Aviation turbine fuel (ATF) quality: Why are large quantities of polynuclear aromatics undesirable in aviation fuel (kerosene range)?

Introduction:
Aviation turbine fuels (jet kerosenes) must meet stringent low-temperature flow and combustor smokiness limits. Fuel composition, particularly the level of polynuclear aromatics (PNAs), strongly influences these properties.

Given Data / Assumptions:

• Fuel: kerosene-range aviation turbine fuel (e.g., Jet A/ATF).
• Property targets: low freeze/pour point, adequate smoke point, good thermal stability.

Concept / Approach:
PNAs are heavy aromatic species with higher melting points and strong sooting tendencies. Elevated PNA content raises pour/freezing points (worsening cold flow) and lowers smoke point (more soot formation). While viscosity index is more relevant for lubricants, and autoignition temperature is not the limiting concern for turbine combustors, the pour/smoke impacts are the key drawbacks of high PNA content.

Step-by-Step Solution:

Verification / Alternative check:
ATF specifications (e.g., smoke point minimums) correlate performance detriment with higher heavy aromatics content.

Why Other Options Are Wrong:

• Low viscosity index: Not the central specification for ATF; viscosity-temperature profile is specified differently.
• High self-ignition temperature: Not a cited disadvantage; combustors operate with continuous ignition.
• All (a), (b), (c): Overbroad; only (a) correctly captures the key issues.
• Higher density benefit: Not asked; density effects do not offset pour/smoke penalties.

Common Pitfalls:
Applying lube-oil concepts (viscosity index) to jet fuel specifications; conflating engine knock concepts with turbine combustion.

Final Answer:
High pour point and low smoke point