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Flame Dynamics And Chemi Ion Flows Driven By Applied Electric Fields
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Book Synopsis Flame Dynamics and Chemi-Ion Flows Driven by Applied Electric Fields by : Jesse A. Tinajero
Download or read book Flame Dynamics and Chemi-Ion Flows Driven by Applied Electric Fields written by Jesse A. Tinajero and published by . This book was released on 2017 with total page 146 pages. Available in PDF, EPUB and Kindle. Book excerpt: The enhancement to laminar, non-premixed flames by the application of an external electric field is studied. It has long been known that naturally occurring ions are produced through chemical reactions during the combustion of hydrocarbon flames. Chemi-ionization has been noted in the literature as the source of naturally occurring flame ions and electrons. Because chemi-ions exist in very small quantities within the flame (109--10 10 ions/cm3), they contribute very little to the overall natural combustion process and can usually be neglected in conventional combustion applications/studies. However, with the application of an external electric field, the chemi-ions/electrons can have a dramatic effect on combustion through ion driven winds.Ion current measurements are characterized for conical-type methane flames stabilized on axially symmetric burners with longitudinal electric fields applied. The ion currents are used to correlate the flux of chemi-ions to measured flame characteristics. The manipulation of the flame by ion winds is analyzed through CH* chemiluminescence where flame geometry and light emission are the main targets to be studied. The modification to the thermal flow field is analyzed through schlieren imagery. The visualization through schlieren demonstrates how ion winds enhance the exhaust gas and provides a means of analyzing the interaction between ion fluxes and surrounding neutral flow. Numerical CFD models are described and validated. Ion wind body forces are generalized to simple body forces to test the extent to which ion winds can be used to describe the experimental observations. The numerical models provide a means of studying more in-depth complicated interactions of the flame and gaseous flows to enhanced body forces. Finally, a theoretical model is developed which highlights the important mechanisms involved in the modification of flame and gas flow dynamics by body forces due to gravity and external electric fields.Ion winds are shown to be the dominant mechanism in external electric field enhanced combustion. Ion winds explain nearly all of the observed effects on flames by external fields. The relatively small disparities that do exist between the experimental results and numerical results are likely from the uncertainties associated with chemical kinetics of minor species with extremely small concentrations and the use of simplified transport in the simulation.
Book Synopsis Dynamics of Chemi-ion Driven Flows in an Applied Electric Field by : Jesse Alexander Tinajero
Download or read book Dynamics of Chemi-ion Driven Flows in an Applied Electric Field written by Jesse Alexander Tinajero and published by . This book was released on 2015 with total page 93 pages. Available in PDF, EPUB and Kindle. Book excerpt: Chemi-ions are produced during combustion of a hydrocarbon fuel. If an external electric field is present, a charge separation occurs due to the electrical force acting on the positively and negatively charged species. These ions traverse in the direction of the electrode of opposite potential. Along their path, they continuously collide with neutral molecules within the surrounding bulk gas until they are able to recombine and neutralize at the downstream electrode. During each collision, the charged species give up their acquired momentum to the neutral molecules. Macroscopically, this transfer of momentum has been best described mathematically as a body force acting on the bulk gas. The effect is commonly referred to as an ion wind effect. Gravity effects make the electric field effects on combustion difficult to study with earth-based experiments. This is because the gravity-driven buoyancy effects behave as a body force also acting on the bulk gas. Buoyancy and electrical body forces act on the same order of magnitude. The two forces are coupled through temperature since the production of ions is temperature dependent. Between the two, the contribution to the net momentum of the gas is then difficult to distinguish. On the other hand, micro- gravity experiments allow for the direct study of electric field effects in the absence of gravity. Micro-gravity experiments on-board the International Space Station through NASA's Advanced Combustion via Micro-gravity Experiments program, or ACME, are planned for 2016-17. Nevertheless, preliminary studies are needed in preparation for the ISS experiments. These studies are described in this thesis. A replica of the ISS experiment for the electric field effects on laminar diffusion flames (EFIELD Flames) that is part of ACME was recreated in a ground based laboratory. A schlieren system was built to visualize the effect an applied electric field has on the flame's buoyant thermal plume when the electric field is given a step function. Thermal plumes created by natural convection are well understood and can be related to parameters such as heat release and local velocity. Thus, when studying thermal plumes created by forced convection, i.e., ion wind effects, it is thought that similar relations can be made with electro-hydrodynamic parameters such as ion current and electric potential. High-speed videos captured the disturbance in the bulk gas due to a sudden presence of an applied electric field. These videos reveal a never before seen wave phenomenon that is created as the bulk gas transitions from a buoyancy driven gas flow to an electrically driven gas flow. Total ion current measurements were taken by using a shunt resistor in series with the high voltage power supply and the two electrodes. The experiments performed were focused on transient effects in order to characterize time-scales related to generation of both an ion current and ion wind. It was seen that the generation of an ion current was fully established within 10ms. This time-scale, however, may have been inhibited by a characteristically slow high voltage power supply system. The first noticeable appearance of an ion wind effect being generated was also seen to be 10ms. The time-scale related to a volume of \ion wind driven" gas cloud to travel the length of the electrode space region was seen to be 40ms for a 3.5cm electrode space length. The time-scale related to the time it takes for the bulk gas to reach a new steady state was seen to be 100ms. Finally, it was also observed that the time-scale related to the disappearance of visible soot when the flame was compressed by an ion wind was 300ms. These experimental time-scales were then compared to time-scales developed through simplified electrical aspects of combustion theory. Both theoretical and experimental time-scales appeared to agree within reason.
