EN 590 Diesel: Full Specification, CFPP Grades and Export Supply

The standard is published by CEN, the European Committee for Standardization, and is adopted verbatim as a national standard in every CEN member country — the same document appears as BS EN 590, DIN EN 590, NF EN 590 and so on. It has been revised repeatedly since the first edition in 1993, mostly to tighten sulphur and to accommodate fatty acid methyl ester (FAME) blending. When a contract says ‘EN 590’ without an edition, that is the first ambiguity to close: name the edition, or name the specific limits you require.

What makes EN 590 useful to a trader is that almost every line in it is tied to a named EN ISO test method. A specification clause without a method is unenforceable, because two laboratories using different apparatus will legitimately return different numbers for the same drum. EN 590 removes that argument. If the contract says sulphur maximum 10.0 mg/kg by EN ISO 20846, then a result produced by a hand-held field analyser is not an answer to the question.

What EN 590 is not

• It is not a marine fuel specification. Marine gas oil is specified under ISO 8217, in the distillate grades DMX, DMA, DMZ and DMB, with different sulphur, viscosity and cleanliness requirements — and note that ISO 8217 quotes viscosity at 40 °C for its distillate grades and at 50 °C for the residual grades, never at 100 °C. The two products overlap in the refinery but not in the contract.
• It is not heating oil. Heating gas oil is covered by national standards and is normally dyed and fiscally marked. Selling EN 590 into a heating oil market, or the reverse, is a customs problem before it is a technical one.
• It is not a single product. EN 590 covers eleven cold-flow variants and, in practice, several sulphur levels depending on the regulatory regime of the destination. ‘EN 590 diesel’ on its own does not describe a cargo.
• It is not an assurance of provenance. The standard describes what the fuel must do, not where it came from or how it was made. Straight-run gas oil, hydrocracker distillate and blended streams can all meet it.

How the standard is structured

The requirement tables split into three groups. The generally applicable requirements apply to every grade and class: cetane, density, sulphur, flash point, carbon residue, ash, water, contamination, corrosion, oxidation stability, lubricity and FAME. The temperate climate grades A to F differ from each other only in cold filter plugging point. The arctic and severe winter classes 0 to 4 change several properties at once — CFPP, cloud point, density, viscosity, cetane and the distillation curve all move together, because you cannot make a fuel flow at minus forty without making it lighter.

National annexes then decide which grades and classes are legal in which country and in which months. That is why a cargo that is perfectly compliant loading in a Gulf summer can be non-compliant on discharge in a northern European November.

Cetane number and cetane index

Cetane number is a measure of ignition quality: how quickly the fuel starts to burn once it is injected into hot compressed air. EN ISO 5165 measures it directly in a standardised single-cylinder variable-compression engine, comparing the sample against reference blends. A minimum of 51.0 is what the standard requires. Low cetane lengthens the ignition delay, which means more fuel accumulates before combustion starts, which produces the harsh knocking sound, higher peak pressures, hard starting in cold weather and white smoke on a cold engine.

Cetane index, minimum 46.0 by EN ISO 4264, is a calculated value derived from density and distillation temperatures. It is not the same measurement and it is not a substitute. The gap between the two matters commercially: cetane improver additives — typically 2-ethylhexyl nitrate — raise the measured cetane number but do not raise the calculated index, because they do not change density or the distillation curve. A fuel showing cetane number 51.5 and cetane index 44 is telling you it is a low-quality base stock carrying a heavy additive dose. It meets the number and fails the index, and the standard requires both for exactly this reason.

Density at 15 °C

The 820.0 to 845.0 kg/m³ band by EN ISO 12185 does two jobs. Technically it constrains the energy content per litre and interacts with the fuel injection system, which meters by volume. Commercially it is the number that converts your cargo between litres and metric tonnes, and it is the single most consequential figure on the certificate for anyone paying by weight and selling by volume. Density must be reported at 15 °C, and observed density at ambient must be corrected using the petroleum measurement tables. A cargo measured at 35 °C in a Gulf summer and reported without correction will misstate the quantity by well over one percent.

Sulphur content

Ten milligrams per kilogram is one part in a hundred thousand. At that level the measurement itself needs care: EN ISO 20846 uses ultraviolet fluorescence and EN ISO 20884 uses wavelength-dispersive X-ray fluorescence, and both are referee methods for the 10 mg/kg limit. Handheld or energy-dispersive XRF instruments used for 500 or 2000 ppm gasoil do not have the resolution to certify a 10 mg/kg cargo. If a certificate shows sulphur at 10 mg/kg by ASTM D4294, that is a finding worth raising before the cargo moves.

