Diesel Additive Low-Temperature Flow Improver Testing

Low-temperature flow improvers, also known as cold flow improvers (CFIs), are polymeric diesel fuel additives that modify wax crystallization to keep diesel engines and fuel systems operable in cold climates. Professional testing by accredited third-party laboratories verifies additive effectiveness through cold filter plugging point (CFPP), cloud point, pour point, and low-temperature flow performance evaluations in accordance with standards such as EN 116, ASTM D6371, ASTM D4539, and ISO 3016. Comprehensive testing supports additive manufacturers, refineries, and fuel distributors in product development, quality control, and regulatory compliance.

Technical Overview

Low-temperature flow improvers are specialty diesel fuel additives designed to control the crystallization behavior of normal paraffins (n-alkanes) as ambient temperature decreases. Diesel fuel typically contains 10–25% straight-chain paraffins, which provide excellent cetane quality but precipitate as wax crystals when the fuel cools below its cloud point. These wax crystals grow, agglomerate, and settle, ultimately plugging fuel filters, lines, and injection system components, resulting in engine stall or failure to start.

Cold flow improvers work through several complementary mechanisms: modifying wax crystal morphology so that crystals remain small and pass through filters, co-crystallizing with paraffins to arrest crystal growth, dispersing wax particles, and reducing wax settling during static cold storage. Common chemistries include ethylene-vinyl acetate (EVA) copolymers, poly(alkyl methacrylate) esters, maleic anhydride–olefin comb copolymers, and nitrogen-containing wax anti-settling additives (WASA).

Testing of low-temperature flow improvers evaluates both the performance effect of the additive on diesel fuel—typically expressed as CFPP depression, pour point depression, and low-temperature flow improvement relative to an untreated base fuel—and the physicochemical quality of the additive concentrate itself. Accredited third-party laboratories conduct this testing using internationally recognized methods to substantiate product claims, support formulation development, and demonstrate compliance with finished fuel specifications such as EN 590, GB 19147, and ASTM D975.

Testing Samples

Cold Flow Improver Additive Concentrates

Neat additive products submitted in their commercial concentrate form for physicochemical characterization, composition fingerprinting, and quality verification prior to performance evaluation.

Reference Base Diesel Fuel

A well-characterized, unadditized diesel fuel sample that serves as the untreated baseline against which all cold-flow improvements are measured. Standardized reference fuels may also be used for comparability.

Treated Diesel Fuel Blends

Base diesel fuel dosed with the flow improver at specified treat rates, typically ranging from 50 to 1,000 ppm (v/v), prepared under controlled conditions and homogenized before testing.

Commercial Finished Diesel Grades

Market diesel samples, including ultra-low-sulfur diesel and FAME-blended diesel (e.g., B7), tested to verify winter operability and conformance to seasonal cold-flow requirements.

Testing Items

Low-Temperature Performance Evaluation

• Cold filter plugging point (CFPP) and CFPP depression relative to base fuel
• Cloud point and cloud point change
• Pour point and pour point depression
• Low-temperature flow test (LTFT) performance at target temperatures
• Wax appearance temperature (WAT) and wax appearance point
• Wax anti-settling performance after extended cold storage
• Filter blocking tendency and low-temperature filterability
• Treat-rate response curves across multiple dosage levels

Physicochemical Properties of the Additive Concentrate

• Appearance, homogeneity, and phase stability
• Density at 15°C
• Kinematic viscosity at 40°C
• Flash point (closed cup)
• Water content (Karl Fischer titration)
• Total acid number or base number
• Sulfated ash content
• Nitrogen content
• FTIR spectroscopic composition fingerprint and polymer identification

Fuel Quality Verification After Treatment

• Distillation curve (recovery at 95% point)
• Lubricity via high-frequency reciprocating rig (HFRR) wear scar diameter
• Sulfur content
• Copper strip corrosion
• Oxidation and high-temperature storage stability
• Compatibility with lubricity improvers, cetane improvers, and detergent additives

Testing Methods

Cold Filter Plugging Point

CFPP is the primary indicator of cold-flow additive performance and is determined in accordance with EN 116, ASTM D6371, IP 309, and SH/T 0248. The fuel is cooled at a controlled rate while suction is applied through a standardized 45-micron screen filter; the CFPP is the highest temperature at which 20 mL of fuel fails to pass within a specified time. Specimens are preheated to erase thermal history and avoid wax memory effects.