Book Synopsis Electric Field-driven Flame Dynamics by : Sunny Vijay Karnani
Download or read book Electric Field-driven Flame Dynamics written by Sunny Vijay Karnani and published by . This book was released on 2011 with total page 133 pages. Available in PDF, EPUB and Kindle. Book excerpt: Hydrocarbon flames naturally produce charged intermediate species during the chemical-to-thermal energy conversion process. Although low in concentration, chemi-ions can dramatically influence flame behavior due to their electrical nature. The body force exerted on these species by an electric field is lost through mean free path collisions to neighboring neutral molecules. The frequent collisions of the ions help quickly establish a drift velocity governed by their mobility, along with a small, but measurable, net velocity of neutral molecules in the same direction. This ion-driven wind, analogous to buoyancy, can alter the flow environment, which produces a complex coupling that can affect flame shape, luminosity, and stability limits. This ability to globally influence flame behavior can potentially create a powerful sensing and actuation platform. This dissertation describes a fundamental study on the complex interaction between chemi-ionization in flames and any physical changes in a flame which are created by an electric field-driven convective flow. A theoretical and historical background is included to give the reader the necessary foundation to appreciate the tests performed and their implications. Because natural convection and the ion wind have a similar influence, in addition to testing in a 1g environment, this dissertation discusses results from a number of tests performed in a reduced gravity environment at the NASA Glenn 2.2-s Drop Tower. Depending on the testing environment, various imaging and diagnostic techniques are employed to interrogate flame behavior: flame photographs, chemiluminescence measurements, Planar Laser Induced Fluorescence, and Schlieren. Results present evidence of a relationship between the measured ion current and CH chemiluminescence, illuminate the impact of soot on ion current measurements, as well as the limitations of the ion current as a representative measurement of chemi-ionization. In addition, numerical models developed in OpenFOAM contribute toward an understanding of ion formation in non-premixed jet and coflowing flames.
Book Synopsis Electrical Aspects of Impinging Flames by : YuChien Chien
Download or read book Electrical Aspects of Impinging Flames written by YuChien Chien and published by . This book was released on 2015 with total page 240 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation examines the use of electric fields as one mechanism for controlling combustion as flames are partially extinguished when impinging on nearby surfaces. Electrical aspects of flames, specifically, the production of chemi-ions in hydrocarbon flames and the use of convective flows driven by these ions, have been investigated in a wide range of applications in prior work but despite this fairly comprehensive effort to study electrical aspects of combustion, relatively little research has focused on electrical phenomena near flame extinguishment, nor for flames near impingement surfaces. Electrical impinging flames have complex properties under global influences of ion-driven winds and flow field disturbances from the impingement surface. Challenges of measurements when an electric field is applied in the system have limited an understanding of changes to the flame behavior and species concentrations caused by the field. This research initially characterizes the ability of high voltage power supplies to respond on sufficiently short time scales to permit real time electrical flame actuation. The study then characterizes the influence of an electric field on the impinging flame shape, ion current and flow field of the thermal plume associated with the flame. The more significant further examinations can be separated into two parts: 1) the potential for using electric fields to control the release of carbon monoxide (CO) from surface-impinging flames, and 2) an investigation of controlling electrically the heat transfer to a plate on which the flame impinges. Carbon monoxide (CO) results from the incomplete oxidation of hydrocarbon fuels and, while CO can be desirable in some syngas processes, it is usually a dangerous emission from forest fires, gas heaters, gas stoves, or furnaces where insufficient oxygen in the core reaction does not fully oxidize the fuel to carbon dioxide and water. Determining how carbon monoxide is released and how heat transfer from the flame to the plate can be controlled using the electric field are the two main goals of this research. Multiple diagnostic techniques are employed such as OH chemiluminescence to identify the reaction zone, OH PLIF to characterize the location of this radical species, CO released from the flame, IR imaging and OH PLIF thermometry to understand the surface and gas temperature distribution, respectively. The principal finding is that carbon monoxide release from an impinging diffusion flame results from the escape of carbon monoxide created on the fuel side of the flame along the boundary layer near the surface where it avoids oxidation by OH, which sits to the air side of the reaction sheet interface. In addition, the plate proximity to the flame has a stronger influence on the emission of toxic carbon monoxide than does the electric field strength. There is, however, a narrow region of burner to surface distance where the electric field is most effective. The results also show that heat transfer can be spatially concentrated effectively using an electric field driven ion wind, particularly at some burner to surface distances.
