• Energy Research
• Energies close

Temporally and spatially resolved laser-induced breakdown spectroscopy (LIBS) was applied to a four-stroke, single-cylinder test engine’s cyclic exhaust gas to demonstrate engine performance. The LIBS technique provided quantitative air-to-fuel ratio (A/F) measurements by generating localized breakdown plasma during the compression and exhaust strokes. The results showed that the timing and duration settings of the emission energy ionization and molecular spectra affect the intensity peaks. Optimum measurements performed between 200 ns and 10 ms after breakdown resulted in observed atomic spectra of CI (248 nm), Hβ (485 nm), Hα (656 nm), NI (745, 824 nm), and OI (777, 844 nm). The intensities of CI (248 nm) and Hα (656 nm) decreased with increasing A/F, whereas the intensity ratios of NI and OI remained constant. A decrease in the intensity ratio of C/O and Hα/O was observed as the A/F increased. This study is a major step toward defining a means of using LIBS to control the A/F ratio in gasoline engines by focusing on the exhaust gas rather than the flame.

The relationship between the flow field and flame propagation is essential in determining the dynamics and effects of turbulent flow in an optical SI engine. In this study, high turbulence flow at stable operations was achieved using 12,000 rpm engine speed, 60 kPa absolute intake pressure, 14.7 A/F, and 15 deg. BTDC spark timing. The turbulent flow field and flame propagation interplay were analyzed through the simultaneous high-speed PIV measurements of the in-cylinder flow and flame front propagation under firing conditions. The intensity of the seeder used was optimized by changing the crank angle. Successful simultaneous detection of the flame front and turbulent flow was demonstrated. Strong turbulence was produced at the flame front simultaneously with the flame movement. After ignition timing, the flame accelerated in the unburned region, and a vital turbulence region occurred.