NOx reduction based on N2 dilution in a swirled-stabilized magnesium flame.

• The impact of an air dilution by N 2 on the nitrogen oxides (NOx) produced by a swirled-stabilized magnesium flame is investigated. • For each dilution conditions (0, 30 and 50 %), the NOx (NO + NO 2) mole fraction versus the equivalence ratio follows a parabolic shape. • The maximal NOx emissions decrease by a factor 2 with a dilution of 50%. • No N 2 O is produced from the magnesium flame. • The combustion efficiency is higher than 98%, whatever the dilution conditions. New sources of clean energy with reduced greenhouse gas emissions must be considered because of global warming. Among these alternative sources, metal fuels such as aluminum or magnesium are promising. The present study focuses on the impacts of an air dilution by N 2 and of the equivalence ratio on the amount of nitrogen oxides (NOx) produced by a swirled-stabilized magnesium flame. A polydispersed aerosol of pure magnesium in the size fraction 50–70 µm was injected in the combustion chamber. Different air–fuel ratios – from 0.14 to 1.0 – were obtained by changing the mass flowrate of the injected fuel. Thermocouples and a pyrometer were implemented to monitor the gas and flame temperatures. On-line paramagnetic analyzers were used to measure the oxygen (O 2) and NOx concentrations. For each dilution condition (0, 30 and 50 %), the NOx mole fraction versus the equivalence ratio follows a parabolic shape. The amount of NOx first increases when increasing the air–fuel ratio as the power dissipated by the flame increases, leading to the rise of the gas temperature. For the highest air–fuel ratios, the NOx production is disfavored in the rich mixture. The maximal NOx emissions are shifted to higher equivalent ratios when increasing the dilution level and it decreases by a factor 2 with a dilution of 50 %, for a constant value of the air–fuel ratio. The gas temperature in the flame decreases due to the N 2 dilution. The NOx emissions become negligible for an equivalence ratio of 1 at a 50 % dilution. Nevertheless, under the tested experimental conditions, the level of NOx never exceeded 7 gNOx/kWh, which is lower than the maximal value of NOx emissions from a gasoline engine. [ABSTRACT FROM AUTHOR]