Service Communautaire d'Information sur la Recherche et le Développement - CORDIS

Visualisation and analysis of injection and combustion of last generation injection systems

To analyse small engines equipped with new generation Common Rail Injection systems a transparent engine was used to collect pictures of the injection and combustion phenomena.

The visualisations were performed with different injection strategies: the standard one (pilot and main) and the multiple one with different values of the After Dwell Time (490, 1090 and 1350µs), that is the time between the end of the main injection and the start of after injection.

Pilot and pre-injections show similar spray pattern:

- Relatively low tip penetration avoiding wall impingement.
- A high vaporisation rate and a long ignition delay that leads to a completely premixed combustion without visible flame (soot).

Also the main injection characteristics are very similar. In this case the spray plumes hit the chamber wall. For both injection strategies, the frames show that soot appears generally in zones located at the combustion chamber centre on the spray plume edge downstream of the swirl motion. After the start of combustion, the flame rapidly tends to propagate towards the bowl wall, thus increasing the interaction with swirl motion. This stage of the combustion process is an important key in controlling exhaust NOx-soot trade-off: with the standard strategy, a high swirl velocity during late expansion could significantly improve the soot oxidation process.

With the presence of the after injection, an interaction between the after injection's spray plumes and the spot flames of the main combustion is evident. No or very short ignition delay seems to characterise the after injection. During the first phase of after combustion, the flames are located in the bowl central area where air is still available. This is a first factor that contributes to improve air-fuel mixing with multiple injections. Subsequently, also the unburned fuel of the after injection propagates towards the bowl periphery, interacting with the flame spots of the previous main injection. This is another critical factor that controls the local over-rich fuel/air zone in a swirl supported combustion system.

Reported by

Via Guglielmo Marconi 8
80125 NAPOLI
See on map