A review on autoignition in laminar and turbulent nonpremixed flames

Abstract

This chapter presents a condensed review on the autoignition in laminar and turbulent nonpremixed flames. Both experimental and numerical aspects are discussed. Fundamental studies on autoignition in turbulent flows revealed that random ignition spots are initially observed in the lean mixtures where the scalar dissipation rate is low. The mixture fraction corresponding to this lean mixture is usually referred as the "most reactive mixture fraction". The increase in initial turbulent intensity and mixing delays autoignition. For most of the fuels, autoignition is observed as a two-stage process with a negative temperature coefficient. Besides, the physical and chemical properties of the fuels, the complex chemical kinetics also affect auto-ignition as well as combustion characteristics. Autoignition is also a dominant flame stabilization mechanism at the base of the lifted flames. Fundamental experimental investigations on autoignition in turbulent flows are very much limited, and most of the previous work is specifically focused on the Berkley vitiated coflow burner and the Cambridge burner. The combustion models developed so far can capture the trends observed in the experiments and the direct numerical simulation (DNS) studies. However, none of the combustion models developed so far can capture the trends quantitatively.