Fuel Properties and Their Impact on Stochastic Pre-Ignition Occurrence and Mega-Knock in Turbocharged Direct-Injection Gasoline Engines 2020-01-0614

Stochastic Pre-Ignition (SPI) or Low Speed Pre-Ignition (LSPI) is an abnormal combustion event that can occur during the operation of modern, highly boosted direct-injection gasoline engines. This abnormal combustion event is characterized by an undesired and early start of combustion that is not initiated by the spark plug. Early SPI events can subsequently lead to violent auto-ignitions that are referred to as Mega- or Super-Knock in literature and have the potential to severely damage engines in the field.

Numerous studies to analyze impact factors on SPI occurrence and severity have been conducted in recent years. While initial studies have focused strongly on engine oil formulation, calibration and engine design and their respective impact on SPI initiation, the impact of physical and chemical properties of the fuel have also become of interest in recent years. There is still significant uncertainty about the best way to characterize a fuels’ impact on SPI occurrence and severity though. Therefore, an experimental study that attempts to link fuel characteristics to SPI event occurrence was performed. All experiments were conducted in the same production turbocharged, homogeneous direct-injection gasoline engine with a common rail high pressure injection system and side mounted multi-hole injectors. The tests were performed 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. The experimental results of the performed tests were subsequently correlated to the characteristics of the tested fuels.