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NH3 is a carbon-free fuel, so it has the potential to reduce CO2 emission from the power plant when used as a fuel. However, NH3 has combustion characteristics different from conventional hydrocarbon fuels. The N atom in the ammonia molecule causes high NOx emission through combustion reactions. To develop a gas-turbine combustor, which burns a combination of NH3 and natural gas with controlled emissions, combustion characteristics have been studied experimentally and numerically by using a swirl-burner, which is typically used in gas-turbines.
Detailed exhaust gas compositions of the burner have been measured under atmospheric pressure and fuel lean conditions. As equivalence ratio increases, amounts of unburnt species (NH3, CO and THC (Total Hydro Carbon)) decrease in contrast to NO and N2O emissions. The burner achieves combustion efficiencies above 97% for ammonia-mixing-ratios below 50%. It has been found that it is difficult to achieve both, low emissions and high combustion efficiency, in single-stage combustor. Therefore, a low-emission combustion concept using two-stage combustion was devised. Calculations revealed that this concept offers controllability of NOx and unburnt gas species emissions.