Flame kernel evolution and shock wave propagation with laser ignition in ethanol-air mixtures

Research output: Contribution to journalArticlepeer-review


Colleges, School and Institutes

External organisations

  • Xihua University
  • University of Birmingham
  • Tsinghua University
  • School of Automobile and Transportation
  • State Key Laboratory of Automotive Safety and Energy


Flame kernel evolution and shock wave propagation in ethanol/air mixtures with laser ignition in a constant-volume chamber was investigated by means of high-speed Schlieren photography. At initial pressure of 0.1 MPa and temperature of 333 K, ignition was performed using a pulsed laser at the second harmonic wavelength with six different laser energies from 75 to 200 mJ, for the equivalence ratios ranging from 0.8 to 1.4. A cross-shaped plasma spot is captured ∼3.0 µs after the laser triggering, whereas the shape of the flame kernel is initially circular and then transforms to an ellipsoid structure. Following the contraction of the plasma, the flame kernel growth rate is initially very different in the four directions and then approaches a steady flame speed. The contraction of the plasma zone is accompanied by a rapid shock wave propagation where, the wave propagation speed is found to be negligibly influenced by the variations in either laser energy or mixture equivalence ratio. Under the test conditions in this study for ethanol/air mixtures, the initial shock wave speed is ∼480 m/s which decays to ∼380 m/s after 20 µs. The shock wave front propagates with a time dependency of about t 0.6 when t < 20 µs, and then it becomes an approximately linear function of time.


Original languageEnglish
Pages (from-to)86-98
Number of pages13
JournalApplied Energy
Early online date16 Oct 2018
Publication statusPublished - 1 Jan 2019


  • Constant-volume chamber, Flame kernel development, Laser ignition, Shock waves