Detergents, dispersants and antioxidants work together to keep engines clean and deposit-free
Because combustion deposits can cause extensive damage in an engine, motor oil manufacturers use a full arsenal of additives in order to guard against their formation. Detergents keep the engine’s metal surfaces clean and protect against the degrading effects of combustion byproducts on both the oil and the engine’s parts, while dispersants keep soot and wear particles suspended in the oil, preventing their coagulation into larger particles that form sludge, clog the engine oil passageways and starve the engine of lubrication.
Industry changes and trends have affected the future of engine oils and additives. Driving change is the continuing work on less volatile, more fuel efficient engine oils, as well as pushes for extended rain intervals and stricter engine emission regulations. New oils and additives must also address changes in the engine environment: the kinds and amounts of contaminant exposure, temperatures, the residence time of the oil in the piston ring zone’s severe environment and more. New oils developed to address new issues will be subject to higher rates and different paths of degradation, calling for more and different additives.
Antioxidants work to prevent lubricant degradation. By reacting with free radicals that are generated at high temperature and stresses, they quench the degradation chain and preserve lubricant integrity. Antioxidants fall into one of two categories: primary antioxidants and secondary antioxidants. While primary antioxidants function mainly as chain-breaking antioxidants, secondary antioxidants react with hydroperoxides to yield non-radical, nonreactive products.
Starting with the premise that the many types of thermo-oxidative stresses suffered by gasoline and diesel engine oils are dependent on different engine types, combustion processes, running conditions and fuel quality, causing various degradation patterns and changes in the lubricants, Ciba conducted an investigation into several primary antioxidant chemical structures.
Two degradation types dominate. Primary degradation is thermo-oxidative degradation that leads to volatility losses and reactive components in the bulk phase, while secondary degradation processes lead to bulk-phase viscosity increase and sludge formation, Lacquer/varnish formation on the metal surface-oil interface and corrosive attack on the metal surface due to acid formation.
Ciba’s investigation compared the engine oils’ performance in engine tests and bench tests. The bench tests served to assess the oils’ propensities for specific degradation patterns. If the bench test results were the same as the engine test results, it was concluded that the same pathway dominated engine oil degradation in both tests.
Several different bench tests were run in order to assess the different engine oils’ tendencies toward specific degradation patterns. The study team ran pressure differential scanning calorimetry (PDSC) in the presence of an air-nitrogen oxide (NOx) gas mixture to investigate the oils’ primary degradation patterns. The Ciba viscosity increase test (VIT) and the Ciba deposit oxidation test (DOPT) were used to investigate the secondary degradation process.
The findings of the study are intriguing, with most tests showing a combination of both primary and secondary degradation. For example, in the OM364A engine test, the oil was attacked in the first phase by nitro-oxidation (primary degradation), which when led to deposit formation (secondary degradation).
Conclusions drawn from the testing reveal that different antioxidant chemistries can behave differently to suppress oil degradation along various well-known mechanistic pathways. Engine, catalysts and after treatment systems are becoming more and more sensitive to the components of engine oils. Selecting the right additive system ensures that equipment and engine oil work together to the highest efficiency.
In order to ensure its lubricants are of the utmost quality. AMSOIL places great important on additive selection. Only the finest detergents, dispersants and antioxidants in the world are used, guarding against degradation and ensuring unsurpassed performance and wear protection for extended drain intervals.
