Characterization of Gaseous and Particulate Emissions From a Turboshaft Engine Burning Conventional, Alternative, and Surrogate Fuels

Abstract

The effect of fuel composition on the operability and gaseous and particulate matter (PM) emissions of an Allison T63-A-700 turboshaft engine operated at four power settings was investigated in this effort. Testing was performed with a specification JP-8, a synthetic paraffinic kerosene, and four two-component surrogate mixtures that comprise compound classes within current and future alternative fuels. Comparable engine operability was observed for all fuels during this study. Major gaseous emissions were only slightly effected, with trends consistent with those expected based on the overall hydrogen content of the fuels. However, minor hydrocarbon and aldehyde emissions were significantly more sensitive to the fuel chemical composition. Linear correlations between speciated hydrocarbon and aldehyde emissions were observed over the full engine operating range for the fuels tested. The corresponding slopes were dependent on the fuel composition, indicating that fuel chemistry affects the selectivity to specific decomposition pathways. Unburned fuel components were observed in the engine exhaust during operation with all fuels, demonstrating that completely unreacted fuel compounds can pass through the high temperature/pressure combustion zone. Nonvolatile PM emissions (soot) were strongly affected by the fuel chemical composition. Paraffinic fuels produced significantly lower PM number and mass emissions relative to aromatic-containing fuels, with the paraffin structure affecting sooting propensity. The observations are consistent with those expected based on simplified soot formation mechanisms, where fuels with direct precursors for polycyclic aromatic hydrocarbon formation have higher PM formation rates. The effect of a specific chemical structure on the relative PM production is important as this would not be evident when comparing sooting tendencies of fuels based on bulk fuel properties. All fuels produced similar single log-normal size distributions of soot, with higher sooting fuels producing larger mean diameter particles. It is hypothesized that the controlling growth and formation mechanisms for PM production are similar for different fuel chemistries in this regime, with composition primarily affecting soot formation rate. This hypothesis was supported by preliminary TEM analyses that showed similar soot microstructures during operation with either conventional JP-8 or alternative fuels. Overall, this study provides additional and improved insight into the effect of fuel chemical composition on complex combustion chemistry and emissions propensity in a gas turbine engine, and can assist with the successful development of predictive modeling tools.

Evaluation of Non-volatile Particulate Matter Emission Characteristics of an Aircraft Auxiliary Power Unit with Varying Alternative Jet Fuel Blend Ratios

“…In all cases, the size distributions were observed to be lognormal, and the geometric mean diameter (GMD) varied from 22.5nm to 49nm and the geometric standard deviation (GSD) ranged 1.58 -1.99. These results are consistent with those reported for other gas turbine engines burning conventional and alternative fuels [8,13,23,30,31]. For the three APU operating conditions, GMD decreased linearly with increasing fuel hydrogen content.…”

“…The reduction in EIm is greater than EIn for the corresponding fuel hydrogen content. This trend has also been observed for larger gas turbine engines at high thrust conditions [8,14] and a turboshaft engine [13] For a 50:50 blend of UCO-HEFA and Jet A-1, which would meet current ASTM specifications, the average reduction in nvPM number-based emissions was ~35%, while that for mass-based emissions was ~60%. However, the 2% and 5% UCO-HEFA fuel blend ratios are also of interest since they are representative of possible near to midterm 'real world' situation under a flightpath 2020 comingled supply scenario.…”

“…Studies investigating the emissions of aircraft engines burning either neat FT fuels or 50:50 blends of FT and HEFA fuels with conventional jet fuel have shown that non-volatile particulate matter (nvPM) and sulfur oxides are dramatically reduced [8,[11][12][13][14][15]. However, the systematic evaluation of incremental variations in fuel composition of a single synthetic fuel on the production of nvPM emissions has not been explored.…”

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

“…Identification and quantification of unreacted fuel in turbine engine exhaust demonstrates that fuel-rich pockets can survive the high pressure and temperature combustion zone without reaction. Unreacted fuel constituents have been observed in the exhaust of the aforementioned T63 engine, and during recent testing from higher-efficiency turbine engines (CFM56 and F117) (Cain et al, 2013). The measurement and quantitation of the unreacted fuel make up a relatively simple analysis that can be performed directly using a flame ionization detector (FID).…”

Aircraft engine exhaust emissions and other airport-related contributions to ambient air pollution: A review

“…The aviation industry is nowadays investing significant effort towards the use of alternative fuels (Blakey et al, 2011;Williams et al, 2012). Since aircraft emissions are recognised to be closely linked to the fuel composition (Beyersdorf et al, 2013 and reference therein), recently the introduction of synthetic fuels and bio-fuels instead of common oil-derivate jet fuels has been much discussed in terms of beneficial effects upon exhaust emissions (e.g., Corporan et al, 2005Corporan et al, , 2007DeWitt et al, 2008;Timko et al, 2010a;Corporan et al, 2011;Lobo et al, 2011;Williams et al, 2012;Cain et al, 2013). Among others, the FischereTropsch (FT) fuel seems to be a potential candidate for replacing, or mixing with, oil-derived conventional jet fuels.…”