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-ig niting 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 fluoresce nce 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 relativ e 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 m aximum, 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 s pecies fluorescence signal. These maxims and minima mark unambiguously the time interval in which combustion evolves in premixed and diffusion control led conditions, when pyrolitic species formation occurs.