Laser induced spark ignition of methane-oxygen mixtures
25 Sep 1991-
TL;DR: In this article, an experimental study of laser induced spark ignition of methane-oxygen mixtures was conducted at atmospheric pressure and 296 K under laminar pre-mixed and turbulent-incompletely mixed conditions.
Abstract: 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.
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TL;DR: In this paper, the authors review past work to identify some fundamental issues underlying the physics of the laser spark ignition process and research needs in order to bring the laser ignition concept into the realm of reality.
Abstract: Laser ignition has become an active research topic in recent years because it has the potential to replace the conventional electric spark plugs in engines that are required to operate under much higher compression ratios, faster compression rates, and much leaner fuel-to-air ratios than gas engines today. It is anticipated that the igniter in these engines will face with pressures as high as 50 MPa and temperatures as high as 4000 K. Using the conventional ignition system, the required voltage and energy must be greatly increased (voltages in excess of 40 kV) to reliably ignite the air and fuel mixture under these conditions. Increasing the voltage and energy does not always improve ignitability but it does create greater reliability problem. The objective of this paper is to review past work to identify some fundamental issues underlying the physics of the laser spark ignition process and research needs in order to bring the laser ignition concept into the realm of reality.
334 citations
Patent•
15 Mar 1996TL;DR: Two or more laser light pulses with different temporal lengths and peak pulse powers can be employed sequentially to regulate the rate and duration of laser energy delivery to fuel mixtures, thereby improving fuel ignition performance over a wide range of fuel parameters as discussed by the authors.
Abstract: Two or more laser light pulses with certain differing temporal lengths and peak pulse powers can be employed sequentially to regulate the rate and duration of laser energy delivery to fuel mixtures, thereby improving fuel ignition performance over a wide range of fuel parameters such as fuel/oxidizer ratios, fuel droplet size, number density and velocity within a fuel aerosol, and initial fuel temperatures.
85 citations
Patent•
04 Aug 2005TL;DR: In this article, a spark delivery system for generating a spark using a laser beam is provided, and includes a laser light source and a laser delivery assembly including a hollow fiber and a launch assembly comprising launch focusing optics to input the laser beam in the hollow fiber.
Abstract: A spark delivery system for generating a spark using a laser beam is provided, and includes a laser light source and a laser delivery assembly. The laser delivery assembly includes a hollow fiber and a launch assembly comprising launch focusing optics to input the laser beam in the hollow fiber. The laser delivery assembly further includes exit focusing optics that demagnify an exit beam of laser light from the hollow fiber, thereby increasing the intensity of the laser beam and creating a spark. Other embodiments use a fiber laser to generate a spark. Embodiments of the present invention may be used to create a spark in an engine. Yet other embodiments include collecting light from the spark or a flame resulting from the spark and conveying the light for diagnostics. Methods of using the spark delivery systems and diagnostic systems are provided.
53 citations
Patent•
04 Aug 2005TL;DR: In this article, a spark delivery system for generating a spark using a laser beam is provided, and includes a laser light source and a laser delivery assembly including a hollow fiber and a launch assembly comprising launch focusing optics to input the laser beam in the hollow fiber.
Abstract: A spark delivery system for generating a spark using a laser beam is provided, and includes a laser light source and a laser delivery assembly. The laser delivery assembly includes a hollow fiber and a launch assembly comprising launch focusing optics to input the laser beam in the hollow fiber. The laser delivery assembly further includes exit focusing optics that demagnify an exit beam of laser light from the hollow fiber, thereby increasing the intensity of the laser beam and creating a spark. Other embodiments use a fiber laser to generate a spark. Embodiments of the present invention may be used to create a spark in an engine. Yet other embodiments include collecting light from the spark or a flame resulting from the spark and conveying the light for diagnostics. Methods of using the spark delivery systems and diagnostic systems are provided.
46 citations
TL;DR: In this paper, a laser ignition of premixed flames is studied in supersonic channel flow via a focused frequency-doubled (532 nm) Nd:YAG laser.
Abstract: Laser ignition of premixed flames is studied in supersonic channel flow. Breakdown of natural gas air kernels occurs via a focused frequency-doubled (532 nm) Nd:YAG laser. A calibrated double photodiode energy measurement system is employed to differentiate incident energy from deposited energy. Supersonic ignition kernels are similar to their subsonic counterparts: they are elliptic at early times, have a third lobe resulting from vorticity associated with plasma back-streaming, and have similar growth with respect to time. However, supersonic kernels have some interesting differences: the third lobe appears offset from the laser axis and the kernel size depends on the Mach number because Mach number can affect the static density. Kernel data are processed to expose the dependence of flame growth on the ignition event. The influence of the breakdown event decays as the time from breakdown increases, i.e. the breakdown memory fades with time. Suggested laser settings and independence times to minimize the influence of the breakdown event on flame speed measurements are given. The influence of Mach number and equivalence ratio on the ignition event are also discussed.
10 citations
References
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TL;DR: In this article, the authors measured the radius of the luminous globe or "ball of fire" which spread out from the centre of the first atomic explosion in New Mexico, and the radius, R, was determined for a large range of values of t, the time measured from the start of the explosion.
