Downsized boosted Gasoline Direction Injection (GDI) engines are a promising technology to achieve these goals. However, this technology is constrained by abnormal combustion phenomena, such as pre-ignition (i.e. super-knock).
Pre-ignition leads to the limitation to engine downsizing, the decrease in engine efficiency, the initiation of super-knock, and the permanent damage of engine.
In turbo-charged engines, recent work suggests pre-ignition is characterized by1 a) spasmodic rise of gas-phase pre-ignition, b) auto-ignition at very high temperatures and pressures, c) direct injection of fuel striking on cylinder liner
and stripping lubricant oil from them, and d) lubricant oil and fuel mixing with the main hot charge, leading to the lower auto-ignition temperature.
The primary outcome of this study will be measurements that allow the generation of a semi-empirical expression, called the Pre-Ignition Propensity Index (PIPI) that accurately captures this sensitivity and is capable of predicting the propensity
of a given fuel/lubricant/engine operating environment combination.
Other expected outcomes include the characterization of lubricant oils, and the impact of oil impurity, fuel compositions, and fuel-air mixtures on the propensity of pre-ignition
This work will focus on the lubricant oil droplet-induced pre-ignition, similar to the cause in engines due to the direct injection of fuel. A constant volume vessel will be designed and built for the study such that the real engine operation conditions
(20-30 bar, 600-650 K) where the spark ignition takes place can be simulated.
Conditions required to be taken into account for the initiation of pre-ignition include3 a) the auto-ignition delay time of the oil droplet, b) the critical heat of the initiation of auto-ignition, and c) the critical heat of the initiation of
Other considerations include droplet size (Dd), droplet dilution with fuel (impurity), mixture equivalence ratio (Φ), and initial temperatures (Tm, Td) and pressures (Pm).