Download or read book Development and Application of a High performance Framework for High fidelity Simulations of Plasma assisted Ignition of Hydrocarbon Fuels Using Nanosecond Pulsed Discharges written by Nicholas E. Deak and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The application of non-equilibrium plasma (NEP) pulses to ignite hydrocarbon/air mixtures has emerged as a promising technology for ensuring reliable ignition and combustion stability in difficult regimes. Despite its promise, major challenges and limitations still remain, particularly in the realm of conducting high-fidelity multidimensional numerical studies. The aim of this thesis is to develop, implement, and apply a robust and efficient computational framework that addresses some of these shortcomings. As a preliminary step, the ignition of hydrocarbon/air mixtures by nanosecond pulsed discharges (NSPD) is investigated using a zero dimensional isochoric adiabatic reactor. A state-of-the-art two-temperature kinetics model, comprised of an experimentally-verified NEP plasma mechanism coupled with a hydrocarbon/air oxidation mechanism, is used. Simulations are performed to assess the impact of changing initial pressure (which varies from 1 to 30 atm) and fuel type (methane and ethylene). It is found that at lower pressures, plasma-assisted ignition (PAI) imparts a benefit over thermal ignition for both fuel types, through the creation of combustion radicals O, H, and OH. At higher pressures, PAI of methane loses efficiency compared to ethylene, due to a lack of available H radicals (which are swept up by O2), which limits the conversion of formaldehyde to formyl. Next, a robust and efficient framework for simulating NSPD in multiple dimensions is developed. The reactive Navier-Stokes equations are extended to include a drift-diffusion plasma-fluid model with a local field approximation (LFA) in a finite-volume solver, which uses an adaptive mesh refinement (AMR) strategy to address the wide separation of length scales in the problem. A two-way coupling strategy is used whereby the plasma-fluid model and reactive Navier-Stokes equations are integrated simultaneously. An effective grid refinement approach is developed in order to ensure that the physical structures that arise during and after the NSD (including the propagating streamer heads, electrode sheaths, and expansion wave during the inter-pulse period) are resolved efficiently. Severe time step size restrictions that arise from the explicit temporal integration of the transport terms are mitigated through use of a semi-implicit approach for solving Poisson's equation for the electric potential, and an implicit strategy for evaluating electron diffusion terms. A series of numerical studies are then conducted to investigate the ignition and propagation phases of atmospheric air streamers in axisymmetric discharge configurations. A range of conditions and configurations are explored to characterize the streamer, with an emphasis on the cathode sheath region, which supports steep gradients in charged species number densities as well as strong electric fields. The formation of the cathode sheath is shown to be a consequence of processes at the cathode surface, driven by electron losses at the boundary, and a strong dependence on the emission of secondary electrons. Finally, the oxidation of ethylene/air mixtures mediated by NSPD is simulated in a pin-to-pin configuration. All phases of the plasma discharge are simulated explicitly (including streamer ignition, propagation, and connection, as well as the subsequent spark phase), along with the evolution of the plasma during the inter-pulse period. Temporally and spatially-resolved results are presented, with an emphasis on the analysis of heating and energy deposition, as well as of the evolution of the concentration of active particles generated during the NSPD and their influence on ignition. The impact of pin thickness is discussed, and it is shown that the use of thin pins limits the regions of energy deposition and temperature increase near the pin tips, hindering ignition. The application of multiple pulses is explored and it is shown that multiple voltage pulses of the same strength leads to substantial energy deposition and temperature increases O(1,000 - 10,000 K) near the pin tips. Discussion is rounded out by addressing how pulse frequency and initial mixture control the generation of active particles and combustion products. Finally, recommendations for future work are provided

Download or read book Plasma Enhanced Combustion of Hydrocarbon Fuels and Fuel Blends Using Nanosecond Pulsed Discharges written by and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This project had as its goals the study of fundamental physical and chemical processes relevant to the sustained premixed and non-premixed jet ignition/combustion of low grade fuels or fuels under adverse flow conditions using non-equilibrium pulsed nanosecond discharges.

