Mayer, M., Hofmann, P., Geringer, B., Williams, J. et al., "Influence of Different Oil Properties on Low-Speed Pre-Ignition in Turbocharged Direct Injection Spark Ignition Engines," SAE Technical Paper 2016-01-0718, 2016, doi:10.4271/2016-01-0718.
In recent years concern has arisen over a new combustion anomaly, which was not commonly associated with naturally aspirated engines. This phenomenon referred to as Low-Speed Pre-Ignition (LSPI), which often leads to potentially damaging peak cylinder pressures, is the most important factor limiting further downsizing and the potential CO2 benefits that it could bring. Previous studies have identified several potential triggers for pre-ignition where engine oil seems to have an important influence. Many studies ,  have reported that detached oil droplets from the piston crevice volume lead to auto-ignition prior to spark ignition. Furthermore, wall wetting and subsequently oil dilution  and changes in the oil properties by impinging fuel on the cylinder wall seem to have a significant influence in terms of accumulation and detachment of oil-fuel droplets in the combustion chamber. For this reason the interaction of fuel and engine oil at the combustion chamber walls was investigated in a comprehensive parameter variation. During these investigations the parameters oil temperature, start of injection and injection strategy were varied. Other studies ,  have demonstrated the influence of metal-based detergents on pre-ignitions. To investigate this hypothesis the influence of various additives on pre-ignitions were examined. Besides the investigations on different additive treat rates the focus was on metal-based detergents. While various test oils with different calcium-based detergents show a strong influence on preignition frequency a specially blended detergent-free test oil showed no tendency to pre-ignite.