Author: Elliot Hing-Gwok LimPublisher:
ISBN:
Category :
Languages : en
Pages : 164
Book Description
Effect of Spark Kernal Dynamics on Laser-induced Minimum Ignition Energies of Combustible Gases
Author: Elliot Hing-Gwok LimPublisher:
ISBN:
Category :
Languages : en
Pages : 164
Book Description
Effect of Spark Kernel Dynamics on Laser-induced Minimun Ignition Energies of Combustible Gases
Author: Elliot Hing-Gwok LimPublisher:
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.
Laser Induced Spark Ignition of Methane-Oxygen Mixtures
Author: National Aeronautics and Space Adm NasaPublisher: 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...
Laser Ignition of Internal Combustion Engines
Author: Martin WeinrotterPublisher: 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.
Effect of Initial Temperature on Minimum Spark-ignition Energy
Author: I. R. KINGFundamentals of Combustion Processes
Author: Sara McAllisterPublisher: 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
The Dynamics of Laser Induced Breakdown in Gases
Author: Matt YoungPhotochemical Ignition Studies
Author: Andrzej W. MiziolekPublisher:
ISBN:
Category :
Languages : en
Pages : 29
Book Description
Gas mixtures of CH4/air, CH4/N2O, C3H8/air, C3H8/N2O, & C2H2/air were ignited above a slot burner by focusing three different laser beams whose wavelengths are 193 nm, 248 nm, & 532 nm. Minimum ignition energies were determined over a wide range of equivalence ratios & over the energy range of 0.1-40 mjoule/pulse for each gas/laser combination. A substantial wavelength dependence of the minimum ignition energy was observed for the ArF (193 nm) and KrF (248 nm) lasers acting on the different gas mixtures & was attributed to molecule-specific multiphoton-induced photochemistry of the various fuel & oxidizer molecules. Here, the necessary radicals & /or ions which are needed to cause ignition to occur are apparently produced in a controlled way. The Nd:YAG second harmonic (532 nm) laser exhibited a much smaller minimum ignition energy range for the various gas mixtures due to a different ignition mechanism involving gas breakdown, i.e., a laser-produced spark. This process appears to be much harder to control with respect to energy deposition than the photochemical one. The most efficient laser-driven ignition system was the one where the ArF (193 nm) laser acted on C2H2/air & laser energies as low as 0.2 mjoule caused ignition. Our results further indicate that there should be a number of ways to improve the efficiency of the photochemical ignition process. Thus, this new type of ignition source appears to possess considerable potential for utility in both practical applications as well as in allowing direct, time-resolved studies of the chemistry of ignition itself, which is an area of considerable current interest.
Chemical Abstracts
Author: Laser Spark Ignition of Chemically Reactive Gases
Author: John H. LeePublisher:
ISBN:
Category : Combustion
Languages : en
Pages : 10
Book Description