Shimizu, K., Takahata, S., Miura, K., Shoji, H. et al., "Influence of Calcium-Based Additives with Different Properties on Abnormal Combustion in an SI Engine," SAE Technical Paper 2016-32-0007, 2016, doi:10.4271/2016-32-0007.
Technologies for further improving vehicle fuel economy have attracted widespread attention in recent years. However, one problem with some approaches is the occurrence of abnormal combustion such as low-speed pre-ignition (LSPI) that occurs under low-speed, high-load operating conditions. One proposed cause of LSPI is that oil droplets diluted by the fuel enter the combustion chamber and become a source of ignition. Another proposed cause is that deposits peel off and become a source of ignition. A four-stroke air-cooled single-cylinder engine was used in this study to investigate the influence of Ca-based additives having different properties on abnormal combustion by means of in-cylinder visualization and absorption spectroscopic measurements. The results obtained for neutral and basic Ca-based additives revealed that the former had an effect on advancing the time of autoignition.