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With a view to understanding the air-fuel mixing behavior and the effects of the mixture quality on the emissions formation and engine performance, a new quantitative factor of the in-cylinder air-fuel homogeneity named Homogeneity Factor (HF) has been developed. Its characteristics under various injection conditions and air swirl motions within the cylinder have been investigated with CFD simulation. The results have shown that air-fuel homogeneity is essentially affected by the spatial and temporal fuel distribution within the combustion chamber. Higher injection pressure, longer dwell time and increased pilot fuel quantities can contribute to better mixing quality resulting in increased HF and optimum engine performance with low fuel consumption and soot emissions. With regard to the in-cylinder air motion, increasing swirl ratio enhances the air-fuel mixing quality which has been reflected in the variation of the HF.

In this work we propose an automatic tuning method for the calibration of PID controllers of the idle speed functionality in Diesel engines. The tuning method is based on a closed-loop identification technique, which is employed to estimate the parameters of a first order model with integrator and delay. It is shown that this simple model has sufficient fidelity to provide satisfactory PID gains. The identification algorithm and the performance of the resulting PID controllers have been tested in different vehicles. The proposed methodology has the potential to automate the calibration process of idle speed controllers while satisfying requirements on stability, performance, and robustness of the closed-loop system.