Analytical report to reveal causes of fuel contamination

by L. S. Ananda WEDAARACHCHI

The vehicle engines of cars, trucks, buses, cranes and trains were damaged due to the use of contaminated diesel. Samples of the contaminated diesel stocks in question were sent abroad for laboratory test and the report is expected.

Cyril Suduwella

The committee appointed by Petroleum Industries Minister Susil Premajayantha to study the issue has not identified the cause for the damage to vehicles.

According to reports over 250 State owned buses, 1,000 private buses, 18 cranes and around 50 train engines were damaged by the contaminated diesel during the past four weeks.

The Sunday Observer interviewed CPC's former head of Laboratory and Technical Services and Charted Petrochemist Cyril Suduwella on the quality of Diesel.

Q: Can you explain why recently imported diesel has failed to perform satisfactorily in automotive diesel engines and other categories of diesel engines?

A: The answer is not simple. It may be due to contamination of either used lube oil or deliberate blending of low cost alternative diesel manufactured by non conventional cracking process and other illegal methods.

These cracked materials are dangerous to engine parts, fuel injection system and combustion process. If alternative fuel is blended, the standard quality assurance test alone may not be sufficient to detect unwanted materials in the diesel sample tested.

As prices of petroleum products increase large numbers of alternative diesel products are manufactured worldwide. Without having adequate knowledge about these products, petroleum procurement committee may not be able to detect contamination of low cost products by looking at Quality certificate or third party inspection report alone.

Q: What is a diesel engine?

A: The Diesel engine is now established in a variety of applications on land and in marine use. On land, it serves to power trains, buses, trucks, and automobiles; to run construction, petroleum drilling, and other off-road equipment; and to be the prime mover in wide range of power generation and pumping applications.

The diesel engine is a high-compression, self-ignition engine. Fuel is ignited by the heat of the high compression and no spark plug is used. The diesel cycle consists of charging the combustion chamber with air, compressing the air, injecting the fuel which ignites spontaneously, expanding the burned gases and expelling the products of combustion.

Q: What are the basic requirements of diesel fuel?

A: Selection of proper fuel is not an easy procedure. It depends upon many variables. The basic fuel requirements for land

and marine diesel engines and for gas turbines are satisfactory ignition and combustion under the conditions existing in the combustion chamber, suitability for handling by the injection equipment and convenient handling at all stages from the refinery to the engine fuel tank without suffering degradation and without harming any surface which it may normally contact.

Diesel and gas-turbine fuels were originally straight-run products obtained from the distillation of crude oil. Today with the various refinery cracking processes, these fuels may contain varying amounts of selected cracked distillates. This permits an increase in the volume of available fuel at minimum cost. The boiling range of distillate fuels is approximately 150 to 400 C. The relative merits of the fuel types to be considered will depend upon the refining practices employed, the nature of crude oil from which they are produced, and the additive package (if any) used.

Q: Are you satisfied with the existing quality procedure?

A: I am not satisfied with the entire quality assurance process and the analytical methods used.

As diesel power came into prominence, equipment manufacturers developed engine designs and fuel handling processes to use the new blended fuels more efficiently. Petroleum refiners, diesel fuel suppliers and vessel operators quickly found that existing specifications and test methods were not completely adequate for their needs. Ad hoc quality and test procedures proliferated. Fuel quality disputes frequently resulted in long, expensive and inconclusive litigation. The need for a general standard for diesel fuels became clear.

Q: Are there any additives to improve diesel fuel quality?

A: Additives may be used to improve diesel fuel performance. Cetane improvers such as alkyl nitrates and nitrites can improve ignition quality. Pour-point depressants can improve low-temperature performance. Antismoke additives may reduce exhaust smoke which is a growing concern as more and more attention is paid to atmospheric pollution. Antioxidant and sludge dispersants can minimize or prevent the formation of insoluble compounds. Fuels formulated with cracked stock compounds, which could cause fuel line and filter plugging.

For a given diesel engine, a higher fuel cetane number causes a shorter ignition delay period and a smaller amount of fuel in the combustion chamber when the fuel ignites. Consequently, high cetane number fuels generally cause lower rates of pressure rise and lower peak pressure. Both tend to lessen combustion noise and permit improved control of combustion, resulting in increased engine efficiency and power output.

In addition to these advantages, higher cetane number fuels tend to result in easier starting, particularly in cold weather, and faster warm-up. Reduced exhaust smoke and odor are also associated with higher cetane numbers. High-speed diesel engines are normally supplied with fuels in the range of 45 to 50 cetane number.

Q: In Sri Lanka do we have sufficient quality testing facilities in our laboratories?

A: What is more important is knowledgeable petro chemists and experienced hands. State-of-the-art equipment available today are fully computerised. Application of basic principles in Petroleum Analytical Chemistry is essential to make use of these analytical instruments.

Q: Do you think that the diesel imported recently is contaminated?

A: Yes. But what is important is to find out where it happened and how it happened. Careful investigation from the crude oil source through refining and shipping to the refined product receiving tank is necessary to tell exactly what has happened.

Q: Irrespective of how it got contaminated is there any possibility of improving its quality to be used for vehicles?

A: Yes. It is possible as there are many ways. However, the appropriate method of correction depends on the analytical report, details of the origin of crude oil used to manufacture such products and the port of landing.

Q: Has this contaminated diesel been imported or locally produced?

A: Our refinery at Sapugaskanda manufactures light crude oil and UOP (Universal Oil Products) process technology. The quality standard in our refinery is stringent. The locally produced diesel meets quality requirements or international standards.