Nowadays, most engines which equip agricultural machines, ships and cars are diesel ones with a common-rail high-pressure direct injection system. They are providing the advantages of fuel economy, low emission level, and reduced noise in comparison to conventional direct or indirect injection systems. The heart and the most stressed part of the common-rail system is the high-pressure fuel pump which is driven by the engine camshaft, and its role key is to compress the fuel at pressures over 2000 bar. The high-pressure fuel is delivered from pump to the engine combustion chamber via high rail pipes, high-pressure accumulator (rail) and injectors. Compressing the fuel and sending it towards high-pressure accumulator (rail), in some specific cases the pump generates an audible disturbing noise that gets louder than the engine combustion noise. The paper first offers an overview of our experiments performed on common-rail high-pressure fuel pumps in order to find the noise contributor and to develop measures to reduce the disturbing noise. The experimental investigations have proved that the noise occurs when the fuel is compressed and the outlet valve is opening. Then, our experimental study focuses on outlet valve behaviour from design and noise emissions point of view at idle engine speed.
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