Matthew J. DeWitt

Impacts of Biodiesel on Pollutant Emissions of a JP-8–Fueled Turbine Engine

Abstract The impacts of biodiesel on gaseous and particulate matter (PM) emissions of a JP-8–fueled T63 engine were investigated. Jet fuel was blended with the soybean oil-derived methyl ester biofuel at various concentrations and combusted in the turbine engine. The engine was operated at three power settings, namely ground idle, cruise, and takeoff power, to study the impact of the biodiesel at significantly different pressure and temperature conditions. Particulate emissions were characterized by measuring the particle number density (PND; particulate concentration), the particle size distribution, and the total particulate mass. PM samples were collected for off-line analysis to obtain information about the effect of the biodiesel on the polycyclic aromatic hydrocarbon (PAH) content. In addition, temperature-programmed oxidation was performed on the collected soot samples to obtain information about the carbonaceous content (elemental or organic). Major and minor gaseous emissions were quantified using a total hydrocarbon analyzer, an oxygen analyzer, and a Fourier Transform IR analyzer. Test results showed the potential of biodiesel to reduce soot emissions in the jet-fueled turbine engine without negatively impacting the engine performance. These reductions, however, were observed only at the higher power settings with relatively high concentrations of biodiesel. Specifically, reductions of ∼15% in the PND were observed at cruise and takeoff conditions with 20% biodiesel in the jet fuel. At the idle condition, slight increases in PND were observed; however, evidence shows this increase to be the result of condensed uncombusted biodiesel. Most of the gaseous emissions were unaffected under all of the conditions. The biodiesel was observed to have minimal effect on the formation of polycyclic aromatic hydrocarbons during this study. In addition to the combustion results, discussion of the physical and chemical characteristics of the blended fuels obtained using standard American Society for Testing and Materials (ASTM) fuel specifications methods are presented.

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

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 NOX, 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 NOX; (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 NOX 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.

Gaseous and Particulate Emissions Results of the NASA Alternative Aviation Fuel Experiment (AAFEX)

The Aircraft Alternative Fuels Emissions experiment (AAFEX) was conducted at National Aeronautic and Space Administration (NASA) Dryden Flight Research Center (DFRC) Aircraft Operations Facility (DAOF) in Palmdale, California, during January and February 2009. The purpose was to systematically investigate the effect of alternative fuels on both gas-phase and particle emissions from a CFM56-2C1 engine on NASA’s DC-8 aircraft parked on the ground as functions of engine power, fuel composition, and exhaust plume age. Emissions parameters were measured at 6 engine power settings, ranging from idle to maximum thrust, in samples collected at 1, 30, and 145 meters (m) downstream of the exhaust plane as the aircraft burned three pure fuels and two fuel blends. The fuels included JP-8, two fuels produced using the Fischer-Tropsch process and 50/50 blends by volume of the F-T fuels with JP-8. The 1 m sampling rakes contained multiple gas and particle inlet probes and could also be traversed in order to measure the spatial variation of emissions across the engine exhaust plane. The #2 inboard engine on the left side always burned JP-8 while the #3 inboard right side engine was fueled with the various fuels and fuel blends. In addition, emissions from the Auxiliary Power Unit (APU) were also evaluated with both JP-8 and one pure F-T fuel. Both gaseous and particulate emissions are presented. Results show that the synthetic fuels reduced pollutant emissions while having relatively little effect on engine operation or performance.Copyright

Hydroprocessed Renewable Jet Fuel Evaluation, Performance, and Emissions in a T63 Turbine Engine

