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 NOx emissions range. Below equivalence ratio of 0.4, the NOx 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 NOx formation. While the uniform temperature distribution in swirl flames lowers its NOx formation and enhances flame stability. A NOx response model has also been proposed for the swirl configuration to further promote its usage. NOx 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.