John Kinsey

Presented here is an overview of nonvolatile particulate matter (nvPM) emissions, i.e., “soot”, as assessed by TEM analyses of samples collected after the exhaust of a J-85 turbojet fueled with Jet-A as well as with blends of Jet-A and Camelina biofuel. A unifying explanation is provided to illustrate the combustion dynamics of biofuel and Jet-A fuel. The variations of primary particle size, aggregate size, and nanostructure are analyzed as a function of biofuel blend across a range of engine thrust levels. The postulate is based on where fuels start along the soot formation pathway. Increasing biofuel content lowers aromatic concentration while placing increasing dependence upon fuel pyrolysis reactions to form the requisite concentration of aromatics for particle inception and growth. The required “kinetic” time for pyrolysis reactions to produce benzene and multiring PAHs allows increased fuel–air mixing by turbulence, diluting the fuel-rich soot-forming regions, effectively lowering their equivalence ratio. With a lower precursor concentration, particle inception is slowed, the resulting concentration of primary particles is lowered, and smaller aggregates were measured. The lower equivalence ratio also results in smaller primary particles because of the lower concentration of growth species.

Biomass pellets are a source of renewable energy; although, the air pollution and exposure risks posed by the emissions from burning pellets in biomass boilers (BBs) are uncertain. The present study examines the organic species in fine particle matter (PM) emissions from an BB firing switchgrass (SwG) and hardwood (HW) biomass pellets using different test cycles. The organic and elemental carbon (OC and EC) content and select semivolatile organic compounds (SVOCs) in filter-collected PM were identified and quantified using thermal-optical analysis and gas chromatography–mass spectrometry (GC–MS), respectively. Fine PM emissions from the BB ranged from 0.4 g/kg to 2.91 g/kg of pellets burned of which 40% ± 17% w/w was carbon. The sum of GC–MS quantified SVOCs in the PM emissions varied from 0.13 to 0.41 g/g OC. Relatively high levels of oxygenated compounds were observed in the PM emissions, and the most predominant individual SVOC constituent was levoglucosan (12.5–320 mg/g OC). The effect of boiler test cycle on emissions was generally greater than the effect due to pellet fuel type. Organic matter emissions increased at lower loads, owing to less than optimal combustion performance. Compared with other types of residential wood combustion studies, pellet burning in the current BB lowered PM emissions by nearly an order of magnitude. PM emitted from burning pellets in boilers tested across multiple studies also contains comparatively less carbon; however, the toxic polycyclic aromatic hydrocarbons (PAH) in the PM tested across these pellet-burning studies varied substantially, and produced 2–10 times more benzo[k]fluoranthene, dibenz[a,h]anthracene and indeno[1,2,3-c,d]pyrene on average. These results suggest that further toxicological evaluation of biomass pellet burning emissions is required to properly understand the risks posed.

The fine particulate matter (PM) emissions from the use of two types of Fischer–Tropsch aviation fuels and their 50:50 blends with military JP-8 were quantified as part of the first Alternative Aviation Fuel Experiment (AAFEX). Measurements were made 30-m downstream of a CFM56-2C1 engine for PM mass and number, particle size distribution, black carbon (BC), and volatile PM (sulfate + organics) using selected online instrumentation. The PM number emission index (EI_N) ranged from ∼2 × 10¹⁵ to 7 × 10¹⁶ particles/kg fuel burned depending on fuel flow, fuel composition, and sampling temperature with the magnitude of the emissions inversely correlated to fuel flow. The PM mass emissions (EI_M) measured in the study varied from ∼5 to 680 mg/kg fuel, again depending on fuel flow, fuel type, and sampling temperature with a characteristic U-shaped curve of EI_M with respect to fuel flow observed from the data. At low fuel flow (corresponding to low engine power), particle number and volume size distributions contained a single mode, whereas at higher engine power, a bimodal distribution was observed. The BC emissions varied from ∼3 to 415 mg/kg fuel depending on fuel type and were found to exponentially increase with engine power (fuel flow). The volatile PM varied with sample temperature, fuel type, and increasing fuel flow within the range of EIs from ∼0.4 to 11 mg/kg fuel with the highest values being at low fuel flow. Finally, the use of the two neat alternative fuels reduced the EI_N by a median value of 70–73% and the EI_M by ∼94% as compared to JP-8 across all power conditions tested.

