Gasoline-related factors that affect low-speed pre-ignition (LSPI) include the distillation properties of gasoline, manganese (Mn), ethanol, diesel fuel, detergent for aftermarket, and iron (Fe).
The combined effect of Mn with ethanol or high calcium engine oil (high-Ca oil) has not been sufficiently clarified. Therefore, appropriate countermeasures for LSPI have not yet been implemented.
To clarify the effect of the gasoline properties and additives on LSPI, engine tests were conducted using gasoline with different “PM Index” values, an indicator of distillation properties, different concentrations of Mn, ethanol, diesel fuel, detergent, Fe, and high-Ca oil.
The results showed that the LSPI frequency tended to increase with the PM Index, Mn up to 60 ppm, diesel fuel up to 2 vol.%, and detergent up to three times the standard amount.
Compared with gasoline with 30 ppm Mn, LSPI frequency increased 1.8 times for gasoline with 30 ppm Mn and 20 vol.% ethanol, and 1.2 times for gasoline with 30 ppm Mn and high-Ca oil.
Ethanol up to 20 vol.% only and 10 ppm Fe with light gasoline had no effect on the LSPI frequency.
There exists a relationship between the particulate number (PN) in the normal combustion and the LSPI frequency. The sensitivity of the PN to the LSPI frequency was approximately 2.0 times greater for the Mn-added gasoline than for the hydrocarbon-based gasoline.