The two-fluid plasma equations describing a magnetized plasma, originating from truncating moments of the Vlasov-Boltzmann equation, are increasingly used to describe an ion-electron plasma whose transport phenomena occur on a time scale slower and a length scale longer than those of particle collisions. A similar treatment under more stringent constraints gives the single-fluid magnetohydrodynamic (MHD) equations for low-frequency macroscopic processes. Since both stem from kinetic theory, the two-fluid plasma and MHD equations are necessarily related to each other. Such a connection is often established via ad hoc physical reasoning without a firm analytical foundation. Here, we perform a sequence of formal expansions for the dimensionless ideal two-fluid plasma equations with respect to limiting values of the speed-of-light c, the ion-to-electron mass ratio M, and the plasma skin depth dS. Several different closed systems of equations result, including separate systems for each limit applied in isolation and those resulting from limits applied in combination, which correspond to the well-known Hall-MHD and single-fluid ideal MHD equations. In particular, it is shown that while the zeroth-order description corresponding to the c→∞ limit, with M and dS fixed, is strictly charge neutral, it nonetheless uniquely determines the perturbation charge non-neutrality at the first order. Furthermore, the additional M→∞ limit is found to be not required to obtain the single-fluid MHD equations despite being essential for the Hall-MHD system. The hierarchy of systems presented demonstrates how plasmas can be appropriately modeled in situations where only one of the limits applies, which lie in the parameter space in between where the two-fluid plasma and Hall-MHD models are appropriate.

In this work, the spray and auto-ignition characteristics of light naphtha (LN), primary reference fuels (PRF65, PRF95), Haltermann gasoline (CARB LEVIII, 10 vol% ethanol), and a gasoline surrogate were studied in an optically accessible constant volume combustion chamber. An outwardly opening hollow cone piezoelectric gasoline direct injection fuel injector was used. Five ambient temperatures from 650 to 950 K with a 75 K step were selected with a fixed ambient density of 3.5 kg/m, similar to the Spray G density defined by the engine combustion network (ECN). Fuel auto-ignition was achieved with varying ignition delays for the five investigated fuels depending on the selected experimental conditions. Results show that the auto-ignition locations are randomly distributed in the combustion chamber. Differences in ignition delay times among the five fuels are more significant when the ambient temperature is lower than 750 K. When the ambient temperature is lower than 750 K, PRF95 always has the longest ignition delay and LN has the shortest. Ignition delays of the five fuels are almost identical when the ambient temperature exceeds 750 K. Meanwhile, the five fuels have a similar spray front penetration length and spray angles before the occurrence of auto-ignition under all the investigated conditions.

The oxidation chemistry of complex hydrocarbons involves large mechanisms with hundreds or thousands of chemical species and reactions. For practical applications and computational ease, it is desirable to reduce their chemistry. To this end, high-temperature fuel oxidation for large carbon number fuels may be described as comprising two steps, fuel pyrolysis and small species oxidation. Such an approach has recently been adopted as ‘hybrid chemistry’ or HyChem to handle high-temperature chemistry of jet fuels by utilizing time-series measurements of pyrolysis products. In the approach proposed here, a shallow Artificial Neural Network (ANN) is used to fit temporal profiles of fuel fragments to directly extract chemical reaction rate information. This information is then correlated with the species concentrations to build an ANN-based model for the fragments’ chemistry during the pyrolysis stage. Finally, this model is combined with a C0-C4 chemical mechanism to model high-temperature fuel oxidation. This new hybrid chemistry approach is demonstrated using homogeneous chemistry calculations of n-dodecane (n-C12H26) oxidation. The experimental uncertainty is simulated by introducing realistic noise in the data. The comparison shows a good agreement between the proposed ANN hybrid chemistry approach and detailed chemistry results.

We present an investigation of the dynamic behavior of an electrostatically actuated clamped–clamped microbeam, under the simultaneous excitation of primary and subharmonic resonance. The simultaneous excitation of primary and subharmonic resonances of similar strength is experimentally investigated by using different combinations of AC and DC voltages. It is observed that the response of the resonator is governed by a mixed effect of both excitations. Subharmonic-dominated response shows sharp amplitude transitions and smaller monostable regime, while primary-dominated response shows gradual amplitude transition and larger monostable regime. Two potential applications are experimentally demonstrated. The first is a resonator-based MEMS AND logic gate based on AC only subharmonic excitation. The second is a charge sensor based on the transition from subharmonic-dominated response to primary-dominated response, which is potentially capable of detecting a small amount of electric charges.