Book Synopsis Electric Field Induced Stability Modifications in Pre-mixed Hydrocarbon Flames by :
Download or read book Electric Field Induced Stability Modifications in Pre-mixed Hydrocarbon Flames written by and published by . This book was released on 2006 with total page 91 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work focuses upon the effects of electric fields on the stability of pre-mixed hydrocarbon flames fueled by methane, propane and butane. For all fuels studied, over varying flow rates and equivalence ratios, electric-field-induced modification of the flame front stability over wide ranges has been observed and documented. Specifically, the electric pressure effect has been used to force pre-mixed hydrocarbon/air flame fronts to transition from flow-induced hydrodynamic-instability-dominated behavior, to field-stabilized laminar flow, and finally to field-induced thermal-diffusive-instability-dominated turbulent flame fronts. The effects are best described from a combustion dynamics viewpoint as a continuously variable electric-field-induced diminution of the flame Lewis number from typical values (> 1), past the flame critical Lewis number (0.6-0.9), to thermal-diffusive-instability dominated values below the critical Lewis number at higher applied potentials. A possible field-driven ion chemistry process that could produce those effects is the dissociative recombination of the flame ion (H30+) at the burner surface.
Book Synopsis U.S. Government Research Reports by :
Download or read book U.S. Government Research Reports written by and published by . This book was released on 1963 with total page 262 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Computational Study of a Charged Flow Under the Influence of Electric Fields by : Niphon Lapanaphan
Download or read book Computational Study of a Charged Flow Under the Influence of Electric Fields written by Niphon Lapanaphan and published by . This book was released on 2001 with total page 250 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis 36th AIAA Plasmadynamics and Lasers Conference: 05-4654 - 05-4931 by :
Download or read book 36th AIAA Plasmadynamics and Lasers Conference: 05-4654 - 05-4931 written by and published by . This book was released on 2005 with total page 648 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis The Measurement and Application of Electric Effects in Combustion by : Daniel Corrigan Murphy
Download or read book The Measurement and Application of Electric Effects in Combustion written by Daniel Corrigan Murphy and published by . This book was released on 2015 with total page 134 pages. Available in PDF, EPUB and Kindle. Book excerpt: The existence of interactions between flames and electric fields has been known for quite some time and has received experimental and theoretical study over the years but remain an active topic of research in the combustion community. The present work specifically investigates the sensitivity of premixed flames electric fields. Prior work has demonstrated that electric fields may be used to enhance and control combustion, but full potential and range of applications for this effect have not been explored. Multiple theories have been presented to explain the process, but there is not yet a truly complete understanding of how electric fields fundamentally change the process of combustion. This work serves to explore new applications of electric-flame interactions and to provide experimental measurements to support the development of detailed theoretical models. Thermo-diffusive and acoustic instabilities in freely propagating flames can trigger the formation of wrinkled flames and turbulence, which may or may not be desirable in different scenarios. Electric fields present a means to interact with such instabilities either by generating direct hydrodynamic forces ('ionic wind') or by modifying the rate of combustion. Experiments performed on downward-propagating hydrocarbon flames have demonstrated that electric fields can be applied to excite or suppress existing instabilities and control the onset of turbulence. Numerical models following from these experiments indicate that subtle spatial variations in chemical reactivity can achieve similar control of inherently unstable flames. A practical limitation of combustion is the phenomenon of quenching, where heat losses to the surroundings extinguish a flame. The enhancement achieved by electric fields is shown to dramatically increase flame propagation speed and reduce quenching in methane-air flames, which may permit the miniaturization of combustion-based power generation systems. In the course of these experiments, flames were found to exhibit different behavior depending on the direction of the applied field. This result is consistent with a proposed model of ion transport in laminar flames, although the experiments have shown a greater degree of enhancement than predicted. Ultimately, modeling the electrical aspects of combustion should be based on detailed accounting of the ion species present in flames. To support the ongoing development of detailed ion-chemistry mechanisms, a non-intrusive microwave interferometer for use in shock tube studies of combustion kinetics was developed. This was used to measure the formation and consumption of free electrons in shock-induced combustion. The range of equivalence ratios tested and the variety of hydrocarbon fuels used provide a rich dataset. Comparison of these results to complementary chemical kinetics simulations have been used to validate proposed improvements to existing mechanisms.
