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 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 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 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 Non equilibrium Kinetic Studies of Repetitively Pulsed Nanosecond Discharge Plasma Assisted Combustion written by Mruthunjaya Uddi and published by . This book was released on 2008 with total page 177 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: The dissertation presents non-equilibrium chemical kinetic studies of large volume lean gaseous hydrocarbon/ air mixture combustion at temperatures (~300K) much below self ignition temperatures and low pressures (40-80torr), in ~25 nanosecond duration repetitive high voltage (~18kV) electric discharges running at 10 Hz. Xenon calibrated Two Photon Absorption Laser Induced Fluorescence (TALIF) is used to measure absolute atomic oxygen concentrations in air, methane-air, and ethylene-air non-equilibrium plasmas, as a function of time after initiation of a single 25 nsec discharge pulse at 10Hz. Oxygen atom densities are also measured after a burst of nanosecond discharges at a variety of delay times, the burst being run at 10Hz. Each burst contains sequences of 2 to 100 nanosecond discharge pulses at 100 kHz. Burst mode measurements show very significant (up to ~0.2%) build-up of atomic oxygen density in air, and some build-up (by a factor of approximately three) in methane-air at [phi]=0.5. Burst measurements in ethylene-air at [phi]=0.5 show essentially no build-up, due to rapid O atom reactions with ethylene in the time interval between the pulses. Nitric oxide density is also measured using single photon Laser Induced Fluorescence (LIF), in a manner similar to oxygen atoms, and compared with kinetic modeling. Fluorescence from a NO (4.18ppm) +N2 calibration gas is used to calibrate the NO densities. Peak density in air is found to be ~ 3.5ppm at ~ 225us, increasing from almost initial levels of ~ 0 ppm directly after the pulse. Kinetic modeling using only the Zeldovich mechanism predicts a slow increase in NO formation, in ~ 2 ms, which points towards the active participation of excited N2 and O2 molecules and N atoms in forming NO molecules. Ignition delay at a variety of fuel/ air conditions is studied using OH emission measurements at ~ 308nm as ignition foot prints. The ignition delay is found to be in the range of 6-20ms for ethylene/ air mixtures. No ignition was observed in the case of methane/ air mixtures. All these measurements agree well with kinetic modeling developed involving plasma reactions and electron energy distribution function calculations.

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 Experimental Study of the Effects of Nanosecond pulsed Non equilibrium Plasmas on Low pressure Laminar Premixed Flames written by Ting Li and published by . This book was released on 2014 with total page 194 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this dissertation, the effects of nanosecond, repetitively-pulsed, non-equilibrium plasma discharges on laminar, low-pressure, premixed burner-stabilized hydrogen/O2/N2 and hydrocarbon/O2/N2 flames is investigated using optical and laser-based diagnostics and kinetic modeling. Two different plasma sources, both of which generate uniform, low-temperature, volumetric, non-equilibrium plasma discharges, are used to study changes in temperature and radical species concentrations when non-equilibrium plasmas are directly coupled to conventional hydrogen/hydrocarbon oxidation and combustion chemistry. Emission spectroscopy measurements demonstrate number densities of excited state species such as OH*, CH*, and C2* increase considerably in the presence of the plasma, especially under lean flame conditions. Direct imaging indicates that during plasma discharge, lean hydrocarbon flames "move" upstream towards burner surface as indicated by a shift in the flame chemiluminescence. In addition, the flame chemiluminescence zones broaden. For the same plasma discharge and flame conditions, quantitative results using spatially-resolved OH laser-induced fluorescence (LIF), multi-line, OH LIF-thermometry, and O-atom two-photon laser-induced fluorescence (TALIF) show significant increases in ground-state OH and O concentrations in the preheating zones of the flame. More specifically, for a particular axial position downstream of the burner surface, the OH and O concentrations increase, which can be viewed as an effective "shift" of the OH and O profiles towards the burner surface. Conceivably, the increase in OH and O concentration is due to an enhancement of the lower-temperature kinetics including O-atom, H-atom and OH formation kinetics and temperature increase due to the presence of the low-temperature, non-equilibrium plasma. High-fidelity kinetic modeling demonstrates that the electric discharge generates significant amounts of O and possibly H atoms via direct electron impact, as well as quenching of excited species rather than pure thermal effect which is caused by Joule heating within the plasma. These processes accelerate chain-initiation and chain-branching reactions at low temperatures (i.e. in the preheat region upstream of the primary reaction zone in the present burner-stabilized flames) yielding increased levels of O, H, and OH. The effects of the plasma become more pronounced as the equivalence ratio is reduced which strongly suggest that the observed effect is due to plasma chemical processes (i.e. enhanced radical production) rather than Joule heating supports the kinetic modeling.

