Sludge Formation in OTTO Cycle Engines

A review of the specialized literature was carried out to study the process of sludge formation and to understand the reasons for the increasing occurrences of these deposits in Brazil. The following items of consensus were reached:

• sludge precursors arise from the partial oxidation of fuels;
• fuel composition has a direct influence on sludge formation;
• blow-by is the main contact between fuel derived products and the oil.

Based on this information and on the accumulated experience in investigating occurrences of sludge, a test methodology was developed for evaluating the sludge formation characteristics of lubricating oils.