Due to potential beneficial environmental impacts and increased supply availability, alternative fuels derived from renewable resources are evolving on the forefront as unconventional substitutes for fossil fuel. Focus is being given to the evaluation and certification of Hydroprocessed Renewable Jet (HRJ), a fuel produced from animal fat and/or plant oils (triglycerides) by hydroprocessing, as the next potential synthetic aviation fuel. Extensive efforts have recently been performed at the Air Force Research Laboratory (AFRL) at Wright Patterson Air Force Base (WPAFB) to evaluate the potential of two HRJ fuels produced from camelina and tallow feedstocks. These have included characterization of the fuel chemical, physical fuel characteristics and Fit-for-Purpose properties (FFP). The present effort describes general combustion performance and the emission propensity of a T63-A-700 Allison turbine engine operated on the HRJs and 50/50 (by volume) HRJ/JP-8 fuel blends relative to a specification JP-8. In addition, engine and emission testing with a blend of the tallow-derived HRJ and 16% bio-derived aromatic components was completed. Fundamental engine performance characterization allows for determination of the suitability of potential synthetic fuels while quantitation of gaseous and particulate matter emissions provides an assessment of the potential environmental impact compared to current petroleum-derived fuels. In addition, an extended 150 h endurance test was performed using a 50/50 blend of tallow-derived HRJ with JP-8 to evaluate the long-term operation of the engine with the synthetic fuel blend. This paper discusses the laboratory testing performed to characterize HRJs and results from the basic engine operability and emissions studies of the alternative fuel blends.

Probing emissions of military cargo aircraft: description of a joint field measurement Strategic Environmental Research and Development Program.

Abstract To develop effective air quality control strategies for military air bases, there is a need to accurately quantify these emissions. In support of the Strategic Environmental Research and Development Program project, the particulate matter (PM) and gaseous emissions from two T56 engines on a parked C-130 aircraft were characterized at the Kentucky Air National Guard base in Louisville, KY. Conventional and research-grade instrumentation and methodology were used in the field campaign during the first week of October 2005. Particulate emissions were sampled at the engine exit plane and at 15 m downstream. In addition, remote sensing of the gaseous species was performed via spectroscopic techniques at 5 and 15 m downstream of the engine exit. It was found that PM mass and number concentrations measured at 15-m downstream locations, after dilution-correction generally agreed well with those measured at the engine exhaust plane; however, higher variations were observed in the far-field after natural dilution of the downstream measurements was accounted for. Using carbon dioxide-normalized data we demonstrated that gas species measurements by extractive and remote sensing techniques agreed reasonably well.

Characterization of Particulate Matter and Gaseous Emissions of a C-130H Aircraft

Abstract The gaseous and nonvolatile particulate matter (PM) emissions of two T56-A-15 turboprop engines of a C-130H aircraft stationed at the 123rd Airlift Wing in the Kentucky Air National Guard were characterized. The emissions campaign supports the Strategic Environmental Research and Development Program (SERDP) project WP-1401 to determine emissions factors from military aircraft. The purpose of the project is to develop a comprehensive emissions measurement program using both conventional and advanced techniques to determine emissions factors of pollutants, and to investigate the spatial and temporal evolutions of the exhaust plumes from fixed and rotating wing military aircraft. Standard practices for the measurement of gaseous emissions from aircraft have been well established; however, there is no certified methodology for the measurement of aircraft PM emissions. In this study, several conventional instruments were used to physically characterize and quantify the PM emissions from the two turboprop engines. Emissions samples were extracted from the engine exit plane and transported to the analytical instrumentation via heated lines. Multiple sampling probes were used to assess the spatial variation and obtain a representative average of the engine emissions. Particle concentrations, size distributions, and mass emissions were measured using commercially available aerosol instruments. Engine smoke numbers were determined using established Society of Automotive Engineers (SAE) practices, and gaseous species were quantified via a Fourier-transform infrared-based gas analyzer. The engines were tested at five power settings, from idle to take-off power, to cover a wide range of operating conditions. Average corrected particle numbers (PNs) of (6.4–14.3) × 107 particles per cm3 and PN emission indices (EI) from 3.5 × 1015 to 10.0 × 1015 particles per kg-fuel were observed. The highest PN EI were observed for the idle power conditions. The mean particle diameter varied between 50 nm at idle to 70 nm at maximum engine power. PM mass EI ranged from 1.6 to 3.5 g/kg-fuel for the conditions tested, which are in agreement with previous T56 engine measurements using other techniques. Additional PM data, smoke numbers, and gaseous emissions will be presented and discussed.

