Sludge and Deposit Control in Automotive Engines - Chemical Leads and Mechanism

Advances in Engine design such as fast-burn combustion and foul air ventilation have combined with higher blowby rates and smaller oil sumps to increase the sludge load on the lubricant. The nature of the sludge deposits has also changed from a soft to a significantly harder sludge. Progress has been made in understanding how oil-related deposits form in automotive engines. Engine deposits and used oil composition studies have supported the hypothesis that the oil's dispersant is rendered ineffective by greater interaction with the fuel blowby acids leading to increased and harder sludge deposits. Moreover, deposits/used oil analysis, using X-ray Photoelectron Spectroscopy (XPS), indicate that deposits precursors reside in the pentane insolubles of the used field engine oils. A bench test has been developed which simulates deposit formation in engines and which shows potential as a screener for the industry Sequence VE engine test. Compositional studies have substantiated a chemical connection between the sludge produced in the lab bench test with that encountered in field engines. These developments are discussed in greater detail and confirm the importance of oil composition on hard sludge formation.