| 1. |
- Dai, P., et al.
(författare)
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Autoignition and detonation development from a hot spot inside a closed chamber : Effects of end wall reflection
- 2021
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier. - 1540-7489 .- 1873-2704. ; 38:4, s. 5905-5913
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Tidskriftsartikel (refereegranskat)abstract
- The advancement of highly boosted internal combustion engines (ICEs) with high thermal efficiency is mainly constrained by knock and super-knock, respectively, due to the end gas autoignition and detonation development. The pressure wave propagation and reflection in a small confined space may strongly interact with local end gas autoignition, leading to combustion characteristics different from those in a large chamber or open space. The present study investigates the transient autoignition process in an iso-octane/air mixture inside a closed chamber under engine-relevant conditions. The emphasis is given to the assessment of effects of the pressure wave-wall reflection and the mechanism of extremely strong pressure oscillation typical for super-knock. It is found that the hot spot induced autoignition in a closed chamber can be greatly affected by shock/pressure wave reflection from the end wall. Different autoignition modes respectively from the hot spot and the end wall reflection are identified. A non-dimensional parameter quantifying the interplay between different length and time scales is introduced, which helps to identify different autoignition regimes including detonation development near the end wall. It is shown that detonation development from the hot spot may cause super-knock with devastating pressure oscillation. However, the detonation development from the end wall can hardly produce pressure oscillation strong enough for the super-knock. The obtained results provide a fundamental insight into the knocking mechanism in engines under highly boosted conditions.
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| 2. |
- Liberman, Michael A.
(författare)
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Combustion Physics : Flames, Detonations, Explosions, Astrophysical Combustion and Inertial Confinement Fusion
- 2021
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- This book provides the latest achievements and original research work in physics of combustion processes and application of the methods developed in combustion physics for astrophysical problems of stars burning, supernovae explosions and a confined thermonuclear fusion. All the materials in the book are presented in a concise and easily accessible way, but at the same time provides a deep physical inside in the phenomena considered. It is an effective theoretical course with the direct practical implications in engineering fields of engine’s development, energy production, safety issues inherent to terrestrial combustion, as well as in thermonuclear combustion in the inertial fusion. This book is aimed at university students, Ph.D. students and engineers, as well as professionals in combustion, energy-related research, astrophysics and researchers in neighboring fields.
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| 3. |
- Liberman, Michael A.
(författare)
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Hydrogen atom in a magnetic field as an exactly solvable system without dynamical symmetries?
- 2022
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Ingår i: Physics Letters A. - : Elsevier BV. - 0375-9601 .- 1873-2429. ; 445
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Tidskriftsartikel (refereegranskat)abstract
- According to the generally accepted classification, there are supersymmetric superintegrable systems for which the Schrödinger equation is separable in more than one coordinate system and which admit an exact solution. A classic example of a superintegrable system is a hydrogen atom. It is believed that the converse is also true: an exactly solvable system has many integrals of motion corresponding to the separation constants of the Schrödinger equation in more than one coordinate system, which also means a high symmetry group of the system. It is shown that the existence of an exact solution for a hydrogen atom in an arbitrary strong uniform magnetic field apparently contradicts this classification.
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| 4. |
- Liberman, Michael, et al.
(författare)
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Dynamics of flames in tubes with no-slip walls and the mechanism of tulip flame formation1
- 2023
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Ingår i: Combustion Science and Technology. - : Informa UK Limited. - 0010-2202 .- 1563-521X. ; 195:7, s. 1637-1665
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Tidskriftsartikel (refereegranskat)abstract
- A hydrogen/air flame propagation and the development of tulip-shaped flame in 2D tubes of different aspect ratios with both closed ends and in a half-open rectangular channel were studied using high resolution direct numerical simulations of the fully compressible Navier–Stokes equations coupled with a detailed chemistry. Flame propagation in a 3D rectangular channel was studied using large eddy simulations and compared with the results of direct numerical simulations of flame propagation in a 2D rectangular channel with the same aspect ratio. It is shown that the interaction of the rarefaction wave generated by the flame at the deceleration stage with the “positive” flow of unburned gas generated by the flame at the previous accelerating stage leads to a significant decrease of the velocity of the unburned gas flow in the near field zone ahead of the flame front. As a result, the thickness of the boundary layer in the near-field zone ahead of the flame increases significantly, and the profile of the axial velocity of the unburned gas in the near-field zone ahead of the flame front takes the form of a tulip or an inverted tulip, which leads to corresponding changes in the velocities of different parts of the flame front, the flame front inversion, and the formation of a tulip-shaped flame.