Influence of Fuel Chemical Composition on Particulate Matter Emissions of a Turbine Engine

The effects of fuel chemical composition on particulate matter (PM) emissions of a T63 engine were investigated. Fuels with different aromatic, cycloparaffin (naphthene), iso-paraffin and normal paraffin levels were evaluated in the turboshaft engine and compared to the performance of a typical JP-8 fuel. The fuels studied include: a semi-synthetic jet fuel, two high naphthenic experimental fuels, three Exxon solvents (Isopar M, Isopar H and Norpar-13) and methylcyclohexane. The effect of blending solvents in JP-8 on PM emissions was also assessed. Commercially available particulate instruments were used to measure particle number density, particulate mass concentration and particle size distribution. Results showed a general trend of higher particulate concentrations and larger diameter soot particles with decreasing fuel hydrogen-to-carbon (H/C) ratio or increasing aromatic content. However, for several fuels with approximately the same H/C ratio, significant differences in PND and calculated mass were observed. Furthermore, blends of JP-8 with solvents of similar H/C ratio but varying chemical composition produced significantly different particulate emissions. These findings demonstrate that particulate emissions from hydrocarbon-fueled combustion processes are not solely a function of the H/C ratio or aromatic concentration of the fuel, but that other properties or constituents also impact soot emissions. Chemical and physical properties of the fuels and their potential effect on particulate emissions are discussed. These findings provide insight into fuel properties that impact PM emissions, which may aid in the development of fuel additives to reduce particulate emissions from turbine engine combustors.Copyright

Development of methodologies for identification and quantification of hazardous air pollutants from turbine engine emissions.

Aircraft turbine engines are a significant source of particulate matter (PM) and gaseous emissions in the vicinity of airports and military installations. Hazardous air pollutants (HAPs) (e.g., formaldehyde, benzene, naphthalene and other compounds) associated with aircraft emissions are an environmental concern both in flight and at ground level. Therefore, effective sampling, identification, and accurate measurement of these trace species are important to assess their environmental impact. This effort evaluates two established ambient air sampling and analysis methods, U.S. Environmental Protection Agency (EPA) Method TO-11A and National Institute for Occupational Safety and Health (NIOSH) Method 1501, for potential use to quantify HAPs from aircraft turbine engines. The techniques were used to perform analysis of the exhaust from a T63 turboshaft engine, and were examined using certified gas standards transferred through the heated sampling systems used for engine exhaust gaseous emissions measurements. Test results show that the EPA Method TO-11A (for aldehydes) and NIOSH Method 1501 (for semivolatile hydrocarbons) were effective techniques for the sampling and analysis of most HAPs of interest. Both methods showed reasonable extraction efficiencies of HAP species from the sorbent tubes, with the exception of acrolein, styrene, and phenol, which were not well quantified. Formaldehyde measurements using dinitrophenylhydrazine (DNPH) tubes (EPA method TO-11A) were accurate for gas-phase standards, and compared favorably to measurements using gas-phase Fourier-transform infrared (FTIR) spectroscopy. In general, these two standard methodologies proved to be suitable techniques for field measurement of turbine engine HAPs within a reasonable (5–10 minutes) sampling period. Details of the tests, the analysis methods, calibration procedures, and results from the gas standards and T63 engine tested using a conventional JP-8 jet fuel are provided. Implications: HAPs from aviation-related sources are important because of their adverse health and environmental impacts in and around airports and flight lines. Simpler, more convenient techniques to measure the important HAPs, especially aldehydes and volatile organic HAPs, are needed to provide information about their occurrence and assist in the development of engines that emit fewer harmful emissions.