Download or read book Flow Reactor Studies of Non equilibrium Plasma Assisted Combustion Kinetics written by Nicholas Tsolas and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A new experimental facility was developed to study the reactive chemical kinetics associated with plasma-assisted combustion (PAC). Experiments were performed in a nearly isothermal plasma flow reactor (PFR), using reactant mixtures highly diluted in an inert gas (e.g., Ar, He, or N2) to minimize temperature changes from chemical reactions. At the end of the isothermal reaction zone, the gas temperature was rapidly lowered to terminate any continuation in reaction. Product composition as a result of any observed reaction was then determined using ex situ techniques, including non-dispersive infrared (NDIR), and by sample extraction and storage into a multi-position valve for subsequent analysis by gas chromatography (GC). Hydroxyl radical concentrations were measured in situ, using the laser induced fluorescence (LIF) technique. Reactivity maps for a given fuel system were achieved by fixing the flow rate or residence time of the reactant mixture through the PFR and varying the isothermal temperature. Fuels studied were hydrogen, ethylene and C1 to C7 alkane hydrocarbons, to examine pyrolysis and oxidation kinetics with and without the effects of a high-voltage nanosecond pulse duration plasma discharge, at atmospheric pressure from 420 K to 1250 K. In select instances, experimental studies were complimented with detailed chemical kinetic modeling analysis to determine the dominant and rate-controlling mechanisms, while elucidating the influence of the plasma chemistry on the thermal (neutral) chemistry.In the hydrogen oxidation system, no thermal reaction was observed until 860 K, consistent with the second explosion limit at atmospheric pressure, at which point all the hydrogen was rapidly consumed within the residence time of the reactor. With the plasma discharge, oxidation occurred at all temperatures examined, exhibiting a steady increase in the rate of oxidation starting from 470 K, and eventually consuming all the initial hydrogen by 840 K. For ethylene, kinetic results with the discharge indicated that pyrolysis type reactions were nearly as important as oxidative reactions in consuming ethylene below 750 K. Above 750 K, the thermal reactions coupled to the plasma reactions to further enhance the high temperature fuel consuming chemistry. Modeling analysis of plasma-assisted pyrolysis revealed that ethylene dissociation by collisional quenching with electronically-excited argon atoms formed in the presence of the plasma, resulted in the direct formation of acetylene and larger hydrocarbons by way of the ethyl radical. Similarly, during plasma-assisted oxidation, excited argon was able to directly dissociate the initial oxidizer to further enhance fuel consumption, but also facilitate low temperature oxidative chemistry due to the effective production of oxygenated species controlled by R+O2 chemistry. At the highest temperatures, the radical production by neutral thermal reactions became competitive and the effectiveness associated with the plasma coupled chemistry decreased. Under the effects of the plasma, alkane fuels exhibited extended limits of oxidation over the entire temperature range considered, compared to that of the thermal reactions alone. At atmospheric pressure, propane and butane exhibited cool flame chemistry between 420 K to 700 K, which normally occurs at higher pressures (P > 1 atm) for thermally constrained systems. This chemistry is characterized by the alkylperoxy radical formation, isomerization to the hydroperoxyalkyl radical, followed by dissociation to form aldehydes and ketones. Whereas, intermediate temperature chemistry between 700 K to 950 K, is characterized by beta-scission of the initial alkyl radical to form alkenes and smaller alkanes. The culmination of these studies demonstrate new insight into the kinetics governing PAC and provides a new experimental database to facilitate the development and validation of PAC-specific kinetic mechanisms.