Download or read book Nanosecond Pulsed Plasma assisted Combustion written by Moon Soo Bak and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In this study, the use of non-equilibrium plasmas is examined as possible methods of active control of combustion. The plasmas investigated here include nanosecond-pulsed repetitive discharges as well as nanosecond-pulsed laser-produced breakdowns. These sources are used to stabilize both premixed and jet-diffusion flames of various fuel types. The use of nanosecond-pulsed repetitive discharges to stabilize lean premixed fuel-air mixtures is found to extend the equivalence ratio for complete combustion to lower values, in some cases, below the so-called lean flammability limits. This extension depends strongly on the pulse repetition frequency or average discharge power. Simulations reveal that a significant production of radicals associated with gas heating is responsible for flame stabilization and this is attributed mainly to a dissociative quenching of electronically excited species by molecular oxygen. In jet diffusion flames, anchoring of the flame-base is best when the discharge plasma is positioned where the local equivalence ratio is between 0.8 and 1.9. Lastly, the discharge plasma source is replaced by laser-induced breakdowns. Two successive laser pulses with a variable time delay are employed to mimic repetitive breakdowns expected from a future high frequency laser source of sufficient power. From studies first carried out in pure air, it is found that the first laser breakdown causes a temporal region virtually transparent to the subsequent laser pulse during the interval from 100 ns to 60 μs. This is attributed to heating by the plasma, reducing the density below threshold levels needed for absorption of a laser pulse. In premixed fuel-air mixtures, the first breakdown induces a second region of transparency during the interval from 100 μs to 2 ms after the pulse due to the heat released by combustion. These findings limit the laser repetition rate to a maximum of 500 Hz when the equivalence ratio is 1. Time-resolved imaging of CH* chemiluminescence reveals flame front merging confirming that flame stabilization can be achieved at these moderate laser repetition rates.

Download or read book Ignition of Hydrocarbon Fuels by a Repetitively Pulsed Nanosecond Pulse Duration Plasma written by Ainan Bao and published by . This book was released on 2008 with total page 188 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: The dissertation presents experimental and kinetic modeling studies of ignition of hydrocarbon-air flows by a high voltage, repetitively pulsed, nanosecond pulse duration plasma. A high reduced electric field during the pulse results in efficient electronic excitation and molecular dissociation, and extremely low duty cycle of the repetitively pulsed nanosecond discharge improves the plasma stability and helps sustain a diffuse and uniform nonequilibrium plasma.

