Experimental study of combustion instability and emission characteristics of ethanol/ammonia co-firing swirl flame

Abstract

Ammonia and ethanol are promising carbon–neutral alternative fuels that can be produced through renewable energy sources. This study investigates the combustion instability and emission characteristics of ethanol/ammonia co-firing flame with ammonia heat fraction up to 40% in a swirl burner. Three different ammonia blending strategies are studied: premixed addition, root injection, and middle injection. The co-firing flame exhibited intense combustion instability under certain operating conditions with a pulsating frequency of about 150 Hz. The instability intensity weakens as the ammonia ratio increases. The pulsating pressure and OH* chemiluminescence intensity first increase and then decrease with the equivalence ratio, reaching a peak value near Ф=0.35. Adding a small amount of ammonia will cause CO and NOx emissions to increase simultaneously, but when αNH3 > 0.15, CO and NOx emissions will decrease. When the Ф increases, NOx emissions of premixed addition gradually decrease, while the NOx emissions of root injection and middle injection do not change significantly. The unburned NH3 significantly decreases with increasing Ф, and ammonia combustion is more efficient with the middle injection method.