2-COLOR 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 Diese l engine. A preliminary analysis of the theoretical uncertainty involv ed in performing the two-colour soot emission measurements is carried out. It is found that, with interference filters at 600 and 1000 nm, a nd reducing the data with the appropriate numerical algorithm, the tot al accuracy about soot temperature and volume fraction-values is confi ned respectively under +/- 57 K and +/- 30%. The in-cylinder measureme nts 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 cont ent strongly influences the engine soot loading amount, but, at a furt her increase of cetane number (over 62), any significant difference be tween fuel sooting behaviour with different aromatic content vanishes; c) for aromatic fuels at the cetane level 50 and 58 the sum of di- an d tri-aromatics is a candidate to be a better indicator of fuel sootin g tendency with respect to the total fuel aromatic content.