Effect of Spark Kernel Dynamics on Laser-induced Minimun Ignition Energies of Combustible Gases PDF Download
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Author: Elliot Hing-Gwok Lim Publisher: ISBN: Category : Languages : en Pages : 82
Book Description
Lewis and von Elbe's data on minimun spark ignition energies in gases have been the standard for many years, howewer, these data still do not agree with the most detailed computational models available. Current models predict lower minimun ignition energy values. An experimental program was initiated to better characterize the ignition source and to study its effect on minimun ignition energies. The apparatus constits of a laser ignition source operating either as a Q-switched nanosecond or a pulsed mode-locked picosecond laser. For mixtures of varying equivalence ratio, the minimun ignition energy was bracketed through repeated trials at varying laser spark energies. The current study has shown that laser sparks of different pulse durations produce larger minimun ignition energies (MIEs) in comparison to electric discharge and that the MIE is a function of laser pulse duration. The laser ignition experiments are consistent with Lewis and von Elbe's measurements for lean and rich mixtures ; howewer, neared to stoichiometric mixtures, the laser ignition values are significantly higher. To better understand these differences, measurements of the spark size and dynamics of spark propagation were made using visible emission, schlieren and interferometric imaging. It is found that although the laser energy is deposited in a small volume (typically a nearly-spherical region of 0.3 mm radius), the thermal energy deposited by the spark expands to a size much larger than the calculated minimun flame kernel on a time scale much shorter than the time scale for ignition. This indicates that the energy remaining within the initial deposition region is only a small fraction of the total deposited energy. Consequently, the energy deposition process does not necessarily couple efficiently into the ignition process. The picosecond and nanosecond pulse duration sparks were also seen to exhibit different expansion properties, with the nanosecond source yielding (for the same energy deposition) larger kernels after completion of the expansion process. From these observations it is concluded that the minimun ignition energies are strongly influenced by the dynamics of spark propagation, which in turn vary for different energy sources. In particular, it appears unlikely that the short-duration laser ignition sources are capable of yielding minimun ignition energies as low as longer-duration electric spark sources.
Author: Elliot Hing-Gwok Lim Publisher: ISBN: Category : Languages : en Pages : 82
Book Description
Lewis and von Elbe's data on minimun spark ignition energies in gases have been the standard for many years, howewer, these data still do not agree with the most detailed computational models available. Current models predict lower minimun ignition energy values. An experimental program was initiated to better characterize the ignition source and to study its effect on minimun ignition energies. The apparatus constits of a laser ignition source operating either as a Q-switched nanosecond or a pulsed mode-locked picosecond laser. For mixtures of varying equivalence ratio, the minimun ignition energy was bracketed through repeated trials at varying laser spark energies. The current study has shown that laser sparks of different pulse durations produce larger minimun ignition energies (MIEs) in comparison to electric discharge and that the MIE is a function of laser pulse duration. The laser ignition experiments are consistent with Lewis and von Elbe's measurements for lean and rich mixtures ; howewer, neared to stoichiometric mixtures, the laser ignition values are significantly higher. To better understand these differences, measurements of the spark size and dynamics of spark propagation were made using visible emission, schlieren and interferometric imaging. It is found that although the laser energy is deposited in a small volume (typically a nearly-spherical region of 0.3 mm radius), the thermal energy deposited by the spark expands to a size much larger than the calculated minimun flame kernel on a time scale much shorter than the time scale for ignition. This indicates that the energy remaining within the initial deposition region is only a small fraction of the total deposited energy. Consequently, the energy deposition process does not necessarily couple efficiently into the ignition process. The picosecond and nanosecond pulse duration sparks were also seen to exhibit different expansion properties, with the nanosecond source yielding (for the same energy deposition) larger kernels after completion of the expansion process. From these observations it is concluded that the minimun ignition energies are strongly influenced by the dynamics of spark propagation, which in turn vary for different energy sources. In particular, it appears unlikely that the short-duration laser ignition sources are capable of yielding minimun ignition energies as low as longer-duration electric spark sources.
Author: National Aeronautics and Space Adm Nasa Publisher: Independently Published ISBN: 9781792830068 Category : Languages : en Pages : 34
Book Description
Results from an experimental study of laser induced spark ignition of methane-oxygen mixtures are presented. The experiments were conducted at atmospheric pressure and 296 K under laminar pre-mixed and turbulent-incompletely mixed conditions. A pulsed, frequency doubled Nd: YAG laser was used as the ignition source. Laser sparks with energies of 10 mJ and 40 mJ were used, as well as a conventional electrode spark with an effective energy of 6 mJ. Measurements were made of the flame kernel radius as a function of time using pulsed laser shadowgraphy. The initial size of the spark ignited flame kernel was found to correlate reasonably well with breakdown energy as predicted by the Taylor spherical blast wave model. The subsequent growth rate of the flame kernel was found to increase with time from a value less than to a value greater than the adiabatic, unstretched laminar growth rate. This behavior was attributed to the combined effects of flame stretch and an apparent wrinkling of the flame surface due to the extremely rapid acceleration of the flame. The very large laminar flame speed of methane-oxygen mixtures appears to be the dominant factor affecting the growth rate of spark ignited flame kernels, with the mode of ignition having a small effect. The effect of incomplete fuel-oxidizer mixing was found to have a significant effect on the growth rate, one which was greater than could simply be accounted for by the effect of local variations in the equivalence ratio on the local flame speed. Santavicca, D. A. and Ho, C. and Reilly, B. J. and Lee, T.-W. NASA-CR-188689, NAS 1.26:188689 NAG3-966...
