Effect of a novel piston geometry on the combustion process of a light-duty compression ignition engine: An optical analysis

The development of new piston geometries has shown great potential to achieve the low levels of soot emissions required by regulation. Thus, the present paper aims to characterize the influence of a new piston design over combustion process. It is characterized by the introduction of protrusions around the periphery of the bowl, evenly spaced. The performance of this geometry is compared to other geometries that have been extensively analyzed in literature, under similar operating conditions. To achieve this objective, a single cylinder optical compression ignition engine was used with full-quartz pistons representing three bowl geometries: re-entrant, stepped lip and wave-stepped lip. Two optical techniques (OH∗ chemiluminescence and Natural Luminosity-NL) were applied for identifying the near-stoichiometric zones and the differences in the combustion evolution. The flame movement was analyzed by applying the combustion image velocimetry (CIV) algorithms. In addition, an in-cylinder pressure analysis was performed for each piston at 4.5 bar and 7.5 bar IMEP and the differences in terms of Rate of Heat Release were highlighted. A more intense reverse flow was clearly identified when using wave protrusions inside the bowl. The stepped lip and wave-stepped lip bowl present faster late cycle oxidation with much near-stoichiometric zones than re-entrant piston. •New bowl geometries were studied in a compression ignition optical engine.•CIV technique allows characterizing flame movement for different bowl geometries.•Wave protrusions direct flames towards bowl center and smooth flames collisions.•The stepped-lip bowl with wave protrusions accelerates the late oxidation stage.