Lubricating Oil Droplets from Piston Crown on Abnormal Combustion in Supercharged SI Engine 2020-32-2302
In recent years, the supercharged spark ignition engine (SI engine) is spread out in the field of passenger vehicle. However, it has a problem of abnormal combustion which is called Low Speed Pre-ignition (LSPI). It is cleared gradually that the character of lubricating oil effects on LSPI. The lubricating oil which has a tolerance for LSPI has been introduced already in the market nowadays. However, cause and mechanism of LSPI occurrence does not clear sufficiently. In previous conference SETC 2018, it was reported that the peculiar behavior of LSPI corresponded with behavior of lubricating oil from piston crown [1, 2, 3].
This paper focuses on frequency of lubricating oil scattering from piston crown. The behavior of lubricating oil from piston crown has four steps as follows, firstly, lubricating oil goes up along with piston side toward piston crown. Secondly, lubricating oil which reaches piston crown continues to accumulate against reciprocating motion. Thirdly, accumulated lubricating oil scatters toward combustion chamber by reciprocating motion. It is needed time of several thousand crank shaft revolutions from engine start. It is tested 4 test oils which is different viscosity (35, 71, 99, 134cSt) and 2 test engines.
The frequency of lubricating oil scattering from piston crown is 4.5 times per 1000 cycles in maximum number of this paper. The experimental data show dangerous mean piston speed for LSPI is under 5.0 m/s and some lubricating oil has a peak of scattering frequency. The frequency from piston crown suggests rational explanation of LSPI occurrence in supercharged SI engine.