Talks and Poster Presentations (with Proceedings-Entry):

G. Liedl, D. Schuöcker, B. Geringer, J. Graf et al.:
"Laser induced ignition";
Talk: GCL/HPL, Gmunden, Austria (invited); 2006-09-04 - 2006-09-08; in: "Proceedings SPIE", SPIE, (2006), 1 - 6.

English abstract:
Nowadays, combustion engines and other combustion processes play
an overwhelming and important role in everyday life. As a result,
ignition of combustion processes is of great importance, too.
Usually, ignition of a combustible material is defined in such a
way that an ignition initiates a self-sustained reaction which
propagates through the inflammable material even in the case that
the ignition source has been removed. In most cases, a well
defined ignition location and ignition time is of crucial
importance. Spark plugs are well suited for such tasks but suffer
from some disadvantages, like erosion of electrodes or restricted
positioning possibilities. In some cases, ignition of combustible
materials by means of high power laser pulses could be beneficial.
High power lasers offer several different possibilities to ignite
combustible materials, like thermal ignition, resonant ignition or
optical breakdown ignition. Since thermal and resonant ignitions
are not well suited on the requirements mentioned previously, only
optical breakdown ignition will be discussed further. Optical
breakdown of a gas within the focal spot of a high power laser
allows a very distinct localization of the ignition spot in a
combustible material. Since pulse duration is usually in the range
of several nanoseconds, requirements on the ignition time are
fulfilled easily, too. Laser peak intensities required for such an
optical breakdown are in the range of 10E11W/cm2. The hot
plasma which forms during this breakdown initiates the following
self-propagating combustion process. It has been shown previously
that laser ignition of direct injection engines improves the fuel
consumption as well as the exhaust emissions of such engines
significantly. The work presented here gives a
brief overview on the basics of laser induced ignition. Flame
propagation which follows a successful ignition event can be
distinguished into two different regimes.
Combustion processes within an engine are usually quite slow - the
reaction velocity is mainly determined by the heat conductivity of
the combustible. Such deflagrations processes show propagation
velocities well below the speed of sound. On the other hand,
detonations show much higher propagation velocities. In contrast
to deflagrations, detonations show propagation velocities higher
than the speed of sound within the combustible. The shock front
which propagates through a combustible in the case of a detonation
is responsible for a considerable pressure gradient moving at
supersonic velocity. Basics and possible examples of laser induced
ignitions of deflagrations and detonations are given and pros and
cons of laser ignition systems are discussed briefly.

laser ignition, deflagration, q-switch, detonation,

Electronic version of the publication:

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