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In the past application of alternative fuels was mostly concentrated to special markets - e.g. for ethanol and ethanol blends Brazil or Sweden. Now an increasing sensitivity towards dependency on crude oil significantly enhances the interest in alternative fuels. With spark ignited engines, ethanol and gasoline / ethanol blends are the most promising alternative fuels - besides CNG. The high octane number of ethanol and the resulting excellent knock performance gives significant benefits, especially with highly boosted engines. However, the evaporation characteristics of ethanol result in challenges regarding cold start and oil dilution with GDI application. This paper deals with investigations on a turbocharged DI engine operated on ethanol fuel in order to improve challenges of ethanol fuel, such as oil dilution and cold start. Cold start can be improved by injecting fuel late in the compression stroke (high pressure start) based on a refined engine design and operation strategies.

An optical imaging technique has been developed which allows the visual observation of fuel vapour within selected planes in optically accessed combustion chambers of Spark Ignition engines. The technique utilises fluorescence radiation of hydrocarbon molecules to image fuel vapour distribution. This fluorescence radiation is induced by a pulsed laser light sheet projected into the transparent combustion chamber and it can be observed with an intensified camera gated synchronously with the pulsed laser at any selected time instant of the engine cycle. In addition to recording mixture distribution, the camera arrangement also allows visualisation of the gasoline flame propagation. These imaging methods are used for he investigation of mixture formation and flame development in a transparent, disc-shaped combustion chamber under low speed and low load conditions.

Formation, ignition and combustion of diesel fuel sprays have been observed in the combustion chamber of an optically accessed single cylinder diesel engine. Two different combustion chamber geometries allowed the fuel sprays to be studied under quiescent and cross flow conditions. The study of the spatial distribution with different single shot photography techniques is complemented with an investigation of the temporal development of spray and flame propagation by an electronic high-speed line-scan technique. This continuous, time resolved analysis technique allows to resolve the influence of temporal variations imposed on the spray propagation and combustion by the fuel injection schedule. The application of these methods to the investigation of diesel sprays highlights mechanisms which govern the propagation and distribution of fuel sprays, fuel evaporation and the formation of a combustible fuel-air mixture.