Emissions and stability characteristics of syngas combustion with swirl and non-swirl micromix configurations

In traditional combustion technologies, swirl and bluff bodies effectively control flame emissions and stability. However, their impact on micromix combustion technology that suitable for hydrogen-containing fuels remains unclear. Two micromix configurations with swirl and non-swirl flow fields have been proposed in our research group. Through experimental and numerical simulation efforts, the emissions and stability characteristics have been compared in a wide range of operating conditions for the two proposed designs. The results indicate that swirl and non-swirl configurations exhibit similar and broad operating conditions for reaching low CO emissions while swirl flames show a broader low NO_x emissions range. Below equivalence ratio of 0.4, the NO_x emissions for the swirl and non-swirl configurations were less than 3 ppm and 10 ppm, respectively. Within the equivalence ratio range of 0.3–0.8, CO emissions for both configurations were below 10 ppm. The high-temperature regions of the non-swirl flame exhibit a concentrated radial distribution and longer residence time, therefore resulting in higher NO_x formation. While the uniform temperature distribution in swirl flames lowers its NO_x formation and enhances flame stability. A NO_x response model has also been proposed for the swirl configuration to further promote its usage. NO_x emissions increase with the residence time and temperature, becoming highly sensitive after exceeding 20 ppm. Considering both stability and emissions, swirl flames are appropriate for main-stage nozzles, while non-swirl flames are suitable for pilot-stage nozzles.