Riassunto analitico
Engine development has nowadays to deal with a stringent legislation on the pollutant emissions, and a constant attempt to reduce the fuel consumption, as required from the marketing, the governments and the customers. The engine development is high complicated process and CFD simulations play a significant role. They are used at various stages of the design process with different purposes. The goal of this work is to develop a procedure to simulate the mixture formation and wall impingement in GDI engines. In particular, the work is focused on the air motion in-cylinder, on the injection phase, until the mixture formation before the ignition and the research of a correlation between the wall impingement and soot measurement. The ideal workflow is to consider also combustion simulation to relate soot formation estimation with experimental data of emission. The simulation of combustion in gasoline engines is nowadays still in the research phase, and it is generally not used for the engine design. Although it constitutes an interesting research topic, it requires a computation and experimental effort far beyond the current state of the art in the daily engine development process, and it is not covered in this work. On the other end the experimental procedure to measure liquid film formation in engines during the injection process is highly complicated and require facilities not available for this work. All these limitation from simulation and experiments point of view lead us to the decision of correlating wall wet formation of simulation with PN measurement from experiments. The methodology developed is divided in three main simulation: cold flow simulation, injection simulation and wall wet analysis. In the first part the engine flow is validated focusing the attention on velocity magnitude and turbulent kinetic energy fields. In parallel the injection model is calibrated and validate in the spray box, using as target the experimental spray penetration length and droplets size distribution. Once the first 2 simulation are validate, the injection model is implemented in the engine simulation to evaluate the liquid film formation. If a correlation between the in-cylinder wet surface and soot measurement is found, in the future engine development process will be possible to use CFD to estimate liquid film and from that have a prediction of soot formation. This methodology allows to save time and money that always represents a critical point in the engine development.
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