The role of spray-enhanced swirl flow for combustion stabilization in a stratified-charge DISI engine

Journal Article · Wed Jun 01 00:00:00 EDT 2016 · Combustion and Flame

DOI:https://doi.org/10.1016/j.combustflame.2016.03.015· OSTI ID:1257800

Zeng, Wei ^[1]; Sjöberg, Magnus ^[1]; Reuss, David L. ^[2]; Hu, Zongjie ^[3]

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1. Sandia National Lab. (SNL-CA), Livermore, CA (United States)
2. Sandia National Lab. (SNL-CA), Livermore, CA (United States); Univ. of Michigan, Ann Arbor, MI (United States)
3. Tongji Univ., Shanghai (China)

Implementing spray-guided stratified-charge direct-injection spark-ignited (DISI) engines is inhibited by the occurrence of misfire and partial burns. Engine-performance tests demonstrate that increasing engine speed induces combustion instability, but this deterioration can be prevented by generating swirling flow during the intake stroke. In-cylinder pressure-based heat-release analysis reveals that the appearance of poor-burn cycles is not solely dependent on the variability of early flame-kernel growth. Moreover, cycles can experience burning-rate regression during later combustion stages and may or may not recover before the end of the cycle. Thermodynamic analysis and optical diagnostics are used here to clarify why swirl improves the combustion repeatability from cycle to cycle. The fluid dynamics of swirl/spray interaction was previously demonstrated using high-speed PIV measurements of in-cylinder motored flow. It was found that the sprays of the multi-hole injector redistribute the intake-generated swirl flow momentum, thereby creating a better-centered higher angular-momentum vortex with reduced variability. The engine operation with high swirl was found to have significant improvement in cycle-to-cycle variations of both flow pattern and flow momentum. This paper is an extension of the previous work. Here, PIV measurements and flame imaging are applied to fired operation for studying how the swirl flow affects variability of ignition and subsequent combustion phases. PIV results for fired operation are consistent with the measurements made of motored flow. They demonstrate that the spark-plasma motion is highly correlated with the direction of the gas flow in the vicinity of the spark-plug gap. Without swirl, the plasma is randomly stretched towards either side of the spark plug, causing variability in the ignition of the two spray plumes that are straddling the spark plug. Conversely, swirl flow always convects the spark plasma towards one spray plume, causing a more repeatable ignition. The swirl decreases local RMS velocity, consistent with an observed reduction of early-burn variability. Broadband flame imaging demonstrates that with swirl, the flame consistently propagates in multiple directions to consume fuel–air mixtures within the piston bowl. In contrast, operation without swirl displays higher variability of flame-spread patterns, occasionally causing the appearance of partial-burn cycles.

• Research Organization: Sandia National Lab. (SNL-CA), Livermore, CA (United States)
• Sponsoring Organization: USDOE Office of Energy Efficiency and Renewable Energy (EERE), Sustainable Transportation Office. Vehicle Technologies Office; USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: AC04-94AL85000
• OSTI ID: 1257800
• Alternate ID(s): OSTI ID: 1324346
• Report Number(s): SAND2016-3152J; PII: S0010218016300232
• Journal Information: Combustion and Flame, Vol. 168, Issue C; ISSN 0010-2180
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

33 ADVANCED PROPULSION SYSTEMS
Spray-guided stratified-charge DISI engine
Combustion stabilization
Swirl flow and swirl-spray interaction
Flame propagation
High-speed PIV
Flame natural luminosity imaging