Auto-ignited kernels during knocking combustion in a spark-ignition engine

Nobuyuki Kawahara, Eiji Tomita, Yoshitomo Sakata

Research output: Contribution to journalConference articlepeer-review

108 Citations (Scopus)


In this study, auto-ignition of end-gas due to flame propagation and intensity oscillations caused by Shockwaves that occur during knocking combustion were visualized in a compression-expansion engine using a high-speed video camera. Chemical luminescence emissions of the end-gas were detected to analyze the chemical reactions caused by the auto-ignition. Four main conclusions were drawn from this study. When the end-gas region was compressed due to the propagating flame front, auto-ignited kernels appeared near a negative curvature of the flame front. This negative curvature was related to low-temperature chemistry. The large amount of unburned mixture generated a strong pressure wave caused by the auto-ignited kernels explosion. Visualized images of a regular propagating flame front and auto-ignited kernels confirmed that the knocking intensity had a strong relationship with the mass fraction of the unburned mixture. Oscillations of OH* radicals were synchronized with the in-cylinder pressure oscillations, which were produced due to the resulting Shockwave. Before auto-ignition of the end-gas occurred, weak OH* radicals and very weak HCHO* radicals appeared in the end-gas region due to low-temperature chemistry. The OH* radicals played an important role in the low-temperature kinetic reactions. This confirms low-temperature chemical reaction of auto-ignited kernel in the end gas region. OH* radicals are a good indicator of the transition from low-temperature chemistry to high-temperature auto-ignition.

Original languageEnglish
Pages (from-to)2999-3006
Number of pages8
JournalProceedings of the Combustion Institute
Volume31 II
Publication statusPublished - Sept 24 2007
Event31st International Symposium on Combustion - Heidelberg, Germany
Duration: Aug 5 2006Aug 11 2006


  • Auto-ignited kernels
  • Engine knock
  • Low-temperature chemistry
  • Pressure wave formation in knocking combustion
  • Spark-ignition engine

ASJC Scopus subject areas

  • Chemical Engineering(all)
  • Mechanical Engineering
  • Physical and Theoretical Chemistry


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