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| 5. |
- Moskalenko, S. A., et al.
(författare)
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Two-Dimensional Electron-Hole System under the Influence of the Chern-Simons Gauge Field Created by the Quantum Point Vortices
- 2021
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Ingår i: Semiconductors (Woodbury, N.Y.). - : Pleiades Publishing Ltd. - 1063-7826 .- 1090-6479. ; 55:SUPPL 1, s. S35-S48
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Tidskriftsartikel (refereegranskat)abstract
- The Chern-Simons (CS) gauge field theory was widely used to explain and to deeper understand the fractional quantum Hall effects. In this work, we apply the Chern-Simons gauge field theory to a two-dimensional (2D) electron-hole (e-h) system in a strong perpendicular magnetic field under the influence of the quantum point vortices creating by the Chern-Simons (CS) gauge field. The composite electron-hole particles with equal integer positive numbers phi of the attached quantum point vortices are described by the dressed field operators that obey to either the Fermi or Bose statistics depending on the even or odd numbers phi. It is shown that the phase operators, as well as the vector and scalar potentials of the CS gauge field, depend on the difference between the electron and the hole density operators. They vanish in the mean field approximation, when the average values of the electron and of the hole densities coincide. Nevertheless, even in this case, quantum fluctuations of the CS gauge field lead to new properties of the 2D e-h system. It is found that the numbers of vortices attached to each electron and hole are the same. This result is not obvious, and a different distribution of vortices in the environment of electron-hole pairs could be expected. A simple analytical formula is obtained for the shift of the magnetoexciton energy level at the point k = 0 due to the influence of the CS gauge field.
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| 6. |
- Podlesny, I. V., et al.
(författare)
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Metastable bound states of the quasi–bimagnetoexcitons in the lowest Landau levels approximation
- 2020
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - : Elsevier B.V.. - 1386-9477 .- 1873-1759. ; 115
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Tidskriftsartikel (refereegranskat)abstract
- Four different spin structures of two electrons and of two holes situated on the lowest Landau levels (LLLs) are taken into account to investigate possible bound states of the two-dimensional magnetic biexciton formed of two magnetoexcitons with opposite wave vectors and antiparallel dipole moments. The singlet and triplet states of the spins of two electrons and of two holes separately, as well as of two para- and two ortho-magnetoexcitons are considered. The general expressions describing the binding energy of the bound states and the normalization conditions characterized by the effective spin parameter η=±1,±1/2 for the corresponding wave functions are derived. The most favorable of the four considered spin configurations happened to be the triplet-triplet spin structure of two electrons and of two holes. In its frame a metastable bound state with activation barrier comparable with two ionization potentials of the magnetoexciton is revealed.
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| 7. |
- Qian, Chengeng, et al.
(författare)
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Convergence properties of detonation simulations
- 2020
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Ingår i: Geophysical and Astrophysical Fluid Dynamics. - : Taylor & Francis. - 0309-1929 .- 1029-0419. ; 114:1-2, s. 58-76
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Tidskriftsartikel (refereegranskat)abstract
- We present a high-resolution convergence study of detonation initiated by a temperature gradient in a stoichiometric hydrogen-oxygen mixture using the PENCIL CODE and compare with a code that employs a fifth order weighted essentially non-oscillating (WENO) scheme. With Mach numbers reaching 10-30, a certain amount of shock viscosity is needed in the PENCIL CODE to remove or reduce numerical pressure oscillations on the grid scale at the position of the shock. Detonation is found to occur for intermediate values of the shock viscosity parameter. At fixed values of this parameter, the numerical error associated with those small wiggles in the pressure profile is found to decrease with decreasing mesh width like down to . With the WENO scheme, solutions are smooth at , but no detonation is obtained for . This is argued to be an artifact of a decoupling between pressure and reaction fronts.
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