Emulsified Water

Canonical Definition

Water dispersed in fuel or oil as microscopic droplets — typically 1–100 µm diameter — stabilised by surfactant-like fuel additives or degradation products, creating a stable emulsion that appears cloudy or milky. Unlike free water, emulsified water does not settle by gravity and cannot be removed by drain valves alone — coalescing filtration is required to force droplets together into larger drops that settle or drain. Emulsified water content in diesel fuel is measured by Karl Fischer titration (ASTM D6304/ISO 12937); concentrations above 100–200 ppm by mass accelerate filter plugging and HPCR injector corrosion.

Engineering Context

Modern ultra-low-sulphur diesel (ULSD) is less tolerant of water contamination than legacy high-sulphur diesel because ULSD contains fewer natural surfactants. Water entering ULSD through storage tank condensation or cross-contamination rapidly forms fine, stable emulsions that pass through conventional filter media without separation. Coalescing filter technology — HYDROCORE and TURBOCORE three-stage systems — is specifically engineered to break and remove ULSD emulsions before fuel contacts HPCR injection components rated to tolerances of 1–3 µm and clearances of 1–2 µm.

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