An Experimental Study of 2-Propanol Pyrolysis Chemistry.

In the present study, 2-propanol pyrolysis experiments were conducted in a rapid compression facility for a range of temperatures from 965 to 1193 K, pressures from 4.4 to 10.0 atm conditions, and times ranging from 2 to 47 ms after end-of-compression. Mixtures were composed of 2-propanol, nitrogen, and argon with the 2-propanol concentration held constant at 1.5% by mole fraction. The production of seven stable intermediate species (methane, acetylene, ethene, ethane, acetaldehyde, propene, and acetone) were measured using fast-gas sampling and gas chromatography. The high concentrations of propene observed experimentally indicated thermal decomposition of 2-propanol via dehydration was significant at all conditions studied. The observation of the simultaneous presence of methane and acetone indicated H atom abstraction from 2-propanol by H and CH3 radicals was also significant at all conditions. The relative concentrations of methane and acetone indicated an increase in the 2-propanol + CH3 channel at higher temperature. The experimental data showed negligible sensitivity to over a factor-of-two increase in pressure, indicating pressure-dependent reactions, like the thermal decomposition of 2-propanol via dehydration, were in the high-pressure limit. The experimental results were compared with model predictions made using a recently developed kinetic mechanism for C3-C4 alcohols, and the results showed generally good agreement. The most significant discrepancies were for 2-propanol consumption at the highest temperature condition (T = 1193 K), where 2-propanol consumption was predicted as much higher by the model (by more than an order of magnitude) compared with the experimental results, and at the lowest temperature (T = 965 K), ethane production was predicted as much lower (by more than an order of magnitude) compared with the experimental results.

Experimental evaluation of aerosol mitigation strategies in large open-plan dental clinics.

BACKGROUND: Aerosols are generated routinely during patient care in dentistry. Managing exposure risk requires understanding characteristics of aerosols created during procedures such as those performed using high-speed drills that operate at 200,000 revolutions per minute. METHODS: A trained dentist performed drilling procedures on a manikin's incisors (teeth nos. 8 and 9) using a high-speed drill and high-volume evacuator. The authors used high-speed imaging to visualize the formation and transport of aerosol clouds and particle sampling to measure aerosol concentration and size distribution at several locations. The authors studied several aerosol mitigation strategies. RESULTS: Aerosols produced during high-speed drilling were erratic and yielded high concentrations that were at least an order of magnitude above baseline. High-speed imaging showed aerosols initially travelled at 1 m per second. Owing to erratic behavior of aerosols, supplemental suction was not effective at collecting all aerosols; however, barriers were effective. CONCLUSIONS: Barriers are the most effective mitigation strategy. Other methods studied have limitations and risks. To the authors' knowledge, this article presents the first characterization of aerosols generated during high-speed drilling by a dentist. PRACTICAL IMPLICATIONS: With thorough preoperative planning and the use of this investigation's findings about effectiveness of mitigation strategies as a guide, dental offices may be able to return to prepandemic productivity.

Combustion Chemistry of Ethanol: Ignition and Speciation Studies in a Rapid Compression Facility.

Ethanol remains the most important alternative fuel for the transportation sector. This work presents new experimental data on ethanol ignition, including stable species measurements, obtained with the University of Michigan rapid compression facility. Ignition delay times were determined from pressure histories of ignition experiments with stoichiometric ethanol-air mixtures at pressures of ∼3-10 atm. Temperatures (880-1150 K) were controlled by varying buffer gas composition (Ar, N2, CO2). High-speed imaging was used to record chemiluminescence during the experiments, which showed homogeneous ignition events. The results for ignition delay time agreed well with trends on the basis of previous experimental measurements. Speciation experiments were performed using fast gas sampling and gas chromatography to identify and quantify ethanol and 11 stable intermediate species formed during the ignition delay period. Simulations were carried out using a chemical kinetic mechanism available in the literature, and the agreement with the experimental results for ignition delay time and the intermediate species measured was excellent for the majority of the conditions studied. From the simulation results, ethanol + HO2 was identified as an important reaction at the experimental conditions for both the ignition delay time and intermediate species measurements. Further studies to improve the accuracy of the rate coefficient for ethanol + HO2 would improve the predictive understanding of intermediate and low-temperature ethanol combustion.

In vivo biodistribution and physiologically based pharmacokinetic modeling of inhaled fresh and aged cerium oxide nanoparticles in rats.

