Effects of a CFD-improved dimple stepped-lip piston on thermal efficiency and emissions in a medium-duty diesel engine
Diesel piston-bowl shape is a key design parameter that affects spray-wall interactions and turbulent flow development, and in turn affects the engine’s thermal efficiency and emissions. It is hypothesized that thermal efficiency can be improved by enhancing squish-region vortices as they are hypothesized to promote fuel-air mixing, leading to faster heat-release rates. However, the strength and longevity of these vortices decrease with advanced injection timings for typical stepped-lip (SL) piston geometries. Dimple stepped-lip (DSL) pistons enhance vortex formation at early injection timings. Previous engine experiments with such a bowl show 1.4% thermal efficiency gains over an SL piston. However, soot was increased dramatically [SAE 2022-01-0400]. In a previous study, a new DSL bowl was designed using non-combusting computational fluid dynamic simulations. This improved DSL bowl is predicted to promote stronger, more rotationally energetic vortices than the baseline DSL piston: it employs shallower, narrower, and steeper-curved dimples that are placed further out into the squish region. In the current experimental study, this improved bowl is tested in a medium-duty diesel engine and compared against the SL piston over an injection timing sweep at low-load and part-load operating conditions. No substantial thermal efficiency gains are achieved at the early injection timing with the improved DSL design, but soot emissions are lowered by 45% relative to the production SL piston, likely due to improved air utilization and soot oxidation. However, these benefits are lost at late injection timings, where the DSL piston renders a lower thermal efficiency than that of the SL piston. Energy balance analyses show higher wall heat transfer with the DSL piston than with the SL piston despite a 1.3% reduction in the piston surface area. Vortex enhancement may not necessarily lead to improved efficiency as more energetic squish-region vortices can lead to higher convective heat transfer losses.
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Availability:
- Find a library where document is available. Order URL: http://worldcat.org/issn/14680874
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Supplemental Notes:
- © IMechE 2022.
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Authors:
- Wu, Angela
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0000-0002-6456-5786
- Cho, Seokwon
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0000-0003-1378-0344
- Lopez Pintor, Dario
- Busch, Stephen
- Perini, Federico
- Reitz, Rolf D
- Publication Date: 2023-5
Language
- English
Media Info
- Media Type: Web
- Features: References;
- Pagination: pp 2223-2232
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Serial:
- International Journal of Engine Research
- Volume: 24
- Issue Number: 5
- Publisher: Sage Publications, Incorporated
- ISSN: 1468-0874
- EISSN: 20413149
Subject/Index Terms
- TRT Terms: Diesel engine exhaust gases; Diesel engines; Fluid dynamics; Heat transfer; Pistons; Thermal efficiency
- Subject Areas: Energy; Environment; Highways; Vehicles and Equipment;
Filing Info
- Accession Number: 01884397
- Record Type: Publication
- Files: TRIS
- Created Date: Jun 1 2023 9:32AM