Engine Oil Development for Preventing Pre-Ignition in Turbocharged Gasoline Engine

Kosuke Fujimoto; Minoru Yamashita; Satoshi Hirano; Katsuyoshi Kato; Izumi Watanabe; Koki Ito

doi:10.4271/2014-01-2785

Gasoline engine downsizing combined with a turbocharger is one of the more effective approaches to improve fuel efficiency without sacrificing power performance. The benefit comes from lower pumping loss, lower mechanical friction due to ‘downsizing’ of the engine displacement and ‘down-speeding’ of the engine by using higher transmission gear ratios which is allowed by the higher engine torque at lower engine speeds. However abnormal combustion referred to as Low-Speed Pre-ignition (LSPI) is known to be able to occur in low-speed and high-torque conditions. It is a potential restriction to maximize the engine performance and its benefit, therefore prevention of LSPI is strongly desired for long-term durability of engine performance.

According to recent technical reports, auto-ignition of an engine oil droplet in a combustion chamber is believed to be one of major contributing factors of LSPI and its formulations have a significant effect on LSPI frequency. Toyota has reported that the oxidation stability of engine oil can be a dominant factor of its auto-ignition, which is a function of its base oil and additive components, of which an example was found that calcium-based detergents significantly increase LSPI frequency.

Based on these findings, we have developed a new engine oil product which can reduce LSPI frequency to less than 10% of that of conventional ILSAC certified gasoline engine oils. High quality base oils (Group III, Group IV) and optimized additive components were formulated in which the amount of calcium-based detergent was reduced to levels lower than general ILSAC oils, and a sufficient amount of anti-oxidants were added. This newly developed engine oil is scheduled to be introduced for Toyota's new turbocharged gasoline engine vehicles. The new engine was released in July 2014 in the Japanese market. Toyota plans to subsequently launch the engine in Europe and the rest of the world.

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Engine Oil Development for Preventing Pre-Ignition in Turbocharged Gasoline Engine 2014-01-2785

SAE MOBILUS