Experimental root cause analysis of low-speed pre-ignition mechanisms on a turbocharged gasoline engine with direct-injection

The concept of increasing power density is a successful approach to improving the conflict between efficiency and emission behavior of spark-ignition engine drive units for light-duty vehicles. This leads to highly charged gasoline engines with direct injection and high specific torque and power densities, promoting a not yet fully understood combustion anomaly known as low-speed pre-ignition (LSPI). This unpredictable, multicyclic phenomenon limits the depictable in-cylinder pressures, further efficiency gains and engine reliability. Only with a holistic understanding of the LSPI root cause mechanisms and processes can targeted countermeasures be taken and further efficiency gains achieved. A novel methodology pathway for LSPI root cause analysis was developed to accompany the entire LSPI event emergence process path by means of a multi-experimental approach on a modern high efficiency engine. This includes the identification of key LSPI activity – engine parameter specification relations, minimally invasive high-speed endoscopic imaging and further LSPI key experiments. Only the accumulation of inorganic substances originating from lubricating oil additives enables specific deposits/particles to ignite the surrounding mixture over a multicyclic process due to the resulting increased oxidation reactivity. Through a final synthesis step of all results, a multi-cycle oxidation-reactivity-enhanced deposit/particle-driven LSPI root cause mechanism is established.