Lube oil chemistry influences on autoignition as measured in an ignition quality tester

Derived Cetane Numbers (DCNs) of engine lubricating oil/ 95 Research Octane Number gasoline surrogate mixtures are measured in an Ignition Quality Tester. These measurements separately screen for effects of (1) calcium- and magnesium-based detergent additive, (2) oil degradation, and (3) base oil on mixture ignition propensity at conditions relevant to low speed pre-ignition (LSPI) in gasoline engines. Initial testing of ≤ 25% mass oil in the gasoline surrogate indicates a positive linear relationship between DCN and blend fraction, and also demonstrates the sensitivity of the measurement technique to mixture composition. Despite variation in Ca and Mg concentrations, DCN responses for 5, 10, and/or 25% oil-surrogate blends indicate no statistically significant effect of either Ca or Mg concentration relative to the reference oil. Similarly, neither aging of the oils nor peroxide addition yields a significant effect on measured DCNs of oil-surrogate blends. Notwithstanding these results, a distinct response is found with variation of the base oil: at 25% oil blending with gasoline surrogate, the measured DCNs range from 19.6 to 42.1.