Tunable excimer lasers are used to obtain 2-D images of molecular (and some state-specific) density distributions inside a cylinder of a modified four-cylinder in-line engine that has optical access. Natural fluorescence (i.e., without a laser) is used for some OH pictures, normal laser-induced fluorescence (LIF) for those of NO and of the isooctane fuel, and laser-induced predissociative fluorescence (LIPF) for other OH pictures and for those of O(2). Relevant spectroscopy is done to find the laser and fluorescence frequencies needed to measure isolated species. LIPF works well at high pressures, is state specific, and is ideally suited to follow turbulent processes. No similar measurements in engines have been previously reported. Pictures are taken in succeeding engine cycles. Their sequence is either at a particular point of the engine's cycle to show cyclic fluctuations, or at succeeding portions of the cycle to illustrate the progress of the gasdynamics or of the combustion.

Dispersed LIF spectra of O 2 in the Schumann-Runge band were measured with a modified tunable ArF laser in a flame. Spin-state selective predissociation of the B state was directly observed in fluorescence excitation spectra, revealing the relative coupling matrix elements of the triplet components to the manifold of repulsive states. Such data determines the symmetries of the important predissociating curves for each observed B-state vibrational level and shows that past interpretation of absorption linewidth data is in error. Due to the fast predissociation, quench-free emission spectra arising from laser prepared single rovibronic levels in the B state were observed even in an atmospheric flame. Fluorescence to X-state vibrational levels as high as v" = 35 was observed and relative emission probabilities were derived.

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.

Inside the combustion chamber of a spark-ignition engine, NO fluorescence is excited with a narrow-band tunable KrF excimer laser. The fluorescence light is detected by an intensified CCD camera that yields images of the NO distributions. Rotational-vibrational transitions of NO are excited by the A(2)Σ+ ? X(2)Π (0, 2) band system around 248 nm. Single laser shot planar NO distributions are obtained with good signal-to-noise ratio at all crank angles and allow us to locate areas of NO formation during combustion. The pressure within the combustion chamber is measured simultaneously with the NO distributions, which allows the evaluation of correlations between indicated work and NO formation. The crank-angle-resolved sequences of two-dimensional NO distributions and averaged pressure traces are presented for different engine-operating conditions. In addition, laser-induced predissociation fluorescence of OH excited by the same laser source is measured in order to visualize the corresponding flame front propagation and to compare the time of formation of NO relative to that of OH.

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