Download or read book Pulsed Plasma Generator Development and Low temperature Plasma assisted Combustion at Atmospheric Pressure written by Mathew Evans and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "This thesis presents an experimental study of the engineering and physics of high-voltage nanosecond-pulsed diffuse discharges, and their application to the enhancement of lean-premixed combustion at atmospheric pressure. The technology development in this work is focused on providing appropriate low-temperature radical pools, and the experiments are aimed at demonstrating the effect of these pools for combustion actuation. The experimental results are focused on the explanation of the physical processes associated with these discharges. The discharge propagation and emission spectrum were examined, the distribution functions of particles along internal energy levels were calculated, and the resulting enhancement of combustion was observed. This work shows that the plasma emission from fuel-lean mixtures is primarily composed of high vibrational populations of electronically excited nitrogen molecules, upon which a low-temperature is measured on the rotational manifold. Previous work shows that these low-temperature excited particles will collide with molecular oxygen, or fuel molecules, to produce species (atomic/molecular ground/excited oxygen, fragmented fuel molecules...) that accelerate chain-branching reactions in the combustion reaction mechanism. This work shows that the majority of the electronically excited vibrational states of nitrogen molecules, in a diffuse discharge, decay rapidly after the application of a high-voltage pulse. These findings set the framework for the implementation of diffuse plasma to laboratory-scale combustion enhancement. As an integral part of this work, the design and development of electrical generators that can produce such a reactive medium in large volume is included, and extensively detailed. An inexpensive solid-state pulse generator, based on commercially available amorphous ferromagnetic materials, is designed and developed to drive capacitive loads. The generator is used to produce large volumes of diffuse plasma and increase the blow off velocity of stagnation flames. To further investigate this enhancement, an optically accessible plasma burner is implemented and used for the detailed study of stagnation flame plasma actuation. This work shows that significant actuation can be provided to a flame, when diffuse plasma is placed upstream, and directly in contact with the combustion front. The displacement of the leading edge of a flame, into the fresh unburned mixture, is measured following a high-voltage actuating pulse. The displacement of the leading edge strongly points toward low-temperature reactivity enhancement. The optical and electrical characteristics of the diffuse plasma are reported for both the non-combusting and combusting flows. These provide a more accurate picture of the thermal characteristics and complex phenomena occurring in this transient discharge. Streamer propagation dynamics and coupled energy measurements are reported to provide further insight regarding the delicate balance that exists between plasma and flame sheet in this experimental configuration. It can be concluded that diffuse plasma is an effective low-temperature chemical actuation method for combustion enhancement at atmospheric pressure.To conclude this work, the first step toward high-pressure actuation of combustion with diffuse plasma was explored. The task of producing diffuse plasma above atmospheric pressure was undertaken. This work presents the development of a second solid-state pulse generator with increased power delivery capabilities. The generator is used to produce large volumes of diffuse plasma in a high-pressure vessel filled with air. It is found that diffuse plasma actuation could eventually be implemented in a high-pressure combustion experiment using this technology." --

Download or read book Nanosecond Pulsed Plasmas in Dynamic Combustion Environments written by Colin A. Pavan and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Plasma assisted combustion (PAC) is a promising technology for extending combustion operating envelopes with a low energy cost relative to flame power. It has been investigated for use in various situations, particularly those where combustion is being performed near flammability limits imposed by equivalence ratio, residence time, etc. While the fundamental processes allowing plasma to modify combustion dynamics have been well studied, there are still many unresolved questions in determining the relative contribution of different actuation pathways in different situations (thermal enhancement, kinetic enhancement or transport-induced effects) and how the plasma will evolve and interact with the flame in a dynamic combustion environment. The plasmas being used for PAC are typically non-equilibrium and are often produced by the nanosecond repetitively pulsed discharge (NRPD) strategy. The development of these discharges is highly dependent both on applied voltage and also on the gas environment (composition, temperature, flow field, etc.). As the plasma affects the combustion, so too does the combustion affect the plasma structure and energy deposition pathways. This two-way coupling means that the plasma's ability to modify the combustion, and the mechanisms by which it achieves these effects, will vary as the environment changes due to combustion dynamics. This impact of the combustion on the plasma has received considerably less attention than the other direction of interaction, especially in environments with transient or propagating flames. The first main objective of this thesis is to explore the development of NRPDs in dynamic combustion environments and in particular how the plasma develops on the timescales of transient combustion (many accumulated pulses). This is performed first in a laminar, mesoscale platform to probe the interaction in detail, and the important insights are later shown to be relevant to high power systems of practical interest. While the impact of the plasma on the flame has been considerably better studied and the fundamental processes are well understood, there are still hurdles that must be overcome before PAC systems can begin to be designed and implemented for use outside of the laboratory. The development of versatile and flexible engineering models of the impact of the plasma will be necessary to allow system designers to make predictions about combustor operation when plasma is applied. The second main objective of this thesis is to develop such an engineering model and demonstrate its predictive capabilities across a variety of configurations. The model is developed for a laminar mesoscale platform and is shown to correctly predict the impact of the plasma in several different configurations, indicating a path forward towards physics[1]informed design of PAC systems. The model also provides important physical insight of the impact of plasma on flame, such as the role of pressure waves in disturbing the flame dynamics, even when considering uniform DBD discharges.