BACKGROUND: Cerium oxide (CeO2) nanoparticles used as a diesel fuel additive can be emitted into the ambient air leading to human inhalation. Although biological studies have shown CeO2 nanoparticles can cause adverse health effects, the extent of the biodistribution of CeO2 nanoparticles through inhalation has not been well characterized. Furthermore, freshly emitted CeO2 nanoparticles can undergo an aging process by interaction with other ambient airborne pollutants that may influence the biodistribution after inhalation. Therefore, understanding the pharmacokinetic of newly-generated and atmospherically-aged CeO2 nanoparticles is needed to assess the risks to human health. METHODS: A novel experimental system was designed to integrate the generation, aging, and inhalation exposure of Sprague Dawley rats to combustion-generated CeO2 nanoparticles (25 and 90 nm bimodal distribution). Aging was done in a chamber representing typical ambient urban air conditions with UV lights. Following a single 4-hour nose-only exposure to freshly emitted or aged CeO2 for 15 min, 24 h, and 7 days, ICP-MS detection of Ce in the blood, lungs, gastrointestinal tract, liver, spleen, kidneys, heart, brain, olfactory bulb, urine, and feces were analyzed with a mass balance approach to gain an overarching understanding of the distribution. A physiologically based pharmacokinetic (PBPK) model that includes mucociliary clearance, phagocytosis, and entry into the systemic circulation by alveolar wall penetration was developed to predict the biodistribution kinetic of the inhaled CeO2 nanoparticles. RESULTS: Cerium was predominantly recovered in the lungs and feces, with extrapulmonary organs contributing less than 4 % to the recovery rate at 24 h post exposure. No significant differences in biodistribution patterns were found between fresh and aged CeO2 nanoparticles. The PBPK model predicted the biodistribution well and identified phagocytizing cells in the pulmonary region accountable for most of the nanoparticles not eliminated by feces. CONCLUSIONS: The biodistribution of fresh and aged CeO2 nanoparticles followed the same patterns, with the highest amounts recovered in the feces and lungs. The slow decrease of nanoparticle concentrations in the lungs can be explained by clearance to the gastrointestinal tract and then to the feces. The PBPK model successfully predicted the kinetic of CeO2 nanoparticles in various organs measured in this study and suggested most of the nanoparticles were captured by phagocytizing cells.

Effects of Bond Location on the Ignition and Reaction Pathways of trans-Hexene Isomers.

Chemical structure and bond location are well-known to impact combustion reactivity. The current work presents new experimental autoignition and speciation data on the three trans-hexene isomers (1-hexene, trans-2-hexene, and trans-3-hexene), which describe the effects of the location of the carbon-carbon double bond. Experiments were conducted with the University of Michigan rapid compression facility to determine ignition delay times from pressure time histories. Stoichiometric (ϕ = 1.0) mixtures at dilution levels of buffer gas:O2 = 7.5 (mole basis) were investigated at an average pressure of 11 atm and temperatures from 837 to 1086 K. Fast gas sampling and gas chromatography were also used to quantitatively measure 13 stable intermediate species formed during the ignition delay period of each isomer at a temperature of ∼900 K. The measured ignition delay times and species measurements were in good agreement with previous experimental studies at overlapping conditions. The results were modeled using a gasoline surrogate reaction mechanism from Lawrence Livermore National Laboratory, which contains a submechanism for the trans-hexene isomers. The model predictions captured the overall autoignition characteristics of the hexene isomers well (within a factor of 2), as well as the time histories of several of the intermediate species (e.g., propene). However, there were discrepancies between the model predictions and the experimental data for some species, particularly for the 3-hexene isomer.

Effects of new Ab initio rate coefficients on predictions of species formed during n-butanol ignition and pyrolysis.

