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Reference EntryDOI

5 Laser Ignition

15 Jul 2010-
TL;DR: In this article, the authors proposed a hot gas model for laser-induced gas breakdown and evolution in high-speed and highly turbulent streams, and developed a Diode-Powered solid state laser for laser ignition.
Abstract: The sections in this article are 5.1 Introduction 5.2 Laser Ignition Energy 5.3 Breakdown Threshold Laser Energy 5.3.1 Multiphoton Ionization 5.3.2 Cascade Breakdown Ionization 5.4 Spark Evolution 5.5 Ignition Mechanism 5.5.1 Homogeneous Hot-Gas Model 5.5.2 Blast Wave Ignition Model 5.5.3 A Hot Gas Model 5.6 Potential Applications and Research Needs 5.6.1 Laser-Induced Gas Breakdown and Evolution in High-Speed and Highly Turbulent Streams 5.6.2 Laser Ignition for Stabilization of Ultra-Lean and High Speed Combustion Applications 5.6.3 Laser Ignition under Engine and/or Engine-Like Conditions 5.6.4 Development of a Diode-Pumped Solid State Laser for Laser Ignition Applications 5.7 Conclusions Keywords: gas turbine engines; fuel-lean flame; jet engines; laser ignition; modeling; spark evolution
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Journal ArticleDOI
TL;DR: This paper has now been declassified, and though it has been superseded by more complete calculations, it seems appropriate to publish it as it was first written, without alteration, except for the omission of a few lines, the addition of this summary, and a comparison with some more recent experimental work as discussed by the authors.
Abstract: This paper was written early in 1941 and circulated to the Civil Defence Research Committee of the Ministry of Home Security in June of that year The present writer had been told that it might be possible to produce a bomb in which a very large amount of energy would be released by nuclear fission—the name atomic bomb had not then been used—and the work here described represents his first attempt to form an idea of what mechanical effects might be expected if such an explosion could occur In the then common explosive bomb mechanical effects were produced by the sudden generation of a large amount of gas at a high temperature in a confined space The practical question which required an answer was: Would similar effects be produced if energy could be released in a highly concentrated form unaccompanied by the generation of gas? This paper has now been declassified, and though it has been superseded by more complete calculations, it seems appropriate to publish it as it was first written, without alteration, except for the omission of a few lines, the addition of this summary, and a comparison with some more recent experimental work, so that the writings of later workers in this field may be appreciated An ideal problem is here discussed A finite amount of energy is suddenly released in an infinitely concentrated form The motion and pressure of the surrounding air is calculated It is found that a spherical shock wave is propagated outwards whose radius R is related to the time t since the explosion started by the equation R = S (γ)tt E tρ-t, where ρo is the atmospheric density, E is the energy released and S (γ) a calculated function of of γ, the ratio of the specific heats of air

1,281 citations

Journal ArticleDOI
TL;DR: In this paper, the authors examined the role of multiphoton absorption and inverse bremsstrahlung or cascade collisional ionization in the early stages of the formation of plasma.
Abstract: Powerful flashes of ultraviolet, visible and near-infrared laser light can cause breakdown and plasma formation in gases which are normally transparent at these wavelengths. The ionization processes involved are multiphoton absorption and inverse bremsstrahlung or cascade collisional ionization, in competition with deionization by diffusion, recombination and radiative energy losses. The relative importance of these mechanisms and their roles in leading to the initiation of breakdown and the earliest stages of plasma formation is examined. Theoretical treatments are summarized, and experimental results obtained with a variety of gases and metal vapours at pressures from millitorrs to hundreds of atmospheres and with flashes from picosecond duration to quasi-continuous illumination are reviewed.

395 citations

Journal ArticleDOI
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.

334 citations

Journal ArticleDOI
TL;DR: In this article, an experimental study of laser-induced spark ignition of flammable, gaseous premixtures is reported, with theoretical interpretations, in an explosion bomb equipped with four variable-speed fans that facilitated the study of quiescent and isotropic turbulent conditions.

320 citations

Journal ArticleDOI
TL;DR: A critical review and comparison of the initiation of combustion processes by conventional electric spark or thermal means with laser sources is presented in this paper, where a description of the fundamentals of ignition processes is used as the basis for interpretation of experimental and theoretical studies of laser ignition.
Abstract: A critical review and comparison of the initiation of combustion processes by conventional electric spark or thermal means with laser sources is presented. A description of the fundamentals of ignition processes is used as the basis for interpretation of experimental and theoretical studies of laser ignition. It is shown that many features of laser ignition can be understood on the basis of simple thermal concepts, particularly when the effects of thermal or radical losses are considered. It is proposed that the main advantages of laser sources are likely to be in the timing and placement of ignition rather than the inherent energy requirements. Potential applications to combustion systems of practical importance, e.g., high-speed propulsion systems, are discussed and instructive laboratory-scale experiments are suggested.

285 citations