Download or read book Model and Igniter Development for Plasma Assisted Combustion written by and published by . This book was released on 2004 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: Recent progress on the authors' efforts to develop a detailed kinetic mechanism for C(sub 8)H(sub m) hydrocarbons and practical plasma igniters for plasma-assisted combustion are discussed. Shock tube validation experiments made in argon using a fixed stoichiometry (PHI = 1.0), pressures of approximately 0.95 and 1.05 atm, and temperatures ranging from 850 to 1200 K (post-reflected shock) are presented. The mechanism is being expanded to include electron kinetics and to allow for a degree of nonequilibrium modeled with separate electron and gas temperatures. Quantum calculations used to derive needed electron impact ionization/dissociation cross-sections for hydrocarbons are discussed. In addition, ignition of ethylene fuel in a Mach 2 supersonic flow with a total temperature of 590 K and pressure of 5.4 atm is demonstrated using a low frequency discharge with peak and average powers reaching 8 kW and 2.8 kW, respectively. (7 figures, 28 refs.).

Download or read book Toward Plasma Assisted Ignition in Scramjets written by and published by . This book was released on 2003 with total page 27 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Air Force plasma ignition program is assessing the prospect of main-fuel ignition with plasma generating devices in a supersonic flow. As the study progresses baseline conditions of operation are being established such as the required operational time of the device to initiate a combustion shock train. The two plasma torches currently under investigation consist of a DC constricted-arc design from the Virginia Polytechnic Institute and State University and an AC unconstricted-arc design based on a modified spark-plug from Polytechnic University. The plasma torches are realistic in size and operate within current power constraints while differing substantially in orifice geometry. In order to compare the potential of each concept the flow physics of each part of the igniter/fuel-injector/combustor system are being studied. In each step of the program, we utilize CFD and experiments to help define and advance the ignition process. To understand the constraints involved with ignition process of a hydrocarbon fuel jet an experimental effort to study gaseous and liquid hydrocarbons is underway, involving the testing of ethylene and JP-7 fuels with nitrogen and air plasmas. Results from the individual igniter studies have shown the plasma igniters to produce hot pockets of highly excited gas with peak temperatures up to (and in some cases above) 5000 K at only 2-kW total input power. In addition ethylene and JP-7 flames with a significant level of OH as determined by OH PLIF were also produced in a Mach-2 supersonic flow with a total temperature and pressure of 590 K and 5.4 atm respectively.

Download or read book Plasma Assisted Combustion written by and published by . This book was released on 2007 with total page 372 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report results from a contract tasking Moscow Institute of Physics and Technology as follows: The contractor will investigate the use of high voltage, nano-second plasma discharges to ignite and efficiently combust fuel/air mixtures in high speed flows. This strongly nonequilibrium low-temperature plasma has a high mean energy of electrons and will provide a source of reactive atoms, radicals, and excited molecules which has been shown to enhance ignition and combustion. The short duration of the pulses results in relatively low power requirements for generating the discharge. The goal is to demonstrate and understand the physics of energy exchange, ignition and combustion . Also, the use of this type of plasma for aerodynamic flow control will be investigated. Finally, applicability to use this type of discharge to directly initiate a detonation wave will be investigated.

Download or read book Plasma Induced Ignition and Plasma Assisted Combustion in High Speed Flow written by and published by . This book was released on 2003 with total page 14 pages. Available in PDF, EPUB and Kindle. Book excerpt: The paper is dedicated to the experimental demonstration of plasma technology abilities in the field of high speed combustion. It is doing in three principal directions: control of the structure and the parameters of the duct driven flows; the ignition of air fuel composition at low mean gas temperature; and the mixing intensification inflow.

