Numerical modeling of distributed combustion without air dilution in a novel ultra-low emission turbulent swirl burner

Abstract

Distributed combustion, often associated with the low-oxygen condition, offers ultra-low NOx emission. However, it was recently achieved without combustion air dilution or internal flue gas recirculation, using a distinct approach called mixture temperature-controlled combustion. Here, the fuel-air stream is cooled at the inlet to delay ignition and, hence, foster homogeneous mixture formation. This numerical study aims to understand its operation better and present a robust framework for distributed combustion modeling in a parameter range where such operation was not predicted before by any existing theory. Further, liquid fuel combustion was evaluated, which brings additional complexity. Four operating conditions were presented at which distributed combustion was observed. The reacting flow was modeled by flamelet-generated manifold, based on a detailed n-dodecane mechanism. The Zimont turbulent flame speed model was used with significantly reduced coefficients to achieve distributed combustion. The droplets of airblast atomization were tracked in a Lagrangian frame. The numerical results were validated by Schlieren images and acoustic spectra. It was concluded that the reactant dilution ratio remained below 0.25 through the combustion chamber, revealing that the homogeneous fuel-air mixture is the principal reason for excellent flame stability and ultra-low NOx emission without significant internal recirculation. The potential applications of these results are boilers, furnaces, and gas turbines.