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

TL;DR

This study numerically investigates a novel ultra-low emission turbulent swirl burner operating without air dilution, using mixture temperature control to achieve distributed combustion with stable flames and minimal NOX emissions.

Contribution

It introduces a new modeling framework for distributed combustion without air dilution, validated with liquid fuel, expanding understanding of this combustion mode.

Findings

Distributed combustion observed at four operating conditions.

Reactant dilution ratio remained below 0.25, ensuring low NOX emissions.

Homogeneous fuel-air mixture is key to flame stability.

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. The aim of this numerical study aims to understand the operation of this combustion concept 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 that 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.