Download or read book Finite Volume Methods for Hyperbolic Problems written by Randall J. LeVeque and published by Cambridge University Press. This book was released on 2002-08-26 with total page 582 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book, first published in 2002, contains an introduction to hyperbolic partial differential equations and a powerful class of numerical methods for approximating their solution, including both linear problems and nonlinear conservation laws. These equations describe a wide range of wave propagation and transport phenomena arising in nearly every scientific and engineering discipline. Several applications are described in a self-contained manner, along with much of the mathematical theory of hyperbolic problems. High-resolution versions of Godunov's method are developed, in which Riemann problems are solved to determine the local wave structure and limiters are then applied to eliminate numerical oscillations. These methods were originally designed to capture shock waves accurately, but are also useful tools for studying linear wave-propagation problems, particularly in heterogenous material. The methods studied are implemented in the CLAWPACK software package and source code for all the examples presented can be found on the web, along with animations of many of the simulations. This provides an excellent learning environment for understanding wave propagation phenomena and finite volume methods.

Download or read book Design and Implementation of a Combined High Voltage Nanosecond Radiofrequency Excitation Non thermal Plasma System written by Dante Filice and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: "The world is rapidly transitioning its energy and chemical feedstocks from carbon intensive sources to renewable sources. Many existing and new technologies that utilize renewable electricity will need to come online in order to reduce CO2 emissions and reach carbon neutral goals. Plasma-driven systems for NH3 synthesis and reactions involving CO2 conversion can not only meet the challenges of carbon neutrality, but also have the potential to increase performance and reduce operational costs.Common excitation sources for non-thermal plasma processing include high voltage nanosecond (ns) pulsed plasma sources and radiofrequency (RF) sources. High voltage ns pulsed plasma sources are effective at igniting and sustaining plasmas in atmospheric pressure gases and gas mixtures. These pulses produce large quantities of excited species and highly reactive radicals participating in the desired chemical reaction pathways. When sufficiently separated in time, the power delivery of each pulse is relatively discrete resulting in minimal memory effect. The rapid quenching of the electron and excited species densities causes the discharge to essentially face re-ignition conditions every pulse. This dynamic load impedance leads to low efficiency of power delivery from the electrical mains to the plasma. On the other hand, conventional RF discharges can provide high electrical power-to-plasma chemical energy conversion efficiency, however sustaining a uniform discharge at atmospheric pressure proves to be challenging. Commercially available RF power supplies cannot reach the breakdown voltage thresholds required to ignite electrical discharges at atmospheric pressure in most gas mixtures and useful interelectrode gaps. This Master's thesis focuses on developing a plasma excitation source that combines a high voltage ns pulsed source with a RF source. Each power supply was designed and characterized to determine the electrical performance of the excitation system. Gas mixtures containing increasing amounts of N2 in Ar were introduced into the system to observe the effects on the plasma characteristics. High speed imaging was also used to focus in on the transition period from high voltage ns pulsed excitation to RF excitation.A parameterization sweep was performed to determine the operational characteristics of the RF power supply with varying gas mixture ratios. Observable RF discharge effects were present in reactor conditions with N2 concentrations up to 50% in Ar. The temporal RF discharge evolution was captured with a high-speed camera, providing insight into the mechanisms involved in obtaining RF discharge effects"--

