Autoignition and combustion of n-hexane spray in subcritical and supercritical environments

In this study, processes of a liquid fuel spray ignition and heat release during its combustion were under investigation. The purpose of this study was to elucidate whether the ignition properties and heat release process of a liquid fuel injected into the environments of parameters exceeding its critical values differ from those obtained for subcritical regimes. Therefore, the fuel was injected into the environments of parameters below, around and above its critical values. The ignition and combustion processes were observed by monitoring the pressure in the combustion chamber and by using a high-speed camera through transparent piston. The ignition process was characterized by ignition delay, while the combustion process by heat release and rate of heat release. The ignition delay was determined by pressure rise according to tangential method. Ignition delay determined that way included both physical delay and chemical delay. Obtained results revealed stochastic nature of the spray ignition of n-hexane. No major difference in ignition delay in terms of exceeding critical parameters was noticed. The only parameter directly influencing the ignition delay was the injectant initial temperature.