21794 research outputs found
Sort by
Autoignition-Assisted Flame Regimes In Ammonia And Dimethyl Ether Blends: A Sustainable Aviation Fuel
No full textAs the global energy landscape transitions towards sustainable alternatives, ammonia and dimethyl ether (NH3/DME) mixtures have emerged as promising, low-carbon surrogate fuels with an existing production infrastructure and the potential for net-zero carbon emissions. However, the combustion behavior of surrogate mixtures at conditions representative of advanced engines and gas combustors remains insufficiently understood. This dissertation addresses this gap by investigating both autoignition and flame propagation in NH3/DME mixtures and by benchmarking its combustion properties against conventional jet fuels (e.g., JP-8 and JP-5) to evaluate their suitability as sustainable aviation fuels.The initial research focuses on investigating autoignition behavior using a rapid compression machine (RCM). Ignition delay times were measured at end-of-compression pressures of 5, 10, and 20 bar, with gas temperatures of 621–725 K, for stoichiometric NH3/DME mixtures with 10% to 50% DME by mole. Results indicated that increasing the DME fraction from 10% to 50% reduced ignition delays by up to 65% across all pressures, underscoring DME’s significant role as an ignition promoter. These experiments provided high-fidelity ignition data at elevated thermodynamics conditions, with the 30% DME mixture’s ignition delay closely matching that of conventional jet fuels under comparable conditions. Subsequently, the research examines laminar flame speeds using a novel RCM–Flame configuration, enabling the study of two distinct regimes: autoignition-assisted flame propagation (affected by pre-flame autoignition chemistry) and conventional laminar flame propagation (unaffected by pre-flame autoignition chemistry). Validation experiments with methane (3.04 bar, 740–765 K) and n-heptane (6.85 bar, 595–621 K) confirmed the reliability and reproducibility of this novel experimental approach. These tests showed that the effects related to chamber size, temperature inhomogeneity, data analysis methodology, and flame stretch on flame dynamics are negligible, ensuring high measurement fidelity. Considering uncertainties, measurement accuracies are within 7.5% of the established literature values, confirming the technique’s robustness and reliability. Comparison with one-dimensional and three-dimensional simulations further validated the technique’s capabilities and revealed limitations in current kinetic mechanisms under autoignition conditions. Building on these validation findings, experiments with stoichiometric NH3/DME mixtures at pressures of 5, 10, and 15 bar and gas temperatures of 540–710 K identified distinct pressure-, temperature-, and density-dependent characteristics and elucidated the effect of first-stage ignition delay on flame propagation. A numerical comparison offered further insight into how effectively existing kinetic models represent the underlying chemistry and flame dynamics of NH3/DME surrogates. The results indicate that 50% DME in an NH3/DME mixture can successfully mimic the combustion characteristics of conventional jet fuel characteristics under analogous conditions. Furthermore, the results show that post-first-stage ignition flame speeds were more sensitive to temperature variations than to changes in pressure and/or unburned gas density. Finally, these findings provide a foundational dataset and deeper understanding of NH3/DME combustion, offering the potential for guiding future fuel formulations, optimizing combustion system design, and improving kinetic mechanism development for cleaner, more efficient propulsion and power generation applications
Optimization Of Free-Time Controlled Constrained Sweeping Processes And Applications
No full textOptimization and optimal control have a wide range of applications across fields like engineering, biology, data science, and economics. This dissertation is devoted to advanced optimal control problems discontinuous constrained differential inclusions of the sweeping type involving the duration of the dynamic process into optimization, which are truly challenging and underinvestigated in control theory while being highly important for various applications. To attack such problems, we use the method of discrete approximation while establishing its well-posedness and strong convergence to optimal solutions of the controlled sweeping process. This approach, married to advanced tools of variational analysis, enables this research to derive necessary optimality conditions for the original problem with a wide range of applications, including nanoparticle dynamics, marine surface vehicles, and robotics models. Key contributions also include the development of numerical algorithms to solve these optimization problems, using the Python Dynamic Optimization library GEKKO to simulate solutions to the posed robotics problems in the case of any fixed number of robots
The Politics of Style: How Black Fashion Redefined Identity in the Civil Rights Movement (1950s-1970s)
No full textThis paper explores how fashion served as a powerful political tool during the Civil Rights Movement of the 1950s-70s, tracing its evolution from the polished Sunday Best to the Afro and militant style of the Black Panther Party. By examining respectability politics, the rise of the Black is Beautiful movement, and the Black Panthers’ visual strategies, this research explores how clothing and style reflected shifting approaches to resistance. It argues that Black Americans used fashion to challenge Eurocentric standards, reclaim heritage, and express pride, leaving a legacy of empowerment that continues to influence social movements
Beyond the Binary: Gender & Space in the Art of Helen McNicoll (1879-1915)
No full textIn recent art history discourse, scholars have proposed reworking the binarism perpetuated by separate sphere ideology that led to a lack of nuance. This paper situates itself within this renewed framework, using McNicoll’s market scenes which breaks down the rigid dichotomous nature of gendered spaces and confronts how labor and class relations complicate the gender-spatial dynamic. I propose that these images begin to collapse the binaries of the public/private and urban/rural debates, creating more fluid binaries
Spinning Bodies into Gold: Thread, Labor, and Choice in Karen Russell’s “Reeling for the Empire” and Paul Thomas Anderson’s Phantom Thread
No full textThis article uses the tale of “Rumpelstiltskin” as a framing device to explore Paul Thomas Anderson’s feature film Phantom Thread (2017) and Karen Russell’s short story “Reeling for the Empire” (2013) as contemporary fairy tales that illuminate the relationship thread, production, and bodies have to exploitation, specifically in relation to gender. It argues that Anderson and Russell both draw on fairy tale to examine the murky exchanges embedded in advanced capitalist modes of production
