Wide Range Of Initial Pressures Research Articles

Efficient Lithium Metal Cycling at a Wide Range of Pressures from an Anion-Derived Solid-Electrolyte Interphase Framework

Novel electrolytes have been developed to improve the cyclability of lithium (Li) metal anodes, yet their working mechanisms remain unclear. The dependence of the performance on the operational pressure can provide valuable insights on the Li plating mechanisms in different electrolytes. Here, we study Li cycling performance evolution against pressure in 1 M LiFSI/fluorinated 1,4-dimethoxylbutane (FDMB) electrolyte, one of the highest-performing electrolytes for Li metal to date. We show that it enables excellent Coulombic efficiency (CE) in a pouch cell format under a wide range of initial pressures (30-600 psi). We discover that this is due to a completely different Li plating mode with superior deposition morphologies compared to that in a conventional carbonate electrolyte, which exhibits increasing cycle stability with increased pressure. We show that this is enabled by the properties of an anion-derived residual solid-electrolyte interphase (rSEI) framework on the electrode surface, an undercharacterized structure with profound implications for Li metal cycling. The plating morphology enabled by this anion-derived rSEI chemistry is likely the key to a prolonged cycle life in high performance electrolytes for Li metal.

Study on the effects of initial pressure and temperature on the explosion characteristics of DME-blended LPG mixtures in an obstructed confined pipeline

Numerical analyses were conducted to study the explosion characteristics of premixed LPG/DME/Air mixture in an obstructed confined pipeline of length 3 m and diameter 0.1 m under a wide range of initial pressures (100 to 300 kPa) and temperatures (−20 to 200 °C). The explosion overpressure, flame temperature and flame propagation along axial direction were investigated. The results indicated that the maximum explosion overpressure was raised significantly with increasing initial pressure, while decreased with the increase of initial temperature. Under lower initial pressure (P0 ≤ 150 kPa), there was an obvious increase in the peak flame temperature as the initial pressure increased. However, when the initial pressure exceeded 150 kPa, the effect of the initial pressure on the peak flame temperature was not significant. At the same time, however, the peak flame temperature increased almost linearly with the increase of initial temperature. The structure of flame front experienced a change of “spherical flame - finger flame - tulip flame” at all conditions. The change of flame velocity was also divided into three stages in the study, namely rapid growth, gradual decline, backward propagation. In the “rapid growth” stage, both the velocity and the acceleration of the flame increased with initial pressure and temperature rising, but the influence of the initial pressure on the flame velocity became weak when the initial pressure exceeded 200 kPa.

Flame morphology and self-acceleration of syngas spherically expanding flames

The self-acceleration of spherically expanding flames were investigated using a constant volume combustion chamber for CO/H2/O2/N2 mixtures over a wide range of initial pressure from 0.2 to 0.6 MPa, CO/H2 ratio from 50/50 to 10/90 and equivalence ratio from 0.4 to 1.5. The adiabatic flame temperature was kept constant by adjusting O2/N2 ratio at different equivalence ratios. Schlieren images were recorded to investigate the flame front evolution of spherically expanding flames. Local acceleration exponents were extracted using a proper equation to study the process of flame self-acceleration. Results show that the flame cells develop on the smooth flame fronts and finally reach fractal-like structures due to the hydrodynamic and diffusional-thermal instabilities, resulting in flame self-accelerative propagation. The critical Peclet number corresponding to the onset of self-acceleration, Pecr increases nonlinearly with the Markstein length, Ma. The observation further reveals that the onset of self-acceleration is mainly controlled by the diffusional-thermal effect. There exists two distinct flame propagation regimes in the self-acceleration, namely quick transition accelerative and quasi self-similar accelerative regimes. The quick transition regime is controlled by the destabilization effect of hydrodynamic perturbation and stabilization effect of flame stretch. While the quasi self-similar regime is primarily affected by the cascading process of flame front cells controlled by hydrodynamic instability. The self-similar acceleration exponent, αs varies with the initial pressure and Lewis number, Le. The values of αs are measured to be 1.1–1.25 (smaller than 1.5), indicating the flame dose not attain self-turbulization.

Characteristics of Flameless Combustion in 3D Highly Porous Reactors under Diesel Injection Conditions

The heat release process in a free volume combustion chamber and in porous reactors has been analyzed under Diesel engine-like conditions. The process has been investigated in a wide range of initial pressures and temperatures simulating engine conditions at the moment when fuel injection starts. The resulting pressure history in both porous reactors and in free volumes significantly depends on the initial pressure and temperature. At lower initial temperatures, the process in porous reactors is accelerated. Combustion in a porous reactor is characterized by heat accumulation in the solid phase of the porous structure and results in reduced pressure peaks and lowered combustion temperature. This depends on reactor heat capacity, pore density, specific surface area, pore structure, and heat transport properties. Characteristic modes of a heat release process in a two-dimensional field of initial pressure and temperature have been selected. There are three characteristic regions represented by a single- and multistep oxidation process (with two or three slopes in the reaction curve) and characteristic delay time distribution has been selected in five characteristic ranges. There is a clear qualitative similarity of characteristic modes of the heat release process in a free volume and in porous reactors. A quantitative influence of porous reactor features (heat capacity, pore density, pore structure, specific surface area, and fuel distribution in the reactor volume) has been clearly indicated.