Dual-pump coherent anti-Stokes Raman spectroscopy (CARS) was used to measure the mole fractions of major species as well as the rotational and vibrational temperatures of molecular nitrogen in a hydrogenfueled dual-mode scramjet flowpath operated in the

A sensor based on cavity-enhanced absorption spectroscopy (CEAS) was implemented for the first time in a rapid compression machine (RCM) for carbon monoxide concentration measurements. The sensor consisted of a pulsed quantum cascade laser (QCL) coupled to a low-finesse cavity in the RCM using an off-axis alignment. The QCL was tuned near 4.89μm to probe the P(23) ro-vibrational line of CO. The pulsed mode operation resulted in rapid frequency down-chirp (6.52 cm-1/μs) within the pulse as well as a high time resolution (10 μs). The combination of rapid frequency down-chirp and off-axis cavity alignment enabled a near complete suppression of the cavity coupling noise. A CEAS gain factor of 133 was demonstrated in experiments, resulting in a much lower noise-equivalent detection limit than a single-pass arrangement. The sensor thus presents many opportunities for measuring CO formation at low temperatures and for studying kinetics using dilute reactive environments; one such application is demonstrated in this work using dilute n-heptane/air mixtures in the RCM. The formation of CO during first-stage ignition of n-heptane was measured over 802-899K at a nominal pressure of 10bar. These conditions correspond to the NTC region of n-heptane and such results provide useful metrics to test and compare the predictions of low-temperature heat release by different kinetic models.

This paper presents a study of the quality factor dependence on the geometrical parameters of in-plane clamped-clamped micro- and nano-beams capacitive structures at low-to-high pressure range. We found that smaller length and larger beam thickness maximize the quality factor. To minimize squeeze film damping, the structures have been fabricated with large capacitive air gaps. Despite the high ratio of the gap/thickness, we report significant effect of the gap width on the quality factor. It is found that, for micro-beams, this effect is limited at low pressure while for nano-beams, it continues until high pressure range. The geometry and the air gap effects on the damping of beams resonators have been examined experimentally. A finite-element study of the effect of the capacitive gap for in-plane resonators of one and two-side electrodes is presented. It is found that the presence of the double electrodes for in-plane resonators can cause significant drop of the quality factor compared to the single-sided beam resonator.

A silicon based nanoelectromechanical resonator is fabricated and is actively tuned through electrostatic actuation. We present multifrequency excitation of a NEMS resonator to dynamically perform all the fundamental logic operations (NOT, NOR, XNOR, NAND, OR, AND, and XOR). The multifrequency excitation allows to uniquely define resonant and non-resonant states as high and low logic outputs for all fundamental logic gates. The performance of this logic device is examined in terms of its speed of operation, energy consumption, and integration density. This work paves the way towards energy efficient nano-elements-based mechanical computing.

We investigate the influence of process-induced shrinkage and subsequent annealing on the thermomechanical behavior of unidirectional laminates made of continuous glass fiber-reinforced polypropylene (GFPP). We use two different industrial lamination processes: static hot-press (SHP), and double-belt press (DBP) that are characterized by different cooling rates and pressure levels and most importantly, by the use of a closed mold in the case of SHP manufacturing. We measure the longitudinal and transverse shrinkage during the manufacturing and annealing processes using embedded fiber Bragg gratings (FBGs). The SHP molding reveals much lower induced shrinkage in GFPP as compared to the DBP process, although the relatively slow cooling should promote a higher degree of crystallization. We ascribe this to the constraining effect of the metallic mold used with the SHP process. The poor thermal conductivity of the mold is also responsible for a layer-like crystal microstructure in the GFPP matrix, causing a specific relaxation effect during the post-process heating treatment. Annealing generates additional shrinkage that is due to an increased degree of crystallinity and to the partial relaxation of residual stresses. However, the thermal expansion properties remain impacted by the process-induced strain state of the GFPP laminates and are still process-dependent after annealing.

Measuring parameters related to each damage mode of composites subjected to impact is very challenging because of the complex damage phenomenology. Here, we developed an experimental methodology for evaluating the micro-scale fracture characteristics of two principal damage modes, i.e., transverse crack and delamination, and providing the corresponding fracture toughness. We demonstrated the capability of the method by comparing and providing additional insights about two materials, namely homopolymer-based (ductile) and copolymer-based (less-ductile) glass/polypropylene thermoplastic composites. We found that (i) transverse crack behavior of both composites is similar as indicated by a small difference in their fracture toughness, (ii) delamination growth in copolymer-based composites is slower than in homopolymer-based composites, (iii) the fibrillation induced by rubber particles in copolymer-based composites is responsible for decelerating the delamination growth and improving its fracture toughness during delamination. This method is deemed useful and quick for determining the micro-scale fracture behavior of composite laminates under impact in order to support the material selection process.