In-cylinder soot evolution analysis in a transparent research DI Diesel engine fed by oxygenated fuels.

This paper describes a characterisation of the combustion behaviour in an optical Common Rail diesel engine fed by different advanced fuels, via the application of the two-colour pyrometry technique. The acquired images were processed in order to calculate the instantaneous flame temperature and soot volume fraction. For the measurements, a single test point was chosen as representative of the reference four-cylinder engine performance in the European driven cycle ECE+EUDC. The test point was the 1500 rpm and 22 mm 3 /stroke of injected fuel volume, correspondent to the engine point of 1500rpm @ 5 bar of BMEP for the 4-cylinder engine of 1.9L of displacement. As general overview, the flame luminosity from combustion of the fuel injected during pilot injection was always below the threshold of sensitivity of the detection system. As regard the effect of fuel quality on flame evolution, it is confirmed that the presence of oxygen in the fuel reduces the in-cylinder soot loading, but in our experiments, the reduction is observable only for an oxygen content over 15% in weight. Moreover, interesting differences on the effect of fuel oxygen were noted in terms of local soot concentration and global in-cylinder soot loading.