Influence of Different Oil Properties on Low-Speed Pre-Ignition in Turbocharged Direct Injection Spark Ignition Engines 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 [1], [2] 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 [3] 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 [4], [5] 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.