Margaret S. Wooldridge

ABSTRACT A perturbation analysis modeling approach based on a genetic algorithm was used to identify possible reaction pathways to explain previous experimental observations of the strong acceleration of syngas auto‐ignition by trimethylsilanol (TMSO). Organosilicon reactions were taken from an existing chemical kinetic mechanism for tetramethylsilane pyrolysis which also contained TMSO reactions. The experimental targets for optimization were ignition delay times and peak OH radical concentrations in the range 1010–1070 K, 5 atm with dilute (4%) ϕ = 0.1 syngas mixtures in N 2 /Ar containing 0, 200, and 1000 ppm TMSO. Hundreds of thousands of trials resulted in three models which accurately predicted the experimental auto‐ignition times and peak OH concentrations. Rate of production analyses indicated that TMSO forms dimethylsilanediol, which then reacts creating two “catalytic loops.” The net effect of the loops is to accelerate the reaction H 2 + O = OH + H at a faster effective rate than H 2 /O 2 kinetics alone, thus enhancing the reactivity of syngas. The formation of the loops may be attributable to the high Si–C bond energies in siloxanols, reducing rates of thermal decomposition and allowing dimethylsilanediol to react with H 2 for a longer duration compared with its alkane analog. The results of the current work provide valuable direction for fundamental studies of these new hypothesized reaction pathways.

ABSTRACT In the current work, a hybrid and flipped (hybrid+flipped) course structure integrating open‐access pre‐recorded videos and in‐person class sessions was piloted with the objective of improving student experiences in a core undergraduate thermodynamics class in mechanical engineering. To minimize the barrier to instructor adoption, the course structure leveraged open‐access videos on the fundamentals of thermodynamics for the flipped portion of the class. The hybrid+flipped format allowed increased use of engaged‐learning tools during classroom sessions; methods known to improve learning outcomes (e.g., in‐class demonstrations, “think‐pair‐share” activities, and content and activities leveraging open‐access thermodynamics property data). Survey data from over 200 student participants from 2022 to 2023 document the student concerns at the start and exit of participation in the hybrid+flipped course sections. While the academic outcomes were unchanged compared with standard course delivery, student perceptions were dramatically affected. The survey data show significant positive shift in student concerns regarding online learning (44.2% were negative at the start of the course to 28.2% at the end of the class), and a large fraction of the students (45.6%) felt the hybrid+flipped format improved their learning outcomes. While the case study provides a valuable detailed example of how to successfully implement a hybrid+flipped class structure using open‐access tools, the results also show such efforts must correspondingly maintain high standards for organization and supplement the digital materials with community building and student and instructor engagement.

Large-eddy simulations are performed to quantify the influence of nozzle geometry on combustion efficiency, local mixing, and blowout resistance in non-assist methane flares. Five canonical nozzle shapes are evaluated under relevant industrial flare conditions, including a circle, low-aspect-ratio ellipse, high-aspect-ratio ellipse, diamond, and square. Cornered geometries are shown to enhance near-field recirculation, promote mixing, and sustain flame attachment, resulting in up to a 5 % improvement in combustion efficiency compared with streamlined nozzles. Square nozzles perform best, irrespective of wind direction, and maintain combustion efficiency above 96.5 % even at the highest tested crosswind velocities, while streamlined designs exhibit early flame lift-off, reduced recirculation, and efficiency losses. Sharp-edged nozzles also accelerate scalar homogenization and buffer flames against crosswind-induced strain, significantly improving blowout resistance. Despite the widespread use of circular nozzles in industry, these results highlight a passive geometric modification as a practical route to enhanced flare performance. • Nozzle corners enhance recirculation and increase flare combustion efficiency. • Square nozzles maintain > 96.5 % efficiency under strong crosswinds. • Cornered shapes delay blowout and outperform circles regardless of wind direction. • Mixing analysis reveals sharp edges accelerate fuel–air homogenization.

