Basic investigations on the cause of initial pre-ignition in a constant volume combustion cell

This paper investigates the effect of lubricant oil and the additives on low-speed pre-ignition (LSPI). The abnormal combustion phenomenon of LSPI is still an important issue in the development of modern internal ombustion engines. Despite numerous studies to understand the potential sources for low-speed pre-ignition, this phenomenon has not yet been fundamentally understood. Therefore, this paper provides a test procedure to investigate the necessary thermodynamic conditions leading to LSPI. A major goal of this study was to reduce the complexity in a gasoline engine arising from the interaction of diverse processes typically taking place in an engine. Therefore, the experiments were conducted by using a newly developed constant volume combustion chamber as
a centerpiece of a completely new testbed. Additionally, a device to generate a defined small amount of tempered oil droplets in the size range of microns into the combustion cell was designed and used for this study. This experimental approach focuses on lubricant oils as a potential trigger for pre-ignition. Therefore, three oils with different contents of Calcium and Magnesium were used to study ignition delay times and self-ignition temperatures of oil under various engine-like pressure conditions. ... mehrFurthermore, to separate possible evaporation effects of the liquid oil droplets, the different oil samples were also admixed to the base fuel. The test results showed that in the Calcium range of 0.025% to 0.075%, the Calcium detergents impact LSPI activity as promoters.
In addition, from the length of the ignition delay time for oil droplets in the hot air, it could be concluded that an oil droplet in the engine combustion chamber cannot initiate a pre-ignition in the same working cycle. However, an oil droplet, deposited on a hot component in the engine may lead to a pre-ignition in a further working cycle.