Effects of Synthetic Atmosphere and Strain Rate on NO Emission from a Biogas/Hydrogen Mixture in MILD Combustion

This study analyzes the structure and emission of a biogas-hydrogen diffusion flame in a synthetic atmosphere composed by oxygen, nitrogen and carbon dioxide in a flameless regime. Particular attention is paid to the oxygen content in the oxidizer and the chemical effect of CO2 on the flame structure. The study is carried out in a laminar counter flow configuration over a wide range of strain rates. Detailed chemistry (GRI 3.0 mechanism) and complex thermal and transport properties are adopted in the calculations. The results obtained indicate that the structure of the flame, temperature and species, is very sensitive to the composition and to the amount of oxygen in the oxidizer stream. Pollutant species such as NO are reduced by a combination of decreased O2 content and increased CO2 volumes in the oxidant stream. The CO2 chemical effect is present as long as the O2 concentration is greater than 3% for the whole strain rate range. This effect leads to a decrease in temperature peaks, OH and NO.