Two dimensional DNS of n-dodecane spray autoignition at low temperature is conducted. The general autoignition process and the propagation characteristic of cool flame are analyzed. Results show that the cool flame spots firstly occur in the fuel lean regions and propagate into the regions where the mixture fraction is larger. The ignition instant is identified by the time derivative of maximum temperature of the flow field. The chemical reaction rate and heat release rate of second stage are much more intense than that of first stage. There exist occurrence, mergence and quenching during the propagation process of cool flame. The evolution curve of the front speed exhibits a general 'U' shape except several instants, which correspond to mergence and quenching of cool flame. Thus the general 'U' shape of speed curve is split into several little 'U' shapes. The temperature gradient at the reaction front is negatively correlated with the front speed of cool flame.
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