Author: Martin Weinrotter Publisher: GRIN Verlag ISBN: 3640881346 Category : Technology & Engineering Languages : en Pages : 183
Book Description
Doctoral Thesis / Dissertation from the year 2006 in the subject Electrotechnology, grade: 1, mit Ausgezeichnung bestanden, Vienna University of Technology (Insitut für Photonik), language: English, abstract: In this PhD thesis different fundamental aspects and the practical usability of a laser ignition system as a new, innovative and alternative ignition approach for internal combustion engines were investigated in great detail mainly experimentally. Ignition experiments in combustion chambers under high pressures and elevated temperatures have been conducted. Different fuels were investigated. Also the minimum breakdown energy in dependence of the initial temperature and pressure with the help of an aspheric lens with a high numerical aperture was studied. High-speed Schlieren diagnostics have been conducted in the combustion chamber. The different stages like the ignition plasma within the first nanoseconds via the shock wave generation to the expanding flame kernel were investigated. With the help of multi-point ignition the combustion duration could be reduced significantly. The controlled start of auto-ignition of n-heptane-air mixtures by resonant absorption of Er,Cr:YSGG laser radiation at 2.78 μm by additionally introduced water has been proven in combustion chamber experiments as a completely new idea. Beside experiments in the combustion chambers and long term tests under atmospheric conditions, various tests in SI engines up to 200 h, have been made. Different sources of contamination of the window surface have been identified. First experiments with a longitudinally diode-pumped, fiber-coupled and passively Q-switched solid-state laser α-prototype system with maximum pulse energy of 1.5 mJ at about 1.5 ns pulse duration were performed which allowed to ignite the engine successfully over a test period of 100 h. In cooperation with Lund University in Sweden, experiments have been performed on another engine test bed running in HCCI mode revealing the laser spark to be able to stimulate the auto-ignition process and to trigger the onset of combustion. In another international cooperation conducted with the Southwest Research Institute in Texas, U.S.A., the potential of laser ignition in combination with the so called HEDGE concept was studied. As a final direction of the work, first calculations and experiments of a β- prototype ignition laser of an own design have been conducted. The concept of a longitudinally diode-pumped, fiber-coupled and passively Q-switched solid-state laser was chosen as the most promising. Emitted pulse energy of 2 mJ within around 1 ns pulse duration was achieved easily allowing generating a laser-induced breakdown in air.
Author: Sara McAllister Publisher: Springer Science & Business Media ISBN: 1441979433 Category : Science Languages : en Pages : 315
Book Description
Fundamentals of Combustion Processes is designed as a textbook for an upper-division undergraduate and graduate level combustion course in mechanical engineering. The authors focus on the fundamental theory of combustion and provide a simplified discussion of basic combustion parameters and processes such as thermodynamics, chemical kinetics, ignition, diffusion and pre-mixed flames. The text includes exploration of applications, example exercises, suggested homework problems and videos of laboratory demonstrations
Author: Martin Hattwig Publisher: John Wiley & Sons ISBN: 3527612475 Category : Science Languages : en Pages : 718
Book Description
The new definitive reference in the field. Between them, the renowned team of editors and authors have amassed unparalleled experience at such institutes as BAM, PTB, Pittsburgh National Institute for Occupational Health and Safety, BASF AG, and the University of Göttingen. In this work -- the first of its kind for 35 years -- they describe in detail those measures that prevent or limit industrial explosions and the damage so caused. They cover various preventative methods, as well as the current state of technology combined with data gained through experimentation. This handbook offers operational, planning, design and safety engineers working in industry, government agencies and professional associations in-depth knowledge of the scientific and technical basics, allowing them to apply explosion protection according to any given situation.
Author: Michael Günther Publisher: Springer ISBN: 3319455044 Category : Technology & Engineering Languages : en Pages : 324
Book Description
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.
Author: Hans Peter Lenz Publisher: Springer ISBN: 148992762X Category : Technology & Engineering Languages : en Pages : 417
Book Description
Twentyfour years have gone by since the publication of K. Lohner and H. Muller's comprehen sive work "Gemischbildung und Verbrennung im Ottomotor" in 1967 [1.1]' Naturally, the field of mixture formation and combustion in the spark-ignition engine has wit nessed great technological advances and many new findings in the intervening years, so that the time seemed ripe for presenting a summary of recent research and developments. There fore, I gladly took up the suggestion of the editors of this series of books, Professor Dr. H. List and Professor Dr. A. Pischinger, to write a book summarizing the present state of the art. A center of activity of the Institute of Internal-Combustion Engines and Automotive Engineering at the Vienna Technical University, which I am heading, is the field of mixture formation -there fore, many new results that have been achieved in this area in collaboration with the respective industry have been included in this volume. The basic principles of combustion are discussed only to that extent which seemect necessary for an understanding of the effects of mixture formation. The focal point of this volume is the mixture formation in spark-ignition engines, covering both the theory and actual design of the mixture formation units and appropriate intake manifolds. Also, the related measurement technology is explained in this work.
Author: Elliot Hing-Gwok Lim
Author: Elliot Hing-Gwok Lim
Author: Elliot Hing-Gwok Lim
Author: National Aeronautics and Space Adm Nasa
Author: Martin Weinrotter
Author: Sara McAllister
Author: 
Author: Martin Hattwig
Author: Alessandro Parente
Author: Michael Günther
Author: Hans Peter Lenz