Comparisons of Emissions Characteristics of Several Turbine Engines Burning Fischer-Tropsch and Hydroprocessed Esters and Fatty Acids Alternative Jet Fuels

A summary of the impacts of alternative fuel blends on the gaseous and particulate matter (PM) (mostly soot) emissions of aircraft turbine engines is presented. Six engines were studied under several US Air Force and NASA sponsored programs to assess the impacts of the alternative (non-petroleum) fuels on emissions and/or to support the certification of military aircraft for the use of 50/50 (by volume) alternative fuel/JP-8 blends. One turboshaft (T63) and five turbofan (CFM56-7, CFM56-2, F117, TF33 and PW308) engines were studied. Fuels derived from coal and natural gas produced via Fischer-Tropsch (FT) synthesis, and fuels from animal fats and plant oils produced via hydroprocessing [Hydroprocessed Esters and Fatty Acids (HEFA)] were evaluated. Trends of alternative fuel impacts on emissions compared to conventional fuel for the different engine types are discussed. Results consistently show significant reductions in PM emissions with the alternative fuel blends compared to operation with conventional fuels. These relative reductions were observed to be lower as engine power increased. Engines operated with different alternative fuel blends were found to produce similar slopes of normalized particle number to engine power with only the magnitude of the reductions being a function of the fuel type. These results suggest that it may be plausible to predict particle number emissions from turbine engines operated on alternative fuels based on engine, engine setting, limited PM data and fuel composition. Gaseous emissions measurements show modest reductions of carbon monoxide, unburned hydrocarbons and hazardous air pollutants (HAPs) with the alternative fuels for several engines; however, no clear dependency of fuel impacts based on engine characteristics were observed.Copyright

Emissions Characteristics of a Legacy Military Aircraft

Emissions from aircraft and associated ground equipment are major sources of local pollution at airports and military bases. These pollutant emissions, especially particulate matter (PM), have been receiving significant attention lately due to their proven harmful health and environmental effects. As the U.S. Environmental Protection Agency (EPA) tightens environmental standards, it is likely that military operations, including the basing of advanced and legacy aircraft, will be impacted. Accurate determination of emission indices from aircraft is necessary to properly assess their environmental burden. As such, the gaseous and PM emissions of a B-52 Stratofortress aircraft were characterized in this effort. This emissions study supports the Strategic Environmental Research and Development Program (SERDP) project WP-1401 to determine emissions factors from military aircraft. The main purpose of the project is to develop a comprehensive emissions measurement program using both conventional and advanced techniques to determine emissions factors for pollutants of fixed and rotating wing military aircraft. Standard practices for the measurement of gaseous emissions from aircraft have been well established; however, there is no certified methodology for the measurement of aircraft PM emissions. In this study, several conventional aerosol instruments were employed to physically characterize the PM emissions from two of the aircraft’s TF33 turbofan engines. Exit plane pollutant emissions were extracted via probes and transported through heated lines to the analytical instruments. Particle concentrations, size distributions and mass emissions, as well as engine smoke numbers (SN), soot volatile fraction and total hydrocarbon emissions were measured. The engines were tested at four power settings, from idle to 75% normal rated thrust (NRT) (95% N2 – turbine speed). Test results show relatively consistent PM and gaseous emissions between the two engines for most conditions tested. The measured TF33 PM mass emission indices (EI), including estimated sampling line losses, were in the range of 1.0–3.0 g/kg-fuel and the particle number (PN) EI were between 4.0–10.0E+15 particles/kg-fuel. The particle size data followed a single mode lognormal distribution for all power settings with particle geometric mean diameters ranging from 52 to 85 nm. In general, the aerosol instrumentation provided consistent and reliable measurements throughout the test campaign, therefore increasing confidence on their use for turbine engine PM emissions measurements.Copyright