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Quantitative determination of planar fuel/air mixture distribution in an internal SI engine are obtained using planar laser induced fluorescence of acetone. In order to get quantitative informations different fuel tracer substances have been investigated. Special requirements have to be fulfilled by the tracer molecule with regard to the application under the unstationary and hostile conditions of internal combustion. The most important is that the fluorescence intensity has to be directly proportional to the fuel density. It must be unaffected by surrounding gas composition, temperature-and pressure-fluctuations. As it turned out during the experiments acetone meets this unusual requirements almost perfectly.The experiments were carried out in one cylinder of a modified production line four cylinder SI engine from Volkswagen AG. Time resolved planar fuel distributions were obtained for the whole mixture formation process during the intake, the compression and at the beginning of the combustion stroke. Single shot and cyclic averaged measurements revealed a) cycle-to-cycle variations as well as recurring structures of the fuel distribution, b) mixture uniformity and c) flow field structures. The direct relationship between the acetone fluorescence intensity and the fuel density allows the quantitative determination of 2-D fuel/air ratio maps for a multitude of different cran kangles.

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Planar laser-induced predissociative fluorescence is applied to image state-specific densities of OH and hot O(2) inside an internal-combustion car engine. Improved instrumentation is described. It includes better imaging optics and a spectrometer that permits desired molecular quantum states to be selected and identified in real time. The OH (nu'' = 0) images are cleanly separated from the isooctane fuel and they display a thin superequilibrium region at the flame front. In contrast, vibrationally excited O(2) (nu'' = 6 or nu'' = 7) is uniformly distributed behind the front. Uneven and broken flame fronts are commonly observed.

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