Paul D. Ronney

Lewis and von Elbe’s data on minimum spark ignition energies in gases have been the standard for many years, however, these data still do not agree with the most detailed computational models available. With this motivation, their classic experiment was revisited using laser ignition sources, with an emphasis on better characterization of the ignition source and its effect on minimum ignition energy. The apparatus consisted of a laser ignition source operating either as a Q-switched nanosecond or a pulse mode-locked picosecond laser. For CH4-ąir mixtures of varying stoichiometry the minimum ignition energy was bracketed through repeated trials at varying laser spark energies. Laser spark kernel sizes were quantified by imaging the visible emission of these sparks. Results showed that the laser ignition experiments are consistent with Lewis and von Elbe’s measurements for lean and rich mixtures, however, for near-stoichiometric mixtures, the laser ignition values were higher. These results are interpreted in the context of the size of the energy deposition region. Further studies to assess this interpretation are identified.

Hydrocarbon fuels contain approximately 50 times more energy per unit mass than commercial batteries, thus converting even 10% of the energy contained in hydrocarbon fuels to electrical energy could present a more mass-efficient electrical energy source than batteries. Considering the storability of hydrocarbon fuels compared to hydrogen, the viability of direct hydrocarbon polymer electrolyte membrane fuel cells was examined. With extremely pure (> 99.99%) propane, the cell Open-Circuit Voltage (OCV) was only 0.05 V and produced negligible power. However, with addition of trace quantities of unsaturated hydrocarbons, the cell had an OCV of 0.85 V and produced power, even after the unsaturated hydrocarbon addition was discontinued. At sufficiently high current densities, power output gradually decreased then the cell rapidly “extinguished” but by periodically shutting off the current for short time intervals the average power density could be increased significantly. Chemical analysis revealed that no significant amounts of hydrocarbon intermediates or CO were present in the effluent and that conversion of the hydrocarbon fuel to CO 2 and H 2 O was nearly complete. An analytical model incorporating the relative rates of conversion of active anode catalyst sites to inactive sites and vice versa was developed to interpret this behavior. The model predictions were consistent with the experimental observations; possible physical mechanisms are discussed.

A unique curriculum adaptation of a Computer-Aided Design (CAD) course was developed for visually impaired students.This initiative was undertaken to ensure equitable access and foster an inclusive learning environment.The curriculum was designed to familiarize students with the functionalities and limitations of CAD software and the foundational processes of design, and to facilitate their interaction with other engineers using these tools.The teaching approach predominantly involves a series of 3D printed models accompanied by detailed text documentation, illustrating the CAD creation process behind these models.A teaching assistant (TA) is assigned to guide students following the adapted curriculum through examples and assignments aligned with the standard class syllabus.Assignments were tailored to include both the study of pre-made 3D printed parts and the oral description of steps for creating similar parts in Siemens NX.This method not only addresses the unique needs of visually impaired students but also provided insights into the effectiveness of tactile and descriptive learning in CAD education.The broader impact of this work lies in its demonstration of the potential for personalized teaching techniques in engineering education, particularly for students with visual impairments.It underscores the importance of inclusivity in technical fields and paves the way for more accessible and diverse educational environments.

G-equations are popular level set Hamilton–Jacobi nonlinear partial differential equations (PDEs) of first or second order arising in turbulent combustion. Characterizing the effective burning velocity (also known as the turbulent burning velocity) is a fundamental problem there. We review relevant studies of the G-equation models with a focus on both the existence of effective burning velocity (homogenization), and its dependence on physical and geometric parameters (flow intensity and curvature effect) through representative examples. The corresponding physical background is also presented to provide motivations for mathematical problems of interest. The <italic>lack of coercivity</italic> of Hamiltonian is a hallmark of G-equations. When either the curvature of the level set or the strain effect of fluid flows is accounted for, the Hamiltonian becomes <italic>highly nonconvex and nonlinear</italic> . In the absence of coercivity and convexity, the PDE (Eulerian) approach suffers from insufficient compactness to establish averaging (homogenization). We review and illustrate a suite of Lagrangian tools, most notably min-max (max-min) game representations of curvature and strain G-equations, working in tandem with analysis of streamline structures of fluid flows and PDEs. We discuss open problems for future development in this emerging area of dynamic game analysis for averaging noncoercive, nonconvex, and nonlinear PDEs such as geometric (curvature-dependent) PDEs with advection.

G-equations are popular level set Hamilton-Jacobi nonlinear partial differential equations (PDEs) of first or second order arising in turbulent combustion. Characterizing the effective burning velocity (also known as the turbulent burning velocity) is a fundamental problem there. We review relevant studies of the G-equation models with a focus on both the existence of effective burning velocity (homogenization), and its dependence on physical and geometric parameters (flow intensity and curvature effect) through representative examples. The corresponding physical background is also presented to provide motivations for mathematical problems of interest. The lack of coercivity of Hamiltonian is a hallmark of G-equations. When either the curvature of the level set or the strain effect of fluid flows is accounted for, the Hamiltonian becomes highly non-convex and nonlinear. In the absence of coercivity and convexity, PDE (Eulerian) approach suffers from insufficient compactness to establish averaging (homogenization). We review and illustrate a suite of Lagrangian tools, most notably min-max (max-min) game representations of curvature and strain G-equations, working in tandem with analysis of streamline structures of fluid flows and PDEs. We discuss open problems for future development in this emerging area of dynamic game analysis for averaging non-coercive, non-convex, and nonlinear PDEs such as geometric (curvature-dependent) PDEs with advection.

The effect of confinement on the propagation of lean hydrogen–air flames in a Hele-Shaw cell, formed by two parallel plates separated by a small distance, is studied numerically. The influence of momentum loss on the flame structure and propagation rates is analyzed by examining two limits: (i) the limit of very small distance between the plates, for which a quasi-three-dimensional (quasi-3D) Darcy’s law-based approximation is used, and (ii) the limit of unconfined geometry, for which the full set of two-dimensional (2D) Navier-Stokes equations is considered. The influence of heat losses is also included. The chemistry is described by a one-step reduced kinetics with a simple model for transport properties. The results demonstrate that momentum loss primarily increases the flame surface area by elongating the cellular structures in a finger-like form, with a relatively small enhancement of the reactivity at the flame front, consistent with a mechanism of hydrodynamic nature. This elongation leads to approximately a 50% increase in flame speed compared to the absence of confinement. Conversely, heat losses are observed to flatten the large-scale continuous flame front and, if significant enough, can lead to the formation of isolated propagating flame cells of the two-headed or, ultimately, one-headed type. The present results are in good agreement with recent experiments.

In tropical and subtropical ocean gyres, Trichodesmium colonies account for up to half of the total N2 fixation in the ocean, making it one of the most ecologically significant N2-fixing cyanobacteria. The processes whereby Trichodesmium colonies and large-scale surface blooms form have not been investigated thoroughly. In particular, the effects of fluid motion have not been included in previous studies. As the first step toward understanding the mechanical processes associated with Trichodesmium colony synthesis, we propose a shear-related flow-based growth model to enlighten how fluid dynamics affect bacteria colony formation and growth. To investigate the possibility that early growth characteristics are strongly dependent on the shear rate, a two-way coupled fluid-colony interaction is developed using the lattice Boltzmann method for a porous colony. This model captures the exponential growth trend during the colony formation phase found in experiments. Our results show that the flow field significantly impacts both the colony growth rate and shape. In pure shear conditions, colonies grow in circular shapes, whereas in uniform flow, they take filament-like forms. Additionally, the Reynolds number (Re) plays a crucial role in shaping the colonies, especially in uniform flow conditions where its effect is more profound.