The injection process optimization plays a key role in diesel engine development activities, both for pollutant formation control and performance improvement. The present paper focuses on relatively small diesel units, equipped with fully mechanical injection systems; in detail, the considered system layout is based on the use of spring injectors; the amount of delivered fuel is controlled by the positioning of the pump plunger groove. The paper highlights the role of the inline pump and the influence of fuel characteristics on the system operation. By means of a three-dimensional numerical flow study, the behavior of pump fuel passages and delivery valve is simulated. Then, on the basis of the system features, a complete lumped/one-dimensional numerical model is realized, in which the discharge coefficients evaluated through the three-dimensional simulation are employed. Fuel injection rate and local pressure time histories are investigated, paying specific attention to the occurrence of the relevant phenomena in the system components. Obtained results are compared with experimental data.

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