Flash point above 55 °C

The Pensky-Martens closed-cup test to EN ISO 2719 determines the lowest temperature at which the vapour above the fuel will ignite. Above 55 °C is what the standard requires, and it is what places diesel in a different handling category from gasoline or kerosene. It also acts as a contamination detector: if a diesel cargo returns a flash point of 40 °C, it has been contaminated with a lighter product somewhere between the refinery and the sample — a dirty line, a shared pump or a previous cargo in the compartment. A low flash point is almost never a refining problem; it is almost always a custody problem.

Lubricity — the 460 micrometre limit

This line exists because of the sulphur reduction. Diesel fuel injection equipment, particularly rotary and unit injector pumps, is lubricated by the fuel itself. The natural lubricity of diesel came largely from polar sulphur- and nitrogen-bearing compounds, and the deep hydrotreating needed to reach 10 mg/kg strips them out. Early ultra-low-sulphur fuels destroyed fuel pumps. The high-frequency reciprocating rig test, EN ISO 12156-1, presses a steel ball against a steel plate under the fuel at 60 °C and measures the resulting wear scar; the corrected diameter must not exceed 460 micrometres. Modern ULSD meets this only because a lubricity improver is dosed at the refinery or the terminal. It is an additive-dependent property, which means it can be lost by blending an unadditised stream into an additised one.

Water, total contamination and ash

Water maximum 200 mg/kg by Karl Fischer coulometric titration, EN ISO 12937, is the dissolved and entrained water at the point of delivery. Total contamination maximum 24 mg/kg by EN 12662 is the insoluble solid material recovered on a filter membrane — rust, scale, dust, degraded product. Ash maximum 0.01 % m/m by EN ISO 6245 is the inorganic residue after combustion. Together these three are the cleanliness group, and they are the lines that predict filter blocking and injector wear. They are also the lines most easily failed by the tank, the hose and the barge rather than by the refinery.

Carbon residue and polycyclic aromatics

Carbon residue on the 10 % distillation residue, maximum 0.30 % m/m by EN ISO 10370, measures the coking tendency of the heaviest fraction of the fuel — what will build up on injector tips and in the combustion chamber. Polycyclic aromatic hydrocarbons, maximum 8.0 % m/m by EN 12916, are limited for emissions and health reasons; they raise particulate output and are the fraction of most concern in exhaust toxicity.

Oxidation stability

Two different tests appear, and which one applies depends on whether the fuel contains FAME. EN ISO 12205 heats the fuel with oxygen at 95 °C for 16 hours and measures total insolubles, limit 25 g/m³ — this is the mineral-diesel stability test. EN 15751 is the Rancimat induction period method, minimum 20.0 hours, which is the meaningful test once FAME is present because the ester component oxidises by a different and faster route. A B7 cargo certified only by EN ISO 12205 has not been tested for the instability that actually threatens it.

The single most common specification error on diesel cargoes

It is the cold-flow grade. A buyer orders ‘EN 590 10 ppm’, the seller supplies a fully compliant Grade A or Grade B, and the cargo arrives at a northern port in December where the national annex requires Grade E or F. The fuel meets EN 590. It is still the wrong fuel, and by the time anyone notices, it is in a tank or in a truck.

The failure mode is physical. Diesel contains normal paraffins that crystallise out as wax as the temperature falls. The cloud point is where the first wax crystals become visible and the fuel goes hazy. The cold filter plugging point, measured to EN 116, is the temperature at which the waxy fuel can no longer be drawn through a standard 45 micrometre wire mesh in 60 seconds — it is a laboratory proxy for a blocked vehicle fuel filter. The pour point is lower still, the temperature at which the fuel stops flowing at all. In service, the vehicle stops at CFPP, not at pour point, which is why EN 590 grades on CFPP.

Practical rules that avoid the dispute:

• Specify the grade letter or class number in the contract, not just ‘EN 590’. Write ‘EN 590 Grade E, CFPP maximum -15 °C by EN 116’.
• Grade to the coldest point in the supply chain, including inland trucking, unheated overnight storage and the highest altitude in the delivery area — not to the average winter temperature at the port.
• Allow for transit and storage time. A cargo loading in September for a December discharge needs the December grade.
• Do not plan to fix it with additive at destination. Cold-flow improvers work by modifying wax crystal growth, and they must be dosed into the fuel above its cloud point and fully homogenised. Dosing a cold tank of already-clouded fuel achieves nothing. Additives also lower CFPP without meaningfully lowering the cloud point, so a fuel that passes CFPP can still throw wax in a settled tank overnight.
• Watch FAME in winter. Saturated methyl esters, particularly from palm-derived feedstock, have poor cold behaviour and can precipitate above the CFPP of the blend. This is a distinct failure from paraffin wax and is why some winter specifications restrict the FAME feedstock as well as the volume.