Regimes of chemical reaction waves initiated by nonuniform initial conditions for detailed chemical reaction models

Regimes of chemical reaction wave propagation initiated by initial temperature nonuniformity in gaseous mixtures, whose chemistry is governed by chain-branching kinetics, are studied using a multispecies transport model and a detailed chemical model. Possible regimes of reaction wave propagation are identified for stoichiometric hydrogen-oxygen and hydrogen-air mixtures in a wide range of initial pressures and temperature levels, depending on the initial non-uniformity steepness. The limits of the regimes of reaction wave propagation depend upon the values of the spontaneous wave speed and the characteristic velocities of the problem. It is shown that one-step kinetics cannot reproduce either quantitative neither qualitative features of the ignition process in real gaseous mixtures because the difference between the induction time and the time when the exothermic reaction begins significantly affects the ignition, evolution, and coupling of the spontaneous reaction wave and the pressure wave, especially at lower temperatures. We show that all the regimes initiated by the temperature gradient occur for much shallower temperature gradients than predicted by a one-step model. The difference is very large for lower initial pressures and for slowly reacting mixtures. In this way the paper provides an answer to questions, important in practice, about the ignition energy, its distribution, and the scale of the initial nonuniformity required for ignition in one or another regime of combustion wave propagation.

Characterization of low- and high-temperature oxidation processes under non-premixed diesel-engine-like conditions

Low- and high-temperature oxidation processes, including thermal auto-ignition under diesel-engine-like conditions (non-premixed mixtures), have been investigated. A special combustion chamber, characterized by constant volume and adiabatic conditions, has been used as an engine simulator. The investigated processes are very complex in nature, and depend significantly on the temperature and pressure. There are five characteristic regions of the process characterized by different delay times, reaction rates and number of recognizable oxidation reactions: region 1 corresponds to processes occurring at low initial pressures over a wide range of initial temperatures; region 2 corresponds to low initial temperatures over a wide range of initial pressures; region 3 corresponds to middle pressures and higher temperatures; region 4 corresponds to middle temperatures and higher pressures; and region 5 corresponds to high initial pressures and high temperatures. by analogy to a negative temperature coefficient (as discussed in the literature), a positive pressure coefficient has been introduced here. This indicates that in the selected range of pressures, the delay time of low-temperature oxidation processes is the shortest, and the rate of these reactions is the highest. Further increases in the pressure behind the positive pressure coefficient range increase the delay time and decrease the reaction rate. The positive pressure coefficient has been observed at lower temperatures (mostly corresponding to cool-flame reactions and transitions to blue flames). Generally, the ignition delay time reduces with increasing chamber temperature and pressure.

Laminar burning velocity measurements of liquid fuels at elevated pressures and temperatures with combustion residuals

The laminar burning velocity is a fundamental property of a fuel that affects many aspects of its combustion behaviour. Experimental values are required to validate kinetic simulations, and also to provide input for models of flashback, minimum ignition energy and turbulent combustion. A constant volume vessel (rated at 3.4 MPa) in conjunction with a multi-zone model was used to calculate burning velocity from pressure and schlieren data, allowing the user to select data uncorrupted by heat transfer or cellularity. Using the pressure rise data allows measurements to be derived for much higher pressures and temperatures than when the constant pressure data are used. A 12 term correlation for burning velocity was fitted to the data. n-Heptane, iso-octane, toluene, ethylbenzene and ethanol were tested over a wide range of initial pressures (50, 100, 200 and 400 kPa), temperatures (310, 380 and 450 K) and equivalence ratios (0.7–1.4), along with tests using combustion residuals at mole fractions of up to 0.3. The results compared favourably with the limited data already published, especially at high pressures. Conditions at the onset of cellularity are given for iso-octane.

Spinning detonation and velocity deficit in small diameter tubes

Detonation velocities and soot patterns of H 2/O 2 mixtures were measured in glass tubes of 3, 6 and 10 mm diameters at pressures ranging from 70 to 400 Torr and equivalence ratios of 0.5–1.5. It was confirmed that the transition from a multi-head to a spinning detonation occurred at the pressure where the cell size is equal to the length of circumference. At this transition pressure, the velocity was 95% of the C-J detonation. Stable spinning detonations were observed at wide range of initial pressures below the transition point. Detonation velocities were continuously decreasing with decreasing initial pressures in this pressure region. Spinning detonations with velocities down to 85% of the C-J detonation were observed. Those deficits in detonation velocities were well predicted by the modified ZND model with full detailed chemical kinetics. Heat and momentum losses were taking into account in this model. Validity of the modified ZND model to define the limit of detonation propagation was discussed.

