Autoignition of a Lubricating Oil Droplet with Fuel Ingredients on Abnormal Combustion of Supercharged SI Engine

The supercharged spark ignition engine (SI engine) has a problem of abnormal combustion. It is called Low Speed Pre-ignition (LSPI). The lubricating oil which has a tolerance for LSPI has been introduced already in automobile market nowadays. However, cause and mechanism of LSPI does not clear sufficiently. It has been reported that the peculiar behavior of LSPI corresponded with behavior of lubricating oil from piston crown [1, 2].

This paper focuses on effect of fuel ingredients on autoignition of a lubricating oil droplet about LSPI. On the ignition source point of view, it is important to clear the mechanism of a lubricating oil droplet autoignition in cylinder. This paper will be tried to clear its mechanism fundamentally by using of electric furnace which is heated an oil droplet. As a result, the activation energy E is found for quantitative evaluation of ignition sauce of LSPI. The experimental data which is heated a lubricating oil droplet by electric furnace show concentration of fuel in an oil droplet is strongly effect on autoignition compared with octane number. The effect of octane number with fuel is little for LSPI on the autoignition of a lubricating oil droplet. More than 30% concentration of fuel in lubricating oil occur autoignition remarkably. It is confirmed that carbon number of fuel ingredients effect strongly on autoignition. These experimental results are evaluated by the calculation with Livengood-Wu integral. The activation energy which is under 6200 [×10^4 J/mol] is dangerous region of autoignition of lubricating oil droplet for abnormal combustion as LSPI. The calculated results suggest that there is safety condition under low speed and high boost operation.