A Direct Numerical Simulation study of a turbulent lifted flame in hot oxidizer

This paper presents a Direct Numerical Simulation (DNS) study of the stabilisation of a turbulent lifted flame in hot oxidizer, a problem of practical significance in diesel engines, gas turbines, and recirculating industrial burners. A slot jet of fuel issuing into a hot co-flow oxidizer stream is simulated using a single-step chemistry model and assuming unity Lewis number. A jet Reynolds number of 5,300 was enabled by the use of scalable high-order numerical methods and highly parallel computation. The basic structure of the flame is described noting features of the flame base and trailing premixed and diffusion flames. The flame base is studied to determine whether the stabilisation is due auto-ignition, premixed flame propagation, or another mechanism. The flame index (FI) is used to distinguish non-premixed flames from premixed flames close to the flame base. The time evolution of temperature, reaction rate and scalar dissipation rate along with iso-lines of appropriate temperature and most reactive mixture fraction are analysed to identify the flame base. It is concluded that the flame base exists on the outer boundary of the jet and consists of mainly non-premixed flames followed by a vigorous trailing rich premixed flame region inside the jet.