Abstract: Photographs by J. E. Mack of the first atomic explosion in New Mexico were measured, and the radius, R, of the luminous globe or 'ball of fire' which spread out from the centre was determined for a large range of values of t, the time measured from the start of the explosion. The relationship predicted in part I, namely, that R$^{\frac{5}{2}}$ would be proportional to t, is surprisingly accurately verified over a range from R=20 to 185 m. The value of R$^{\frac{5}{2}}$t$^{-1}$ so found was used in conjunction with the formulae of part I to estimate the energy E which was generated in the explosion. The amount of this estimate depends on what value is assumed for $\gamma $, the ratio of the specific heats of air. Two estimates are given in terms of the number of tons of the chemical explosive T.N.T. which would release the same energy. The first is probably the more accurate and is 16,800 tons. The second, which is 23,700 tons, probably overestimates the energy, but is included to show the amount of error which might be expected if the effect of radiation were neglected and that of high temperature on the specific heat of air were taken into account. Reasons are given for believing that these two effects neutralize one another. After the explosion a hemispherical volume of very hot gas is left behind and Mack's photographs were used to measure the velocity of rise of the glowing centre of the heated volume. This velocity was found to be 35 m./sec. Until the hot air suffers turbulent mixing with the surrounding cold air it may be expected to rise like a large bubble in water. The radius of the 'equivalent bubble' is calculated and found to be 293 m. The vertical velocity of a bubble of this radius is ${\textstyle\frac{2}{3}}\ \surd $(g29300) or 35$\cdot $7 m./sec. The agreement with the measured value, 35 m./sec., is better than the nature of the measurements permits one to expect.
661 citations
01 Jan 1988
TL;DR: In this paper, a review of recent advances in the understanding of the structure, propagation, and extinction of laminar flames under the influence of stretch, as manifested by the existence of flame curvature, flow nonuniformity, and flame motion, is reviewed.
Abstract: Recent advances in the understanding of the structure, propagation, and extinction of laminar flames under the influence of stretch, as manifested by the existence of flame curvature, flow nonuniformity, and flame motion, are reviewed. The emphasis is on premixed flames because of the richness and subtlety of the phenomena involved. The review distinguishes the influences of the tangential and normal velocity gradients on the flame response, both at the hydrodynamic scale and within the flame structure, and emphasizes the importance of the preferential diffusion nature of heat and mass transport, as well as the extent to which the flame can freely adjust its location in response to stretch in order to achieve complete reaction. It is then demonstrated that stretch has only minimal effect on an adiabatic, unrestrained, diffusionally-neutral flame with complete reaction in that the temperature, propagation rate, and thickness of the flame are invariant to stretch, and that stretch alone cannot extinguish such a flame. In the presence of preferential diffusion and/or when the flame movement is restrained, the response of the flame to stretch becomes more sensitive and extinction is also possible. The concept of flame stretch is applied to interpret such practical flame phenomena as flame stabilization and flame-front instability, determination of laminar flame speeds and flammability limits, concentration and temperature modifications in flame chemistry, and modeling of turbulent flames. The properties of stretched diffusion flames are then briefly discussed. The review closes with suggestions for further research.
387 citations
01 Jan 1979
TL;DR: In this paper, the initiation and subsequent propagation of flame fronts by breakdown, are and glow discharge ignition devices have been investigated by time resolved interferometry in CH4-air mixtures.
Abstract: The initiation and subsequent propagation of flame fronts by breakdown, are and glow discharge ignition devices have been investigated by time resolved interferometry in CH4-air mixtures (1/Ф=1.0, 1.11, 1.25, 1.4) at 4 bar. Based on size, effective expansion velocity, and radial temperature profiles across the flame fronts as functions of time after spark onset, it is shown that the breakdown controls the inflammation process up to ≈1 ms. The breakdown is far better suited for inflaming combustible mixtures than are or glow discharge due to very high energy transfer efficiency (≈95%), large double sided contact areas with the unburnt mixture, very steep gradients of temperature and particle density, and reignition capabilities at ≈300 μs. Thus extremely lean (1/Φ≈1.6) mixtures ignited at high flow velocities with high inflammation probabilities.
227 citations
TL;DR: In this paper, the structure and propagation of stretched premixed flames with preferential diffusion are analyzed using an approximate integral approach which yields algebraic relations for the characteristic scales, overall conservation requirements, and balances and continuity between the various scalar properties and their transport rates.
Abstract: The structure and propagation of stretched premixed flames with preferential diffusion are analyzed using an approximate integral approach which yields algebraic relations for the characteristic scales, overall conservation requirements, and balances and continuity between the various scalar properties and their transport rates. Specific flame configurations studied include the one-dimensional steadily propagating planar flame, the steady curved flame in nonuniform flow, and the outwardly/inwardly propagating spherical flame. Linearized results agree with those obtained from asymptotic analysis assuming small stretch. The present work yields enhanced insight into the dominant and coupled physical processes governing these complex flame phenomena, and demonstrates the utility of the integral analysis in theoretical combustion studies.
141 citations
01 Feb 1978
TL;DR: In this paper, preliminary test results are presented for a spark ignition engine which uses a focused, laser beam and conventional spark ignition as ignition sources for a steady running, single cylinder engine with minimum spark for best torque (MBT) spark timing and fixed throttle position.
Abstract: Preliminary test results are presented for a spark ignition engine which uses a focused, laser beam and conventional spark ignition as ignition sources For a steady running, single cylinder engine with minimum spark for best torque (MBT) spark timing and fixed throttle position, laser ignition provides improved engine performance and efficiency, extension of the lean limit of operation by five air/fuel ratios, and increased nitric oxide production Carbon monoxide and hydrocarbon emissions are essentially the same With the laser, the spark location was found to have little effect on performance except when it was moved near the combustion chamber wall The minimum laser pulse energy required for steady engine operation seems to be dictated by the minimum energy required to achieve breakdown of the laser pulse in air at the same pressure Raising the spark energy above this minimum level is desirable to produce a steady running engine The use of exhaust gas recirculation (EGR) was found to be effective in reducing nitric oxide levels The nitric-oxide specific fuel consumption tradeoff with 16% EGR showed the laser to be superior to the standard ignition system
133 citations