Two-colour pyrometry measurements of soot loading in a Diesel engine burning model fuels of varying quality

In the present paper the two-colour technique is applied to study the in-cylinder soot volume fraction evolution in a Direct Injection Diesel engine. A preliminary analysis of the theoretical uncertainty involved in performing the two-colour soot emission measurements is carried out. It is found that, with interference filters at 600 and 1000 nm, and reducing the data with the appropriate numerical algorithm, the total accuracy about soot temperature and volume fraction-values is confined respectively under ± 57 K and ± 30%. The in-cylinder measurements are performed at fixed engine angular speed and injected fuel mass, varying the injection timing and the fuel quality. Employing the two-colour pyrometry technique the following results can be obtained: a) the fuel cetane number controls the soot loading of paraffinic fuels; b) at a fixed level of cetane number (up to 58) the fuel aromatic content strongly influences the engine soot loading amount, but, at a further increase of cetane number (over 62), any significant difference between fuel sooting behaviour with different aromatic content vanishes; c) for aromatic fuels at the cetane level 50 and 58 the sum of di- and tri- aromatics is a candidate to be a better indicator of fuei sooting tendency with respect to the total fuel aromatic content.