DISI (Direct Injection Spark Ignition)
Background: In order to reduce hazardous emissions and the fuel consumption, a direct-injection spark-ignition (DISI) concept was introduced in the gasoline engine technologies. The uniqueness of DISI engines is its operation in stratified mode during low loads and idling by injecting small amount of fuel in a limited region within the combustion chamber to achieve a combustible mixture and a ultra-lean mixture elsewhere.
The wall-guided concept, which uses the internal flow (e.g. tumble and reverse tumble) for the stratified mixture preparation, was introduced as the first type of a stratified DISI engine. However, the internal flow is significantly influenced by operation condition variation such as engine speed and valve timing. Therefore, combustion stability of stratified wall-guided DISI engines is sensitive for the given operation condition. In addition, hydrocarbon(HC) and smoke emissions were high due to the fuel impingement on the piston, which is inevitable for the stratified mixture preparation.
Therefore, the spray-guided concept, which only uses the spray momentum for the stratified mixture preparation, is recognized as a more appropriate system for the stratified DISI engine due to its stable operation and less piston-spray interaction.
KAIST engine laboratory are investigating the combustion and spray characteristics in a spray guided DISI engine using various visualization techniques.
The DISI research scope in KAIST;
- Effect of fuel (Gasoline, ethanol blended gasoline (E10~E80), LPG)
- Effect of injection strategies (split injection, high pressure injection)
- Effect of boosting
- Effect of EGR
In addition, downsizing engine (turbocharged stoichiometric DISI engine) became the hottest issue in the gasoline engine research these days.
Combustion enhancement in a downsized gasoline engine is also the important research subject in KAIST engine lab.
The Downsizing research in KAIST;
- Effect of valve timing
- Effect of turbocharger type (material and capacity)
- Effect of injection strategies