Combustion Products of Petroleum Jet Fuel, a Fischer–Tropsch Synthetic Fuel, and a Biomass Fatty Acid Methyl Ester Fuel for a Gas Turbine Engine

Abstract

We report combustion emissions data for several alternatives to petroleum based Jet A jet fuel, including a natural gas–derived Fischer–Tropsch (FT) synthetic fuel; a 50/50 blend of the FT synthetic fuel with Jet A-1; a 20/80 blend of a fatty acid methyl ester (FAME) with jet fuel; and a 40/60 blend of FAME with jet fuel. The chief distinguishing features of the alternative fuels are reduced (for blends) or negligible (for pure fuels) aromatic content and increased oxygen content (for FAME blends). A CFM International CFM56-7 gas turbine engine was the test engine, and we measured NO_X, CO, speciated volatile organic compounds (including oxygenates, olefins, and aromatic compounds), and nonvolatile particle size distribution, number, and mass emissions. We developed several new methods that account for fuel energy content and used the new methods to evaluate potential fuel effects on emissions performance. Our results are categorized as follows: (1) regulated pollutant emissions, CO, and NO_X; (2) volatile organic compound emissions speciation; and (3) particle emissions. Replacing all or part of the petroleum jet fuel with either FAME or FT fuel reduces NO_X emissions and may reduce CO emissions. Combustion of FT fuel and fuel blends increases selectivities and in some cases yields of oxygenates and some hydrocarbon volatile organic compound emissions relative to petroleum jet fuel. Combustion of FAME fuel increases propene and butene emissions, but despite its oxygen content does not strongly affect oxygenate emissions. Replacing petroleum jet fuel with zero aromatic alternatives decreases the emissions of aromatic hydrocarbons. The fuel effects become more pronounced as the size of the aromatic molecule increases (e.g., toluene is reduced more strongly than benzene). Particle emissions are decreased in particle size, number density, and total mass when petroleum jet fuel is replaced with the zero aromatic fuels. The effects of fuel composition on particle emissions are most pronounced at lower power conditions, i.e., when combustion temperature and pressure are lower, and less efficient mixing may lead to locally higher fuel/air ratios than are present at higher power.

Keywords:

• Alternative fuels
• Emissions
• Gas turbine engine

ACKNOWLEDGMENTS

The Federal Aviation Administration supported the emissions characterization through the PARTNER Center of Excellence, Carl Ma Program Manager, via the Missouri University of Science and Technology's Center of Excellence for Aerospace Particulate Emissions Reduction Research. CFM International funded the engine testing, and GE Aviation engineers operated the engine during the emissions study. The U.S. Air Force provided the Fischer–Tropsch synthetic fuel and fuel blend. Boeing generously provided the FAME fuel and fuel blends. We thank GE Aviation, CFM International, Boeing, AFRL, and Missouri University of Science & Technology personnel for their support during the engine tests and post-test data evaluation.

Notes

^a Emission index of unburned hydrocarbons.

^b Data from the International Civil Aviation Organization databank (ICAO, 1995), rated for “standard day” conditions: 15°C, 1.0 bar.

^a All fuel properties courtesy of Air Force Research Laboratory.

^b Measured at 15°C.

^c Emission index of CO₂ calculated from the measured C:H:O fuel content.

^d Measured heat of combustion (higher heating value).

^e Kinematic viscosity at −20°C.

^f As specified in ASTM D1655.

^g Specification for Jet A-1/JP-8.

^h Specification for Jet A.

^a Initial boiling point.

^b Final boiling point.

^a Determined using ASTM D3343.

^b Determined using ASTM D1319-03, except where noted.

^c Inferred from zero aromatic content of 100% FAME fuel and blending ratio with Jet A-1.

^a Data collected using ASTM D2425.

^b Composite average of 13 fuels, data taken from Hadaller and Johnson, (2006).

^a Defined as three times the noise at the stated time resolution.

^b Quantum-cascade tunable infrared laser differential absorption spectrometer (Aerodyne Research, Inc.).

^c Proton-transfer reaction mass spectrometer, Ionicon Analytik.

^d C₂-benzene implies o-xylene, m-xylene, p-xylene, and ethylbenzene.

^e Gas chromatograph proton-transfer reaction mass spectrometer.

^a Detection limits defined for the specified time resolution.

^b Condensation particle counter, model 3022A (TSI).

^c Scanning mobility particle sizer, consisting of a differential mobility analyzer, model 3080 (TSI), and condensation particle counter, model 3022A (TSI); deployed only during APEX-3.

^d Multi-angle absorption photometer (Thermo) (Petzold and Schonlinner, 2004).

^e The SMPS registers particle size as mobility diameter, D_M, defined as the diameter of a spherical particle with the same velocity as the particle of interest as measured in a constant electric field.