The quality of all grades of oil produced and refined in South Africa is subpar in terms of international standards and industry best practices, according to Kyalami-based wear control company Filter Focus.

Filter Focus COO Craig FitzGerald tells Engineering News that the quality of oil refined by South African oil refineries is prescribed by government legislation and the low standard of International Organisation of Standardisation (ISO) classification.

“Local oil refineries do their best to meet the ISO standard, but it is a little known secret that not much more is done to further refine oil products that still contain millions of microscopic contaminants.”

For example, the contaminants found in engine oil and diesel are so fine that most are not visible to the human eye, which can see particles of up to 40 μm, says FitzGerald. He adds that smaller-size particles will require a high degree of magnification before they become visible to the human eye.

In-line fuel and oil filters used by original- equipment manufacturers (OEMs) serve only as minimum protection against contaminants, he states, noting that OEMs and filter manufacturers cannot use filter membranes that are too fine because they will block prematurely and subsequently require frequent replacement.

The OEMs have tried to occupy the middle ground regarding oil filtration in vehicle-engine systems. However, in-line filters cannot handle small particles of dirt or other contaminants adequately. “Most in-line filters are rated to filter out particulate of 10 μm to 20 μm; however, we find that 99% of contamination is below the 5 μm range, therefore passing through all the filters,” adds FitzGerald.

He explains that diesel vehicles that are about 25 years old used low-pressure and low flow rates, resulting in the bulk of the diesel supplied to the engine being consumed. New common rail diesel engines use only a portion of the diesel supplied to the engine, with surplus fuel returning to the fuel tank.

“Nowadays, diesel engines operate at higher pressures with [lower] tolerances in fuel injectors to meet emission control and fuel consumption standards imposed as a result of a global push for ecofriendly vehicles,” says FitzGerald.

This results in more contaminates being forced into fuel injectors, creating a sandblasting effect, which ultimately increases fuel injector tolerances and subsequently decreases fuel atomisation. The persistent decrease in fuel atomisation will eventually lead to the fuel dribbling into the cylinder instead of being sprayed into the cylinder as a fine mist that is ideal for combustion to take place.

Lower fuel atomisation results in decreased power and incomplete burn in the engine cylinders. The incomplete burn leads to the burn being extinguished in a fire box in the exhaust system, resulting in a vehicle producing smoke from the exhaust.

Cleaner Fuels Decrease Lubricity
The global trend of extracting more sulphur from diesel to create a so-called ‘cleaner’ diesel has created another issue.

“Sulphur is a natural ingredient of diesel and it acts as a lubricant for the moving components of a diesel engine,” says FitzGerald, adding that diesel is too light and thin to lubricate the engine on its own.

“If you remove sulphur, you need to add lubricity enhancers to the fuel to attain a satisfactory level of lubrication to ensure vital engine components do not seize,” he adds.

Moreover, by removing sulphur, a change in the viscosity of diesel also occurs, thereby further compromising its lubricating qualities. “A higher-viscosity diesel is definitely more advantageous, as a high-sulphur content in diesel will have about 4.6 centistokes, compared with a low-sulphur content of about 2.2 centistokes,” explains FitzGerald.

He adds that removing the sulphur in traditional diesel fuel almost halves its viscocity.

Transport and Storage Issues
Transporting and storing oil and diesel are major concerns, says FitzGerald, as oil could leave the refinery relatively dirt-free, only to be contaminated during transport, storage and/or delivery to another depot.

He says contamination problems start with dirty oil tankers transporting the diesel, as they are hardly ever checked for cleanliness and are, therefore, rarely cleaned. “Then, at the depot, the diesel is pumped through dirty hoses, which seldom have end-caps fitted during transportation,” FitzGerald notes, adding that a used diesel pipe attracts dirt, as it will stick to the oily surface.

Further, additional contamination occurs in holding tanks, owing to poorly installed breather pipes, coupled with diesel’s hygroscopic properties, which compound the situation as the fuel absorbs moisture from the atmosphere.