Coal-derived syngas MILD combustion in parallel jet forward flow combustor

•MILD combustion is achieved with reaction zone covering the entire combustion chamber.•Critical air-fuel momentum flux ratio for the occurrence of MILD combustion is identified.•MILD regime can be established for syngas fuel under extremely lean operating condition.

The effect of air-fuel momentum flux ratio on MILD (Moderate or Intense Low-oxygen Dilution) combustion of coal-derived syngas was examined in parallel jet forward flow combustor. The results were presented on flow field using non-reactive numerical simulations and on OH∗ radicals distribution and exhaust emissions using experiments. The predicted gas recirculation ratios in the combustor are high enough to establish the reaction condition of MILD scheme. Lower air-fuel momentum flux ratio associated with higher heat load benefits the drop of peak flame temperature and the increase of reaction zone volume. The critical air-fuel momentum flux ratios below which MILD combustion occurred were identified for three MILD configurations. The MILD configuration equipped with larger air nozzles and smaller fuel nozzles was observed to achieve MILD combustion at leaner condition. The MILD regime was established for syngas fuel with lean operational limit and ultra-low NOx and CO emissions.