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• The LBV and AFT gradually increase with X H 2. • The hydrogen addition can increase the NO emissions and suppress the CO formation. • Reducing the equivalence ratio can significantly reduce the NO emission. • The most important reaction promoting the formation of NO is NNH + O = NH + NO. • The most important reaction that promotes CO consumption is H + CO = H + CO 2. The influence of hydrogen addition (0–100%) on the combustion and emission characteristics (NO and CO formation) of laminar-premixed methane flame under gas turbine relevant operating conditions was numerically studied. The PREMIX code of ANSYS CHEMKIN-PRO and the GRI-Mech 3.0 were utilized. The study of the effect of increasing hydrogen content in the methane-hydrogen mixtures on combustion and emissions at T = 298 K, P = 1 atm can provide a reference for our subsequent research on gas turbine conditions (T = 723 K, P = 16.5 atm). The LBV (laminar burning velocity) and AFT (adiabatic flame temperature) with different hydrogen contents (X H 2 =0–100%) and equivalence ratio (Φ = 0.6–1.4) were investigated. In addition, under gas turbine relevant lean burning conditions (Φ = 0.6, 0.8), the effect of hydrogen addition on the NO and CO emissions were investigated. The rate and sensitivity coefficients of NO/CO production were also examined. The results show that the LBV and AFT increase with the hydrogen content. Both the mole fraction of H, O and OH radicals and the flame temperature were observed to increase with the hydrogen content. Furthermore, the hydrogen addition can significantly increase the NO emissions and on the other hand suppress the CO formation. Reducing the equivalence ratio (from 1.2 to 0.6) can significantly reduce the NO emission. The addition of hydrogen can also increase the combustion stability of methane fuel under fuel-lean conditions. This is a good hint for gas turbine device to reduce NO emissions at fuel-lean side (Φ < 1). [ABSTRACT FROM AUTHOR]

• The reaction images for different equivalence ratio were shown. • The OH* imges and NO x production in the MILD combustion zone were analyzed. • The NO x reduction mechanism prevails over the NO x formation mechanism under MILD mode. The effect of equivalence ratio and staging ratio on the CH 4 MILD (Moderate or Intense Low-oxygen Dilution) combustion was examined in an axially staged MILD combustor. The results were presented on reactant temperature and dilution as well as the ignition delay time through CRN (chemical reaction network) calculation. Also, the data on the OH* radicals distribution and exhaust emissions were obtained using experiments. Higher staging ratio induces the high temperature low oxygen thermodynamic condition required for MILD scheme, yet reduces the ignition delay time. An expanded and downstream moved reaction region was observed at higher equivalence ratio. Reduced and even negative NO x emissions from the MILD combustion zone are acquired at high staging ratio, implying that the NO x reduction mechanism is superior to the NO x formation mechanism in the MILD combustion zone. The opposite effect of staging ratio on the CO emission for low equivalence ratio and high equivalence ratio is also observed. With primary air swirled in the primary combustion zone, the staged combustor exhibits an excellence performance with distributed reaction region and ultra-low NO x and CO emissions under gas turbine relevant lean operating condition. [ABSTRACT FROM AUTHOR]

• H 2 containing syngas fuels produce the NO emission mainly through the N 2 O-intermediate and NO-reburning mechanisms, whereas for pure H 2 MILD combustion, the NNH route plays a more important role. • The syngas fuel with higher N 2 and CO 2 content can achieve MILD combustion at leaner condition and with lower NO x emissions. • MILD regime can be established for four typical coal-derived syngas fuels, with single-digit NO x emissions under gas turbine relevant lean operating condition. The MILD (Moderate or Intense Low-oxygen Dilution) combustion of four typical syngas fuels was examined in CRN (chemical reaction network) model and in parallel jet forward flow combustor. The results were presented on the thermodynamics, ignition kinetics and NO chemistry using CRN calculation. The flow field mixing was obtained from numerical simulation, the global flame signatures and exhaust emissions from experiments. The syngas fuel with higher content of inert gas (N 2 and CO 2) and lower concentration of active components (H 2 and CO) exhibited higher mixture ignition temperature under MILD condition, as a result, greater gas recirculation ratio was required to establish the thermodynamic condition of MILD scheme. H 2 -enriched syngas and CO-enriched syngas showed different chemical kinetics in the ignition process of MILD mixture. In the NO chemistry under MILD condition, it was revealed that the H 2 containing syngas fuels produce the NO emission mainly through the N 2 O-intermediate and NO-reburning mechanisms, whereas for pure H 2 MILD combustion, the NNH route plays a more important role. The N 2 component in the syngas fuel had physical effect in delaying the interaction between the air and fuel stream and in favoring the turbulent mixing as well as the gas recirculation. The CO 2 component in the syngas fuel had chemical effect in lowering the reaction rate. The critical equivalence ratio above which MILD combustion occurs (with the reaction region covering the entire combustor) was identified for the four syngas fuels. It was observed that the syngas fuel with higher N 2 and CO 2 content can achieve MILD combustion at leaner condition and with lower NO x emissions. Reduced CO emission and single-digit NO x emissions were achieved for the four syngas fuels. [ABSTRACT FROM AUTHOR]