Chemical kinetic study of methane blended with ammonia cracked gas at elevated temperature and pressure

Abstract

Ammonia (NH3) on-line cracking to produce hydrogen (H2) can avoid direct ammonia combustion and is an important method to enhance combustion performance and control nitrogen oxide (NOx) emissions. This work aims to study the effects of various ammonia energy ratios (ENH3) and cracking ratios (CNH3) on the combustion and NO emission characteristics of methane (CH4) blended with ammonia cracked gas under lean-burn condition. The results showed that methane co-combustion and ammonia cracking significantly enhance the laminar burning velocity (LBV). The chemical effect plays a dominant role in the enhancement of LBV, but its relative contribution gradually decreases with increasing ENH3 and CNH3. A linear relationship between LBV and (O+H+OH+NH2 + CH3)max was observed, with both the slope and intercept being functions of CNH3. At an ENH3 of 20 %, NO emission decrease with increasing CNH3. At an ENH3 of 80 %, NO emission first increase and then decrease. The percentage of thermal NO is less than 1 % under ambient condition and could increase to as much as 22 % under elevated condition (500 K, 10 atm). Additionally, there was a quadratic polynomial relationship between (O+H+OH+NH2)max and the final NO mole fraction within an equivalence ratio range from 0.4 to 0.8. The second-order coefficient exhibits a linear correlation with CNH3, while the first-order and constant coefficient show a quadratic polynomial correlation with CNH3.