Numerical study of the mixture stratification in an ethanol powered IC engine.

The combustion strategy of stratified-charge for a sparkignition IC engine (SCSI) aims at providing better control of ignition process thus improving operation at partial load. This might be achieved by splitting a direct injection into two stages (being the second stage during compression stroke) and having an easily ignitable fuel-air stratification around the spark plug. The configuration producing such air-fuel stratification is here concerned for an ethanol direct injection system.

The study was carried out by numerical simulations on a virtual CFD engine. The spray motion and interaction with the in-cylinder flow was modeled by an Eulerian-Lagrangian approach. The spray was modeled by a statistical distribution relating droplet diameter to volume fraction. The investigated parameters were the amount of fuel in secondary injection and the influence of piston bowl radius in mixture stratification. The results for stratification are presented as concentration contour maps and local probe values. Droplet size after secondary break-up and fuel vaporization are also concerned as a general evaluation of spray quality.