Analysis of soot particles and NOx in the cylinder and at exhaust of a compression ignition engine fuelled with RME and diesel fuel

Particulate matter and nitrogen oxides emissions of a compression ignition engine fuelled with a conventional diesel fuel and rapeseed methyl ester (RME) were evaluated. The investigation was carried out on a transparent engine equipped with the head of a fourcylinder commercial Euro 5 engine. The measurements were performed at 2000 rpm and 5 bar of break mean effective pressure representative of an operating condition of the new European driven cycle. In-cylinder broadband UV-visible flame measurements were carried out to characterize soot formation and oxidation process. 2D images of flame evolution were detected and they were processed by two-color pyrometry technique to assess both the flame temperature and the soot concentration. Moreover, flame temperature was correlated to nitrogen oxides (NOx) emissions. Exhaust emissions were measured by means of commercial instruments and they were correlated to the in-cylinder data. It was found that in-cylinder RME fuel produces larger number of particles but with smaller diameter than the diesel one, the soot oxidation process is faster and NOx emissions are correlated to lower in-cylinder flame temperature.