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Sulphur Levels in Diesel Explained 

Almost all crude oil-derived fuels contain some level of sulphur content. Crown Oil's fuel experts explain what governs how much sulphur is allowed in fuel.

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How much Sulphur is Present in Diesel?

Almost all crude oil-derived fuels contain some level of sulphur content, even after the petroleum has been refined.

But sulphur in diesel is particularly known to cause damage to both engine components and air quality following combustion.

Luckily, modern diesel fuels now contain far less sulphur and particulate content due to advancements in the refining process and legislated changes to fuel standards. This article explains how and why sulphur content has been down to its lowest level in over 100 years.

Why is there sulphur content in diesel?

Sulphur is a naturally occurring element that is tasteless and odourless in its natural form, and is a key component in many amino acids and proteins that are essential to life on earth.

It’s through the abundant presence of amino acids and proteins that sulphur and sulphur-containing compounds can be found in both crude oil and its derivatives after refinement.

Is sulphur harmful to humans?

Sulphur isn’t harmful to humans in extremely low levels in its pure form. The average human consumes around 900mg of sulphur every day through a normal diet.

However, it can be extremely harmful in compound forms – especially those formed after combustion in fuel. It produces sulphur dioxide, which in turn causes corrosive wear on metal engine components and is one of the key atmospheric pollutants that contribute to air pollution and acid rain.

How have levels of sulphur been lowered in fuel?

Historically, additives have been used in engines to reduce the effect that sulphur has on vulnerable components. These ‘detergents’ were often included in engine oils or even in the fuel itself, providing an alkaline base that helps to neutralise the acid or to form a protective layer on the engine’s internal surfaces. Whilst these additives reduced engine wear, they did little to address the longer-term effects of sulphur on the environment.

A more permanent solution arrived in USLD (Ultra Low Sulphur Diesel), which contained dramatically lower levels of sulphur than common diesels at the time – a maximum of 10 milligrams for every kilogram. This minimised the need for detergent additives to reduce engine wear, and also addressed the issues of sulphuric acid concentrations in exhaust emissions.

The EU and UK went on to legislate that all diesel for non-road mobile machinery (e.g. red diesel) must adhere to the Euro V (EU) and BS 2869 (UK) standards, bringing legal sulphur limits in line with ULSD’s standard.

What is the current sulphur content in red diesel?

As of 2010, the limit for sulphur in red diesel is determined by its class.

Class A2 covers all off-road vehicles such as trains or tractors, limiting sulphur content to 0.001% (10ppm).

Class D covers seagoing marine vessels, stationary engines, static generators and heating boilers. The sulphur content of Class D is significantly higher at 0.1% (1,000 ppm).

Our guide to fuel specifications has more information on the standards that fuels must meet and how sulphur content relates to these.

For a supply of high-quality diesel fuels, as well as renewable alternatives, call Crown Oil today

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