Air Force Research Lab Wight-Patterson AFB United States
Gas turbine engines GTEs consume approximately 70 percent of the total fuel purchased by the DoD and are the major source of carbon monoxide CO, unburned hydrocarbons UHC, oxides of nitrogen NOx, and particulate matter PM emissions produced at military airbases. The DoD has established goals for use of synthetic derived alternative JP-8, which will consist of blends of petroleum-based JP-8 and synthetic fuels and potentially fully synthetic fuels. These goals present new challenges for low emissions combustors that will burn alternative fuels. First, the alternative fuels, that could be in the DoD inventory in the next ten to twenty years, are in the early stages of being defined, and second, there is very little fundamental data on the combustion of possible alternative fuels. This SERDP program described in this report was designed to address these challenges by establishing a scientific base for modeling all emissions from GTEs burning alternative fuels and by developing a methodology for selecting future alternative fuels based on their emissions characteristics. Field studies of aircraft engine emissions have identified clear effects of alternative fuels. Alternative fuels have been demonstrated to have an impact on the composition of the UHC emissions. Blending paraffinic alternative fuels into JP-8 has also been found to substantially reduce particulate matter emissions. Field and laboratory studies have also shown that each of the emissions vary substantially as engine power varies. At low power conditions, emissions of unburned hydrocarbons and CO are the highest, and they decrease with increasing power. Soot and NOx emissions are most significant at higher engine power. Thus, it is important to understand the effects of alternative fuels at both low and high power conditions.