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 measured 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 pressure of 3.6 MPa, and all oxygen molar fraction of 0.21. One of these ambient 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 available models relative to processes controlled by atomization, evaporation, quenching, and chemical kinetics. The main result of this analysis has been the characterization of the relationship between ignition delay time and oxygen molar fraction in the ambiance that has been found to be well described by a -2 power law. This behavior supports the low-temperature kinetic scheme for paraffin, which hypothesizes oxygen addition on fuel molecules. Moreover, transcritical and supercritical droplet evaporation regimes have been identified as functions of ambient temperature and pressure.