Large Eddy Simulation of a Swirl-Stabilized Pilot Combustor from Conventional to Flameless Mode

Ehsan Fooladgar,C K Chan

doi:10.1155/2016/8261560

Abstract

This paper investigates flame and flow structure of a swirl-stabilized pilot combustor in conventional, high temperature, and flameless modes by means of a partially stirred reactor combustion model to provide a better insight into designing lean premixed combustion devices with preheating system. Finite rate chemistry combustion model with one step tuned mechanism and large eddy simulation is used to numerically simulate six cases in these modes. Results show that moving towards high temperature mode by increasing the preheating level, the combustor is prone to formation of thermalNOxwith higher risks of flashback. In addition, the flame becomes shorter and thinner with higher turbulent kinetic energies. On the other hand, towards the flameless mode, leaning the preheated mixture leads to almost thermalNOx-free combustion with lower risk of flashback and thicker and longer flames. Simulations also show qualitative agreements with available experiments, indicating that the current combustion model with one step tuned mechanisms is capable of capturing main features of the turbulent flame in a wide range of mixture temperature and equivalence ratios.

Highlights

Ever increasing global energy consumption and environmental concerns combined with the lack of energy resources have put the designers of combustion devices to a difficult test in order to come up with new technologies that are more energy efficient and less polluting
Thermal nitric oxide formation is reduced because flame temperature is generally low and, for hydrocarbon fuels which are leaned by excess air, hydrocarbon and carbon monoxide (CO) emissions are reduced due to complete burnout of fuel
The objective of this paper is to investigate the flame and flow structure of a swirl-stabilized pilot combustor in conventional, high temperature combustion (HiTC), and flameless mode using finite rate chemistry combustion model and large eddy simulation (LES)

Summary

Introduction

Ever increasing global energy consumption and environmental concerns combined with the lack of energy resources have put the designers of combustion devices to a difficult test in order to come up with new technologies that are more energy efficient and less polluting. One common method to increase energy efficiency in almost all combustion systems including lean premixed (LPM) combustion is increasing the mixture temperature using recovered exhaust heat directly. Employing this method in LPM combustion increases the efficiency of the system and improves combustion stability and flammability limits. As outlined by Huang and Yang [1], LPM combustion is the most promising technology for environmentally friendly combustion systems since operating under fuel lean conditions can have low emissions and high efficiency. As explained by Dunn-Rankin [2], achieving these improvements and meeting the demands of practical combustion systems are complicated by low reaction rates, extinction, instabilities, mild heat release, and sensitivity to mixing

Objectives

Methods

Results