Combustion of NH3/CH4 mixtures in a swirl burner: Study of non-premixed flames with radial fuel injection

Abstract

International audienceThe transition to renewable energy is essential in addressing climate change. While natural gas plays a significant role in this transition, it still produces CO2 emissions. Ammonia (NH3) is being investigated as a promising alternative fuel. However, ammonia combustion presents several technical challenges, such as low flame velocity, limited calorific value, difficulties with flame stabilization, and high NOx emissions. This study examines the impact of ammonia addition to methane, equivalence ratio, and swirl number on pollutant emissions (NO, CO, CH4, and CO2), exhaust gas temperature, and flame stability. Experiments are carried out using a swirl burner with a radial fuel injection in a 1-meter high combustion chamber. The burner consists of two concentric tubes, with the inner tube supplying fuel and the outer tube supplying air. The fuel is injected radially through eight holes at the burner exit. The ammonia fraction ranges from 0 to 100 %, the equivalence ratio from 0.8 to 1.0, and the swirl number from 0.8 to 1.4, with a constant flame power of 10 kW. Emissions of NO, CO, CH4, and CO2 are measured in the dry exhaust gases using a multi-gas analyzer, inside chamber temperatures are measured and the flame structure is analyzed via OH* and NH2* chemiluminescence and velocity measurements by LDA technique. The results show that both the swirl number and equivalence ratio significantly alter flame geometry, affecting combustion zones and flame height. Axial velocity measurements indicate that the recirculation zone shrinks with ammonia addition, while a high swirl number increases axial velocity, promoting ammonia combustion and upstream flame propagation. Up to 30 % ammonia, the flame remains stable, but higher ammonia levels lead to fluctuations in stabilization. High ammonia content in the fuel mixture results in reductions of NO, CO, and CO2 emissions, though there is a potential increase in unburned gases. As expected, the inside chamber temperatures decrease as the ammonia fraction increases