💧 Kinematic Viscosity
Determination of kinematic viscosity of petroleum products using glass capillary viscometer at 40°C and 100°C. Fundamental parameter for oil and fuel classification.
Overview
Kinematic viscosity is a measure of a liquid's resistance to flow under gravity. Expressed in mm²/s (centistokes, cSt), it is one of the most important quality parameters of petroleum products. Classification of lubricating oils SAE, industrial oils ISO VG and fuels is based precisely on kinematic viscosity.
The method involves measuring the time for a defined volume of liquid to flow through a calibrated glass capillary viscometer under gravity at strictly controlled temperature. Kinematic viscosity is calculated as the product of measured flow time and viscometer calibration constant. Measurement is performed standardly at 40°C (for industrial oils) and 100°C (for engine oils, SAE classification).
Excessively high diesel fuel viscosity impedes flow through filters and injectors, reducing engine power. Too low viscosity causes insufficient lubrication of fuel system components. For lubricating oils, viscosity determines oil film thickness, low-temperature pumpability and energy efficiency of machinery. Monitoring oil viscosity in service allows detection of fuel contamination, oxidation or thermal degradation.
The viscosity range covered by the standard is from 0.2 to 300,000 mm²/s at temperatures from -20°C to +150°C. The method includes two procedures: A — with manual glass viscometers, B — with automatic viscometer systems.
Method principle
A calibrated glass capillary viscometer is placed in a thermostatic bath with stability ±0.02°C. After thermal equilibrium is achieved, the sample is aspirated/filled above the upper measurement mark of the viscometer. The time for the liquid meniscus to flow between two measurement marks is measured. Kinematic viscosity is calculated from the formula: ν = C × t, where C is the viscometer calibration constant (mm²/s²) and t is the flow time (s). Flow time should be minimum 200 seconds to ensure accuracy. Minimum two determinations are performed; results should not differ by more than the determinability value stated in the standard.
Applications
- Classification of engine oils per SAE J300 (viscosity at 40°C and 100°C)
- Classification of industrial oils per ISO 6743 (ISO VG grades)
- Quality control of diesel fuel (PN-EN 590: 2.0–4.5 mm²/s at 40°C)
- Monitoring condition of lubricating oils in service (tribology)
- Evaluation of base oils and additives
- Quality control of jet fuel (kerosene)
- Calculation of viscosity index (VI) per ISO 2909
- Testing of transformer and hydraulic oils
Key parameters
| Parameter | Value |
|---|---|
| Measurement range | 0.2–300 000 mm²/s (cSt) |
| Measurement temperature | -20°C to +150°C (typically 40°C and 100°C) |
| Bath stability | ±0.02°C |
| Minimum flow time | 200 s |
| Repeatability | ±0.35% of mean (for Newtonian liquids) |
| Reproducibility | ±0.70% of mean |
Standard
- Standard number
- PN-EN ISO 3104:2021
- Title (PL)
- Przetwory naftowe — Ciecze przezroczyste i nieprzezroczyste — Oznaczanie lepkości kinematycznej i obliczanie lepkości dynamicznej
- Title (EN)
- Petroleum products — Transparent and opaque liquids — Determination of kinematic viscosity and calculation of dynamic viscosity
Step-by-step procedure
1. Viscometer selection
Select viscometer with range appropriate to expected sample viscosity. Flow time must be min. 200 s. Check viscometer calibration certificate.
2. Bath preparation
Set thermostatic bath to required temperature (40.00°C or 100.00°C). Stability: ±0.02°C. Wait for temperature stabilization.
3. Viscometer cleaning
Rinse viscometer sequentially with kerosene, toluene and acetone. Dry by passing clean, dry air. Visually check capillary cleanliness.
4. Viscometer filling
Fill viscometer with sample per manufacturer instructions (approx. 7 mL for Cannon-Fenske). Avoid air bubbles.
5. Thermostating
Place filled viscometer in bath. Wait minimum 30 minutes to achieve thermal equilibrium.
6. Flow time measurement
Position liquid meniscus above upper mark. Start timer when meniscus passes upper mark and stop at lower mark.
7. Repeat measurement
Perform second determination on same viscometer (for Ubbelohde type) or on second clean viscometer. Compare results — difference should not exceed determinability.
8. Kinematic viscosity calculation
ν = C × t, where C is viscometer calibration constant, t is average flow time. Report result with appropriate significant figures.
9. Dynamic viscosity calculation (optional)
η = ν × ρ, where ρ is sample density at measurement temperature. Result in mPa·s.
10. Final cleaning
Empty viscometer. Rinse sequentially with kerosene, acetone. Dry and store in vertical position.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Glass capillary viscometer | Cannon-Fenske Routine (transparent), Cannon-Fenske Opaque (opaque), Ubbelohde | 150–600 PLN/pc |
| Thermostatic viscometer bath | Tamson TV 4000, Julabo VISCO BATH, Cannon CT-1000 | 15 000–45 000 PLN |
| Calibrated timer/stopwatch | Digital timer with ±0.1 s accuracy or automatic optical detector | 200–500 PLN (manual), 8 000–20 000 PLN (automatic) |
| Precision thermometer | ASTM thermometer with 0.01°C resolution or Pt100 sensor | 500–2 000 PLN |
| Automatic viscometer system | Cannon miniAV, Schott-Geräte AVS 370, Anton Paar SVM 3001 | 40 000–120 000 PLN |
| Suction bulb for filling viscometer | Rubber bulb with adapter or manual pump | 50–200 PLN |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Viscosity reference oil | — | Certified reference oils (CRM) with known viscosities at 40°C and 100°C, e.g., Cannon S20, S60, S200, N35, N100 |
| Kerosene (cleaning solvent) | 8008-20-6 | For initial washing of viscometers after use with oil samples |
| Acetone | 67-64-1 | Purity ≥99.5%, for final rinsing of viscometers |
| Chromic acid (optional) | 7738-94-5 | Chromic mixture for removing stubborn deposits from capillaries (caution: highly corrosive, carcinogenic — limited use) |
| Toluene | 108-88-3 | Purity ≥99.5%, alternative solvent for cleaning viscometers |
Health and safety (OHS)
- Thermostatic bath — risk of burns when working at 100°C and above
- Solvents (toluene, acetone, kerosene) — work in fume hood, flammable
- Chromic acid — highly corrosive and carcinogenic (Cr⁶⁺), use only as last resort, with full PPE
- Laboratory glassware — viscometers fragile, risk of cuts
- Safety glasses and solvent-resistant gloves mandatory