The spatio-temporal rovibrational excitation and relaxation mechanisms of N2(X) in the post-discarge of a 10 ns high-voltage diffuse discharge are studied by Spontaneous Raman Scattering. It is shown that the vibrational excitation of nitrogen molecules remains high despite the strong electric fields applied during the discharge itself and the relaxation processes are similar to lower voltage ns discharges. The main differences with the lower field discharges are rather visible at the beginning of the discharge with a specific spatial volume distribution and a significant vibrational non-equilibrium between v=0,1 and v>1. The spatial distribution of the rovibrational excitation of the diffuse discharge is very wide radially, consistent with the sustainability of fields greater than 100 Td over nearly 8 mm during propagation. The initial rovibrational excitation is inhomogeneous along the axis. The gas temperature reaches up to about 1200 K close to the pin (85 kV, ambient air) while it remains below 500 K in the rest of the volume. It is possible to control the heating of the discharge without greatly modifying the energy transfer mechanisms by adjusting the duration of the voltage pulse. In terms of reactivity, high atomic oxygen densities seem to be very localized in the vicinity of the pin (10 24 m -3 at 1.5 mm from the pin, corresponding to about 20 % dissociation). This inhomogeneity reflects the distribution of energy in the volume of the discharge. The main effects of humidity are also studied. It amplifies the fast heating and accelerates the decay of atomic oxygen in the post-discharge. No significant acceleration of the V-T relaxation of nitrogen due to the addition of water vapour was observed for the studied conditions. A shock wave was identified which is triggered at around 500 ns.

The study of complex reactive flows met in aeronautical engines is an experimental challenge that requires the development of noninvasive and precise measurement techniques. Coherent anti‐Stokes Raman scattering (CARS) is a standard spectroscopic technique used for temperature measurements, which provides unmatched reliability and accuracy at high repetition rate thanks to its recent adaptation to femtosecond temporal regime. This paper reports the first demonstration of hybrid fs/ps‐CARS thermometry in a representative aeronautical combustor (ONERA MICADO test bench, Reynolds number ≈105). Single‐shot N2 CARS spectra have been recorded at 1 kHz, allowing temperature follow up, statistical and frequency (0.1–500 Hz) analysis of CH4/air flame at 0.34‐MPa total pressure. The achieved results demonstrate the ability of the technique to be applied in representative engines conditions and its maturity for semi‐industrial applications.

Hybrid fs/ps CARS thermometry has been performed in an aeronautical combustor during turbulent CH4/air combustion (3.5 bar). Single shot N2 CARS spectra have been recorded at 1 kHz, allowing statistical and frequency ([0.1-500] Hz) analysis.

Spontaneous Raman scattering noise, limited for thermography in turbulent flames where high spatial and time resolutions are required, is revisited for simultaneous temperature and multispecies concentration single-shot linewise measurements, offering new applications.