Lean Premixed Burners

Publisher Summary This chapter discusses the lean premixed burners. The challenges associated with lean combustion in burners are often under- appreciated because these ubiquitous combustion devices have been operating lean and with low emission reliably, efficiently, and economically for decades. However, as emission requirements tighten, the demands on lean burners increase. Because these systems are usually fan or blower driven, they are susceptible to acoustic feedback; and as the mixtures approach their lean limits, the heat release becomes sensitive to fluctuations. In addition, relatively small changes in fuel composition can produce substantial changes in local stoichiometric conditions because the airflow is rarely controlled relative to the instantaneous fuel content. This combination of challenges means that turndown windows narrow if traditional high-swirl injection is used to provide flame stabilization. This chapter also discusses a reconsideration of the need for recirculation-stabilized flames by presenting a relatively new concept for lean premixed combustion, the low-swirl burner. Many of the factors discussed in this chapter, including sensitivity to fuel composition, the role of high swirl in flame stabilization, and the potential for acoustic instability growth, cut across several lean combustion technologies.