Download or read book Kinetic Modeling and Sensitivity Analysis of Plasma assisted Combustion written by Kuninori Togai and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Plasma-assisted combustion (PAC) is a promising combustion enhancement technique that shows great potential for applications to a number of different practical combustion systems. In this dissertation, the chemical kinetics associated with PAC are investigated numerically with a newly developed model that describes the chemical processes induced by plasma. To support the model development, experiments were performed using a plasma flow reactor in which the fuel oxidation proceeds with the aid of plasma discharges below and above the self-ignition thermal limit of the reactive mixtures. The mixtures used were heavily diluted with Ar in order to study the reactions with temperature-controlled environments by suppressing the temperature changes due to chemical reactions. The temperature of the reactor was varied from 420 K to 1250 K and the pressure was fixed at 1 atm. Simulations were performed for the conditions corresponding to the experiments and the results are compared against each other. Important reaction paths were identified through path flux and sensitivity analyses. Reaction systems studied in this work are oxidation of hydrogen, ethylene, and methane, as well as the kinetics of NOx in plasma.In the fuel oxidation studies, reaction schemes that control the fuel oxidation are analyzed and discussed. With all the fuels studied, the oxidation reactions were extended to lower temperatures with plasma discharges compared to the cases without plasma. The analyses showed that radicals produced by dissociation of the reactants in plasma plays an important role of initiating the reaction sequence. At low temperatures where the system exhibits a chain-terminating nature, reactions of HO2 were found to play important roles on overall fuel oxidation. The effectiveness of HO2 as a chain terminator was weakened in the ethylene oxidation system, because the reactions of C2H4 + O that have low activation energies deflects the flux of O atoms away from HO2. For the ethylene and methane oxidation systems, the reaction pathways important for the formation of intermediate species are discussed. The reactions of CH3 and C2H5 were found to influence the production channels of minor species.In the studies on the kinetics of NOx in plasma, several mechanistic insights were obtained, including the identification of formation and consumption steps of N2O and the extensive review of three NO formation schemes found in the current reaction mechanism. Efforts to address the known inaccuracies of the current model are also reported.

Download or read book Development and Applications of ReaxFF Reactive Force Field Simulations in Combustion written by Chowdhury Ashraf and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: From the last decades, the focus of the combustion research has shifted more and more from experiment to simulations. This is partly because of the difficulty to perform experiments under the conditions at which modern day jet and rocket engines operate and partly because of the advancement of computational technology required to perform theoretical calculations or simulations. Currently, computational fluid dynamics (CFD) based continuum simulations are considered to be an essential part of combustion research, as it can simulate turbulent reacting flows with significant accuracy. One integral part of CFD simulations is the chemical kinetic model and the fidelity of the simulation greatly depends on the chemical model it uses. These chemical models are normally developed and validated against experimental observations. The actual engine condition might vary significantly from the experimental conditions, which can severely restrict the accuracy of the chemical models under such condition. Thus, a computational method is required that can simulate the complex physics and chemistry of complex combustion process and capture the possible reaction pathways without any prior user input. The ReaxFF reactive force field method is one such method, as it can be used to simulate reactions in large (” 1000 atoms) dynamic systems and can provide atomistic-scale insights of the critical reaction steps. In this dissertation, ReaxFF reactive force field simulations have been developed and used in the following research areas ranging from kinetics to dynamics:a) In this dissertation, the first atomistic-scale based method for calculating ignition front propagation speed has been developed with