Numerical and Experimental Studies of a Novel Dimpled Stepped-Lip Piston Design on Turbulent Flow Development in a Medium-Duty Diesel Engine

Wu, Angela; Busch, Stephen; Perini, Federico; Cho, Seokwon; Pintor, Dario Lopez; Reitz, Rolf D.

doi:10.4271/2022-01-0400

Cited by 11 publications

(18 citation statements)

References 36 publications

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“…The surface roughness of the DSL piston is approximately equal to that of the SL piston, therefore, the higher heat transfer losses of the DSL piston cannot be explained by surface roughness effects. The rotational energy (E rot ) of the squish-region vortices and swirl ratio are obtained from previous CFD simulations 14 and plotted in 10 for the SL and DSL pistons with an early main injection timing (SOI main equal to 5.7 CAD aTDCc), after main injection has occurred. Results obtained with the baseline DSL piston are also included for the reader's reference.…”

Section: Resultsmentioning

confidence: 99%

“…Multiple sub-systems allow for precise control of virtually all operating parameters and wellcharacterized experiments. More information on the engine setup can be found in Wu et al, 14 Busch et al, 15 and Cho et al 16 Engine experiments are performed with both the baseline SL piston and the improved DSL piston shown in Figure 3. The surface area of the improved DSL piston is approximately 1.3% smaller than that of the SL piston due to scaling down of the bowl and stepped area.…”

Section: Methodsmentioning

confidence: 99%

“…By using the DSL bowl, the thermal efficiency was improved by 1.4% at near-TDC injection timing relative to the SL piston, but soot emissions increased dramatically by 69% with no penalty in NOx emissions. The possible reasons for higher soot emissions in the baseline DSL piston was not discussed in Wu et al, 14 but will be explored in this study.…”

Section: Introductionmentioning

confidence: 91%

“…13 Recently, this dimple stepped-lip (DSL) geometry was used in a medium-duty diesel engine simulation. 14 The rotational energy within these vortices was increased by 88% in the baseline DSL geometry compared to those in the SL piston even at near-TDC main injection timings. This was hypothesized to further improve peak thermal efficiency and reduce emissions.…”

Section: Introductionmentioning

confidence: 93%

“…A design sensitivity study using non-combusting CFD simulations was performed to improve the DSL piston bowl design. 14 The sensitivity analysis quantified the effects of varying the dimple depth, azimuthal order (ratio of dimple width to azimuthal steepness), radial steepness, and radial location of the dimple on the rotational energy and size of the squish-region vortices. Based on these results, an improved DSL bowl was designed with shallower, narrower, and steeper-curved dimples that are further out into the squish region, as shown in Figure 1.…”

Section: Introductionmentioning

confidence: 99%

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Effects of a CFD-improved dimple stepped-lip piston on thermal efficiency and emissions in a medium-duty diesel engine

Cho

Pintor

et al. 2022

International Journal of Engine Research

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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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Section: Resultsmentioning

confidence: 99%