Air dilution effects on tetradecane spray autoignition in transcritical and supercritical regimes

Autoignition time delay of tetradecane spray injected in nearly quiescent, high-temperature, high-pressure, diluted and not diluted air has been measu red by detecting spontaneous luminous emission. The photodiode location and its spectral sensitivity were carefully tested with preliminary comparison to spectrally resolved measurements hy using a spectrograph equipped with an intensified CCD camera. The measurements were performed starting from a temperature of 873 K, a pre ssure of 3.6 MPa, and all oxygen molar fraction of 0.21. One of these ambie nt conditions Ir?asfuced and the other two parameters, were lowered to 873 K ambient temperature, 1.1 MPa, and 0.06 oxygen molar fraction. The results were analyzed in relation to the expected ones, which were based on the av ailable models relative to processes controlled by atomization, evaporation , quenching, and chemical kinetics. The main result of this analysis has been the characterization of the relat ionship between ignition delay time and oxygen molar fraction in the ambian ce that has been found to be well described by a -2 power law. This behavio r supports the low-temperature kinetic scheme for paraffin, which hypothesi zes oxygen addition on fuel molecules. Moreover, transcritical and supercri tical droplet evaporation regimes have been identified as functions of ambi ent temperature and pressure.