Sir,
Having written a thesis on “Oil Analysis as a Maintenance Tool” and with over 40 years of experience of diesel fuel sulphur content and its effects. I read with great interest and total disbelief the article “Low sulphur diesel damages older vehicles” which appeared in the Saturday April 16 edition of the Cyprus Mail. This article is contrary to the findings of the major oil companies and world leading diesel engine manufactures. Fuels with a high sulphur content most certainly do not put a protective coat on any of the engines metal surfaces, or components, quite the opposite.
Sulphur is an element which occurs naturally in all crude oils. Heavy fuels usually have higher sulphur content. Distillate fuels are usually lower in sulphur content because the sulphur can be reduced or eliminated during the refining process. It is necessary to be aware of the fuel sulphur content as sulphur over 0.5 per cent can severely reduce engine life. In the United States, Canada and Western Europe fuel sulphur content is regulated to 0.5 per cent by law since the early 1970s.
When diesel fuel containing sulphur is burned in an engine’s combustion chamber, oxides of sulphur form and react with water vapour to create sulphuric acid. As with hydrogen sulphide, if these acid vapours condense, they chemically attack the metal surfaces of the engine. For instance, if the temperature of the cylinder liners is lower than the dew point of sulphuric acid and the lubricating oil does not have sufficient alkalinity reserve (TBN) to neutralise the acid, liners can wear ten times more quickly.
When sulphur damage occurs, there will be very little change in engine power. But frequently, corrosive wear will lead to excessive oil consumption and blowby, causing a premature, expensive overhaul.
Steps to Help Prevent Fuel Sulphur Damage
1. Know the sulphur content of your fuel
2. Keep the normal operating temperature in your cooling system above 80?C. This will help limit the condensation of sulphur compound vapours on the cylinder walls.
3. Select the correct grade of lubricating oil with a Total Base Number (TBN) which is 20 times the fuel sulphur content to counteract acid formation.
4. Maintain the crankcase breather system to prevent condensation in the crankcase oil which will cause rapid TBN depletion
Total Base Number (TBN)
Understanding TBN requires some knowledge of fuel sulphur content. Most diesel fuel contains some sulphur. How much depends on the amount of sulphur in the crude oil from which the fuel was produced and/or the refiner’s ability to remove it. One of the functions of the lubricating oil is to neutralise sulphur by-products, namely sulphurous and sulphuric acids and thus retard corrosive damage to the engine. Additives (primarily detergents) in the oil contain alkaline compounds which are formulated to neutralise these acids. The measure of this reserve of alkalinity is known as its TBN. Generally the higher the TBN value, the more reserve alkalinity or acid-neutralizing capacity the oil contains.
Charts giving acceptable specifications for distillate fuels (diesel fuel) can be obtained from ISO, ASTM, British Standards, Japanese JIS, German DIN, US Government and Military Specifications and will confirm the findings in respect of fuel sulphur content.
The 15-year-old engines referred to in the article were all manufactured after the law regarding 0.5 per cent sulphur content was introduced and should have been running for all their life on diesel fuel with low sulphur levels.
The major cause of fuel pump failures are dirty fuel, water in the fuel or refinery fines, low sulphur fuels have no bearing on this matter whatsoever.
John Beaumont
IEng; FSOE; FIPlantE; MIMC; CMC:
Principal Consultant
Danek International Management Consultants,
Kato Paphos
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– 2 – APRIL 18, 2005
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P.O. BOX 61196 • KATO PAPHOS 8131 • CYPRUS
PHONE / FAX: +357 – 26 – 622335 – Email [email protected]
