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A single cylinder engine was modified to study the potential of reducing fuel consumption and emissions in stratified, direct injection, spark ignition engines with the use of air-assisted nozzles. The spray angle of the nozzle was varied (60° and 90°), and two injection strategies were investigated: (I) the fuel was injected in the nozzle prior to transportation into the chamber via the air flow and (II) the fuel was injected directly into the air flow. The results of the engine experiments were compared with the spray characteristic of each configuration. To facilitate the comparison, two-dimensional images of the sprays were recorded under atmospheric conditions. The fuel was visualized using Planar Laser-Induced Fluorescence (PLIF). The optical chamber was equipped with three optical accesses and a standard injection system from a production engine.

A newly developed measurement technique was employed to investigate flame propagation before and during knocking combustion. Two intensified CCD cameras were used in sequence to record the natural flame light during knocking combustion via a fused silica window, which was fitted to the cylinder head of a one-cylinder four-stroke SI-engine. This arrangement enabled acquisition of two images per cycle. While the first camera was triggered by the rapid rise of the cylinder pressure at the beginning of engine knock, the second camera was activated at a prescribed time of delay. Due to the high sensitivity of the intensified CCD cameras, extremly short exposure times of 100 to 250 ns proved to be sufficient. Consequently, acquisition rates of 200 kHz and more - which are substantially higher than those of conventional natural light photography - could be realized.

We report quantitative experimental investigations on the air/fuel distribution in the combustion chamber of a spark ignition engine prior to ignition and during the first stages of combustion. A four cylinder VW four-stroke engine was modified to give optical access to the combustion chamber via the piston. The fuel concentration was visualised by planar laser-induced fluorescence (PLIF). The choice of an appropriate fuel dopant is very important. Several properties have to be considered simultaneously. The most crucial influence results from the sensitivity to quenching by oxygen. Since fuel distributions recorded at different engine operating conditions wore to be compared on a quantitative scale, this effect had to be taken into account most carefully. The long fluorescence lifetime and the extraordinarily low quenching rate of vapour-phase fluoranthene in a high pressure environment as pertaining to engines led to its choice as dopant.

Numerical investigations are reported on the location of sites at which autoignition first develops in the end-gas ahead of a spark-ignited flame in a combustion chamber following rapid compression of an alkane + air mixture to high pressures and temperatures. Attention is drawn to the part played by the reactions that give rise to a negative temperature coefficient of reaction rate in an inhomogeneous temperature field. A ‘reduced’ kinetic mechanism was employed to model the spontaneous oxidation of n-alkanes. Flame propagation was described in terms of the ‘eddy dissipation concept’ and coupled to the more detailed mechanism by means of a switching algorithm. The CFD calculations were performed by use of KIVA II.