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First of all, I’ll preface this by saying that biodiesel has no sulphur and is in many ways already far superior to the highly expensive and complex processes that goes into trying to remove the sulphur from distillate (the mineral diesel that people are used to buying, which is really called “distillate”, not “diesel” as it is constantly branded). I’m only posting this thread as I think that most people who are interested in biodiesel need to be aware of “Low Sulphur Diesel” (LSD) and “Ultra Low Sulphur Diesel” (ULSD).

Why is sulphur so bad?
Sulphur in fuels is nasty when it is burned. Not only does it come out as toxic emissions, causing acid rain and other health hazards, but it also interferers with the ability of a catalytic converter to remove other bad stuff in the exhaust emissions. The catalytic converter in a modern engine sits in the exhaust pipe and helps to get rid of the yucky stuff that is not fully burned. Sulphur can choke this catalytic converter up and prevent it from doing its job. This is why many of the older diesel engines do not have the ability to clean their emissions very well – they were designed for a fuel with a high sulphur content.

Why is sulphur so good?
Lubrication. In the olden days, before everyone realised how horribly toxic petro fuels were and woke up to biodiesel, the pre-LSD fuel did a reasonably good job of lubrication. Diesel engines require a certain amount of “lubricity” from their fuel to keep things running smoothly.

What happens when the sulphur is removed?
To remove the sulphur firstly requires political pressure. The major fuel suppliers will market themselves as the saviours of the planet because they will fall into line with government regulations to clean up their product. In actual fact, removing the sulphur from the fuel is a difficult and costly process for them that requires extra refining. The process of removing the sulphur is called “sweetening”. Most commonly, this involves using hydrogen gas to change the sulphur into hydrogen sulphide (H2S), which is also called “hydrofining”. The H2S is then removed from the distillate for further processing. The process of removing the sulphur also reduces the lubricity of the fuel.

How does this effect engines?
Not only does the lubricity drop, requiring additional additives to the fuel to prevent engine problems, but in older engines, problems can be encountered with hoses and seals going brittle and shrinking. The process of removing sulphur from the fuel has now changed the fuel’s properties. If any components in the fuel system are made from natural rubber (also known as "NBR" or "buna-n" or "nitrile" rubber) then they can encounter problems. Seals in injector pumps can shrink, go brittle and leak with LSD or ULSD.

What are the manufacturers doing about this?
Since the mid 90s (dates vary), most manufacturers have been using components made from synthetic materials, such as FKM (also known as Viton). These materials do not suffer from the above problems. As such, most newer cars do not have a problem with LSD/ULSD.

What is the difference between LSD and ULSD?
Simply put, ULSD has 10 times less sulphur than LSD. LSD permits 500 parts per million (ppm) of sulphur. ULSD permits 50ppm. Before this, the maximum sulphur content in distillate was 5000ppm!

So what standards are governments implementing?
There are many different names for different standards in different countries, but I’ll address the ones that are relevant for Australia. In 2002, LSD was introduced to Australia and was mandated to be fully rolled out across the country by Dec 31st 2002. There was some noise made about this, but for most of the average consumers, it went completely unnoticed.
In Europe, the “Euro4” (ISO EN 590) standard meets the same sulphur content as ULSD and was mandated from 2005. Prior to this the “Euro3” standard was the same as LSD and has been mandated since 2000. “Euro5” (proposed for 2008) will be even cleaner.
The “Euro4” standard has now been introduced in Australia from January 2006, which means that any distillate you buy from a service station in Australia will be ULSD. Oddly, very little information is being offered to the consumer about this.


What does this new standard give us?
This has allowed many of the new “clean diesel” vehicles to be imported from Europe. These vehicles will be able to use cleaner exhaust catalysing technologies, as the sulphur problem no longer exists in the fuel. Vehicle manufacturers can now be sure that you will be putting ULSD into their vehicles, so they can be sure that the more advanced methods of removing emission pollutants (like catalytic converters) will not be poisoned by the sulphur content. This way, everyone knows that your emissions will be less and everyone is happy. This is why this year we will see far more diesel vehicles being imported into Australia, with manufacturers like Volkswagen bringing out a diesel option across their entire range of vehicles.

How does this effect engines?

If any components in the fuel system are made from natural rubber then they can encounter problems.

Simply put, ULSD has 10 times less sulphur than LSD. LSD permits 500 parts per million (ppm) of sulphur. ULSD permits 50ppm.

Remember how the removal of the sulphur caused a lack of lubricity, requiring additives? Guess what the best additive for lubricity is?

So I will be putting a quart of 100% biodiesel before every fill up.