The Department of Defense (DoD) uses three to four billion gallons of aviation fuel per year, approximately 10% of the total aviation fuel used in the United States. It is estimated that 600,000 kilograms of particulates are emitted each year by the combustion of aviation fuel in U.S. military aircraft alone. The National Ambient Air Quality Standards (NAAQS) provide health-based regulations for particulate matter with diameters less than 10 microns (PM10). Based on growing evidence that this regulation was insufficient to eliminate serious health and environmental problems posed by particulate matter with diameters less than 2.5 microns (PM2.5), the Environmental Protection Agency has adopted a revision to the regulation for PM2.5 particles. To comply with these new regulations, DoD must develop ways to reduce the particulate matter generated from the combustion of aviation fuel in gas turbine engines. The objective of this project was to assess the potential of the jet fuel thermal stability additive "+100" to reduce soot particulate and pollutant emissions from several gas turbine engines burning JP-8 fuel.

The +100 additive was developed for use with JP-8 fuel (JP-8+100) to improve the fuel's thermal stability, thereby reducing the formation of carbon deposits in aircraft fuel system and nozzles. Use of JP-8+100 in fighter aircraft has resulted in significant reductions in fuel-related maintenance costs and a three-fold increase in mean time between fuel-related failures. In addition, engine components are cleaner with drastically reduced soot buildup. Furthermore, recent (unpublished) tests in an advanced aircraft engine showed a 20-35% reduction in particulate emissions from turbine engines using the +100 additive. With the primary objective of reducing solid PM2.5 emissions from gas turbine engines, emissions tests were conducted on Air Force transport aircraft. Preliminary results indicated that the Air Force could reduce particulate emissions by 90,000 kilograms per year using JP-8+100 in its transport aircraft, which burn approximately 60% of the total jet fuel consumed by the Air Force.

An extensive test program to evaluate the +100 additive was completed on five engines—two TF33 (B-52), two JT8D-9A (T-43), and one T63 (helicopter). Test results showed that the effects of the additive on emissions were highly dependent on the engine and power setting. For example, measurable reductions (approximately 20-25%, 5.5-7.5 million particles per cubic centimeter) in particle number density (PND) were observed with the additive for the TF33 engine at a near cruise condition; however, negligible effects were observed for all other conditions. For gaseous emissions, reductions of up to 20% in total unburned hydrocarbons (THC) were observed for all conditions for the second TF33 engine tests; similar results were observed in the T63 tests. However, no evidence of improved particulate or gaseous emissions as a function of operation time with the additive was observed in the T63 long duration tests. For the TF33 tests, chemical characterization of the particles showed an increased concentration of polycyclic aromatic hydrocarbons (PAH) as a function of engine power with no significant impacts using the +100 additive. Reductions of up to 40% in PND with the additive were observed for one of the JT8D-9A (T-43 aircraft) engines; however, mixed results were observed for the other four engines.

For most of the test cases evaluated in this project, the +100 additive did not produce reductions in particulate emissions as anticipated. Although immediate benefits with the additive were not observed, long-term benefits in emissions reduction and engine maintenance may result due to the ability of the additive to keep engine parts clean. (Project Completed - 2006)