Experimental, time-resolved species profiles provide critical tests in developing accurate combustion models for biofuels such as n-butanol. A number of such species profiles measured by Karwat et al. [ Karwat, D. M. A.; et al. J. Phys. Chem. A 2011 , 115 , 4909 ] were discordant with predictions from a well-tested chemical kinetic mechanism developed by Black et al. [ Black, G.; et al. Combust. Flame 2010 , 157 , 363 ]. Since then, significant theoretical and experimental efforts have focused on determining the rate coefficients of primary n-butanol consumption pathways in combustion environments, including H atom abstraction reactions from n-butanol by key radicals such as HO2 and OH, as well as the decomposition of the radicals formed by these H atom abstractions. These reactions not only determine the overall reactivity of n-butanol, but also significantly affect the concentrations of intermediate species formed during n-butanol ignition. In this paper we explore the effect of incorporating new ab initio predictions into the Black et al. mechanism on predictions of ignition delay time and species time histories for the experimental conditions studied by Karwat et al. The revised predictions for the intermediate species time histories are in much improved agreement with the measurements, but some discrepancies persist. A rate of production analysis comparing the effects of various modifications to the Black et al. mechanism shows significant changes in the predicted consumption pathways of n-butanol, and of the hydroxybutyl and butoxy radicals formed by H atom abstraction from n-butanol. The predictions from the newly revised mechanism are in very good agreement with the low-pressure n-butanol pyrolysis product species measurements of Stranic et al. [ Stranic, I.; et al. Combust. Flame 2012 , 159 , 3242 ] for all but one species. Importantly, the changes to the Black et al. mechanism show that concentrations of small products from n-butanol pyrolysis are sensitive to different reactions than those presented by Stranic et al.

Activist engineering: changing engineering practice by deploying praxis.

In this paper, we reflect on current notions of engineering practice by examining some of the motives for engineered solutions to the problem of climate change. We draw on fields such as science and technology studies, the philosophy of technology, and environmental ethics to highlight how dominant notions of apoliticism and ahistoricity are ingrained in contemporary engineering practice. We argue that a solely technological response to climate change does not question the social, political, and cultural tenet of infinite material growth, one of the root causes of climate change. In response to the contemporary engineering practice, we define an activist engineer as someone who not only can provide specific engineered solutions, but who also steps back from their work and tackles the question, What is the real problem and does this problem "require" an engineering intervention? Solving complex problems like climate change requires radical cultural change, and a significant obstacle is educating engineers about how to conceive of and create "authentic alternatives," that is, solutions that differ from the paradigm of "technologically improving" our way out of problems. As a means to realize radically new solutions, we investigate how engineers might (re)deploy the concept of praxis, which raises awareness in engineers of the inherent politics of technological design. Praxis empowers engineers with a more comprehensive understanding of problems, and thus transforms technologies, when appropriate, into more socially just and ecologically sensitive interventions. Most importantly, praxis also raises a radical alternative rarely considered-not "engineering a solution." Activist engineering offers a contrasting method to contemporary engineering practice and leads toward social justice and ecological protection through problem solving by asking not, How will we technologize our way out of the problems we face? but instead, What really needs to be done?

On the combustion chemistry of n-heptane and n-butanol blends.

High-speed gas sampling experiments to measure the intermediate products formed during fuel decomposition remain challenging yet important experimental objectives. This article presents new speciation data on two important fuel reference compounds, n-heptane and n-butanol, at practical thermodynamic conditions of 700 K and 9 atm, for stoichiometric fuel-to-oxygen ratios and a dilution of 5.64 (molar ratio of inert gases to O(2)), and at two blend ratios, 80%-20% and 50%-50% by mole of n-heptane and n-butanol, respectively. When compared against 100% n-heptane ignition results, the experimental data show that n-butanol slows the reactivity of n-heptane. In addition, speciation results of n-butanol concentrations show that n-heptane causes n-butanol to react at temperatures where n-butanol in isolation would not be considered reactive. The chemical kinetic mechanism developed for this work accurately predicts the trends observed for species such as carbon monoxide, methane, propane, 1-butene, and others. However, the mechanism predicts a higher amount of n-heptane consumed at the first stage of ignition compared to the experimental data. Consequently, many of the species concentration predictions show a sharp rise at the first stage of ignition, a trend that is not observed experimentally. An important discovery is that the presence of n-butanol reduces the measured concentrations of the large linear alkenes, including heptenes, hexenes, and pentenes, showing that the addition of n-butanol affects the fundamental chemical pathways of n-heptane during ignition.

On the chemical kinetics of n-butanol: ignition and speciation studies.

