Particulate Matter and Organic Vapor Emissions from a Helicopter Engine Operating on Petroleum and Fischer-Tropsch Fuels

Particle and gaseous emissions from a T63 gas-turbine engine were characterized using three fuels: standard military jet fuel (JP-8), Fischer-Tropsch (FT) synthetic fuel, and a 50:50 blend of each. Primary emissions were sampled using a dilution tunnel and sampling trains with both filters and sorbent tubes. Primary particulate matter (PM) and gaseous emissions for the neat FT and blend fuels were reduced relative to emissions when using JP-8 fuel at both idle and cruise loads. At idle load, PM mass emissions are reduced by 65% with neat FT fuel and by 50% for the 50:50 blend compared to neat JP-8 fuel. The JP-8/FT blend thus decreases emissions beyond the linear average of the emissions for the individual fuels. At idle load, FT fuel reduced total hydrocarbon emissions by 20%, while the blend showed no significant change compared to neat JP-8. At cruise load, neat FT fuel resulted in an 80% reduction in primary PM emissions and a 30% reduction in total hydrocarbon emissions compared to neat JP-8. Decreases in PM emissions at idle load come from lower elemental carbon (EC) and primary organic aerosol (POA), while at cruise load emissions, reductions are driven mainly by EC. Gas chromatography-mass spectrometry (GC-MS) and thermo-optical analysis of filter samples indicate that engine oil comprises a significant fraction of the POA emissions. When using FT fuel, POA emissions appear to be largely engine oil, but emissions with JP-8 fuel have a large fraction of partially oxidized organic material. The differences in POA composition may be due to both the presence of partially oxidized fuel as well as greater EC/soot levels when using JP-8 fuel. Thermodenuder and GC-MS measurements indicate that the POA emissions are semi-volatile; therefore, dynamic gas-particle partitioning will alter the contribution of primary emissions to ambient PM. Total gas-phase hydrocarbon emissions greatly outweigh POA emissions, and applying even moderate yields of secondary organic aerosol (SOA) will dominate over POA emissions. A high abundance of unsaturated volatile organic compounds (VOCs) in the gaseous emissions will enhance oxidation chemistry in the exhaust plume and promote the formation of SOA.