The effect of elevated water content on swirl-stabilized ethanol/air flames

Ethanol is currently being considered as a potential alternative to traditional fuels. This study seeks to validate the use of hydrous ethanol in lieu of fossil fuels or anhydrous ethanol in order to reduce the production cost associated with ethanol. Experiments are conducted in a swirl-stabilized combustor, representative of a gas turbine and hydrous ethanol ranging from 0% to 40% water by volume are tested. A stable flame was achieved for fuels up to 35% water and the Lean Blow Out limit was determined for these fuels. Fuels ranging from 0% to 20% water were tested in greater detail which included thermal mapping of the flame, exhaust temperature measurements, exhaust NOx, CO2, and O2 measurement, as well as CH* and OH* imaging of the flame. Equivalence ratio within the combustor was varied to include 0.6, 0.8, 1.0 and 1.1, representing extremely lean, lean, stoichiometric, and rich test conditions, respectively. Results revealed that the exhaust heat rate, combustion efficiency, and combustor thermal efficiency were not affected negatively by elevated water content up to 20%. However, the flame temperature did generally decrease as a result of water addition, particularly in the lower flame region. CH*/OH* emissions in the lower-flame region were also appreciably reduced due to the parasitic heat load of water vaporization and local quenching in the lower parts of the flame. The practical consequence of burning hydrous fuel was reduced exhaust temperature. Reduced peak temperatures lead to reductions of exhaust NOx at all test conditions. This study indicates that hydrous ethanol with up to 20% water can potentially be used in lieu of the more expensive anhydrous ethanol for combustion applications.