BB00.40-P-0136-00A Sulfur In Diesel Fuel
BB00.40-P-0136-00A Sulfur In Diesel Fuel
1. Origins of sulfur
Mercedes-Benz diesel engines are designed for diesel fuel, which complies with respective national and international requirements (DIN EN 590 in Europe).
These requirement standards usually contain a limit for the maximum permissible sulfur content, they do not say anything about any minimum sulfur content required. Neither is this necessary because sulfur does not have any function in the diesel fuel; its presence is down to crude oil, which naturally exhibits a different specific sulfur content. The level of sulfur content in the diesel fuel depends on the origin of the crude oil, desulfurization facilities at the refineries and is limited by standards and/or laws.
2. Sulfur content regulation
2.1 In the EU
There are no technical objections to operating an engine on diesel fuel with a low sulfur content. This is called for to a greater extent by environmental reasons. A maximum of 350 mg/kg is prescribed by the EU as of 1.1.2000 and a maximum of 50 mg/kg or 10 mg/kg has been permitted as of 1.1.2005.
This content (and lesser quantities) is generally known as "low sulfur" or "sulfur-free" (max. 10 ppm). Sulfur-free diesel fuels will be made available by the EU member states as of 1.1.05 within their national boundaries in a "geographically balanced way". At the same time this will act as a "phase-in" period for sulfur-free fuel as of 1.1.2009. In the Federal Republic of Germany low-sulfur fuel (max. 50 ppm) has become prevalent due to the mineral oil tax regulations as of 1.11.2001, and as of 1. 1. 2003 only sulfur-free diesel fuel will be on the German market for the same reason.
In other EU states comparable regulations have likewise led to a lowering of the sulfur content in the fuel.
2.2 In other countries
In many countries even today values around 0.3 % by weight are usual, in some countries as always there are sulfur values around 1.0 % by weight and above. The maximum throughout the United States is 0.05 % by weight. Sheets 136.and 136.2 show the (incomplete) worldwide list of sulfur content in diesel fuel, divided into classes.
3. Effects of sulfur
3.1 "Conventional" emission-control technology
By this we refer to either no exhaust after treatment at all or an emission control by means of an oxidation catalytic converter.
The service life of the engine is impaired with a sulfur content > 0.3 % by weight in the diesel fuel. Sulfur dioxide is given off during the combustion process which together with water then forms sulfurous acid, this in turn can lead to corrosive wear, in particular when running a cold engine. A remedy is available here in the form of strong alkaline-acting engine oils and reductions in the oil change intervals. A high sulfur content of more than approx. 0.5 % by weight is considered to be an extreme operating condition.
Under corresponding operating conditions and when using an oxidation three way catalytic converter, a significant increase in the particulate mass is found depending on the sulfur content of the fuel; this originates from the catalytic oxidation of the sulfur dioxide formed into sulfur trioxide and the associated emission of sulfates or sulfuric acid, absorbed on soot particles.
Clear advantages in emission levels are achieved with fuels that have not only had significant reductions in their sulfur content, but also where other relevant diesel fuel properties such as aromatic compounds/poly aromatic content and density are reduced and ignition quality of the fuel improved.
With a sulfur content < 0.005 (50 ppm) or even < 0.001 % by weight (10 ppm) diesel fuels generally have favorable properties due to their manufacture also in the criteria mentioned.
3.2 "More advanced" emission-control technology
These are understood to include, for example, NOx storage catalytic converters based on earth alkali/rare metal or the "CRT-System" for particulate reduction.
For trouble-free operation these systems require sulfur-free diesel fuel (< 10 ppm). In both cases the sulfur trioxide formed from the fuel sulfur interferes with the catalytic conversion of pollutants, in addition the NOx storage catalytic converter being irreversibly blocked by the formation of earth alkali sulfates.
Conclusion: Where possible Mercedes-Benz vehicles should be operated with sulfur-free diesel fuel.
4. Supporting measures
In general it should be noted that low-sulfur or sulfur-free diesel fuels meet the requirements of EN 590.
In the case of diesel fuels with very low sulfur content, particular importance is to be attached to the question of lubricity (see section on "Lubricate" Sheet 131.0); without an appropriate treatment with additives with lubrication-improving additives, wear in the injection system, particularly the pump is to be reckoned with.