Injection system assessment to optimize performance and emissions of a non - road heavy duty diesel engine : experiments and CFD modelling

The advancing emissions requirements and the customer demand for increased performance and fuel efficiency are forcing the diesel engine technology to keep improving. In particular, the large diesel engines are undergoing to a significant restriction in emission standards. Reaching the new limits requires innovative solutions, improved calibration and controls of the engine combustion technology, as well as the optimization of the injection system that has experienced the most fundamental development over the last decade. The objective of the paper is to present preliminary results of an investigation for the development of an efficient combustion system for marine diesel engines. The effect of different engine parameters on performance and engine out emissions were evaluated. Specifically, different nozzle geometries, injection pressure, injection timings were taken into account. The investigation was carried out both experimentally and numerically. Three different nozzles geometries for three different values of the start of injection were tested. The in-cylinder pressure, rate of heat release, NOx and soot were evaluated for a high load engine condition. The experimental activity was carried out on a large displacement single cylinder direct injection diesel engine equipped with a high-pressure common rail injection system able to manage multiple injections. The engine test bench was equipped with an external air supercharger able to set high air boost levels. The system controls the intake air temperature by means of a heater exchanger. The numerical investigation was carried out using the commercial CFD STAR-CD code in a three-dimensional domain including the cylinder head and piston bowl. Combustion behaviour was simulated using the 3 Zones Extended Coherent Flame Model (ECFM3Z).