Download or read book Experimental Investigation of Plasma assisted Combustion of Heavy Hydrocarbons Using Gliding Rotating Arc written by Jun Hee Han and published by . This book was released on 2016 with total page 92 pages. Available in PDF, EPUB and Kindle. Book excerpt: Rotating/Gliding arc gas discharge is known as a suitable application for plasma aided combustion (PAC). In this study, effects of rotating arc discharge on combustion of diesel and biodiesel fuel are investigated. The main focus of the experiment is to determine the effectiveness of rotating-arc in enhancing combustion performance. The first stage of the burner is designed for the fuel-air mixture to interact with the rotating arc at fuel-rich condition. The second stage of the burner is the main combustion section to make the mixture at overall fuel-lean condition and properly hold the flame inside the combustion chamber. As a result, lean flammability limit determined by equivalence ratio at lean blowout is found to be extended quite a bit when the arc is on. FTIR (Fourier Transform Infrared Spectroscopy) measurements of exhaust gas show that both CO and CO2 concentration become higher and O2 concentration lower for overall fuel-lean combustion with plasma on. Based on the results of level of total carbon oxidation, combustion efficiency is slightly higher with plasma than without plasma. Slightly more NO is produced when the arc is at present for a fixed equivalence ratio. However, with the extension of lean flammability condition achieved by plasma-assisted combustion the minimum NO is produced for PAC case. The increase of reactant temperature due to direct heat transfer from the arc to the surrounding and partial oxidation (exothermal) can mainly account for the observed enhancement of combustion for the PAC.

Download or read book Non thermal Plasma Discharges for Methane Reforming written by Pablo Diaz Gomez Maqueo and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "This thesis presents the experimental study of non-thermal plasmas applied to methane reforming at atmospheric pressure. The resulting hydrogen-containing gas is studied as a potential fuel additive to increase chemical reactivity in gas turbine engine conditions. Reactivity control is proposed as a fuel flexibility technology for low calorific fuels and as a mean to operate in low emission conditions such as lean premixed combustion.The experimental section of the thesis is focused on the characterization of pulsed-powered non-thermal discharge plasmas as fuel reformers. The experimental reactor consists of a pin to plane plasma chamber designed to be optically accessible and to isolate the reacting gases from the surrounding air. The applied voltage pulse duration is on the order of 100 ns to prevent thermalization of the plasma channel and to decouple thermal energy from excitation energy delivered by the discharge. When a voltage pulse is applied to the pin electrode, two stable regimes are identified: a diffuse regime with a plasma that occupies most of the inter-electrode volume, and a filamentary regime with constricted spark-like filaments. The first regime operates at a maximum energy per pulse of 1.3 mJ with negligible conversion efficiency. On the contrary, the filamentary regime reaches a maximum energy per pulse of 13.9 mJ with conversion and energy efficiencies of 26.3 % and 19.7 % respectively. Both regimes have gas temperatures estimated to be near 500 K, and there is no correlation with respect to the energy per pulse. The results suggest that the more energetic filamentary regime is not heating the gas, but rather delivering the energy towards better conversion efficiencies.To study the individual contributions of reactant temperature, pulse repetition frequency, and energy per pulse on the reforming performance of the reactor, a new high voltage pulser was developed and a preheating system capable of reaching 800 K was added. Temperature estimations show that varying the energy per pulse has a minimal effect on the temperature of the gas, while increasing the frequency heats the gas up to 777 K. Increasing reactant temperature is shown to have a negligible effect, while increasing the pulse repetition frequency has the strongest effect on conversion and energy efficiency. Additionally, the best performance is observed in partial oxidation, reaching a maximum conversion efficiency of 68.2 % and an energy efficiency of 31.5 %.The obtained results demonstrate the applicability of nanosecond repetitively-pulsed discharges as methane reformers. Capable of producing mixtures with up to 29.7 % hydrogen, these discharges can be used to increase chemical reactivity in gas turbine engine conditions as shown by the numerical simulations. This conversion is not dependent on the reactant temperature, but rather on the total amount of energy deposited by the discharge. Additionally, increasing the repetition frequency of the discharge seems to have the largest increase in efficiency, pointing towards future optimization of plasma-assisted fuel reforming technologies." --

