Kohärente Kurzzeit‐Strukturen und momentane Brechzahl‐, Dichte‐ und Temperaturprofile in einer n‐Hexan‐Tankflamme

Coherent short‐time structures of a n‐hexan pool flame were shown as a 1000 exposures/sec picture‐sequence using a holographic real‐time synchronous interferometer. These coherent structures have eddies, thermal boundary layers as well as luminous flame fronts. Also gaschromatographically measured concentration profiles of 18 stable molecules of the flame gas mixture were considered. ‐ As a result, the refraction index profiles and also the density and temperature profiles were determined up to 60% by the chemical composition of the pool flame. In the upper flame plume as well as mainly within the thermal boundary layer the density profiles are solely determined by the temperature field. ‐ The quasi‐instantaneous density and temperature profiles are NON‐Gaußian distributed. Within the visible flame field quasi‐instantaneous temperature maxima reach values up to about 2000°C, whereas maximal temperatures within the instantaneous flame neck come up to about 900°C. – This big difference between the maximal flame temperatures can be explained by the momentary number of eddies responsible for the heat and matter exchange. The maximal flame temperatures in the plume are much higher in case of less eddies being in this range than in the neck.