研究目的
Understanding the strong knocking mechanism through high-strength optical rapid compression machines, focusing on the interplay between primary flame propagation and end-gas autoignition progress.
研究成果
The research concludes that strong knocking combustion is significantly influenced by initial pressure and equivalence ratio, quantified by an effective energy density with nonlinear correlations to knocking severity. The interplay between primary flame propagation and end-gas autoignition plays a crucial role, enhancing secondary autoignition events and facilitating transitions to detonation. Ignition modes for strong knocking are primarily in the strong and mixed regimes, with good agreement in the non-dimensional diagram. Future work should focus on turbulence, stratification, and fuel properties using advanced diagnostics.
研究不足
The study is limited to premixed iso-octane/air mixtures in a controlled RCM environment, which may not fully capture all aspects of real engine conditions. Turbulence and thermal heterogeneity parameters are estimated rather than directly measured, potentially introducing uncertainties. The stochastic nature of autoignition events and variations in knocking severity could affect reproducibility.
1：Experimental Design and Method Selection:
The study used a high-strength optical rapid compression machine (RCM) with flat piston design to simulate engine conditions. Synchronization measurement was performed with simultaneous pressure acquisition and high-speed direct photography to visualize combustion processes. Experiments were conducted under spark-ignition (SI) and compression-ignition (CI) conditions by varying initial thermodynamic parameters (initial pressure, temperature, equivalence ratio).
2：Sample Selection and Data Sources:
Premixed iso-octane/air mixtures were used, prepared in a 6.0-L mixing tank with ultra-high purity air (21% O2, 79% N2) and iso-octane fuel (purity >99.9%). Mixture homogeneity was ensured using a magnetic stirring apparatus for about 2 hours.
3：0-L mixing tank with ultra-high purity air (21% O2, 79% N2) and iso-octane fuel (purity >9%). Mixture homogeneity was ensured using a magnetic stirring apparatus for about 2 hours.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: Equipment includes a high-strength optical RCM, piezoelectric pressure transducer (6045A; KISLER), charge amplifier (5064C; KISLER), data acquisition equipment (USB 6366; National Instruments), high-speed camera (SA-Z; Photron), 105-mm lens (AF Micro Nikkor 1:2.8 D), spark plug, and quartz window. Materials include iso-octane fuel and air mixture.
4：8 D), spark plug, and quartz window. Materials include iso-octane fuel and air mixture.
Experimental Procedures and Operational Workflow:
4. Experimental Procedures and Operational Workflow: Mixtures were prepared and introduced into the RCM. For SI cases, spark ignition was triggered at top dead center (TDC). Pressure and high-speed images were recorded simultaneously. Each condition was repeated at least four times for consistency. Data were processed using MATLAB for image analysis and pressure filtering.
5：Data Analysis Methods:
Pressure data were analyzed using fast Fourier transformation to determine knocking severity. Temperature trajectories were computed using adiabatic core hypothesis. Flame images were processed with MATLAB for burned mass fraction calculation. Ignition modes were quantified using a non-dimensional regime diagram based on turbulent Damkohler and Reynolds numbers.
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