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    Experimental Studies of Spark-Ignition Knock in a Novel Dedicated Test Engine

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    Name:
    Hao Shi - Dissertation - Final Draft.pdf
    Size:
    20.52Mb
    Format:
    PDF
    Description:
    PhD Dissertation
    Embargo End Date:
    2023-04-18
    Download
    Type
    Dissertation
    Authors
    Shi, Hao cc
    Advisors
    Turner, James W. G. cc
    Committee members
    Im, Hong G. cc
    Hoteit, Hussein cc
    Akehurst, Sam
    Program
    Mechanical Engineering
    KAUST Department
    Physical Science and Engineering (PSE) Division
    Date
    2022-02
    Embargo End Date
    2023-04-18
    Permanent link to this record
    http://hdl.handle.net/10754/676304
    
    Metadata
    Show full item record
    Access Restrictions
    At the time of archiving, the student author of this dissertation opted to temporarily restrict access to it. The full text of this dissertation will become available to the public after the expiration of the embargo on 2023-04-18.
    Abstract
    Recently, some new technologies (e.g., downsizing, turbocharging) have been widely used in spark-ignition (SI) engines to achieve higher efficiencies and less emissions. However, the improved power density and in-cylinder pressure promote more engine knock, causing violent pressure oscillations and threatening engine integrity. Therefore, it is imperative to study engine knocking combustion more than ever; In-depth understandings of knock mechanism and characteristics are of utmost importance for controlling knock. With this emphasis, this thesis implements systematic studies to bridge the gap between knocking combustion characteristics and knock suppressing strategies. To investigate knock with optical and laser diagnostics, an optical compression-ignition (CI) engine was modified to operate under SI mode. A home-made metal liner with multiple spark plugs was used to trigger more controllable knock events via different spark strategies. Up to six pressure sensors were installed to collect the pressure signals from different sides. Next, the relationships between in-cylinder pressure, knock intensity, pressure fluctuation, heat release, and measurement location are analyzed to study the knock mechanism, influential factors, and measurement methods. The findings indicate a trade-off between the mass fraction and temperature of end-gas. The effects of compression ratio and fuel octane number are also explored. Moreover, the multichannel pressure monitoring is synchronized with high-speed imaging to investigate the flame propagation and knock development processes regarding the different spark strategies. The results give insights into the in-cylinder temperature inhomogeneity and how it affects the spatial distribution of auto-ignition sites. Furthermore, a new method is proposed to detect the local pressure fluctuations by setting a series of virtual flame monitors instead of pressure sensors. The results validate that this method provides a convenient and reliable way to study knock oscillations. Finally, this study presents a hydraulically actuated VCR (variable compression ratio) piston design to address knock challenges. The numerical simulation results show this VCR piston has a good adaptability and could help achieve high engine efficiencies, while keeping reasonable peak pressure to avoid heavy knock at high loads. However, more analysis work still needs to be implemented on its practical applications, e.g., the thermal stress and frictions under different operating conditions.
    Citation
    Shi, H. (2022). Experimental Studies of Spark-Ignition Knock in a Novel Dedicated Test Engine. KAUST Research Repository. https://doi.org/10.25781/KAUST-V8079
    DOI
    10.25781/KAUST-V8079
    ae974a485f413a2113503eed53cd6c53
    10.25781/KAUST-V8079
    Scopus Count
    Collections
    PhD Dissertations; Physical Science and Engineering (PSE) Division; Mechanical Engineering Program

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