Effect of piston bowl geometry on combustion, performance, and emission characteristics of a dual-fuel engine

The piston bowl shape plays a crucial role in turbulence, swirl, and subsequent fuel-air mixing, which in turn affect combustion, emissions, and performance attributes. A cylinder stepped and modified re-entrant combustion chamber was investigated through Ansys Forte 2023 R1 CFD software to analyze combustion, emission, and performance characteristics in a diesel-methane dual-fuel engine. Numerical investigation is performed under 0.44 MPa load, 50% methane energy contribution, 7° start of injection bTDC, and with a 120° spray angle. Methane is injected into the inlet manifold to be premixed with air. The maximum thermal efficiency was found to be 34.11%, and a specific fuel consumption of 270.44 g/kW-h was indicated by the modified re-entrant bowl shape. The combustion duration for a modified re-entrant is 6.73% and 14.38% higher than that of a cylinder and stepped bowl. Higher combustion efficiency, combustion duration, and total apparent heat release demonstrate sustained combustion in the modified re-entrant bowl. Strong early premixed combustion in a cylinder-shaped bowl gives the highest percentage of NOx. The stepped bowl has fuel-rich zones near the center after 19° CA, with lower temperatures near the center, giving higher amounts of UHC and VOC emissions. The amount of O and OH radical formation in the modified re-entrant bowl was lower, and delayed oxidation resulted in a higher amount of CO emission. The modified re-entrant bowl offered the best combustion, performance, and emission attributes among the bowl shapes.