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 Application of a Non thermal Plasma to Combustion Enhancement written by and published by . This book was released on 2004 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt: As a primary objective, researchers in Los Alamos National Laboratory's P-24 Plasma Physics group are aiming to minimize U.S. energy dependency on foreign resources through experiments incorporating a plasma assisted combustion unit. Under this broad category, researchers seek to increase efficiency and reduce NO(subscript x)/SO(subscript x) and unburned hydrocarbon emissions in IC-engines, gas-turbine engines, and burner units. To date, the existing lean burn operations, consisting of higher air to fuel ratio, have successfully operated in a regime where reduced NO(subscript x)/SO(subscript x) emissions are expected and have also shown increased combustion efficiency (less unburned hydrocarbon) for propane. By incorporating a lean burn operation assisted by a non-thermal plasma (NTP) reactor, the fracturing of hydrocarbons can occur with increased power (combustion, efficiency, and stability). Non-thermal plasma units produce energetic electrons, but avoid the high gas and ion temperatures involved in thermal plasmas. One non-thermal plasma method, known as silent discharge, allows free radicals to act in propagating combustion reactions, as well as intermediaries in hydrocarbon fracturing. Using non-thermal plasma units, researchers have developed a fuel activation/conversion system capable of decreasing pollutants while increasing fuel efficiency, providing a path toward future U.S. energy independence.

Download or read book Plasma Assisted Combustion and Flameholding in High Speed Cavity Flows written by Joseph Aloysius Heinrichs and published by . This book was released on 2012 with total page 113 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: This thesis presents an experimental study of non-equilibrium, low temperature, large volume plasma assisted ignition and flameholding in high-speed, non-premixed fuel-air flows. The plasma is produced between two electrodes powered by a high-voltage, nanosecond pulse generator operated at a high pulse repetition rate. Ignition in this type of plasma occurs due to production of highly reactive radicals by electron impact excitation and dissociation, as opposed to more common thermal ignition. Previously, it has been shown that this type of plasma can reduce ignition delay time and ignition temperature. The experiments performed in this thesis focus on application of these plasmas to ignition, and flameholding in high-speed cavity flows. The experiments discussed in this thesis continue previous work using a high-speed combustion test section with a larger cavity, and the previous results are compared to the present work. Several modifications have been made to the test section and electrodes compared to the design used in previous work in order to reduce the cavity effect on the main flow and maintain diffuse plasma between the electrodes in the cavity. The electrodes used in these experiments are placed in a cavity recess, used to create a recirculation flow region with long residence time, where ignition and flameholding can occur. In order to analyze the nanosecond pulse plasma and the flame, various diagnostics were used, including current and voltage measurements, UV emission measurements, ICCD camera imaging, static pressure measurements, and time-averaged emission spectroscopy. The experiments in this thesis were performed at relatively low pressures (P=150-200 torr) using hydrogen and ethylene fuels injected into the cavity. Current and voltage measurements showed that ~1-2 mJ was coupled to the plasma by each pulse. ICCD imaging and UV emission data revealed that the plasma sustained in quiescent air was diffuse. When ethylene was injected into the cavity to ignite the flow, ICCD imaging and UV emission data showed arcing to bare metal surfaces in the test section occurred shortly after ignition, which prompted switching to hydrogen fuel. Using hydrogen, ICCD imaging and UV emission showed that the plasma remained diffuse and confined to the area between electrodes. Time-average emission spectroscopy measurements revealed that the air-flow temperature remained low until fuel was injected and ignition occurred. Pressure and UV emission measurements were used to find velocity limits within which the flow ignited. It was found that the upper limit of velocity depends strongly on the static pressure in the test section. The highest flow velocity at which combustion was achieved in H2-air flows was 270 m/s at 180 torr. This represents considerable improvement compared to previous work using nanosecond pulse discharge for ignition in cavities. Preliminary results show that plasma generation and ignition are possible using a smaller diameter electrode such that the cavity size can be further reduced, and that a supersonic flow can be produced in the present test section using a Mach 2 nozzle placed upstream of the cavity. The appendix details a study on the production of oxygen atoms using a pulsed excimer laser.

Download or read book Generation of Hydrogen rich Gas Using Non Equilibrium Plasma Discharges written by Olufela O. Odeyemi and published by . This book was released on 2013 with total page 250 pages. Available in PDF, EPUB and Kindle. Book excerpt: Advisor: Alexander Fridman, Ph.D.

