Research

Advanced Spark Ignition Engines: Pre-ignition Study

Details

​​Motivation

 
  • Advanced internal combustion engines require enhanced engine performance, improved fuel efficiency, and reduced exhaust emissions.
  • 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.

 

 
 

 

Knock1

 

 

 

 

Pre-ignition2
 
 
 

Aim

  • 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​
 

Approach 

  • ​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 flame propagation.
  • ​​Other considerations include droplet size (Dd), droplet dilution with fuel (impurity), mixture equivalence ratio (Φ), and initial temperatures (Tm, Td) and pressures (Pm).

Constant Volume Vessel

  • Vessel capability:
    • length: 320 mm, OD: 160 mm; ID: 120 mm; volume: 2.4 liter
    • Incorporate droplet injection and suspension system
    • Capable of pressure up to 150 bar
    • Capable of temperature up to 400 C
    • Equipped with pressure and temperature sensors, a safety valve, and a rupture disc
    • quipped with optical accesses for photographic (high-speed and quipped with optical accesses for photographic (high-speed and Schlieren imaging) and laser (chemiluminescence) diagnostics