Cloud Point

Cloud point, the temperature at which wax crystals first become visible, is measured using ASTM D2500 (manual), ASTM D5771, ASTM D5772, and ASTM D5773 (optical automatic methods), ASTM D7397 (miniaturized method), ISO 3015, and GB/T 6986. Because flow improvers modify crystal growth rather than nucleation, cloud point is often largely unchanged, so this parameter mainly confirms that the additive has not worsened the wax onset.

Pour Point

Pour point, the lowest temperature at which fuel continues to flow, is determined by ASTM D97, ISO 3016, and GB/T 3535, with automatic pressure, tilt, and air-pressure techniques available under ASTM D5949, ASTM D5950, and ASTM D6749. Effective flow improvers typically depress pour point by 10–30°C.

Low-Temperature Flow Test

ASTM D4539 (LTFT) provides a more realistic assessment of vehicle operability by cooling fuel at 1°C per hour while drawing samples through a 17-micron screen. LTFT correlates well with field performance and is frequently used for North American winter diesel qualification.

Wax Appearance and Settling Evaluation

Wax appearance temperature is assessed by ASTM D3117, differential scanning calorimetry (DSC), and cross-polarized microscopy. Wax anti-settling performance is evaluated through extended cold-storage protocols in which CFPP and wax content of the upper and lower fuel layers are compared after static holding at low temperature.

Supporting Analytical Methods

• Density: ASTM D4052
• Kinematic viscosity: ASTM D445
• Flash point: ASTM D93
• Water content: ASTM D95 and ASTM D6304
• Acid number: ASTM D664
• Sulfated ash: ASTM D874
• Nitrogen: ASTM D4629
• Distillation: ASTM D86 and GB/T 6536
• Lubricity: ASTM D6079, ISO 12156-1, and SH/T 0765
• Sulfur: ASTM D5453
• Copper strip corrosion: ASTM D130
• Oxidation stability: ASTM D2274 and ASTM D6468
• Filter blocking tendency: ASTM D2068

Applications

Testing services for diesel low-temperature flow improvers support multiple industry needs across the fuel and additive value chain.

• Research and development of new polymer chemistries, copolymer ratios, and additive package formulations
• Quality control and batch release testing for additive manufacturers
• Treat-rate optimization and response-curve development for specific crude slates and refinery blends
• Winter diesel program qualification at refineries and fuel terminals
• Compliance verification against EN 590 seasonal CFPP classes, GB 19147 regional cold-flow grades, and customer specifications
• Substantiation of marketing claims and cold-flow performance labels for retail diesel additives
• Fleet winterization programs and troubleshooting of field filter-plugging incidents
• Import and export conformity assessment for additive and fuel trade

FAQ

What is the difference between cloud point, CFPP, and pour point?

Cloud point is the temperature at which the first wax crystals appear, CFPP is the lowest temperature at which fuel still passes through a standardized filter, and pour point is the lowest temperature at which fuel continues to pour. CFPP is generally considered the most relevant indicator of real-world filter operability, and it is the parameter most effectively improved by flow improver additives.

Do cold flow improvers lower the cloud point?

In most cases, no. Flow improvers act on wax crystal growth, morphology, and dispersion rather than on the onset of crystallization, so the cloud point typically remains within one to two degrees of the untreated fuel. Products claiming significant cloud point reduction require dedicated wax crystal modifier chemistry and separate verification.

How is additive performance quantified?

Performance is reported as the depression, in degrees Celsius, of CFPP, pour point, or LTFT temperature between the untreated base fuel and the treated fuel at a specified treat rate. Reputable laboratories test the base fuel in parallel and may establish response curves at multiple dosages, such as 100, 250, and 500 ppm, to characterize dose-dependent behavior.

What treat rates are typical for cold flow improvers?

Most commercial cold flow improvers are dosed between 100 and 1,000 ppm, with wax anti-settling components sometimes used at similar or higher levels. The optimal treat rate depends on fuel paraffin content, distillation profile, and the target CFPP specification, which is why treat-rate response testing is essential.

Can flow improvers be evaluated in biodiesel-blended fuel?

Yes. Testing can be performed on FAME-containing diesel such as B7, and it is recommended because FAME can interact with wax crystallization and alter additive response. Full fuel quality verification after treatment ensures the additive does not adversely affect lubricity, oxidation stability, or corrosion performance.

How much sample and time are required for testing?

A typical evaluation requires one to two liters of base diesel fuel and 100 to 250 mL of additive concentrate. Standard CFPP, cloud point, and pour point testing can usually be completed within a few working days, while complete packages including LTFT, anti-settling storage studies, and fuel quality verification may require two to four weeks.