Common Rail without Accumulator: Development, Theoretical-Experimental Analysis and Performance Enhancement at DI-HCCI Level of a New Generation FIS

An innovative hydraulic layout for Common Rail (C.R.) fuel injection systems was proposed and realized. The rail was replaced by a high-pressure pipe junction in order to obtain faster dynamic system response during engine transients, smaller pressure induced stresses and sensibly reduced production costs. Compared to a commercial accumulator, whose internal volume ranges from 20 to 40 cm3, such a junction provided a hydraulic capacitance of about 2 cm3 and had the main function of connecting the pump delivery to the electroinjector feeding pipes. In the design of the novel FIS layout, the choice of the high-pressure pipe dimensions was critical for system performance optimization. Injector supplying pipes with length and inner diameter not in the actual production range were selected and applied, so as to stabilize the system pressure level during an injection event and reduce pressure wave oscillations. The new injection system was realized and subjected to experimentation on a high performance test bench Moehwald-Bosch MEP2000-CA4000 under engine-like conditions. For single injections, the performance of the proposed apparatus was shown to be similar to those of commercial-type C.R. systems. On the other hand, with reference to multiple injections, the dynamics of the innovative system resulted to be consistently improved because of a significantly reduced dependence of the overall injected fuel amount on dwell-time in sequential injection shots. Furthermore, fluid dynamic interaction between injectors was minimized by the adoption of hydraulic circuit design solutions such as to prevent the occurrence of resonance phenomena among injectors. The results proved that the rail capacitance was not an essential parameter in the attenuation of pressure wave disturbance, whereas injector inlet-pipe sizes did have a large effect on these and therefore substantiated the feasibility of a new-generation electronically controlled diesel FIS without accumulator. In addition, a modification of latest solenoid-generation commercial Multijet electroinjector was realized so as to sensibly reduce the dwell time bound for fusion-free sequential injection shots, enhancing such component at HCCI combustion application level. The new injector design, based on an integrated experimental-theoretical analysis of system dynamics, was carried out by a pre¬viously developed C.R. numerical model. Experimental results on novel injector performance were examined. Included in: SAE SP-2081 'New Diesel Engines and Components, 2007' ISBN: 978-0-7680-1871-4