Sulphur: how the limit reached 10 mg/kg

The sulphur history is worth knowing because it explains why the rest of the specification looks the way it does. The first EN 590 edition in 1993 allowed 2000 mg/kg. Successive revisions, driven by the EU Fuel Quality Directive, cut that to 500 mg/kg, then 350 mg/kg from 2000, then 50 mg/kg from 2005, and finally to 10 mg/kg — the level marketed as sulphur-free — which became mandatory for road diesel across the EU from 1 January 2009.

The driver was aftertreatment, not sulphur itself. Diesel particulate filters, selective catalytic reduction and NOx storage catalysts are all poisoned or fouled by sulphur. A modern engine cannot meet its emissions limits on high-sulphur fuel, and running it on that fuel damages hardware that costs more than the fuel saving. Two lines in the current specification exist as direct consequences of reaching 10 mg/kg: the lubricity limit, because hydrotreating removed the fuel's natural lubricity, and the conductivity practice discussed under safety, because it also removed the polar species that let static charge dissipate.

Why destination markets still differ

Outside the EU, EEA, UK and a group of markets that have aligned with them, the picture is mixed. Sulphur limits are set nationally and follow the age of the vehicle fleet and the capability of domestic refining. A country whose trucks are pre-Euro IV gains nothing from 10 mg/kg fuel and will not pay the premium for it. The result is a live trade in 50, 500, 1000, 2000 and 5000 ppm gasoil alongside genuine EN 590. Off-road, rail, marine auxiliary and power-generation duty adds further demand at higher sulphur levels in many jurisdictions.

For a buyer this means the phrase ‘EN 590’ is doing two different jobs in the market. Sometimes it means the full standard including 10 mg/kg sulphur. Sometimes it is used loosely to mean ‘automotive gas oil to a European-style specification’ at whatever sulphur the destination allows. Close that gap in writing: state the sulphur maximum in mg/kg and the test method, and state which lines of EN 590 the cargo is warranted against.

Water is the root cause

The specification caps water at 200 mg/kg by EN ISO 12937, but that is dissolved and entrained water in fresh product. Tanks acquire far more. Every temperature cycle makes a partly full tank breathe humid air in and condense moisture on the shell overnight. Poorly drained delivery hoses, rainwater through a defective vent or manway, and leaking heating coils all add to it. Free water settles to the bottom because diesel is lighter, and the interface between the two is where the trouble begins.

FAME makes it worse. Methyl esters are hygroscopic and hold roughly an order of magnitude more dissolved water than mineral diesel, and they release it as the fuel cools. A B7 blend therefore delivers more water to the tank bottom than a FAME-free fuel from the same tanker.

Microbial contamination

The fuel/water interface supports a specific and well-documented microbial community — the fungus Hormoconis resinae (formerly Cladosporium resinae), sulphate-reducing bacteria and various aerobic bacteria. They live in the water layer and feed on the hydrocarbon. What they produce is the problem: a dark, slimy biomass that blocks filters and coalescers, organic acids that corrode steel tank floors and pit aluminium, and hydrogen sulphide from the sulphate reducers. FAME is a more accessible carbon source than mineral diesel, so B7 blends colonise faster. The symptoms — filters blocking in days rather than months, a bad-eggs smell, dark deposits on filter media, unexplained tank-floor pitting — are usually noticed long after the colony is established.

The control is mechanical before it is chemical:

• Drain water bottoms on a written schedule and record what comes out. Free water is the substrate; remove it and the colony cannot establish.
• Keep tanks as full as practical to reduce the headspace that breathes and condenses.
• Draw product above the tank floor using a floating suction or a raised offtake, so the dirtiest layer is never sent to the customer.
• Fit and monitor a water-separating filter or coalescer on the outlet, and record differential pressure rather than waiting for a blockage.
• Filter to a cleanliness target. Modern high-pressure common-rail injection systems are commonly specified to an ISO 4406 cleanliness code of 18/16/13 or better, which is far cleaner than fuel arrives in a road tanker.
• Treat biocide as remediation, not maintenance. Dosing biocide into a tank with an established biofilm kills the organisms but leaves the dead biomass in the fuel, where it blocks filters immediately. Clean the tank first.

