Characterization of Fuel Composition and Altitude Impact on Gaseous and Particle Emissions From a Turbojet Engine

Abstract

The effects of altitude and fuel composition on gaseous and particle emissions from a turbojet engine were investigated as part of the National Jet Fuels Combustion Program (NJFCP) effort. Two conventional petroleum based jet fuels (a “nominal” and a “worst-case” jet fuel) and two test fuels with unique characteristics were selected for this study. The “worst-case” conventional jet fuel with high flash point and viscosity resulted in reduced combustion efficiency supported by the reduced CO2 emissions and corresponding increased CO and THC emissions. In addition, increased particle number (PN), particle mass (PM), and black carbon (BC) emissions were observed. Operating the engine on a bimodal fuel, composed of heavily branched C12 and C16 iso-paraffinic hydrocarbons with an extremely low cetane number did not significantly impact the engine performance or gaseous emissions but significantly reduced PN, PM, and BC emissions when compared to other fuels. The higher aromatic content and lower hydrogen content in the C-5 fuel were observed to increase PN, PM, and BC emissions. It is also evident that the type of aromatic hydrocarbons has a large impact on BC emissions. Reduction in combustion efficiency resulted in reduced CO2 emissions and increased CO and THC emissions from this engine with increasing altitudes. PN emissions were moderately influenced by altitude but PM and BC emissions were significantly reduced with increasing altitude. The reduced BC emissions with increasing altitude could be a result of reduced combustion temperature which lowered the rate of pyrolysis for BC formation, which is supported by the NOx reduction trend.

Comparison of Particle Number Emissions from In-Flight Aircraft Fueled with Jet A1, JP-5 and an Alcohol-to-Jet Fuel Blend

“…A decrease in aromatic content typically causes the hydrogen content to increase which would also affect the nonvolatile particle number emissions . In a lab experiment, Chan et al found that the fuel hydrogen content provided the best correlation with black carbon emission indices . Although both hydrogen and aromatic content affect particle number emissions, they are interdependent (decreasing aromatic content tends to increase the hydrogen/carbon ratio) and therefore it is difficult to credit either one as the main reason for the reduction in particles with the ATJ-SPK blend …”

“…14 In a lab experiment, Chan et al found that the fuel hydrogen content provided the best correlation with black carbon emission indices. 32 Although both hydrogen and aromatic content affect particle number emissions, they are interdependent (decreasing aromatic content tends to increase the hydrogen/carbon ratio) 14 and therefore it is difficult to credit either one as the main reason for the reduction in particles with the ATJ-SPK blend. 12 Also shown in Figure 2, it can be seen that the JP-5 fuel emissions are comparable to Jet A1 fuel.…”

Characterization of Particle Emissions from a DGEN 380 Small Turbofan Fueled with ATJ Blends

“…In addition, it should be considered that increasing the proportion of hydrogen in the fuel also reduces the formation of particulate matter in the soot mode. Reducing the share of aromatics results in an increase in the H/C ratio, therefore it is difficult to say what influences the PM emission to a greater extent [30,46,47].…”

Design and Characterization of a Flame Spray Pyrolysis Apparatus to Compare Soot Emissions from Liquid Fuels

“…For this study, three different liquid aviation fuels were used: Jet A1 (POSF10325), Gevo ATJ (POSF11498), and a custom fuel that will be referred to as "C10" (POSF12345) due to its 74% composition of C10 iso-paraffins. As of 2021, Jet A1 is the only fuel cleared to be used in commercial aircraft [10], but the ATJ and C10 fuels are currently being used by the National Jet Fuels Combustion Program (NJFCP) as potential SAFs for future commercial use [54]. For this study, Jet A1 was chosen as a benchmark fuel, the ATJ was chosen as it is an approved biojet fuel for mixture with Jet A1 and operated on noncommercial flights, and the C10 was chosen because of its high aromatic content.…”

“…Mixing between the two flows takes place and the collected sample is diluted. .... 25 Figure 2.5: Alkane and aromatic mass percent composition of the three test fuels [54]. .…”