Laser excited emission and chemiluminescence from autoigniting spray

The work presented in this paper deals with the synchronous multiwavelength detection of thermal, chemiluminescent and laser-excited (lambda(o)=266nm) emission from spray of a large saturated paraffin (tetradecane) in auto-igniting conditions. Two of these have been selected by varying oxygen molar fraction (0.13 acid 0.21) of high pressure (2MPa), high temperature oxidant (900K) stream yielding non-sooting combustion. The main measured spectroscopic feature was an isolated broadband fluorescence signal detected around lambda=330nm. This signal is here attributed to aldehyde functionality on the basis of both calibration tests, performed on liquid aldehydes with the same Optical set-up, and literature data relative to fluorescence and chemiluminescence measurements in simpler conditions. Furthermore, temporal evolution of this signal, in the conditions reported here, is consistent with two-step ignition kinetics of paraffins to which a large production of aldehydes and ketones is related. Chemiluminescence maximum, due to HCO and Ct radicals, is slightly delayed with respect to the fluorescence maximum and is in synchrony with a minimum of the aldehydic species fluorescence signal. These maxims and minima mark unambiguously the time interval in which combustion evolves in premixed and diffusion controlled conditions, when pyrolitic species formation occurs.