Aviation/jet fuel handling: The Water Separometer Index, Modified (WSIM) reported for a petrofuel primarily indicates which behaviour?

Introduction:
Water management is critical for aviation turbine fuel and other light distillates. The Water Separometer Index, Modified (WSIM) is a standard test result used to indicate how well a fuel will shed dispersed water when passed through coalescer/separator elements.

Given Data / Assumptions:

• Fuel contains trace surfactants and additives that can affect water coalescence.
• WSIM is not a direct ppm water measurement but a performance index.
• Higher WSIM generally indicates better water separation.

Concept / Approach:
WSIM represents the fuel’s ability to release water in a filter-separator. Surfactants and certain additives can stabilise water-in-fuel emulsions, decreasing coalescence and lowering WSIM. Thus, WSIM is used operationally to judge whether a fuel will separate water efficiently through airport filtration systems.

Step-by-Step Solution:

Verification / Alternative check:
Fuel quality manuals use WSIM as a gate for acceptability before aircraft fuelling; poor WSIM prompts additional treatment or filtration.

Why Other Options Are Wrong:

• Emulsification tendency only: Related but WSIM covers separation performance through coalescers.
• Water content: Determined by Karl Fischer or other methods, not WSIM.
• Absorbing capacity/Cloud point: Different properties/tests entirely.

Common Pitfalls:
Assuming WSIM equals water content; it is a separability index.

Final Answer:
Water separation characteristics (coalescence through filters)