Understanding Diesel Fuel Quality and EN590 Standards
This article answers several key questions related to diesel fuel quality and testing:
- How do I know if my fuel is of good quality?
- Why do I need to test my diesel fuel?
- What does BS EN590 mean when I see it on fuel pumps?
- How can a laboratory confirm if fuel is of good quality or contaminated?
- What effect does biodiesel have on my vehicle?
- Why is misfuelling a serious problem, and how can it affect a warranty claim?
What is EN590 and Why is it Important?
The EN590 specification is the legal standard for road diesel in the UK. You’ll often see it displayed on fuel pumps when refuelling. This specification mandates the requirements fuel suppliers must meet, ensuring diesel sold to consumers is safe, high-quality, and suitable for modern diesel engines.
Each batch of fuel undergoes a series of laboratory tests conducted by an independent lab before it is released for sale. These tests validate the fuel’s quality and compliance with EN590. Testing is also performed post-sale to determine if the fuel has been contaminated during storage or use.
Key Laboratory Tests for Diesel Fuel Quality
Here are all the key tests performed to ensure compliance with EN590 standards, including their significance:
- Appearance (Visual Check): Diesel must be clear and bright, with no visible sediment or water. Cloudy or discoloured fuel indicates contamination.
- Cetane Index: A measure of diesel combustion quality. EN590 requires a minimum value of 46 to ensure efficient and smooth engine operation.
- Cold Filter Plugging Point (CFPP): Assesses the diesel’s flow properties in cold conditions. Maximum CFPP is – 5°C for summer and – 15°C for winter blends.
- Density at 15°C: Specifies a range of 820–845 kg/m³. Density outside this range can suggest contamination or improper blending with petrol or biodiesel.
- Distillation Properties: Ensures the correct balance of hydrocarbons for efficient combustion by setting recovery limits at specific temperatures.
- Fatty Acid Methyl Ester (FAME)/Biodiesel Content: Limits biodiesel content to a maximum of 7% (B7). Higher biodiesel levels can affect fuel properties and engine performance.
- Flashpoint: Diesel must have a flashpoint above 55°C for safety. A lower flashpoint can indicate petrol or kerosene contamination.
- Lubricity: Diesel fuel must provide sufficient lubricity to prevent excessive wear in the fuel injection system. EN590 mandates a wear scar diameter of no greater than 460 micrometres using the High-Frequency Reciprocating Rig (HFRR) test.
- Sulphur Content: Sulphur levels must be below 10 mg/kg to reduce emissions and protect modern diesel particulate filters (DPFs). High sulphur content can indicate contamination with off-road diesel.
- Total Contamination: The limit for insoluble contamination (e.g., dirt) is 24 mg/kg. Exceeding this can lead to injector blockage and engine damage.
- Viscosity at 40°C: Diesel viscosity should fall between 2.0 and 4.5 mm²/s to ensure effective lubrication of engine components.
- Water Content: Water levels must not exceed 200 mg/kg. Excess water can cause microbial growth, corrosion, and injector damage.
- Oxidation Stability: This measures the fuel’s resistance to degradation over time, essential for stored fuel. Poor stability can result in sediment and gum formation.
- Ash Content: EN590 limits ash content to 0.01% to prevent deposits in engines and exhaust systems.
- Polycyclic Aromatic Hydrocarbons (PAH): PAH content is capped at 8% to minimise harmful emissions and maintain engine efficiency.
Effect of Biodiesel on Vehicle Performance
Biodiesel, also known as Fatty Acid Methyl Ester (FAME), is a renewable additive used to reduce fossil fuel consumption. While it has benefits like improving lubricity, it also presents challenges:
- Higher Water Absorption: Biodiesel attracts moisture, which can lead to microbial contamination.
- Effect on Engine Components: Vehicles not designed for biodiesel may experience compatibility issues with certain rubber or plastic components.
Always consult your vehicle manufacturer before using biodiesel blends higher than B7.
The Problem of Misfuelling
Misfuelling occurs when petrol is accidentally added to a diesel vehicle. This can have severe consequences:
- Reduced Flashpoint: Petrol contamination lowers the flashpoint of diesel, increasing fire risks.
- Inadequate Lubrication: Diesel engines rely on fuel for lubrication, and petrol lacks the necessary properties, leading to wear and injector damage.
- Warranty Issues: Misfuelling often voids warranties, as it is considered user error.
Summary of EN590 Limits
The following table summarises the key quality parameters for EN590-compliant diesel fuel:
| Parameter | EN590 Limit (Min/Max) | Description |
|---|---|---|
| Appearance | Clear & bright, no sediment | Visual check for contamination |
| Cetane Index | Min 46 | Combustion quality |
| Cold Filter Plugging Point | Max – 5°C (summer), – 15°C (winter) | Flow in cold temperatures |
| Density at 15°C | Min 820 kg/m³, Max 845 kg/m³ | Fuel composition and purity |
| Distillation Properties | Recovery at 250°C Max 65% | Hydrocarbon balance |
| FAME Content (Biodiesel) | Max 7% | Biodiesel blend limit |
| Flashpoint | Min 55°C | Safety measure for flammability |
| Lubricity | Max wear scar 460 µm | Prevents injector wear |
| Sulphur Content | Max 10 mg/kg | Emission control and engine protection |
| Total Contamination | Max 24 mg/kg | Dirt/insoluble particles |
| Viscosity at 40°C | Min 2.0 mm²/s, Max 4.5 mm²/s | Adequate engine component lubrication |
| Water Content | Max 200 mg/kg | Prevents rust and microbial growth |
| Oxidation Stability | Min 20 hours | Resistance to degradation |
| Ash Content | Max 0.01% | Prevents deposits in engine systems |
| Polycyclic Aromatic Hydrocarbons | Max 8% | Limits harmful emissions |
Conclusion
Diesel fuel quality plays a vital role in vehicle performance and longevity. The EN590 standard ensures your fuel meets stringent requirements for safety, reliability, and environmental impact. Regular testing by a professional laboratory provides peace of mind and helps avoid costly repairs.
If you’re unsure about your fuel quality or suspect contamination, consult an independent lab to ensure your fuel complies with EN590 standards.