Book Synopsis Simulations of Low Mach Number Reactive Flows Coupled with Electric Fields by :
Download or read book Simulations of Low Mach Number Reactive Flows Coupled with Electric Fields written by and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Applying electric fields to flames can provide an effective, non-invasive control of the combustion process. In this work, an algorithm recently introduced to handle the interactions between reactive flows and an electric field is extended to handle multiple dimensions and adaptive mesh refinement (AMR), and applied to a series of laminar flames. Experimental data allows to validate the ability of the algorithm to capture the mechanisms driving the flame response to electric fields.
Book Synopsis Electric Field Effects in Combustion with Non-thermal Plasma by : Tiernan Albert Casey
Download or read book Electric Field Effects in Combustion with Non-thermal Plasma written by Tiernan Albert Casey and published by . This book was released on 2016 with total page 139 pages. Available in PDF, EPUB and Kindle. Book excerpt: Chemically reacting zones such as flames act as sources of charged species and can thus be considered as weakly-ionized plasmas. As such, the action of an externally applied electric field has the potential to affect the dynamics of reaction zones by enhancing transport, altering the local chemical composition, activating reaction pathways, and by providing additional thermal energy through the interaction of electrons with neutral molecules. To investigate these effects, one-dimensional simulations of reacting flows are performed including the treatment of charged species transport and non-thermal electron chemistry using a modified reacting fluid solver. A particular area of interest is that of plasma assisted ignition, which is investigated in a canonical one-dimensional configuration. An incipient ignition kernel, formed by localized energy deposition into a lean mixture of methane and air at atmospheric pressure, is subjected to sub-breakdown electric fields by applied voltages across the domain, resulting in non-thermal behavior of the electron sub-fluid formed during the discharge. Strong electric fields cause charged species to be rapidly transported from the ignition zone across the domain in opposite directions as charge fronts, augmenting the magnitude of the electric field in the fresh gas during the pulse through a dynamic-electrode effect. This phenomenon results in an increase in the energy of the electrons in the fresh mixture with increasing time, accelerating electron impact dissociation processes. A semi-analytic model to represent this dynamic electrode effect is constructed to highlight the relative simplicity of the electrodynamic problem admitted by the far more detailed chemistry and transport. Enhanced fuel and oxidizer decomposition due to electron impact dissociation and interaction with excited neutrals generate a pool of radicals, mostly O and H, in the fresh gas ahead of the flame's preheat zone. The effect of nanosecond pulses are to increase the mass of fuel burned at equivalent times relative to the unsupported ignition through enhanced radical generation, resulting in an increased heat release rate in the immediate aftermath of the pulse.
Download or read book Applied Mechanics Reviews written by and published by . This book was released on 1993 with total page 354 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Technical Abstract Bulletin by : Defense Documentation Center (U.S.)
Download or read book Technical Abstract Bulletin written by Defense Documentation Center (U.S.) and published by . This book was released on 1963 with total page 1032 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Air Pollution Abstracts written by and published by . This book was released on 1972 with total page 656 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Scientific and Technical Aerospace Reports by :
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1973 with total page 1102 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Nuclear Science Abstracts written by and published by . This book was released on 1960 with total page 834 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author :United States. National Aeronautics and Space Administration. Scientific and Technical Information Branch Publisher : ISBN 13 : Total Pages :1080 pages Book Rating :4.E/5 ( download)
Book Synopsis Japanese Science and Technology, 1983-1984 by : United States. National Aeronautics and Space Administration. Scientific and Technical Information Branch
Download or read book Japanese Science and Technology, 1983-1984 written by United States. National Aeronautics and Space Administration. Scientific and Technical Information Branch and published by . This book was released on 1985 with total page 1080 pages. Available in PDF, EPUB and Kindle. Book excerpt:
