LIBS; high pressure; fuel-air ratio; ultrafast LIBS;

Application of time-resolved ultrashort-pulse-laser-based laser-induced breakdown spectroscopy (LIBS) is proposed for diagnostics in hydrocarbon flames at elevated pressures. Earlier study in nanosecond-laser-based LIBS for measuring fuel-to-air (F/A) ratios in stable hydrocarbon flame at high pressures is reported to have high measurement instabilities. A correlated measurement of time-resolved LIBS and electron number density measurement is carried out to develop an understanding of the source of the aforesaid measurement instability. The planned correlated measurements of LIBS and electron number density with short picosecond to femtosecond excitations have potentials to significantly reduce the instability in F/A ratio measurements at high pressure.