Single-cylinder engine tests were carried out to assess the influence of several engine operating parameters on HCCI combustion. For the experiments, single-cylinder engines with cylinder volumes of 0.5 and 2 liter were used to represent light and heavy duty application. Engine operation parameters like EGR-rate, air / fuel ratio and injection timing were varied to analyze their influence on the combustion while using different fuels such as Diesel, Gas to Liquid (GtL) and gasoline. Special emphasis was put on synthetic fuels as on the one hand these fuels offer the possibility to “design” them according to the combustion process requirement. On the other hand these GtL — or BtL (Biomass to Liquid) — fuels also lead to a higher independence from fossil fuels. Besides engine out emissions (CO2, CO, NOx, O2, HC, soot) and in-cylinder pressure indication for burning process analysis, optical measurement techniques were used for combustion analysis. With different optical probes in-cylinder soot concentration was measured with the Two-Color-Method. In addition UV radiation of OH-radicals was detected with an intensified camera. This procedure allows the differentiation between the beginning of combustion with OH-radical formation and a possible soot formation due to insufficient homogenization.

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