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The influence of fuel composition on mixture formation and first stage of combustion, occurring in a small high swirl combustion chamber of an IDI Diesel engine, was analyzed from measurements of spectral extinction and flame emissivity. Measurements were carried out in an optically accessible combustion chamber in which an air swirling flow is forced from the main chamber through a tangential passage. A conventional injection system was used to inject Tetradecane, N-heptane and Diesel fuel. The distribution of liquid and vapor and the interaction of the jet with air swirl were detected by UV-visible extinction measurements. The autoignition phase was characterized by UV-visible chemiluminescence measurements. For all fuels examined, it was observed that initially the liquid fuel penetrates almost linearly with time until reaching a maximum characteristic length, slightly dependent on the fuel.

The characterization of a turbulent diesel spray combustion process has been carried out in a divided chamber diesel system with optical accesses. Laser Doppler Anemometry, spectral extinction and flame intensity measurements have been performed from U.V., to visible from the start of injection to the end of combustion, at fixed air/fuel ratio and different engine speeds. Spatial distribution of fuel and vapor as well as the ignition location and soot distribution have been derived in order to study the mechanism of the air-fuel interaction and the combustion process. The analysis of results has shown that the high swirling motion transports the fuel towards the left part of the chamber and breaks up the jet into small droplets of different sizes and accelerates the fuel vaporization. Then, chemical and physical overlapped phases were observed during the ignition delay, contributing both to autoignition.