Abstract Waste gas flares frequently encounter turbulent crosswinds, which pose significant challenges to maintaining the EPA-mandated 96.5% combustion efficiency for non-assist flares. Strong crosswinds can distort flame shapes, disrupt mixing, challenge emissions measurements due to variable speeds and directions, and ultimately degrade flare efficiency. This study quantifies the impact of crosswind turbulence intensity on non-assist flare combustion efficiency using large-eddy simulations coupled with a flamelet progress variable approach. Results show that while jet-induced turbulence enhances mixing and improves combustion efficiency, turbulence from crossflows increases local strain rates and consistently reduces efficiency. Combustion efficiency drops by up to 10% at turbulence intensities approaching 20%. A new correlation for combustion efficiency, obtained using symbolic regression, captures both experimental and simulation data well across natural gas flare flow rates of 2–4 m/s and wind speeds of 0–10 m/s. Incorporating a power-law dependence on turbulence intensity significantly reduces data scatter.

Pyrolysis is a promising thermochemical process for managing sewage sludge while simultaneously producing biochar, a valuable co-product. This study systematically investigated the effects of the pyrolysis parameters of temperature (200–800 °C), residence time (5–60 min), and inert gas flow rate (0.25–1.0 dm 3 /min) on the properties of biochars obtained from sewage sludge. Comprehensive characterization of the biochars was conducted, including composition analyses (ultimate, proximate, elemental, and molecular), acidity, specific surface area and pore size, and the assessment of eight heavy metals (As, Cd, Pb, Cr, Zn, Mn, Ni and Cu) in the biochars and sewage sludge. The results showed pyrolysis temperature and residence time were the most critical parameters affecting biochar quality, with negligible influence of inert gas flow rate. Higher pyrolysis temperatures ( > 500 °C) increased biochar pH to alkaline values ( > 10), ash content, and nutrient concentrations (Ca, K, Mg, P). Temperatures above 600 °C significantly increased biochar surface area, reduced pore size, and yielded H/C ratios below 0.57, improving suitability for soil remediation. Pyrolysis also facilitated volatilization of heavy metals, particularly As and Cd, which were reduced to safe levels, with Cd removal exceeding 90% at 700 °C. Metal analysis confirmed the immobilization of heavy metals in biochar, significantly reducing the environmental risk, from high (PERI = 1158) in the sewage sludge feedstock to low (PERI < 50) in biochar obtained at temperatures above 600 °C. Most heavy metals in biochar at these temperatures were concentrated in oxidizable and residual fractions. The results provide valuable new data to guide development of pyrolysis for the sustainable management of sewage sludge.

Flaring serves as an important safety and emissions compliance tool in industries such as oil and gas production, refineries, and landfills. Nonassisted, low-flow (≤100 thousand cubic feet per day (MSCFD)), utility (pipe) flares are widely used in practice, yet there are limited studies of real-world conditions. Additionally, while shrouds (windshields) are commonly used to mitigate wind effects, their impact on flare performance is previously undocumented. This study introduces a novel outdoor testing facility designed to evaluate low-flow flares and quantitatively assess their performance with and without shrouds. Experiments were conducted at flare-gas flow rates of 5 to 75 MSCFD using natural gas and an 80% natural gas/20% propane blend (by volume) under crosswind speeds from 0 to over 35 miles per hour (MPH). Combustion efficiency (CE) and methane destruction removal efficiency (DRECH4) were determined for all operating conditions. While CE for a baseline utility flare (3-inch diameter pipe equipped with a pilot ignition system) was over 96.5% for crosswinds below 10 MPH, the CE decreased rapidly for crosswinds above 10 MPH, with CE <70% for crosswinds above 30 MPH. The utility flare results were compared with results of prior wind-tunnel studies and prior proposed scaling relationships and incorporated into machine learning (ML) models. The scaling relationships show poor correlation with the body of data, but the ML models yielded good agreement (R2 = 0.84) when crosswind turbulence intensity was incorporated as an input parameter. The current work investigated retrofitting a utility flare with different shroud designs, which increased CE ≥96.5% for all conditions, demonstrating the effectiveness of shrouds as practical and cost-effective strategies to improve utility flare performance. The results showed low sensitivity to different shroud designs.Implications: The U.S. Environmental Protection Agency (EPA), industry and other monitoring organizations commonly assume flares operate at 98% destruction efficiency; however, recent aerial surveys have revealed efficiencies as low as 91.1%, resulting in up to five times more methane emissions than expected. Low-flow (≤100 MSCFD) utility flares, widely deployed at oil and gas production sites, have limited performance data under real world conditions. This study addresses that gap by providing new experimental data on low-flow utility flares, identifying a new parameter important for predicting flare efficiency and demonstrating a practical solution for significantly reducing emissions.

