The standard aerodynamic design of a centrifugal compressor features an unshrouded impeller with a smooth shroud. However, the shape of the shroud significantly influences the final compressor parameters. Previous research has shown that even small geometric changes in the shroud, referred to as casing treatment, can substantially affect the operating characteristics of a rotating machine. This article presents a novel casing treatment for a centrifugal compressor, involving the creation of ten circumferential grooves with a semi-circular profile in a meridional section. The radius of these grooves is approximately equal to the tip clearance. Experimental results demonstrate that the presence of these grooves shifts the surge line toward lower flowrates, increases efficiency in a narrow region between the best efficiency point and the surge line and shifts the choke line toward lower flowrates. External sound pressure measurements indicate a reduction in amplitudes at sub-synchronous frequencies, suggesting a potential link between the compressor map's influence and the suppression of aerodynamic instabilities. Computational fluid dynamics analysis supports the experimental observations, revealing a significant influence of energy dissipation caused by the applied grooves. This study highlights the considerable impact of shroud geometry on centrifugal compressors with unshrouded impellers and offers valuable insights for further research into casing treatments.

Low-pressure exhaust gas recirculation (LP-EGR) is promising strategy for reducing NOx emissions in internal combustion engines, but it presents challenges due to water vapor condensation that can lead to compressor impeller erosion. This study presents a comprehensive thermodynamic analysis to quantify condensate formation and determine dew point temperatures across varying fuels and engine operating conditions. Novel mathematical models are developed to estimate specific humidity and condensation using only standard engine parameters, making them applicable without additional sensors. Results show that both fuel composition - particularly the hydrogen-to-carbon ratio - and LP-EGR rates strongly influence condensation. The study also highlights the impact of alternative fuels and ambient conditions on condensation risk. The developed methodology supports real-time evaluation of condensation potential and offers critical input for erosion risk assessment, component design, and emission control strategy optimization in modern powertrain.