Study on effects of NH3 and/or H2 addition on the characteristics of soot formation and gas emissions in a laminar ethylene diffusion flame

The effects of NH3 and/or H2 addition on the soot formation and gas emission in a laminar ethylene diffusion flame were investigated with laser diagnosis methods, thermophoretic sampling method and a Fourier Transform infrared device in this work. The flame doped with N2 was also studied to evaluate dilution effect. The soot, polycyclic aromatic hydrocarbon (PAH), OH evolutions with flame height and the gas emission were obtained. The flame temperature was simulated to identify the thermal effect, and found the temperature rise of H2 enriched flame is slightly larger than that of the flame with NH3 by <50 K. This indicates the temperature does not dominate the soot evolution. NH3 addition can obviously suppress PAH and soot formation by both dilutive and chemical effects, and the rich soot region moves from the two wings to the flame centerline with flame height increases. However, H2 addition chemically promotes soot formation. The soot formation of flames with NH3-H2 blends is between the flames doped with pure NH3 and H2. Adding the blends with low ratio NH3 and high ratio H2 can achieve dramatic soot reduction and moderate NOx emission. This result is significant for guiding future utilization of carbon-free fuel.