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Auto-ignition and knocking characteristics of gasoline/ethanol blends in confined space with turbulence

  • Pan, Jiaying
  • Hu, Zhen
  • Pan, Zhenhua
  • Shu, Gequn
  • Wei, Haiqiao
  • Li, Tao
  • Liu, Changwen
Publication Date
Jun 15, 2021
GuangZhou Institute of Energy Conversion
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Ethanol as an attractive oxygenate is increasingly applied for blending with gasoline yielding beneficial combustion and emission performance for internal combustion (IC) engines. Due to the complex fuel chemistry and combustion processes, the auto-ignition and knocking mechanism of gasoline-ethanol blends under enginerelevant conditions are not fully understood. In this study, using a novel rapid compression machine chamber featured by forced turbulence, three gasoline-ethanol blends (i.e. E10, E20, and E30 on a volume basis) were investigated at the target pressure of 20 - 50 atm and temperature of 750 - 850 K after compression. With particle image velocimetry for turbulence calibration, auto-ignition initiation and knocking evolutions were synchronously measured using high-speed photography, infrared imaging, and instantaneous pressure acquisition. Aiming at auto-ignition timing and pressure oscillations, the role of fuel reactivity, turbulent mixing, and energy density was comparatively investigated to elucidate the dominant role in strong knocking formation. A detonation peninsula for gasoline-ethanol blends was employed to explore the ethanol blending effect on detonation development. The results show that due to the suppression of ethanol addition on low-temperature reactions, the strong knocking tendency of gasoline-ethanol blends is significantly inhibited, manifesting retarded auto-ignition timing, reduced pressure oscillations, and vanishing fast reaction wave propagation. Turbulent mixing with colder wall boundary layer alleviates knocking intensity through decreasing the thermodynamic states of in-cylinder mixtures, while energy density promotes detonation development owing to the resonance between reaction waves and pressure waves. Nonetheless, fuel reactivity still plays the first-order significance in strong knocking formation and detonation development. The current study highlights the role of key parameters in auto-ignition and knocking characteristics in high-boost/low-temperature engines, and provides useful insights into the gap between RCM platforms and actual IC engines.

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