Direct measurements of intermediates of ignition are challenging experimental objectives, yet such measurements are critical for understanding fuel decomposition and oxidation pathways. This work presents experimental results, obtained using the University of Michigan Rapid Compression Facility, of ignition delay times and intermediates formed during the ignition of n-butanol. Ignition delay times for stoichiometric n-butanol/O(2) mixtures with an inert/O(2) ratio of 5.64 were measured over a temperature range of 920-1040 K and a pressure range of 2.86-3.35 atm and were compared to those predicted by the recent reaction mechanism developed by Black et al. (Combust. Flame 2010, 157, 363-373). There is excellent agreement between the experimental results and model predictions for ignition delay time, within 20% over the entire temperature range tested. Further, high-speed gas sampling and gas chromatography techniques were used to acquire and analyze gas samples of intermediate species during the ignition delay of stoichiometric n-butanol/O(2) (χ(n-but) = 0.025, χ(O(2)) = 0.147, χ(N(2)) = 0.541, χ(Ar) = 0.288) mixtures at P = 3.25 atm and T = 975 K. Quantitative measurements of mole fraction time histories of methane, carbon monoxide, ethene, propene, acetaldehyde, n-butyraldehyde, 1-butene and n-butanol were compared with model predictions using the Black et al. mechanism. In general, the predicted trends for species concentrations are consistent with measurements. Sensitivity analyses and rate of production analyses were used to identify reactions important for predicting ignition delay time and the intermediate species time histories. Modifications to the mechanism by Black et al. were explored based on recent contributions to the literature on the rate constant for the key reaction, n-butanol+OH. The results improve the model agreement with some species; however, the comparison also indicates some reaction pathways, particularly those important to ethene formation and removal, are not well captured.

The effects of the location of Au additives on combustion-generated SnO(2) nanopowders for CO gas sensing.

The current work presents the results of an experimental study of the effects of the location of gold additives on the performance of combustion-generated tin dioxide (SnO(2)) nanopowders in solid state gas sensors. The time response and sensor response to 500 ppm carbon monoxide is reported for a range of gold additive/SnO(2) film architectures including the use of colloidal, sputtered, and combustion-generated Au additives. The opportunities afforded by combustion synthesis to affect the SnO(2)/additive morphology are demonstrated. The best sensor performance in terms of sensor response (S) and time response (τ) was observed when the Au additives were restricted to the outermost layer of the gas-sensing film. Further improvement was observed in the sensor response and time response when the Au additives were dispersed throughout the outermost layer of the film, where S = 11.3 and τ = 51 s, as opposed to Au localized at the surface, where S = 6.1 and τ = 60 s.

The effects of two thick film deposition methods on tin dioxide gas sensor performance.

This work demonstrates the variability in performance between SnO(2) thick film gas sensors prepared using two types of film deposition methods. SnO(2) powders were deposited on sensor platforms with and without the use of binders. Three commonly utilized binder recipes were investigated, and a new binder-less deposition procedure was developed and characterized. The binder recipes yielded sensors with poor film uniformity and poor structural integrity, compared to the binder-less deposition method. Sensor performance at a fixed operating temperature of 330 °C for the different film deposition methods was evaluated by exposure to 500 ppm of the target gas carbon monoxide. A consequence of the poor film structure, large variability and poor signal properties were observed with the sensors fabricated using binders. Specifically, the sensors created using the binder recipes yielded sensor responses that varied widely (e.g., S = 5 - 20), often with hysteresis in the sensor signal. Repeatable and high quality performance was observed for the sensors prepared using the binder-less dispersion-drop method with good sensor response upon exposure to 500 ppm CO (S = 4.0) at an operating temperature of 330 °C, low standard deviation to the sensor response (±0.35) and no signal hysteresis.

H2O absorption spectroscopy for determination of temperature and H2O mole fraction in high-temperature particle synthesis systems.

Water absorption spectroscopy has been successfully demonstrated as a sensitive and accurate means for in situ determination of temperature and H2O mole fraction in silica (SiO2) particle-forming flames. Frequency modulation of near-infrared emission from a semiconductor diode laser was used to obtain multiple line-shape profiles of H2O rovibrational (v1 + v3) transitions in the 7170-7185-cm(-1) region. Temperature was determined by the relative peak height ratios, and XH2O was determined by use of the line-shape profiles. Measurements were made in the multiphase regions of silane/hydrogen/oxygen/ argon flames to verify the applicability of the diagnostic approach to combustion synthesis systems with high particle loadings. A range of equivalence ratios was studied (phi = 0.47 - 2.15). The results were compared with flames where no silane was present and with adiabatic equilibrium calculations. The spectroscopic results for temperature were in good agreement with thermocouple measurements, and the qualitative trends as a function of the equivalence ratio were in good agreement with the equilibrium predictions. The determinations for water mole fraction were in good agreement with theoretical predictions but were sensitive to the spectroscopic model parameters used to describe collisional broadening. Water absorption spectroscopy has substantial potential as a valuable and practical technology for both research and production combustion synthesis facilities.