Numerical Study of the Detonation Structure in Rich Acetylene-Air Mixtures

A numerical simulation of the detonation propagation process of acetylene-air under fuel-rich conditions is carried out using a reduced acetylene reaction model. The loose coupling method is used to solve the conservation equations with source terms. The flow is solved explicitly using a gas kinetic scheme, and the chemical reactions are solved implicitly. The numerical results show that the oxidation reaction is the chain initiation in the self-sustained detonation propagation process in rich acetylene. The self-decomposition reaction of acetylene provides the energy to maintain the coupling between the shock wave and the chemical reaction zone. The results show that the initial induced reaction is still an oxidation reaction due to the low activation energy of the oxidation reaction under the condition of low oxygen content. The intensity of the transverse wave is affected by the acetylene concentration. The post-detonation disturbance of temperature is mainly affected by the strength of the tail of transverse wave and the area of the unreacted pocket. With the increase of acetylene concentration, the self-decomposition process of acetylene increases the intensity of the transverse wave tail and improves the degree of temperature homogenization. This creates a formation-fragmentation-regeneration cycle of polycyclic aromatic hydrocarbons. This process changed the branching ratio of polycyclic aromatic hydrocarbons with different structures and delayed the formation of polycyclic aromatic hydrocarbons. When the acetylene concentration is low, the region where the dominant temperature after detonation is 1500 ~ 2500 K provides a favorable environment for the growth of polycyclic aromatic hydrocarbons.</p

Biomimetics of [NiFe]-Hydrogenase: Nickel- or Iron-Centered Proton Reduction Catalysis?

The [NiFe] hydrogenase (H2ase) has been characterized in the Ni-R state with a hydride bridging between Fe and Ni but displaced toward the Ni. In nearly all of the synthetic Ni-R models reported so far, the hydride ligand is either displaced toward Fe, or terminally bound to Fe. Recently, a structural and functional [NiFe]-H2ase mimic (Nat. Chem. 2016, 8, 1054−1060) was reported to produce H₂ catalytically via EECC mechanism through a Ni-centered hydride intermediate like the enzyme. Here, a comprehensive DFT study shows a much lower energy route via an E­[ECEC] mechanism through an Fe-centered hydride intermediate. Although catalytic H₂ production occurs at the potential corresponding to the complex’s second reduction, a third electron is needed to induce the second proton addition from the weak acid. The first two-electron reductions and a proton addition produce a semibridging hydride with a short Fe–H bond like other structured [NiFe]-biomimetics, but this species is not basic enough to add another proton from the weak acid without the third electron. The calculated mechanism provides insight into the origin of this structure in the enzyme

Hydrodynamic characteristics of knotted and knotless purse seine netting panels as determined in a flume tank

<div><p>Nylon (PA) netting is widely used in purse seines and other fishing gears due to its high strength and good sinking performance. However, hydrodynamic properties of nylon netting of different characteristics are poorly understood. This study investigated hydrodynamic characteristics of nylon netting of different knot types and solidity ratios under different attack angles and flow velocities. It was found that the hydrodynamic coefficient of netting panels was related to Reynolds number, solidity ratio, attack angle, knot type and twine construction. The solidity ratio was found to positively correlate with drag coefficient when the netting was normal to the flow (<i>C</i>_<i>D</i>90), but not the case when the netting was parallel to the flow (<i>C</i>_<i>D</i>0). For netting panels inclined to the flow, the inclined drag coefficient had a negative relationship with the solidity ratio for attack angles between 0° and 50°, but a positive relationship for attack angles between 50° and 90°. The lift coefficient increased with the attack angle, reaching the culminating point at an attack angle of 50°, before subsequent decline. We found that the drag generated by knot accounted for 15–25% of total drag, and the knotted netting with higher solidity ratio exhibited a greater <i>C</i>_<i>D</i>0, but it was not the case for the knotless netting. Compared to knotless polyethylene (PE) netting, the drag coefficients of knotless PA netting were dominant at higher Reynolds number (Re>2200).</p></div

Comparison of inclined hydrodynamic coefficients between knotless netting panels and knotted netting panels at various attack angles and flow velocities.

<p>Comparison of inclined hydrodynamic coefficients between knotless netting panels and knotted netting panels at various attack angles and flow velocities.</p

Experimental samples of knotless nylon (polyacrylamide or PA) netting (left, four-strand braid) and knotted nylon netting (right, single English knot).

<p>Experimental samples of knotless nylon (polyacrylamide or PA) netting (left, four-strand braid) and knotted nylon netting (right, single English knot).</p

Comparison of normal drag coefficients vs. Reynolds number.

<p>Comparison of normal drag coefficients vs. Reynolds number.</p

Drag coefficient for netting parallel to the flow as a function of Reynolds number for various solidity ratios.

<p>Drag coefficient for netting parallel to the flow as a function of Reynolds number for various solidity ratios.</p

Comparison of drag coefficient of inclined nylon netting panels with varied solidity ratios against attack angle.

<p>Comparison of drag coefficient of inclined nylon netting panels with varied solidity ratios against attack angle.</p

Comparison of drag coefficients between knotless nylon (PA) netting and knotless polyethylene (PE) netting.

<p>Comparison of drag coefficients between knotless nylon (PA) netting and knotless polyethylene (PE) netting.</p

Comparison of parallel drag coefficients vs. Reynolds number.

<p>Comparison of parallel drag coefficients vs. Reynolds number.</p