Combustion Noise Predicton in a Small Diesel Engine Finalized to the Optimization of the Fuel Injection Strategy

The paper illustrates both numerical and experimental methodologies aiming to characterize performances and overall noise radiated from a light duty diesel engine. The main objective was the development of accurate models to be included within an optimization procedure, able to define an optimal injection strategy for a common rail engine. The injection strategy was selected to contemporary reduce the fuel consumption and the combustion noise. To this aim, an experimental investigation was firstly carried out measuring engine performances and noise emissions at different operating conditions. Contemporary, a one-dimensional (1D) simulation of the engine under investigation was performed, finalized to predict the in-cylinder pressure cycles and the overall engine performances. The 1D model was validated with reference to the measured data. In order to assess the combustion noise, an innovative study, mainly based on the decomposition of the in-cylinder pressure signal, was utilized. The obtained results were compared with the experimental sound pressure level, measured at 1 meter from the engine. The above procedure was finally coupled to the 1D model of the whole engine, and was linked to an external optimizer (ModeFRONTIER®). The parameters of a pilot-plus-main injection strategy (start of injection, dwell-time and main injection duration) were then continuously varied by the optimizer to the aim of contemporary minimize the fuel consumption and the noise emission. The results clearly highlighted a trade-off between the two objectives and the need to select a compromise solution between them.