Author: houston

By Hope A. Michelsen, Meredith B. Colket, Per-Erik Bengtsson, Andrea D’Anna, Pascale Desgroux, Brian S. Haynes, J. Houston Miller, Graham J. Nathan Heinz Pitsch, Hai Wang

This review presents a glossary and review of terminology used to describe the chemical and physical processes involved in soot formation and evolution and is intended to aid in communication within the field and across disciplines. There are large gaps in our understanding of soot formation and evolution and inconsistencies in the language used to describe the associated mechanisms. These inconsistencies lead to confusion within the field and hinder progress in addressing the gaps in our understanding. This review provides a list of definitions of terms and presents a description of their historical usage. It also addresses the inconsistencies in the use of terminology in order to dispel confusion and facilitate the advancement of our understanding of soot chemistry and particle characteristics. The intended audience includes senior and junior members of the soot, black carbon, brown carbon, and carbon black scientific communities, researchers new to the field, and scientists and engineers in associated fields with an interest in carbonaceous material production via high-temperature hydrocarbon chemistry.

A follow on paper to the "The Molecular Composition of Soot" paper published in Angewandte Chemie has been accepted for publication in the Proceedings of the Combustion Institute.   Group co-authors include Shellie Golden, Jennifer Giaccai, Andrew Kamischke, and Houston Miller.  Other GW authors include Akos Vertes and Andrew Korte. Here, we expand on the application of Chemical Graph Theory to isomer enumeration and validate our findings with group additivity and DFT thermodynamic calculations.

A collaboration between GW Chemistry's Miller and Vertes labs has led to a recent accepted article which is available online in the journal Angewandte Chemie International Edition, a publication of the German Chemical Society.

Abstract: Soot (sometimes referred to as Black Carbon) is produced when hydrocarbon fuels are burned. Our hypothesis is that polynuclear aromatic hydrocarbon (PAH) molecules are the dominant component of soot, with individual PAH molecules forming ordered stacks that agglomerate into primary particles (PP). Here we show that the PAH composition of soot can be exactly determined and spatially resolved by low-fluence laser desorption ionization, coupled with high-resolution mass spectrometry imaging. This analysis revealed that PAHs of 239-838 Da, containing few oxygenated species, comprise the soot observed in an ethylene diffusion flame. As informed by chemical graph theory (CGT), the vast majority of species observed in the sampled particulate matter may be described as  benzenoids, consisting of only fused 6-membered rings. Within that limit, there is clear evidence for the presence of radical PAH in the particulate samples. Further, for benzenoid structures the observed empirical formulae limit the observed isomers to those which are nearly circular with high aromatic conjugation lengths for a given aromatic ring count. These results stand in contrast to recent reports that suggest higher aliphatic composition of primary particles

 

Accepted in the journal Applied Optics

Experimental PHOCS spectra and retrieval fit.  Shown above is an oxygen feature at 7815.67 cm^-1 and a water feature at 7816.74 cm^-1.  Plotted above the spectrum are fit residuals.

 

Abstract: We describe the development of a near-infrared laser heterodyne radiometer (LHR):  Precision Heterodyne Oxygen-Calibration Spectrometer (PHOCS). The prototype instrument is equipped with two heterodyne receivers for oxygen and water (measured near 1278 nanometers) and carbon dioxide (near 1572 nanometers) concentration profiles, respectively. The latter may be substituted by a heterodyne receiver module equipped with a laser to monitor atmospheric methane near 1651 nanometers.). Oxygen measurements are intended to provide dry gas corrections and – more importantly – determine accurate temperature and pressure profiles that, in turn, improve the precision of the CO₂ and H₂O column retrievals. Vertical profiling is made feasible by interrogating the very low-noise absorption lines shapes collected at »0.0067 cm^-1 resolution. PHOCS complements results from the Orbiting Carbon Observatory (OCO-2), Active Sensing of CO₂ Emissions over Nights, Days, and Seasons (ASCENDS), and ground-based Fourier transform spectrometers. In this manuscript we describe the development of the instrument by Mesa Photonics and present the results of initial tests in the vicinity of Washington, D.C.

