SPONTANEOUS RAMAN AND CARS SPECTROSCOPY OF SUPERCRITICAL WATER COMBUSTION

Abstract

Spontaneous Raman spectroscopy (SR) and Coherent Anti-stokes Raman Spectroscopy (CARS) were used to monitor the chemical species and temperature of supercritical water systems. SR was applied to a methane-oxygen diffusion flame burning in supercritical water at 60 MPa and 700 K. All stable species were detected simultaneously. Even in the case of high background luminescence due to flame emission the change of the chemical composition of the exhaust was recorded. CARS spectra of molecular nitrogen were measured at pressures up to 250 MPa and temperatures up to 850 K. The influence of different collision partners on the spectral shape of collapsed N₂ Q-branch signals was investigated, especially that relevant to SCWO (H₂O, CH₄, CO, O₂, Ar). Temperatures of supercritical fluids were determined by fitting computer generated spectral shapes to experimental data using standard quantum mechanical approaches as well as a quasi classical description of rotational relaxation. Within the whole pressure range investigated here, the classical model is in reasonably good agreement with the experimental data.