Flares in the oil and gas industry are assumed to achieve methane destruction efficiency of 98%; however, recent studies reveal significantly lower efficiencies and higher-than-expected methane emissions from some flares. This study combines real-world operating parameters and wind data on actual flares in North Dakota with new experimental measurements of utility flare performance to quantify the effects of wind on methane emissions from these low-flow flares. The results show that wind speeds of 4.5–6.7 m/s (10–15 MPH) reduce the average methane destruction efficiency to 96.4%, doubling methane emissions from low-flow flares relative to current assumptions. Retrofitting utility flares with shrouds can increase efficiencies to ≥98%, reducing methane emissions by half, potentially avoiding on the order of 0.204 million metric tons of carbon dioxide equivalent emissions per year, and highlighting an inexpensive methane mitigation opportunity. The results also indicate that methane source estimates and aerial measurements likely undercount low-flow (≤0.033 m 3 /s or ≤100 thousand standard cubic feet per day, MSCFD) flares, missing an important source of methane emissions.

&lt;div&gt;The California Air Resources Board (CARB) and the United States Environmental Protection Agency (US EPA) have recently introduced targets for tailpipe emissions during high-power cold-start conditions for plug-in hybrid electric vehicles (PHEVs). However, the performance characteristics of hybrid powertrains and the effectiveness of cold-start strategies in PHEVs are not well known. In this two-part study, the performance of a production PHEV is examined with the objective of quantifying the impact of high-power cold-start events on overall tailpipe emissions. High temporal fidelity data of powertrain performance and tailpipe emissions generated during cold-start events for various driving conditions are presented for the first time. The selected P2 hybrid vehicle was tested using (i) the European Real Driving Emissions (RDE) test, (ii) the US06 (Supplemental Federal Test Procedure), and (iii) a custom drive cycle developed for this study. Results show that driving conditions leading to the events vary significantly between the drive cycles. Demand for high vehicle speed and/or high traction power triggered cold-start events despite the high battery state of charge. The results are discussed in detail in terms of the specific regulated air pollutants and powertrain performance monitored in the 50-seconds window following each cold-start event. In the companion study, tailpipe emissions characteristics and engine start strategies are compared across multiple hybrid topologies during a high-power cold-start event. The results from both studies provide valuable new information to enable design of hybrid powertrains for future PHEVs that meet the upcoming cold-start emissions regulations.&lt;/div&gt;

&lt;div&gt;The current work is the second installment of a two-part study designed to understand the impact of high-power cold-start events for plug-in electric vehicles (PHEVs) on tailpipe emissions. In part 1, tailpipe emissions and powertrain signals of a modern PHEV measured over three drive cycles identified that high-power cold-start events generated the highest amounts of gaseous and particulate emissions. The trends in emissions data and powertrain performance were specific to the P2-type hybrid topology used in the study. In this second part of the study, the effects of different PHEV hardware configurations are determined. Specifically, the tailpipe emissions of three production plug-in hybrid vehicles, operated over the US06 drive cycle, are characterized. The approach compared the tailpipe emissions of the test vehicles on the basis of the hybrid topologies and corresponding engine operational characteristics during a high-power cold-start event. Analysis of test results showed differences in the engine startup strategy for different hybrid configurations. Time-resolved tailpipe emissions of CO, NOx, total unburned hydrocarbons (THC), and particulates varied depending on the engine load during the cold-start. The likelihood of experiencing a high-power cold-start on the US06 was dependent on powertrain characteristics including e-motor size and battery state of charge. The results are discussed in detail in terms of the specific regulated air pollutants and the impact of the startup strategy implemented. Lastly, vehicle dynamics including drag and inertia forces were found to be much lower for the smaller power-split hybrid test vehicle, which reduced its propensity to experience a high-power cold-start event. The findings provide insights on how to manage high-power cold-start events in relation to the type of hybrid configuration utilized as well as their capability to meet upcoming emissions targets.&lt;/div&gt;

