Document Type : Original Article
Authors
1 Faculty of Engineering Modern Technologies, Amol University of Special Modern Technologies (AUSMT), Amol, Iran
2 Department of Mechanical Engineering, Technical and Vocational University (TVU), Tehran, Iran
Abstract
This study examines how piston-bowl geometry influences in-cylinder flow and pollutant formation in a large diesel engine. High-fidelity simulations were performed for the baseline combustion chamber and three modified bowl designs (A, B, and C). The model replicates experimental peak pressure within 3%, soot levels with ≤1% error, and NOx emissions within ±3%. The modified bowls increase in-cylinder turbulence and induce stronger squish flows, leading to longer combustion duration but more uniform mixing. As a result, peak cylinder pressures are slightly lower in the re-designed bowls than in the baseline, and the onset of combustion is delayed. Notably, the most highly squish-inducing chamber (A) produced higher peak temperatures but also exhibited the lowest soot emissions, consistent with enhanced mixing. Across the modified chambers, indicated work and cycle efficiency increased relative to the baseline (due to reduced negative work in compression). Emissions of NOx and soot showed opposing trends: chamber A (highest turbulence) generated more NOx (owing to its higher local temperatures) but significantly less soot (owing to more complete combustion), whereas the baseline chamber had higher soot due to local fuel-rich pockets. These results indicate that combustion chamber shape can be tuned to improve mixing and efficiency, at the cost of shifting the NOx–soot trade-off. However, combustion chamber B, simultaneously improves power output by 10%, NOx emissions by 41 %, and soot emissions by 33%.
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