Emission measurements of black carbon (BC) mass were conducted on a T63 turboshaft engine, operated at idle and cruise power with conventional and alternative fuels, using an Artium LII-300 laser induced incandescence (LII) analyzer and AVL Model 483 Micro Soot Sensor (MSS) photoacoustic instrument using the manufacturer’s calibration for both instruments. These measurements were compared to elemental carbon (EC) determined by manual and semi-continuous thermal-optical transmission analyses according to National Institute for Occupational Safety and Health (NIOSH) Method 5040 as the reference method. The results indicate that both the LII and MSS instruments show good linear correlation to NIOSH EC for the two fuels and two engine power conditions evaluated. The LII measurements were observed to be biased high (27- 49%), while the MSS measurements were biased low (24 - 35%) relative to the NIOSH EC. The agreement between the instruments and the reference method was substantially improved by applying a calibration of the instruments against a common BC aerosol source. Test data also suggest that the two instruments show some sensitivity to particle size (or properties related to size), specifically for particles with a geometric mean diameter (GMD) < 30 nm. This sensitivity is problematic since new engines or certain combustion conditions in current engines will produce smaller particles compared to the T63 model tested in this study. Further assessments of instrument performance for particles within this size range are therefore warranted.

The emissions from a Garrett-AiResearch (now Honeywell) Model GTCP85–98CK auxiliary power unit (APU) were determined as part of the National Aeronautics and Space Administration's (NASA's) Alternative Aviation Fuel Experiment (AAFEX) using both JP-8 and a coal-derived Fischer Tropsch fuel (FT-2). Measurements were conducted by multiple research organizations for sulfur dioxide (SO₂), total hydrocarbons (THC), carbon monoxide (CO), carbon dioxide (CO₂), nitrogen oxides (NO_x), speciated gas-phase emissions, particulate matter (PM) mass and number, black carbon, and speciated PM. In addition, particle size distribution (PSD), number-based geometric mean particle diameter (GMD), and smoke number were also determined from the data collected. The results of the research showed PM mass emission indices (EIs) in the range of 20 to 700 mg/kg fuel and PM number EIs ranging from 0.5 × 10¹⁵ to 5 × 10¹⁵ particles/kg fuel depending on engine load and fuel type. In addition, significant reductions in both the SO₂ and PM EIs were observed for the use of the FT fuel. These reductions were on the order of ∼90% for SO₂ and particle mass EIs and ∼60% for the particle number EI, with similar decreases observed for black carbon. Also, the size of the particles generated by JP-8 combustion are noticeably larger than those emitted by the APU burning the FT fuel with the geometric mean diameters ranging from 20 to 50 nm depending on engine load and fuel type. Finally, both particle-bound sulfate and organics were reduced during FT-2 combustion. The PM sulfate was reduced by nearly 100% due to lack of sulfur in the fuel, with the PM organics reduced by a factor of ∼5 as compared with JP-8.

The primary objective of this study was development of an EPA approved interim particulate matter (PM) test method for non-volatile PM that can be applied at the engine exit plane of military turbine engines. New particle (volatile) formation and condensation can occur in the sampling line as the sample gas temperature is lowered through interaction with the cooler sample line walls. A sampling process is defined by which non-volatile PM can be measured accurately by eliminating or accounting for the interference of new particle formation and condensation. A ground-level engine test campaign (Methodology Development Test) was conducted on an F100-220 military gas turbine engine in 2007 to experimentally investigate issues with sampling, instrument comparisons, instrument calibrations, sample line penetration and engine data representativeness. The test measurement protocol was demonstrated during the Validation Test in late 2009 using a different F100-220 engine and the diagnostics, probe-rake system, and sampling system developed for JSF applications.

This paper addresses the need for detailed chemical information on the fine particulate matter (PM) generated by commercial aviation engines. The exhaust plumes of seven turbofan engine models were sampled as part of the three test campaigns of the Aircraft Particle Emissions eXperiment (APEX). In these experiments, continuous measurements of black carbon (BC) and particle surface-bound polycyclic aromatic compounds (PAHs) were conducted. In addition, time-integrated sampling was performed for bulk elemental composition, water-soluble ions, organic and elemental carbon (OC and EC), and trace semivolatile organic compounds (SVOCs). The continuous BC and PAH monitoring showed a characteristic U-shaped curve of the emission index (EI or mass of pollutant/mass of fuel burned) vs fuel flow for the turbofan engines tested. The time-integrated EIs for both elemental composition and water-soluble ions were heavily dominated by sulfur and SO₄^2-, respectively, with a ∼2.4% median conversion of fuel S(IV) to particle S(VI). The corrected OC and EC emission indices obtained in this study ranged from 37 to 83 mg/kg and 21 to 275 mg/kg, respectively, with the EC/OC ratio ranging from ∼0.3 to 7 depending on engine type and test conditions. Finally, the particle SVOC EIs varied by as much as 2 orders of magnitude with distinct variations in chemical composition observed for different engine types and operating conditions.