The design of diesel engine piston bowls plays a fundamental role in the
optimization of the combustion process, to achieve ultralow soot emissions. With
this aim, an innovative piston bowl design for a 1.6-liter light-duty diesel
engine was developed through a steel-based additive manufacturing (AM)
technique, featuring both a sharp step and radial bumps in the inner bowl rim.
The potential benefits of the proposed hybrid bowl were assessed through a
validated three-dimensional computational fluid dynamics (3D-CFD) model,
including a calibrated spray model and detailed chemistry. Firstly, the optimal
spray targeting was identified for the novel hybrid bowl over different injector
protrusions and two swirl ratio (SR) levels. Considering the optimal spray
targeting, an analysis of the combustion process was carried out over different
engine working points, both in terms of flame-wall interaction and soot
formation. At rated power engine operating conditions, the hybrid bowl
highlighted faster mixing-controlled combustion due to the reduced
flame-to-flame interaction and the higher air entrainment into the flame front.
At partial-load operating points, the hybrid bowl showed a remarkable soot
reduction in comparison with the re-entrant bowl due to a more intense soot
oxidation rate in the late combustion phase. Moreover, for the hybrid bowl, a
robust Exhaust Gas Recirculation (EGR) tolerance was highlighted, leading to a
flat soot-brake-specific oxides of nitrogen (BSNOx) trade-off. At
constant BSNOx, a 70% soot reduction was achieved without any
detrimental effect on fuel consumption, suggesting the high potential of the
proposed innovative bowl for soot attenuation.