a hypothesis that this quantity is related to laminar flame speed. This method is based on atomistic-level molecular dynamics (MD) simulations with the ReaxFF reactive force field. Results reported in this study are for supercritical (P=55MPa and Tu=1800K) combustion of hydrocarbons as elevated pressure and temperature are required to accelerate the dynamics for reactive MD simulations. These simulations are performed for different types of hydrocarbons, including alkyne, alkane, and aromatic, and are able to successfully reproduce the experimental trend of reactivity of these hydrocarbons. Moreover, our results indicate that the ignition front propagation speed under supercritical conditions has a strong dependence on equivalence ratio, similar to experimentally measured flame speeds at lower temperatures and pressures, which supports our hypothesis that ignition front speed is a related quantity to laminar flame speed. In addition, comparisons between results obtained from ReaxFF simulation and continuum simulations performed under similar conditions show good qualitative, and reasonable quantitative agreement. b) The ReaxFF method provides an attractive computational method to obtain reaction kinetics for complex fuel and fuel mixtures, providing an accuracy approaching ab-initio based methods, but with a significantly lower computational expense. The development of the first ReaxFF combustion force field by Chenoweth et al. (CHO-2008 parameter set) in 2008 has opened new avenues for researchers to investigate combustion chemistry from atomistic-level. In this dissertation, two issues with the CHO-2008 ReaxFF description has been addressed. While the CHO-2008 description has achieved significant popularity for studying large hydrocarbon combustion, it has some significant limitations for C1 chemistry and properties for graphitic materials. In this dissertation, a newer version of ReaxFF combustion force field has been developed by addressing the limitations of CHO-2008 version, while retaining the accuracy of the previous description for larger hydrocarbons. Thus, ReaxFF CHO-2008 DFT-based training set has been extended by including reactions and transition state structures relevant to the syngas and oxidation initiation pathways and re-trained the parameters. c) Combustion devices such as rocket engines, gas turbines and HCCI engines frequently operate at a pressure higher than the critical pressure of the fuel or the oxidizer. This significantly limits the transferability of existing chemical kinetics models as they are developed and validated at low pressure/temperature conditions, considering only temperature dependence on the reaction rates while neglecting pressure dependence on combustion pathways. Since the experiments are difficult to perform at the supercritical region, this study demonstrates the capability of ReaxFF reactive force field method simulations to study combustion kinetics of fuels and fuel mixtures at these conditions with an objective to investigate how the presence of a highly reactive fuel can alter the properties of a much less reactive fuel during pyrolysis. Two different fuel mixtures are considered, namely JP-10/toluene and n-dodecane/toluene and find that they behave differently at different mixing conditions and densities. This study also compares results with continuum simulation results using a detailed chemical kinetic model and elaborate why the continuum results fail to capture the phenomena predicted by the ReaxFF simulations.d) Syngas (Synthesis Gas), a mixture of CO and H2 gas, has a very high availability and great flexibility of usage. As such, syngas is expected to play a significant role in future energy generation. However, the varying amount of mixture components makes it difficult to develop a reliable reaction mechanism for syngas combustion. The main variable to consider for direct syngas combustion include the carbon monoxide/hydrogen ratio, fluctuating level of carbon dioxide and water and presence of other species that can significantly affect the combustion process. This study investigates the effect of the presence of water molecules in syngas combustion. In these reactive molecular dynamics simulations, two different carbon monoxide/hydrogen ratios are considered and the effect of presence of water molecules in CO2 production is examined at different temperatures. This study indicates that a low amount of water molecules significantly increases carbon dioxide production, which is also observed experimentally. However, beyond that level, water molecules have limited effect on CO oxidation.

