Numerical Study on the Combustion Characteristics of Premixed Ammonia Flames with Methanol/ethanol/n-Butanol Addition

Mixing ammonia (NH3) with alcohols for combustion not only improves the combustion characteristics of NH3 but also retains carbon-neutral when both fuels are produced from renewable energy. To investigate the combustion characteristics of ammonia/alcohol mixtures, this study proposed an ammonia/n-butanol combustion mechanism which is consisted of 101 species and 580 reactions. This mechanism was validated against the measured laminar burning velocities (LBVs) from literature, and the results showed that it is capable of accurately predicting the LBVs of ammonia mixed with methanol, ethanol and n-butanol, respectively. It is found that adding a small amount of alcohol can significantly increase the LBVs of ammonia, n-butanol has the strongest enhancing effect and methanol has relatively weaker enhancing effect when addition fraction of alcohols is lower than 50 % at a wide range of equivalence ratio (Phi). Unlike the dependence of peak flame temperature on alcohol addition fraction, maximum NOx formation varies significantly with different alcohol addition fractions. This study found a strong correlation between NOx emissions and the combined effects of active radicals and NO precursor HNO.