Ammonia combustion properties and performance in gas-turbine burners

Experimental studies were conducted to determine the minimum ignition energy, quenching distance, flame-stability limits, and gas-turbine-burner performance of ammonia-air mixtures. The minimum ignition energy of ammonia was 8 millijoules compared to less than 0.5 millijoules for propane. At stoichiometric conditions, the quenching distance for ammonia-air was 0.275 in. The corresponding reported value for propane-air is 0.08 in. In the flame stability experiments, ammonia would burn at only one-half the air-flow velocity possible with hydrocarbon fuels and the range of equivalence ratios for stable flame was much narrower than for hydrocarbon fuels. These characteristics were essentially substantiated in gas-turbine-burner testing. It was concluded that neat ammonia cannot be used as a substitute fuel for hydrocarbons in conventional gas-turbine burners unless the ignition-system energy is increased, the combustion linear diameter is increased by a factor of approximately 2, and the ammonia injected in the gaseous state. Two approaches were investigated for improving the combustion properties of ammonia. These were to use additives or to partially pre-dissociate the ammonia. Additives were tested in the flame-stability apparatus in concentrations of 5% by volume of the total fuel. At this concentration, none of the additives improved the flame-stability properties to the extent required. The minimum ignition energy, quenching distance, and flame-stability properties of 28% dissociated ammonia were approximately equal to these same properties of methane. Partially dissociated ammonia was also tested in the gas-turbine burner. It was concluded that 28% dissociated ammonia could be used as a substitute fuel in gas-turbine-combustion systems optimally sized for hydrocarbon fuels.