Investigation of ignition dynamics in a H_2/air mixing layer with an embedded vortex

Abstract

Numerical simulations are carried out to study the effect of a vortex on the ignition dynamics of hydrogen/ air in a quiescent mixing layer. The problem has direct implications on the auto-ignition behavior and stabilization mechanism in turbulent non-premixed flames, recirculating burners and supersonic combustion. Similar problems have been studied in the past using different approximations like infinitely fast and single-step chemistry and large activation energy asymptotics. While useful insight is obtained, the role of multi-step reaction chemistry is neglected. More recent work utilizing detailed chemical kinetics has been limited in its scope due to computational requirements. These difficulties are overcome in the present study by utilizing a tabulated approach. Chemistry tabulations are generated utilizing steady-state solutions of the non-premixed flamelet equations. The fluid dynamic simulations are carried out using a lookup table approach. Similar calculations are also performed with detailed chemistry to demonstrate the accuracy of the tabulated approach. The reduction in computational time obtained using the tabulated approach is utilized to conduct a parametric study investigating the effects of vortex strength, characteristic size, center location, and fuel/air temperatures on ignition delay time and location. The effect of these parameters are correlated to the scalar dissipation rate to explain the physical processes leading to ignition.

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