Numerical Investigations of Reignition in Vortex-Perturbed n-Heptane Nonpremixed Flames

Abstract

Numerical investigations of reignition in n-heptane nonpremixed flames perturbed by counter-rotating vortex pairs are performed. The conditions simulated are representative of high-pressure combustion chambers with high-Reynolds-number jet flames. A two-dimensional numerical formulation that employs sixth-order spatial accuracy and fourth-order time integration is used to solve the governing equations for compressible, viscous, and reacting flows. The oxidation of n-heptane is modeled using a 34-species mechanism involving 56 reaction steps. Transport is modeled using the unity Lewis number and the mixture-averaged models. For the conditions simulated, reignition occurs through lateral diffusion of species and heat from the adjoining edge flames to the quenched regions and hence cannot be predicted by one-dimensional flamelet models. Following reconnection of the diffusion flame, a vortical pocket travels on the fuel side and acts as a major source of combustion products such as CO and H 2 . The results show that whereas an increase in the vortex velocity scale results in higher rates of reignition and product formation, an increase in the length scale decreases the rate of reignition and increases the amount of products formed in the vortical pocket. The choice of the transport formulation has a minor influence on the predicted flame temperatures and major species concentrations.