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The November/December 2007 issue of FleetWatch ran a story describing how a new Isuzu truck came to an unhappy standstill after filling up with diesel from a retail fuel franchise. The cause of the breakdown was contaminated diesel which blocked the Isuzu's fuel injection system, a problem that continues to plague truck owners around the country. At a conference held under the auspices of the South African Institute of Tribology, several diesel and truck engine experts shed light on the subject of how and why modern diesel engines fail - and how to prevent such failures. Attending the event was motoring journalist and Auto Dealer editor, Rob Handfield - Jones, who compiled this report which clearly highlights that top experts are painting a gloomy picture of fuel and lubricant contamination in South Africa.


The good news is that South Africa's diesel fuel is of good quality and undeserving of much of the criticism levelled at it. The bad news is that fuel contamination has been fingered as a leading cause of combustion-related diesel engine failures and that critical deficiencies exist in ensuring cleanliness of diesel and lubricants along the supply chain. This emerged from a recent SA Institute of Tribology conference.

Addressing an audience composed largely of tribologists (specialists in lubrication and frictional properties), At von Wielligh of the Faculty of Engineering at the University of Pretoria was forthright about the problem. "A good (diesel) fuel requires good lubricity (lubricating qualities), must be clean and must not contain free water. South African refineries deliver a product which is on spec. The problem is not so much with the quality of our diesel as with what contaminants it picks up between the refinery gate and the engine."

He said that the latest diesel engines operate at fuel injection pressures of around 2000 Bar (200MPa), with pressures of 2800 Bar on the horizon. He said that the only way to make such pressures possible was to reduce tolerances in diesel engines to prevent leakage.

"These are ugly pressures," he commented. "Modern diesels have a higher output, smaller size, higher efficiency, longer life, longer service intervals and emit less pollution. But the tolerances required to make this possible mean that fuel cleanliness is critical."

He said that in modern diesel engines, dust just 2µm (thousands of a millimetre, or 'microns') in diameter can cause fuel injector failure (the thickness of a human hair is 80µm). Dirt can cause deviations in the injector spray pattern which lead to jetting or dripping. Apart from washing lubricating oil off the cylinder walls, an incorrect injector pattern strips pistons of the layer of cooler air which prevents them from melting in the heat of combustion.

Von Wielligh showed several examples of how catastrophic engine failure had been caused by faulty injector spray patterns which were directly related to dirt in the fuel system. He warned that even filters capable of removing particles as small as 2µm had not been sufficient to prevent injector failure in some cases.

"The problem is that the standards of fuel cleanliness only address the mass of particle contamination, not the number of particles," he said. He expressed the concern that even though some contaminant particles were smaller than was considered necessary to cause injector failure, with enough of them present failure could happen anyway.

He went on to say that the removal of sulphur from diesel had presented a huge challenge to tribologists and new additives have been required to restore the lubricity previously provided by sulphur compounds. Without sufficient lubricity, moving parts in a diesel engine fuel supply system, especially the fuel injector needles, can experience premature wear or failure. High fuel consumption can also result.

Contaminants and crooks
Other liquid contaminants can severely reduce lubricity. Von Wielligh said that a typical sample of diesel was able to withstand a load of 800N (Newtons) when subjected to a standardised test developed in the tribology laboratory at the University of Pretoria. However, a petrol/diesel mix withstood only a 300N load - and pure paraffin barely 100N. Water contamination also had dire effects and the lower lubricity of these liquids emerged as instrumental in engine failure.

Nov/Dec 2006
Contaminated fuel blocked the Isuzu’s fuel injection system... a problem that continues to plague truck owners

 
Von Wielligh expressed concern that some fuel resellers and service stations defraud diesel users by diluting diesel with cheaper paraffin. He quoted his own research which showed that a new injector running on paraffin failed after just 22 minutes of continuous running while a control injector running on diesel performed as normal. "If you see a service station offering diesel 20 cents cheaper per litre, ask yourself why," he cautioned. "Put your foot down and drive on to the next service station."

Investigation into fuel additives has revealed that certain additives could improve lubricity and Von Wielligh has used such agents to correct a series of engine failures he was asked to consult on in the United Kingdom

New carbon threat
He also highlighted a new problem in modern diesel engines - called "Black Diesel". Numerous operators have encountered a carbon residue in diesel which clogs fuel filters in a very short time. Research has shown that these residues only form in diesels with modern high-pressure injection systems running at above 1450 bars.