Extensive use of organic silicon compounds in consumer products has led to their presence in landfills and wastewater treatment plants (WWTPs), hindering energy production from waste-derived biogas. This work broadly characterized the scope and scale of volatile silicon species in biogas by consolidating global data from the literature and applying statistical analysis. The current work also includes original data from two United States (US) Midwest landfills for a period of two years. The data from the literature showed siloxanes are present at similar levels worldwide in landfills and WWTPs, with no clear trends over time. Most of the data in the literature were from European countries, with fewer data from US and Asian countries. Statistical analysis shows that trimethylsilanol (TMSO) correlated well with the total siloxane content of landfill biogas (R 2 = 0.96), and decamethylcyclopentasiloxane (D5) correlated well with the total siloxane content of WWTP biogas (R 2 = 0.95). The strong correlations identified in the current work suggest TMSO and D5 can serve as sentinel species for total siloxane content monitoring. Results from sampling the Midwest landfill sites showed similar species and concentration trends as found with the literature data, except for octamethyltrisiloxane (L3). The new quantitative results on local and global siloxane trends provide a foundation of biogas characteristics that may be helpful for species measuring and monitoring, gas clean-up development, and resource recovery. The results also underscore the need for additional data from diverse sources to assess challenges and enable solutions for waste-derived biogas systems.

Abstract Strategies to mitigate cold-start emissions are critical to meet stringent standards for particulate and regulated gaseous emissions from direct injection spark ignition (DISI) engines. The objective of the current work was to establish an experimental protocol for cold-start studies and to identify the in-cylinder phenomena important during engine warming in terms of engine power and stability and engine-out particulates, NOx, and unburned hydrocarbon emissions. Metal-engine experiments were conducted with ambient intake air temperature and coolant air temperature of 20 °C to quantify the sensitivity of the performance of a single-cylinder engine to timing of a strategy using two injection events per power cycle and late spark ignition. The results showed strong sensitivity to the timing of the second injection event and weak sensitivity to the timing of the first injection. Complementary high-speed imaging experiments were conducted with the same engine where the fuel spray and combustion characteristics were visualized during cold-start split-injection operation. The imaging data showed the sources of particulates were due to fuel impingement on combustion chamber surfaces and due to fuel rich regions, in particular regions where the fuel recondensed due to the conditions associated with late ignition timing. The combination of engine-out particulate and imaging measurements indicated smaller particles (10–20 nm) were associated with fuel impingement on surfaces, and larger particles (20–200 nm) were associated with fuel rich “pockets”.

Non-assisted flares are a significant fraction of the flares in use today, but there are few studies at real-world conditions. The current work presents a novel indoor testing facility for characterizing non-assisted flares including the effects of crosswind. Multiple flare designs were tested using flare gas flow rates from 1.8 to 113 thousand standard cubic feet per day (MSCFD) with natural gas and propane at crosswind speeds from 0 to 13.1 miles per hour (MPH). Combustion efficiency (CE) and destruction removal efficiency of methane (DRE CH 4 ) were determined for all operating conditions. CE > 98% was observed for low crosswind conditions for all flare geometries; however, the 3-in. pipe flare underperformed (CE < 96.5%) for natural gas at higher wind speeds and lower flare gas flow rates (e.g., 6.8 MSCFD and >4.6 MPH). Engineered burners significantly improved performance. The results are discussed in the context of EPA assumptions, prior pipe flare wind-tunnel studies, and proposed scaling relations.

) for C-C bond-fission have been under-predicted for this decomposition reaction. Consequently, results from the present studies place an increased emphasis on radical-driven secondary processes in high-temperature pyrolysis of this simplest secondary alcohol.

= 50 and 52 were observed providing insight into secondary reactions. These features have not been previously reported in propanol-pyrolysis literature.

