pyrolysis models.

An algorithm to estimate aircraft cruise black carbon emissions for use in developing a cruise emissions inventory

To provide accurate input parameters to the large-scale global climate simulation models, an algorithm was developed to estimate the black carbon (BC) mass emission index for engines in the commercial fleet at cruise. Using a high-dimensional model representation (HDMR) global sensitivity analysis, relevant engine specification/operation parameters were ranked, and the most important parameters were selected. Simple algebraic formulas were then constructed based on those important parameters. The algorithm takes the cruise power (alternatively, fuel flow rate), altitude, and Mach number as inputs, and calculates BC emission index for a given engine/airframe combination using the engine property parameters, such as the smoke number, available in the International Civil Aviation Organization (ICAO) engine certification databank. The algorithm can be interfaced with state-of-the-art aircraft emissions inventory development tools, and will greatly improve the global climate simulations that currently use a single fleet average value for all airplanes. Implications An algorithm to estimate the cruise condition black carbon emission index for commercial aircraft engines was developed. Using the ICAO certification data, the algorithm can evaluate the black carbon emission at given cruise altitude and speed.

Quantitative determination of species production from the pyrolysis of the Phenolic Impregnated Carbon Ablator (PICA)

Experiments to quantitatively determine detailed species production from the pyrolysis of Phenolic Impregnated Carbon Ablator (PICA) were performed using a reactor assembly adapted from a previous study on phenol-formaldehyde resin decomposition. A step-wise heating procedure that used a 50 K increment from room temperature up to 1250 K was employed for the experiments. The mass loss was measured after each 50 K step for PICA samples with an initial mass of 100 mg. Species production from the pyrolysis process was quantified using state-of-the-art gas-chromatography techniques. Compared to the more traditional mass spectroscopy techniques, gas chromatography allows to measure all species, from hydrogen to large aromatics. The quantitative molar production of species versus temperature is reported in this work. The species product from PICA pyrolysis are quite different from the species obtained in a previous study on a resole type phenolic resin pyrolysis. This suggests that characterizations need to be carried out for all variations of phenolic-matrix based ablators.

Encoding of polycyclic Si-containing molecules for determining species uniqueness in automated mechanism generation

Automated mechanism generation is an attractive way to understand the fundamental kinetics of complex reaction systems such as silicon hydride clustering chemistry. It relies on being able to tell molecules apart as they are generated. The graph theoretic foundation allows molecules to be identified using unique notations created from their connectivity. To apply this technique to silicon hydride clustering chemistry, a molecule canonicalization and encoding algorithm was developed to handle complex polycyclic, nonplanar species. The algorithm combines the concepts of extended connectivity and the idea of breaking ties to encode highly symmetric molecules. The connected components in the molecules are encoded separately and reassembled using a depth-first search method to obtain the correct string codes. A revised cycle-finding algorithm was also developed to properly select the cycles used for ring corrections when thermodynamic properties were calculated using group additivity. In this algorithm, the molecules are expressed explicitly as trees, and all linearly independent cycles of every size in the molecule are found. The cycles are then sorted according to their size and functionality, and the cycles with higher priorities will be used to include ring corrections. Applying this algorithm, more appropriate cycle selection and more accurate estimation of thermochemical properties of the molecules can be obtained.

Updating Our Understanding of JP-10 Decomposition Chemistry: A Detailed JP-10 Combustion Mechanism Constructed Using RMG - an Automatic Reaction Mechanism Generator

We are applying Reaction Mechanism Generator (RMG) to detailed and comprehensive characterization of JP-10 combustion chemistry. JP-10 is a large synthetic fuel with complex high temperature decomposition chemistry for which detailed characterization has been considered intractable; and RMG is a computer program that we developed for automatic construction of predictive kinetic models. In this paper, we present initial results from applying RMG to JP-10 combustion. After considering over 25,000 possible species and more than 1 million possible reactions, we have developed a highly detailed JP-10 combustion mechanism that currently consists of 317 chemical species and 7,715 elementary reactions. Comparisons against existing mechanisms and experimental data in published literature reveal that this RMG-constructed mechanism establishes a new state of the art in JP-10 combustion modeling: ignition delay predictions accurately reproduce experimental observations (to our knowledge, the first detailed mechanism to accomplish this); and our mechanism provides the first detailed insight into the high temperature initial decomposition chemistry of JP-10 in the presence of oxygen, particularly down to C5 hydrocarbons. We are also developing transport property estimates for all species in the mechanism. The final result of this effort will be an experimentally validated comprehensive JP-10 combustion mechanism containing all parameters necessary for application in reacting flow simulations.

Measurement of naphthalene uptake by combustion soot particles.

In this study, we designed and constructed an experimental laboratory apparatus to measure the uptake of volatile organic compounds (VOCs) by soot particles. Results for the uptake of naphthalene (C10H8) by soot particles typical of those found in the exhaust of an aircraft engine are reported in this paper. The naphthalene concentration in the gas phase and naphthalene attached to the particles were measured simultaneously by a heated flame ionization detector (HFID) and a time-of-flight aerosol mass spectrometer (ToF AMS), respectively. The uptake coefficient for naphthalene on soot of (1.11 ± 0.06) × 10(-5) at 293 K was determined by fitting the HFID and AMS measurements of gaseous and particulate naphthalene to a kinetic model of uptake. When the gaseous concentration of naphthalene is kept below the saturation limit during these experiments, the uptake of naphthalene can be considered the dry mass accommodation coefficient.

Green synthesis of linear alkylbenzenes via Diels−Alder cycloaddition between furan and linear alkenes over niobic acid catalyst

ABSTRACT The synthesis of linear alkylbenzenes (LABs) from biomass-derived furan and linear alkenes via Diels−Alder cycloaddition followed by acid-catalyzed dehydration is presented. Furan was reacted with 1-dodecene, the alkene model compound, over the niobic acid catalyst in a laboratory-scale batch reactor. The effects of reaction temperature, catalyst loading, and initial reactant ratio were systematically investigated. Our experiments reveal that 1-alkene isomerization, furan alkylation to produce dodecylfuran, and self Diels−Alder cycloaddition of furan to produce benzofuran are the major side reaction pathways competing with LAB production. The highest conversion of 1-dodecene to 1-phenyldecane, our target LAB, was found to be at approximately 12 mmol/mol. The main reasons for this low LAB yields include high furan activity and volatility, coke formation, and mass transfer limitations. Despite low LAB yields, our work demonstrates for the first time that it is possible to synthesize LABs from biomass-derived furan and linear alkenes over solid acid catalysts. GRAPHICAL ABSTRACT