Although chemical engineers are still researching the exact reactions which take place, Von Wielligh's research has demonstrated that under conditions of high injection pressures, high shear forces and high heat, combined with high impact - all the conditions present in the injector tips of a modern diesel engine - the hydrocarbons in diesel fuel break down into hydrogen and carbon. Although this appears to have a minimal effect on lubricity, the recirculated fuel not used in a combustion cycle returns to the fuel tank and carries the carbon residue back through the fuel filters, causing premature blocking.
 

	This melted piston was the result of contamination-related fuel injector failure.
	"The removal of sulphur from diesel presented a huge challenge to tribologists and new additives have been required to restore the lubricity previously provided by sulphur compounds." At von Wielligh

Modern fuel injector tolerances are so fine that only approved machinery and service providers should be used to service these units.

Corporate ignorance
Another speaker, condition monitoring and contamination control specialist, Boet Olivier, of Kleenoil SA, was scathing of corporate South Africa's sluggishness in ensuring that fuel and lubricating oil used in proprietary equipment remained free of contamination.

"Lubrication excellence is as difficult to find as to realise," he said, adding that most companies operate in what he called an environment of "ignorant incompetence" when it came to ensuring clean fuel and lubricants. 

He explained that bulk fuel and lubricant delivery trucks were often badly laden with dirt and other destructive contaminants such as water which were introduced into the fluids during the transit period from the refinery to the point of offloading.

"In many instances, the fluids are further contaminated through the supply chain into the machines due to poor working practices," said Olivier, adding that quality assurance checks were not conducted due to lack of knowledge in the workplace and management's reluctance to ensure training and development of the workforce with regard to lubrication best practices. 

He pointed out that fluid quality sampling practices were in many instances worthless - and a root cause of failures. Diesel samples for contaminant testing were, for example, often taken from the top of the tank. "Diesel is a low-viscosity liquid. The contaminants have settled to the bottom of the tanker not long after it is out of the refinery gate," he said. "So the samples taken from the top are passed as clean and the dirt at the bottom of the tank is pumped into the client's storage tanks when the tanker offloads."

Filter fiasco
He also cited examples of where breathers on these storage tanks were not protected by filters, and where filter elements on both tank outlets and engine fuel systems had either failed due to contaminant overload or were not present at all.

"I have struggled to get filter manufacturers to supply specs on the maximum contaminant load their filters can accept before they should be changed. If we had these figures, we could run a specific amount of fuel or lubricant through the filters, measure the increase in the filter's weight, establish the rate of contaminant accumulation and then implement proper filter change schedules," he explained.

"Cleanliness is critical. I often see fuel dispensing points filthy dirty, without dust caps. Where is that dust going? Into the fuel." He also criticised companies for not providing wash bays for cleaning construction machinery and heavy vehicles. "A dirty fuel or oil filler cap or breather is guaranteed to introduce contamination into the system. And dirt kills machinery operating at close tolerances." 

Olivier concluded that cross-contamination was common, with mobile service vehicles using the same pumps to supply different kinds of lubricants, and that non-standard containers were being used.

"In one case," he said, "I saw a worker filling a gumboot with oil so he could top up his truck's oil level! And sadly, the practice was condoned by his superior." 

Dirt caused this fuel injector's needle to bind. Eventually the injector tip failed (A). The portion of failed injector fell into the cylinder, destroying the piston (B). The cylinder liner was also destroyed in the failure (C).   Dirt around a diesel tank inlet hole should never be allowed to accumulate. Someone's not checking properly...

Underground diesel storage tanks should never be exposed to water. This one needed just a bit more rain before it ran in to trouble. Cleaning trucks after a day in the mud is one way of preventing dirt entering the fuel tank. "If you see a service  station offering diesel 20 cents cheaper per litre, ask yourself why? Put your foot down and drive on to the next service station." At von Wielligh.

Acknowledgements: 
This article first appeared in AutoDealer. Copyright (c) AutoDealer/Caxton 2006. The original article was restructured by the author especially for FleetWatch so as to include aspects which would be of more interest to our truck fleet-orientated readership. The Editor thanks Rob Handfield - Jones for his fine spirit in allowing us to reproduce the article in this abridged version so as to spread the message. Photo credit goes to our good friend Patrick Swan.