Characterization of Microcellular Biodegradable Polymeric Foams Produced from Supercritical Carbon Dioxide Solutions

The formation of foams of biodegradable poly(ε-caprolactone) (PCL) from CO2 solutions in molten PCL was investigated. This study included characterization of the CO2 diffusion and equilibrium solubility in molten PCL in contact with supercritical CO2 (scCO2). Experiments were performed at 70, 80, and 90 °C at CO2 pressures up to 25 MPa. The effective mutual diffusivity of CO2 in molten PCL was measured as a function of the CO2 pressure. The data revealed a dramatic increase in apparent effective diffusivity at elevated pressure, likely related to the formation of fluid bubbles, phase-separated from the previously homogeneous, molten PCL solution of CO2. Microcellular PCL foams were produced by starting from an equilibrium CO2−PCL solution at 70 °C over a wide range of initial pressures (from 6.9 to 32 MPa) by quenching down to foaming temperatures (from 24 to 30 °C) followed by rapid depressurization to atmospheric pressure. Foam structures were characterized by scanning electron microscopy, and cell sizes and density were determined quantitatively. The various foam structures were analyzed and interpreted in connection with the independently measured kinetics and equilibrium of CO2 sorption in PCL by considering the effects of starting pressure and foaming temperature on bubble nucleation and growth.

Numerical simulation of the structure of two-dimensional gaseous detonation of an H2-O2-Ar mixture

A two-dimensional structure of detonation waves in an 2H2+O2+X Ar mixture is numerically studied in a wide range of initial pressures and degrees of dilution. Good qualitative agreement of the numerical results with experimental data is obtained. The effect of the method of initiation (by one or several sites, symmetric or asymmetric) on the steady structure of detonation waves is studied. The changes in the wave structure induced by variation of the channel width are examined. It is shown that the behavior of the two-dimensional wave structure is qualitatively different for mixtures withX=0 andX>0.

Flame propagation in mixtures of monogermane and oxygen. I. Limits, flame propagation characteristics, and gas-phase products

The concentration limits for flame propagation in GeH4−O2 (air) mixtures are determined over a wide range of initial pressures (0.7–100 kPa) at room temperature. Flame propagation is found to be of a chain-thermal character and excited intermediate particles are involved in the reactions which limit the branching rate. The gas-phase reaction products (H2O2, H2O, and H2) are determined and its is shown that the relative yields of these components and the stoichiometry, as a whole, vary with the composition of the initial gas mixture. Chemically induced decomposition of GeH4 by a branching-chain oxidation process for oxidation of the hydride by oxygen is observed.

Amplification of radiation behind the front of a shock wave in high-pressure H2–F2mixtures

It is shown that the formation of a waveguide behind the front of a shock wave makes it possible to amplify radiation in high-pressure H/sub 2/--F/sub 2/ mixtures. Amplification is predicted for a wide range of initial pressures in the mixture. In a zone where the populations are inverted the concentration of excited particles should reach approx.10/sup 19/ cm/sup -3/ and the gain of the guided modes should be k> or approx. =10/sup -2/ cm/sup -1/.

A study of spontaneous condensation over a wide range of initial pressures

An experimental and theoretical study has been made concerning the flow of saturated vapor through a Laval nozzle with attendant spontaneous condensation, over the range of initial pressures from 2.35 to 29.40 bars. This study has shown that the initial pressure has an appreciable effect on the spontaneous condensation process.

Structure of Shock Fronts in Argon and Nitrogen

The optical reflectivity method was used to investigate the structure of shock fronts in argon from Mach 1.70 to Mach 4.85 and in nitrogen from Mach 2.01 to Mach 3.72. Experimental data were obtained at two wavelengths and over a wide range of initial pressures. The reflectivities, corrected empirically for shock curvature, were fitted to a bimodal profile to yield a maximum-slope density thickness. The reciprocal of the thickness in argon (expressed in terms of the Maxwellian mean free path in the undisturbed gas) rises rapidly to a maximum of approximately 0.31 at about Mach 3.5 and decreases gradually thereafter. Above Mach 3 the thickness is about 50% greater than calculated from the Navier-Stokes equations, using a realistic viscosity-temperature relationship. There is excellent agreement, especially at the higher shock strengths, with recent bimodal calculations carried out by Muckenfuss, using realistic intermolecular potentials. In nitrogen, the shocks are thinner than in argon and appear to attain a minimum value of 2.5 initial mean free paths at about Mach 3.7. Rotational relaxation appears to be as rapid in the strong shocks as previously observed in weak shocks; it appears to be completed within the shock front. The experimental density thicknesses are approximately 50% greater than those calculated from the Navier-Stokes equations, using the experimental shear viscosity μ and a bulk viscosity of 2μ/3. The agreement with these Navier-Stokes solutions is about as good as those in argon.