Analysis of the Impact of Production Lubricant Composition and Fuel Dilution on Stochastic Pre-Ignition in Turbocharged, Direct-Injection Gasoline Engines 2019-01-0256
Abnormal combustion events leading to high peak pressures and severe knock have been reported in recent years during the operation of modern turbocharged, direct-injected gasoline (GTDI) engines. These events have been referred to as Stochastic Pre-Ignition (SPI) or Low-Speed Pre-Ignition (LSPI) and Mega-Knock or Super-Knock. SPI is an abnormal combustion event that is characterized by an undesired start of combustion before the intended start of combustion initiated by the spark plug. Early SPI events in a combustion cycle can subsequently lead to violent auto-ignitions that are often referred to as Mega- or Super-Knock. Mega-Knock leads to characteristic pressure oscillations that can destroy production engines within a few occurrences. SPI occurs mainly at low engine speed and high engine load, thus limiting the engine operating area that is important to achieve good drivability in downsized engines. Recent experimental SPI studies have linked this phenomenon strongly to engine oils. While several studies have been published using target blended oils the presented study focuses on the impact of 2017 production oil composition and fuel dilution levels on SPI events in a production turbocharged, direct-injection gasoline engine with a homogeneous common rail high pressure injection system and side mounted multi-hole injectors. All experiments were conducted on a steady state engine test bench with intake air, coolant, oil and fuel conditioning. The engine was equipped with a prototype engine controller that allows negating the influence of vehicle, knock mitigation or balancing algorithms on combustion. 11 market relevant production engine oils were analyzed regarding their composition using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). All 11 oils were then tested for their impact on SPI occurrence, severity and characteristics. One oil was additionally tested for the impact of fuel dilution on SPI occurrence at several fuel dilution levels. The experimental results were subsequently correlated to the oil analysis results.
Patrick Haenel, Rob de Bruijn, Dean Tomazic, Henning Kleeberg