 

A collaboration between Stanford University, the University of Connecticut, the University of Toronto, and George Washington University published in the journal Fuel.

Chiara Saggese, Ajay V. Singh, Xin Xue, Carson Chu, Mohammad Reza Kholghy, Tongfeng Zhang, Joaquin Camacho, Jennifer Giaccai, J. Houston Miller, Murray J. Thomson, Chih-Jen Sung, Hai Wang,

Abstract Real jet fuels are complex mixtures of many organic components, some of which are aromatic compounds.Towards the high-temperature end of the distillation curve, some of the fuel components are multi-ring com-pounds. A small amount of these high molecular weight species in the fuel could impact soot nucleation in practical engines especially when the fuel is injected as a spray. This work aims to highlight the variation of the sooting propensity of jet fuels as a function of distillate fractions and to examine the validity of a surrogate fuel in emulating soot production from real fuels. Particle size distribution functions and soot volume fractions are studied in a series of laminar premixed stretch-stabilized ethylene flames doped with Jet A, its various distillate fractions, and the 2nd generation MURI surrogate. Soot formation as a result of doping real jet fuel and its distillate fractions is also investigated in counterflow and coflow diffusion flames. The results show that the higher-boiling distillates mostly influence soot nucleation and produce substantially more soot in nucleation controlled flames than the light molecular fraction and jet fuel as received, while such an effect is seen to be small in flames where soot production is controlled by surface growth. The potential impact of distillate fractions on soot nucleation propensities is discussed

 

a Mechanical Engineering Department, Stanford University, Stanford, CA 94305, USA

b Department of Mechanical Engineering, University of Connecticut, Storrs, CT 06269, USA

c. Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, Canada

d. Department of Chemistry, The George Washington University, Washington, DC 20052, USA

Jennifer A. Giaccai and J. Houston Miller

Abstract: Interactions of oxygen with polynuclear aromatic hydrocarbons (PAH) can occur both in the flame and during oxidation of soot atmospherically. Past experimental measurements of PAH in soot samples collected either immediately after combustion, from the atmosphere, or in a flame show a variety of oxygen moieties within the PAH structures. This study investigated the electronic structure of oxygen-containing PAH to gain insight into their interaction with light both to better interpret spectroscopic measurements and to recognize the role of oxygen-containing PAH in atmospheric radiative forcing. Our research has shown that oxygen in ethers and hydroxyl moieties on PAH showed little change to the HOMO-LUMO gap (HLG), whereas ketones and aldehydes show a HLG decrease of 0.5 eV. The effect is enhanced when more than one ketone is present on a PAH molecule and further enhanced in subsequent dehydrogenation to a quinone-like structure. The presence of an oxygen-containing PAH with a ketone functional group in a dimer and trimer will substantially lower the HLG of the PAH stack. This may have a significant effect in the interaction of atmospheric soot with solar radiation.

 

 

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Proceedings of the Combustion Institute,Volume 37, Issue 1, 2019
Pages 903-910

Trump White House quietly cancels NASA research verifying greenhouse gas cuts

Our group developed a collaborative proposal with biologists at GW and the University  of Vermont in early 2017 for this program.  We had an inkling that CMS was in trouble when we were notified that he proposal would not be reviewed.  The Terrestrial Sink is one of the largest "negative feedbacks" for increased carbon dioxide in the atmosphere.  (In plain speak, trees and other terrestrial biomass consume CO₂ that fossil fuels add to atmosphere.)  The magnitude of the terrestrial sink is also very uncertain, but evidence over the last decade suggests that it is changing, and not in a good way: less carbon is being sequestered  by terrestrial biomass.

"You can't manage what you don't measure."

"This type of research is likely to continue, but leadership will pass to Europe."

After several months of preparation both in the classroom and in the laboratory, the first Eco-Equity LuftSinn sensor was installed on the roof of Cardozo High School in Northwest Washington DC.  You can check out data from this and LuftSinn other sensors at our companion site.