Detonationswellen in engen Spalten

Detonation waves run through explosive mixtures at several times the speed of sound and cause an immediate release of energy as well as a strong pressure jump. Subject of this work is the behavior of detonation waves in gaseous mixtures close to the limit of propagation, where the complex internal structure of the wave becomes important. The focus lies on the propagation in narrow gaps at elevated pressures and temperatures, which is of interest in the frame of engine knock, because surface damages found have been traced to detonative forms of combustion. In addition to that questions of plant safety are concerned. After description of the state of science and the measurement techniques developed first some results concerning border subjects are presented: detonation cell sizes of the fuels Iso-octane and n-heptane as well as wall boundary layer and heat fluxes behind waves. Then Fays stream tube model for detonation propagation under effect of wall friction is enhanced and finally the velocity deficit, the pressure profiles, the wave structures and the phenomena of de-coupling and re-formation are discussed. Detonation cells for Iso-octane- and n-heptane-air show to be twice to three times as large as for hydrogen-air and similarly irregular. Mixed with oxygen their size is similar to that of the shorter alcanes ethane, propane und butane. For n-heptane they are somewhat smaller than for Iso-octane. Following the stream tube model the deficit of the wave velocity in respect to the result of the loss-free Chapman-Jouguet theory is close to proportional to the boundary layer displacement thickness at the location of the sonic plane, where the flow in the wave-fixed frame transits from subsonic to supersonic and chemical equilibrium is reached. Friction and heat losses can affect the wave only within the subsonic region. The ratio between the location of the sonic plane (in respect to the front) and the cell width varies in the literature from 0.3 to 9. Own observations now show that this ratio is close to one. The stream tube model is enhanced by the effects of incomplete energy conversion up to the sonic plane and a consistent pressure profile model. For a given displacement thickness both effect result in a remarkably higher deficit as all models known so far. In addition there is a strong influence of the kind of boundary layer. The high-speed wall heat flux measurements show in contrast to present assumptions that the wall boundary layer behind is essentially laminar up to far beyond the sonic plane. An empirical expression for the velocity deficit of detonation waves in narrow gaps was determined. Applied to the conditions of a numerical work dealing with extremely narrow gaps (500~kPa, 800~K, 0.01~mm), which was to be evaluated, it predicts a fast decoupling and quenching of the wave.

Grantor dc:publisher

Mainz

Year dc:date

2007

Author dc:creator

• Weber, Johannes Karl Michael

Contributors dc:contributor

• Olivier, Herbert

• info:eu-repo/classification/ddc/620
• Detonation
• Gasdynamik
• Wärmestrommessung
• Ottomotor
• Grenzschicht
• Ingenieurwissenschaften
• Turbulente Verbrennung
• Spalt
• Detonationswelle
• Ausbreitung
• Klopfen
• gas dynamics
• heat flux measurement
• boundary layer

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

ger

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-124114%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:62550