Download or read book Pulsed Nanosecond Dielectric Barrier Discharge in Nitrogen at Atmospheric Pressure written by Yiyun Zhang (S. M.) and published by . This book was released on 2020 with total page 87 pages. Available in PDF, EPUB and Kindle. Book excerpt: Small power devices are of strong interest as many electronics are made more compact. Those portable power sources are widely used in aerospace applications such as small UAVs and satellite thrusters. Typically, these portable devices rely on batteries, but small power generators based on hydrocarbon fuel micro-combustors have much higher energy densities. However, flame instability and extinction are difficult to avoid at small scales. Because of the high surface to volume ratio, significant heat loss and radical quenching at the walls take place. To address this challenge, plasma has shown capabilities in facilitating combustion through thermal, kinetic and transport effects. In this work, a preliminary study of plasma discharge at atmospheric pressure is conducted as the first step to understand Plasma-Assisted Combustion (PAC) at micro scales. Among various electric discharge mechanisms, Dielectric Barrier Discharge (DBD) is chosen due to its ability to generate non-thermal plasma at atmospheric pressure with a simple geometry and a low power consumption. Repetitive Pulsed Nanosecond Discharge (RPND) technique is also studied. It provides repetitive high voltage pulses on the order of 10 - 20 nanoseconds and is a common technique in non-equilibrium plasma generation. A 1D DBD model is constructed for a volume discharge. It couples particle continuity equations with Poisson's equation, and solves for electric field and charged particle number densities. The numerical model is discretized in space and time to obtain charged particles evolution and electric properties. The model is firstly validated with open literature for both AC and RPND, and is then applied to our DBD setup at atmospheric pressure. In addition, a nitrogen (and air) discharge experiment is designed and operated with RPND. Preliminary results show the capability to generate sustainable and uniform plasma at atmospheric pressure. The appearance is that of a uniform glow plasma free of micro-discharges. Several experimental findings help to understand the discharge physics and set a foundation for future applications in micro-scale combustion.

Download or read book OH LIF Studies of Low Temperature Plasma Assisted Oxidation and Ignition in Nanosecond Pulsed Discharge written by Inchul Choi and published by . This book was released on 2011 with total page 146 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: In recent years, plasma assisted ignition and flame-holding in high speed flows has attracted considerable attention due to potential applications for turbojet engines and afterburners operating at high altitudes, as well as scramjet engines. Conventional methods of igniting a flow in the combustor using a spark or an arc discharge are known to be ineffective at low pressures and high flow velocities, since the ignition kernel is limited by a small volume of the spark or arc filament. Single photon LIF spectroscopy is used to study hydroxyl radical formation and loss kinetics in low temperature hydrogen-air repetitively pulsed nanosecond plasmas. Nanosecond pulsed plasmas are created in a rectangular cross section quartz channel / plasma flow reactor. Flow rates of hydrogen-air mixtures are controlled by mass flow controllers at a total pressure of 40-100 torr, initial temperature T0=300-500 K and a flow velocity of approximately u=0.1-0.8 m/sec. Two rectangular copper plate electrodes, rounded at the corners to reduce the electric field non-uniformity, are attached to the outside of the quartz channel. Repetitively pulsed plasmas are generated using a Chemical Physics Technologies (CPT) power supply which produces ~25 nanosecond pulses with ~20 kV peak voltage. Absolute hydroxyl radical mole fraction is determined as both a function of time after application of a single 25 nsec pulse, and 60 microseconds after the final pulse of a variable length "burst" of pulses. Relative LIF signal levels are put on an absolute mole fraction scale by means of calibration with a standard near-adiabatic Hencken flat flame burner at atmospheric pressure. By obtaining OH LIF data in both the plasma and the flame, and correcting for differences in the collisional quenching and Vibrational Energy Transfer (VET) rates, absolute OH mole fraction can be determined. For a single discharge pulse at 27 °C and 100 °C, the absolute OH temporal profile is found to rise rapidly during the initial ~0.1 msec after discharge initiation and decay relatively slowly, with a characteristic time scale of ~1 msec. In repetitive burst mode the absolute OH number density is observed to rise rapidly during the first approximately 10 pulses (0.25 msec), and then level off to a near steady-state plateau. In all cases a large secondary rise in OH number density is also observed, clearly indicative of ignition, with ignition delay equal to approximately 15, 10, and 5 msec, respectively, for initial temperatures of 27 °C, 100 °C, and 200 °C. Plasma kinetic modeling predictions capture this trend quantitatively.