Analysis of Spray/Wall Interaction Under Diesel Engine Conditions

Detailed experimental investigation of the instationary spray/wall interaction in an injection chamber helps to better understand the fuel injection processes in small diesel engines. They are necessary to improve spray breakup and evaporation models in CFD simulations and furthermore they are useful to validate results of numerical simulation. Experiments using Phase-Doppler-Anemometry (PDA), lightsheet visualization tools, and surface thermocouples under diesel engine conditions show that spray/wall interaction takes place only about 3 mm above the surface. In this area the impinging fuel jet is redirected parallely to the wall and forms a dense wall jet. At the tip of the wall jet vortices with a high number of drops develop. Here the liquid phase is redirected again and will finally be concentrated in a layer up to a distance of a few millimeters above the surface. Depending on the injection parameters the impinging spray causes a wall heat flux up to more than 2 MW/m² in the stagnation region. First numerical simulation of the process using a modified version of the CFD code FLUENT shows the capability of a general wall model to predict the spray penetration. Modeling the breakup processes due to the impact of drops on the wall will need further investigation.