Closer-to-reality artificial ageing of engine oils with implemented nitration

Abstract

Internal combustion engine development is predominantly focusing on emission aspects, where improvements are often achieved by turbocharged engines and higher compression ratios. These trends combined with increasingly higher oil change intervals require increasing stability of engine oils, especially since lubricant condition and tribological performance are strongly interrelated. Various artificial alteration methods have been developed to simulate lubricant degradation in the laboratory, however, nitration as a degradation mechanism is often not considered in standardized tests. Nitration is especially relevant, as it might be tied to emission values and petrol and diesel passenger vehicles show significant differences in this regard. Furthermore, the provision of close-to-reality, defined and reproducible test oils in large quantities are necessary to be able to perform component bench tests or engine dynamometer tests which can reliably predict on performance and lifetime of engine components. This study presents a novel artificial alteration method, where test oils can be produced for engine dynamometer testing or component testing during the development phase. This method is capable of close-to-reality simulation of additive degradation, nitration, oxidation, and various further degradation steps of engine oils in batches up to 200 l. Comparability of various chemical parameters of used oils from a modern turbocharged gasoline passenger car with the artificially altered oils is demonstrated