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Engine oils and their additives are formulated to meet required performance areas such as lubrication, detergency, dispersancy, anti-wear, and so on. Understanding degradation of engine oil additives is important to formulate oils with long time durability. Engine oil additives have been found to affect abnormal combustion in turbocharged gasoline direct injection (TGDI) engines, called low speed pre-ignition (LSPI). Some of metal containing additives such as zinc dithiophosphates (ZnDTP) and molybdenum dithiocarbamates (MoDTC) have been found to reduce LSPI events. In this study, we investigated degradation of ZnDTP and MoDTC in gasoline engine operation and effects of the degradation on LSPI performance.

Many modern engine platforms use turbochargers to meet higher fuel economy performance, which is often combined with downsizing the engine displacement. Operating downsized, turbocharged, direct injection engines at low speeds and high loads has led to an abnormal combustion phenomenon known as Low Speed Pre-Ignition (LSPI), wherein the fuel-air mixture ignites before the spark occurs. LSPI can lead to extremely high pressures in the combustion chamber, which can damage hardware such as pistons, piston rings, and spark plugs. Lubricants, fuels, and engine operating conditions have been shown to impact LSPI. Any of these can be modified to improve LSPI performance. One solution which has been used widely in the industry is reformulating the lubricant additive package. In particular, calcium-based detergents have been shown to promote LSPI, while magnesium detergents appear neutral to LSPI.