Moderne Entwicklungen bei der Untersuchung von Verbrennungsvorgängen

Flammen / Holografische Synchroninterferometrie / Koharente Strukturen 1 Stromungs-Instabilitaten / Transporterscheinungen Coherent structures of pool flames are visualized by the synchronous holographic interferometry. -There are large coherent structures which have periodical properties and small coherent structures both with periodical and statistical properties. The periodical phenomena can be classified into three types of instabilities. The first type is a low-frequency instability with frequencies of the order of 12 Hz (for a n-hexan pool flame, d = 4.6 cm) and depends considerably on the pool diameter. The second and third types have frequencies in the order of 300 Hz and 500 Hz, which depend mainly on the fuel type. -The statistical properties of the small coherent structures indicate that the turbulent exchange coefficients for heat and matter have values six times larger than the exchange coefficients for the momentum. The turbulent Prandtl numbers, Schmidt numbers and Lewis numbers are functions of the distance from the fuel surface. These functions vary between the following limits: 0.16 5 Pr, 5 0.35, 0.19 5 Sc, 0.35 and 0.74 Let 5 1.29.

Periodische und statistische Eigenschaften kohärenter Kurzzeit‐Strukturen in Tankflammen

Brötz

Schönbucher

Banhardt

et al. 1983

Scavenging of Radicals from the Gas Phase by Freezing with Dimethyl Disulfide. 2. Radicals from Discharges and a Flame of Acetylene

Kubitza

Schottler

Homann

1987

The method of detecting radicals from low‐pressure gas‐phase systems by scavenging with dimethyl disulfide (DMD) has been applied to microwave discharges in C2H2/He mixtures and to a C2H2/O2 flame. It was accomplished by condensing a supersonic nozzle beam from the reaction system together with a beam of DMD on a liquid‐N2 cooled surface. The scavenging products were measured by GC/MS after warming‐up. Radicals measured in the discharge were C2H, C4H, C6H, C3H2, C2 besides H atoms. Preliminary measurements on the flame showed that C6H5 (phenyl), CH2, C3H2, besides H and O atoms were prominent radicals at the end of the oxidation zone. The concentration of phenyl is of the same order as that of e.g. naphthalene. The method provides a means to distinguish condensible flame products from those that are formed during the sampling process when no scavenger is added.

Analysis of Radicals from Flames by Scavenging with Dimethyl Disulfide

Hausmann

Homann

1990

Elementary Reactions / Flames / RadicalsLarger hydrocarbon radicals in flames, which are difficult to detect by optical methods, can be analyzed quantitatively by radical scavenging with dimethyl disulfide in the condensed phase. -Gas samples taken from a sooting ethyne/oxygen flame by a nozzle beam were frozen at liquid-Ny-tcmpcraturc on the inner surface of a hollow sphere simultaneously with the radical scavenger dimethyl disulfide. The latter was admitted in large excess as a gas and was condensed uniformly on the inner wall of the sphere. The mixture of condensable stable flame products and scavenging products in the excess CH JSSCH 3 was separated and identified by GC/MS. -Larger hydrocarbons (C,HI' x~6) condensed quantitatively. H, CH 3 , C 4H 3 and the phenyl radical were scavenged as mono(methylthio) compounds; C 2 and the carbenes CH 2 , C 3H 2 , C;H 2 yielded bis(methylthio) compounds; other bis(methylthio) compounds observed were C 2nH 2(SCH 3 h with n = 1, 2, 3 and 4. CH, C 3H and C 2H3 were identified by the respective tris(methylthio) compounds. Any consecutive reactions of radicals with stable flame products and their recombinations in the cold trap were suppressed by their scavenging reaction.