Recently, global warming is becoming seriously. In the field of internal combustion engine, the thermal efficiency has to improve in the practical use. One of the current trends with spark ignition engine (SI engine) is “downsizing” which is equipped supercharger with the downsized displacement. The downsizing engine is popular in the field of the SI engine. However, one of the problems is the abnormal combustion so called Low Speed Pre-Ignition (LSPI) [1]. The LSPI occurs the engine operation which is low speed and high load condition. It has to be avoided, because the SI engine is broken and the improvement of thermal efficiency is obstructed. A lot of researchers have been reported about the mechanism of LSPI [2, 3]. One of the sources of LSPI would be the lubricating oil droplets in cylinder. One of the methods to avoid LSPI, it has been adjusted the ingredients of oil additive in lubricating oil. The state of the art of lubricating oil standard has been established anti-LSPI performance. However, in the future, many kinds of fuels will be adapted to the SI engine on the point of CO2 emission. So, it would be needed that the mechanism of LSPI would be cleared essentially. It has been reported that the ingredients of oil additive strongly effect on the occurring the LSPI.
There are two kinds of information in our previous research. First, the data show that frequency of abnormal combustion is 1/10 of frequency of scattering lubricating oil from the piston crown [4]. Second, autoignition timing of scattering lubricating oil is almost at ATDC, however, several autoignition advanced the timing for BTDC continuously. The results of previous our research have been mentioned about the relation lubricating oil droplet behavior in cylinder and abnormal combustion occurrence which include LSPI [5].
Here, this research focuses on the effect of Ca additive in lubricating oil on the frequency of abnormal combustion which is conducted to the LSPI.