Development of a Standardized Test to Evaluate the Effect of Gasoline Engine Oil on the Occurrence of Low Speed Pre-Ignition - The Sequence IX Test

The study described in this paper covers the development of the Sequence IX Low Speed Pre-Ignition (LSPI) test for the new engine oil category, ILSAC GF-6. The purpose of the Sequence IX test is to evaluate a lubricant’s ability to protect against LSPI events which are prevalent when operating a highly boosted/downsized gasoline direct-injected engine. LSPI is characterized as a combustion event that starts before ignition spark, typically followed by excessive in-cylinder pressures and heavy knock, which can cause severe engine damage and failure. Industry research has shown that oil formulation can contribute to the frequency of LSPI activity. The Sequence IX test was developed using a turbocharged gasoline direct-injected 2.0 liter Ford Ecoboost engine with dual independent variable cam timing. The engine was modified with in-cylinder pressure sensors and a high-resolution crank angle encoder to characterize individual engine combustion cycles and identify potential LSPI events. Multiple designed experiments were conducted to identify the engine operating conditions that would consistently produce LSPI events. Additional testing was conducted at these engine operating conditions using multiple engine oil formulations to evaluate the ability of the test to discriminate between oils. Once the test conditions were selected and the reference engine oils were identified, a precision matrix was conducted at three separate laboratories to establish test repeatability and reproducibility. The Sequence IX LSPI test has been approved for inclusion in the ILSAC GF-6 and API SN Plus categories, and is expected to be an integral part of the testing required to qualify passenger car engine oils.