Investigation on Relationship between LSPI and Lube Oil Consumption and Its Countermeasure

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Investigation on Relationship between LSPI and Lube Oil Consumption and Its Countermeasure

Hitosugi, Hideshi / Kuboyama, Tatsuya / Takaki, Tomoya / Moriyoshi, Yasuo

LSPI (Low speed pre-ignition) is a serious issue in highly boosted gasoline engines. The causes have been studied and lube oil affects the onset. In order to examine the effect of lubricating oil consumption on super knock caused by pre-ignition, measurements of in-cylinder pressure, temperature, oil consumption by sulfur trace at steady and transient conditions were conducted. Also, new piston ring pack was applied to reduce both of blow-by gas and oil consumption. As a result, accumulated oil during deceleration was found to cause pre-ignition after acceleration. The pre-ignition frequency is much higher than in steady condition, however, the amount of oil does not directly affect pre-ignition frequency, but dilution of oil and evaporation of oil/fuel and other parameters, such as temperature, pressure, and oil additives determine pre-ignition onset. In order to see the mechanism of pre-ignition onset, numerical simulations were conducted. Pseudo ignition was made in simulation and strong pressure resonance was found when pre-ignition occurs near intake-side crevice. This is due to the environmental conditions, such as equivalence ratio, temperature and pressure, match up early auto-ignition and fast flame propagation, leading to primary resonance mode. An improved piston ring pack using Labyrinth seal structure and V-cut in third land achieved reductions in both blow-by amount and oil consumption, leading to much less pre-ignition.