Philipp Pischke

Investigation of the influence of multiple gasoline direct injections on macroscopic spray quantities at different boundary conditions by means of visualization techniques

Abstract The reduction of combustion emissions and fuel consumption can be achieved by controlling the fuel mixture to be burned and therefore the fuel injection. In this study a gasoline direct injection (GDI) piezo hollow cone injector is investigated by visualization measurements. Both single and double injection events are examined in a pressurized chamber. For the single injection, the influence of the ambient temperature and pressure is analysed in detail. For the double injection, the ambient conditions and the time interval between two injections are varied. For the single injection, the general shape of the spray, the recirculation eddy formed at the spray edge, the stringy structure of the hollow cone, and defined quantities such as the penetration length or the spray width are examined with respect to the influence of the ambient conditions. For the double injection, the same properties are evaluated, with the focus put not only on the influence of the ambient conditions, but also on the mutual interaction of two spray events. The experimental results show a clear impact of both the ambient conditions and the time difference between two injections. In particular, the investigation of the recirculation eddy may be helpful in determining possible positions for the spark plug, since the spark plug is preferably placed in regions where the air–fuel mixture variations are minimal.

Applying similarity search for the investigation of the fuel injection process

We introduce a distance-based similarity model with application to the optimization of the fuel injection process. Our model allows for an automatic evaluation of huge and complex amount of experimental data originated from optical measurement techniques analyzing the fuel injection process. The goal is to enable researchers to get deeper insight into this process based on an automatically driven analysis.

Influence of Stokes Number on Collisional Interfacial Area Production Terms within the Σ-Y Eulerian Spray Atomization Model

The present study shows the effects of Stokes number on the modeling of collisional interfacial area production terms within the Σ-Y model. This model can be employed for CFD simulations of high Weber and Reynolds number sprays using a RANS turbulence modeling. Within the model production of interfacial area is assumed to result from turbulent stretching and turbulent droplet collisions. The modeling of collisional processes requires the calculation of a characteristic turbulent collision velocity. In the present work this velocity was determined under consideration of Stokes number effects leading to turbulent droplet velocity fluctuations attenuated with respect to the gas phase fluctuations and including partial correlation between the velocities. The influence of this new modeling approach is tested within a 2D spray simulation by comparing the Sauter mean diameters observed to the ones obtained by employing the modeling approaches proposed in the literature which do not consider any Stokes number effects. The reduced collision velocites in the new modeling lead to higher values for Sauter mean diameters in the spray.