Emission Characteristics and Visualization of an Axial-Fuel-Staged MILD Combustor

ABSTRACT

Axial-fuel-staged combustion is a promising approach to control NO_x emission at high combustor outlet temperatures by shortening the residence time of burnt gas in high-temperature region. In this paper, an axial-fuel-staged MILD combustor was studied experimentally. The combustor consists of a first MILD burner producing hot burnt gases and a secondary transverse jet nozzle injecting premixed fuel and air mixtures. By varying the secondary stage equivalence ratio (Φ₂) at several constant overall equivalence ratios (Φ_t), NO_x reduction (up to 35%) has been achieved at higher Φ_t but failed at lower Φ_t. And by increasing Φ₂ at constant first stage equivalence ratios (Φ₁), a continuous NO_x emission increase was observed, which is insensitive to the variation of Φ₁. Furthermore, the liftoff behavior of the reaction region was also studied and it was found to play important roles in the dilution of the jet mixtures, as well as OH* intensities and NO_x emissions. With the decrease of Φ₁, the OH* chemiluminescence images present a decreased OH* intensity when Φ₂ is lean but an increased OH* intensity when Φ₂ is rich. Finally, an opposed-flow flame calculation was performed and the experimental results were well-supported by this numerical study.

KEYWORDS:

• MILD combustion
• axial-fuel-staged combustion
• NOx emissions
• opposed-flow flame analysis

Acknowledgments

The authors acknowledge the financial support of the National Science and Technology Major Project (No. 2017-I-0009-0010) to this research work.

Additional information

Funding

This work was supported by the National Science and Technology Major Project [2017-I-0009-0010].