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Abstract
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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) while holding fuel injection
characteristics and intake conditions constant. 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
tradeoff. All geometric cases preserve the same boundary conditions
and operating parameters, isolating the effect of bowl shape.
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