Oxidative stability and stock rotation

Mineral diesel stored cool, dry and dark is stable for a long time. B7 is not. The ester component oxidises and polymerises, forming gums and insolubles, and the process accelerates with temperature, dissolved oxygen, water and contact with copper or copper alloys — brass fittings and copper lines are catalytic. This is why EN 15751 sets a minimum 20-hour induction period for FAME-containing fuel. In practice, plan stock rotation in months rather than years for B7, keep long-term reserves in FAME-free product where the engine manufacturer permits it, avoid copper and brass in contact with the fuel, and test stored stock periodically for water, appearance and total contamination rather than assuming it is unchanged.

Fire and flammability

Diesel to EN 590 has a closed-cup flash point above 55 °C, which under the CLP and GHS systems places gas oil in flammable liquid category 3 — hazard statement H226, flammable liquid and vapour. For transport it is UN 1202, Class 3, Packing Group III, and it is normally declared as a marine pollutant under the IMDG Code. That flash point means the vapour above a static tank at ordinary ambient temperature is usually too lean to ignite. It does not mean diesel is safe to treat casually, and three situations defeat the flash point entirely:

• Switch loading. Loading diesel into a compartment or tank that last held gasoline leaves a flammable vapour in the headspace. The diesel is irrelevant; the atmosphere is already explosive, and a static discharge from splash filling into it is a classic ignition sequence. Use bottom loading, keep the fill rate low until the inlet is submerged, and follow a formal switch-loading procedure.
• Mist and spray. A pinhole leak in a high-pressure fuel line produces an aerosol that ignites far below the bulk flash point. Any hot surface above about 200 °C in the vicinity — a turbocharger, an exhaust manifold — is an ignition source.
• Heated or contaminated product. Fuel heated near or above its flash point, or cross-contaminated with a lighter cut, behaves like the lighter product. This is why an unexpectedly low flash point on a certificate is a safety finding, not a paperwork one.

Static electricity in ultra-low-sulphur fuel

This hazard is specific to modern diesel and is often missed. The deep hydrotreating that removes sulphur to 10 mg/kg also removes the trace polar compounds that give diesel its natural electrical conductivity. Untreated ULSD can sit in the low single figures of picosiemens per metre, which means charge generated by pumping and filtration relaxes very slowly and can accumulate on the fuel surface in a receiving tank. EN 590 itself sets no conductivity limit, so this is a handling practice rather than a specification line: the widely used industry target is to dose a static dissipator additive so the fuel measures at least 50 pS/m at the handling temperature, measured by EN ISO 6297 or by ASTM D2624 / IP 274, and to combine that with bonding and earthing of all equipment, controlled fill velocities, submerged fill pipes and a relaxation period after filtration and before gauging or sampling. Ask whether the cargo is additised for conductivity and ask for the measured value on the certificate.

Health and environmental hazards

Gas oil carries a well-defined hazard profile that should appear on any Safety Data Sheet supplied with the cargo: aspiration toxicity category 1 (H304) — swallowing even a small quantity that reaches the lungs causes chemical pneumonitis, which is why fuel must never be siphoned by mouth and why vomiting must never be induced; skin irritation (H315), with repeated or prolonged contact defatting the skin and causing dermatitis, so diesel must never be used as a hand cleaner, parts wash or mould-release; carcinogenicity category 2 (H351), driven by the aromatic content, which is why PAH is limited and why contaminated overalls should be changed rather than worn out; acute inhalation toxicity category 4 (H332) and specific target organ toxicity, repeated exposure, category 2 (H373), which together make vapour and mist a ventilation problem rather than a gloves-and-goggles one; and aquatic chronic toxicity category 2 (H411). Classification is product-specific and depends on the refining history of the stream, so the supplier's Safety Data Sheet governs and should be read rather than assumed. On the last point, storage should be bunded to at least the capacity of the largest tank, spill kits should be sized for a realistic release, and any spill to drain or watercourse is normally a reportable incident.

For firefighting, use foam, dry chemical or carbon dioxide. A straight water jet spreads burning fuel and enlarges the fire; water spray is for cooling adjacent surfaces and containers. Tank entry is a confined space operation requiring gas testing for hydrocarbon vapour, oxygen deficiency and hydrogen sulphide, which can accumulate in the headspace of some straight-run gas oils and in microbially contaminated tanks.