Download or read book Plasma Catalysis written by Annemie Bogaerts and published by MDPI. This book was released on 2019-04-02 with total page 248 pages. Available in PDF, EPUB and Kindle. Book excerpt: Plasma catalysis is gaining increasing interest for various gas conversion applications, such as CO2 conversion into value-added chemicals and fuels, N2 fixation for the synthesis of NH3 or NOx, methane conversion into higher hydrocarbons or oxygenates. It is also widely used for air pollution control (e.g., VOC remediation). Plasma catalysis allows thermodynamically difficult reactions to proceed at ambient pressure and temperature, due to activation of the gas molecules by energetic electrons created in the plasma. However, plasma is very reactive but not selective, and thus a catalyst is needed to improve the selectivity. In spite of the growing interest in plasma catalysis, the underlying mechanisms of the (possible) synergy between plasma and catalyst are not yet fully understood. Indeed, plasma catalysis is quite complicated, as the plasma will affect the catalyst and vice versa. Moreover, due to the reactive plasma environment, the most suitable catalysts will probably be different from thermal catalysts. More research is needed to better understand the plasma–catalyst interactions, in order to further improve the applications.

Download or read book Development and Benchmarking of a Hybrid PIC Code For Dense Plasmas and Fast Ignition written by and published by . This book was released on 2014 with total page 165 pages. Available in PDF, EPUB and Kindle. Book excerpt: Radiation processes play an important role in the study of both fast ignition and other inertial confinement schemes, such as plasma jet driven magneto-inertial fusion, both in their effect on energy balance, and in generating diagnostic signals. In the latter case, warm and hot dense matter may be produced by the convergence of a plasma shell formed by the merging of an assembly of high Mach number plasma jets. This innovative approach has the potential advantage of creating matter of high energy densities in voluminous amount compared with high power lasers or particle beams. An important application of this technology is as a plasma liner for the flux compression of magnetized plasma to create ultra-high magnetic fields and burning plasmas. HyperV Technologies Corp. has been developing plasma jet accelerator technology in both coaxial and linear railgun geometries to produce plasma jets of sufficient mass, density, and velocity to create such imploding plasma liners. An enabling tool for the development of this technology is the ability to model the plasma dynamics, not only in the accelerators themselves, but also in the resulting magnetized target plasma and within the merging/interacting plasma jets during transport to the target. Welch pioneered numerical modeling of such plasmas (including for fast ignition) using the LSP simulation code. Lsp is an electromagnetic, parallelized, plasma simulation code under development since 1995. It has a number of innovative features making it uniquely suitable for modeling high energy density plasmas including a hybrid fluid model for electrons that allows electrons in dense plasmas to be modeled with a kinetic or fluid treatment as appropriate. In addition to in-house use at Voss Scientific, several groups carrying out research in Fast Ignition (LLNL, SNL, UCSD, AWE (UK), and Imperial College (UK)) also use LSP. A collaborative team consisting of HyperV Technologies Corp., Voss Scientific LLC, FAR-TECH, Inc., Prism Computational Sciences, Inc. and Advanced Energy Systems Inc. joined efforts to develop new physics and numerical models for LSP in several key areas to enhance the ability of LSP to model high energy density plasmas (HEDP). This final report details those efforts. Areas addressed in this research effort include: adding radiation transport to LSP, first in 2D and then fully 3D, extending the EMHD model to 3D, implementing more advanced radiation and electrode plasma boundary conditions, and installing more efficient implicit numerical algorithms to speed complex 2-D and 3-D computations. The new capabilities allow modeling of the dominant processes in high energy density plasmas, and further assist the development and optimization of plasma jet accelerators, with particular attention to MHD instabilities and plasma/wall interaction (based on physical models for ion drag friction and ablation/erosion of the electrodes). In the first funding cycle we implemented a solver for the radiation diffusion equation. To solve this equation in 2-D, we used finite-differencing and applied the parallelized sparse-matrix solvers in the PETSc library (Argonne National Laboratory) to the resulting system of equations. A database of the necessary coefficients for materials of interest was assembled using the PROPACEOS and ATBASE codes from Prism. The model was benchmarked against Prism's 1-D radiation hydrodynamics code HELIOS, and against experimental data obtained from HyperV's separately funded plasma jet accelerator development program. Work in the second funding cycle focused on extending the radiation diffusion model to full 3-D, continued development of the EMHD model, optimizing the direct-implicit model to speed up calculations, add in multiply ionized atoms, and improved the way boundary conditions are handled in LSP. These new LSP capabilities were then used, along with analytic calculations and Mach2 runs, to investigate plasma jet merging, plasma detachment and transport ...

Download or read book Ignition Systems for Gasoline Engines written by Michael Günther and published by Springer. This book was released on 2016-11-18 with total page 324 pages. Available in PDF, EPUB and Kindle. Book excerpt: The volume includes selected and reviewed papers from the 3rd Conference on Ignition Systems for Gasoline Engines in Berlin in November 2016. Experts from industry and universities discuss in their papers the challenges to ignition systems in providing reliable, precise ignition in the light of a wide spread in mixture quality, high exhaust gas recirculation rates and high cylinder pressures. Classic spark plug ignition as well as alternative ignition systems are assessed, the ignition system being one of the key technologies to further optimizing the gasoline engine.