Purpose The purpose of this study was to evaluate the effectiveness of sustainability-focused, cocurricular, interdisciplinary programming for graduate students at creating future leaders in sustainability, i.e. did interdisciplinary sustainability programming further prepared graduate students in sustainability leadership beyond the scope of the individual student academic programs from the perspective of the student participants. Design/methodology/approach The objective of the study was met by evaluating the University of Michigan Dow Sustainability Fellows Program. With a decade of graduate-student participation, surveys and interviews of Fellows alumni from 2013 to 2020 were used to assess the program impact on creating sustainability leaders. Opportunities for program reflections were included through prompted open-ended questions. Findings A majority (88%) of the Fellows who responded to the survey agreed with the statement that their career path was positively affected by their participation in the program and that the cocurricular program provided opportunities to explore sustainability-related topics from perspectives they would not have experienced otherwise. The interdisciplinary aspect of the program and the focus on practical community sustainability projects were the most valued attributes of the cocurricular programming. Research limitations/implications Supporting cocurricular interdisciplinary programs requires significant resources and intentionality to engage diverse disciplines and diverse partner organizations. Practical implications Programs that provide experiential opportunities to build interdisciplinary team skills successfully enable graduate students to become leaders in sustainability fields in the workplace and in outreach and service. Social implications Cocurricular graduate student programming focused on community sustainability projects can successfully create valued learning experiences while simultaneously supporting communities with practical solutions to sustainability challenges. Originality/value To the best of the authors’ knowledge, this work is the first longitudinal assessment of the effectiveness of the interdisciplinary cocurricular programming on graduate student sustainability leadership outcomes. The results include feedback received from eight years of cocurricular programming.

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;Prior work in the literature have shown that pre-chamber spark plug technologies can provide remarkable improvements in engine performance. In this work, three passively fueled pre-chamber spark plugs with different pre-chamber geometries were investigated using in-cylinder high-speed imaging of spectral emission in the visible wavelength region in a single-cylinder direct-injection spark-ignition gasoline engine. The effects of the pre-chamber spark plugs on flame development were analyzed by comparing the flame progress between the pre-chamber spark plugs and with the results from a conventional spark plug. The engine was operated at fixed conditions (relevant to federal test procedures) with a constant speed of 1500 revolutions per minute with a coolant temperature of 90 &lt;sup&gt;o&lt;/sup&gt;C and stoichiometric fuel-to-air ratio. The in-cylinder images were captured with a color high-speed camera through an optical insert in the piston crown. The images showed plumes of reacting gases originating from the pre-chamber orifices and the subsequent flame development in the main combustion chamber of the engine. Flame characteristics were quantified from the images. Quantitative analysis of the images showed all the pre-chamber spark plugs consistently yielded faster flame development (approximately 4.7 CAD) compared with flames created by the conventional spark plug. The flame fronts from the pre-chamber spark plugs were 1.54-2 times larger than those from the conventional spark plug. The imaging data also showed significant cycle-to-cycle variability during the initial stage of the flame development from the pre-chambers with smaller/later jets for some cycles. However, the flame progress recovered rapidly to more uniform propagation later in the cycles. The different pre-chamber geometries did not lead to significant differences in the combustion characteristics at the studied conditions, although the pre-chamber with asymmetric orifice sizes yielded slightly larger variability and delayed flame development compare with the other pre-chamber designs. The relatively modest effects of the different pre-chamber designs are attributed to potentially offsetting changes in the dominant physical mechanisms affecting the ignition process at the conditions studied.&lt;/div&gt;&lt;/div&gt;

The potential defects during the additive manufacturing (AM) process greatly deteriorate the mechanical properties of the fabricated structures and, as a result, increase the risks of part fatigue failure and even disasters. As laser additive manufacturing is such a complex process, many different physical phenomena such as electromagnetic radiation, optical and acoustic emission, and plasma generation will occur. Unlike vision and acoustic methods, the spectroscopy based smart optical monitoring system (SOMS) provides atomic level information revealing mechanical and chemical condition of the product. By monitoring plasma, multiple information such as line intensity, standard deviation, plasma temperature, or electron density, and by using different signal processing algorithms such as vector machine training or wavelet transforming, AM defects have been detected and classified. Utilizing two fiber optic components, a bifurcated fiber and a split fiber, the experimental results were performed to improve SOMS signal-to-noise ratio. Defects, including subsurface pores and sudden changes of process parameters including shielding gas shut-off and foreign substance, were identified by the spectroscopy based SOMS. For chemical composition characterization, a degree of dilution in terms of chemical element variation is identified by a spectral peak intensity ratio through the SOMS. It turned out that the information on the Cr/Fe ratio of deposit at a certain layer is vital to design the mechanical property in the IN625 deposition on the mild steel case. The SOMS has also demonstrated that the chemistry ratio can be determined from the calibration curve method based on the known alloy samples and that the ratio of the maximum intensities of multiple species provides more information about the quality of the alloy.