FleetWatch Online - 48-Diesel

There is general consensus within the road transport industry that diesel contamination is an ongoing problem affecting engine life, fuel consumption and overall operating costs. The arrival of Euro-spec'd trucks in South Africa in recent years has exacerbated the problem, most notably in common-rail and in-line diesel injector units where higher fuel injection pressures and reduced injector nozzle clearances have proven to be especially susceptible to blockages by fine dust particles, bacteria-promoting water particles, slurry and sludge which lead to premature wear of these components. The introduction of low sulphur diesel in SA, while being more suitable for new-generation truck engines than previous varieties, will not guarantee smoother running of the truck engine. To combat the risks associated with diesel contamination, transporters need to adopt 'good house keeping habits' with regard to their tanks, be they on the ground or on the truck, reports Paul Collings.

Craig Pretorius is a co-director of Filter Focus, a Midrand-based company specialising in "ultra fine depth filtration of diesel and oil." He states that "Euro-spec engines are designed primarily around emissions and this has resulted in an astronomical increase in injector pressures which, in certain instances, are operating at well over 2000 bar. These increased pressures require injector clearances to be greatly reduced and are at present around 1-micron (the equivalent of one, one thousandth of a millimetre). These increased pressures and reduced clearances are to ensure that the atomised diesel particles are as fine as possible. The fine atomisation of the diesel ensures total combustion. Emissions are thus greatly reduced and should theoretically be maintained at a minimum. In practice, however, there are certain external influences that affect the efficient operation of the entire system resulting in the emissions increasing, basically from the first time the engine is turned over."

Particulate busting
While diesel gets 'greener', its efficiency in SA is constantly under threat. "We have identified serious levels of down-line contamination taking place throughout the country. It is a recorded fact that in Southern Africa, we have an extremely high dust content suspended in our atmosphere," says Pretorius. "This dust is drawn into the diesel tanks as levels decrease. As temperatures change and the air inside the tank is subjected to expansion and contraction, dust again enters."

Water is another diesel contaminant that has plagued both OEMs and transporters for many years. "With the changing of temperatures from daytime to night time, condensation is constantly taking place in the tank," explains Pretorius. "This condensation results in water contamination in the form of free water. Diesel is hydroscopic and thus absorbs a percentage of this free water into solution. Water in solution is not visible to the naked eye and is measured in parts per million. In serious cases, this water results in bacteria growth.

"As stated by Bosch, modern high-pressure diesel injector systems require below 50 parts per million of water in solution to operate effectively and efficiently. As mentioned above, injector clearances are approximately 1-micron. It thus makes obvious sense that any particles of contamination larger than 1-micron will be to the detriment of the injectors. Remove the dirt effectively down to below 1 micron and maintain the levels of water in solution down to well below 50 parts per million and most of the markets nightmares will disappear! In short, 2-micron filtration is no longer sufficient in our harsh African conditions."

A cross-section of a commonrail injector nozzle. Clearances are as fine as 2 micron.

Downtime! A diesel injector unit in for repair means lost revenue for the trucker.

The damage done
From worn injectors, adds Pretorius, the following are a direct result: Fuel dilution, turbo failure and injector failure, injector pump failure, glazing of cylinder linings, carbon build-up in piston ring grooves, carbon build-up on inlet valves, melting of piston crowns, high soot content in engine oil, reduction in vehicle power, increase in fuel consumption, sludging of engine oil, general deterioration of engine oil and increased exhaust gas temperatures. The general deterioration of the engine oil will also obviously result in bearing failure.

Fine filling habits
In the world of open pit mining, contaminants are an ever-present threat to diesel quality. According to Pieter Lategan, marketing manager of Liquid Automation Systems (LAS), "bulk diesel is checked for quality by mine officers before it is deposited into their tanks. If any contamination is evident or the diesel is not up to spec, those tanker trucks are not allowed to off-load and are sent back to their depot."

To further ensure diesel cleanliness says Lategan, many mines are fitting filter banks to their diesel storage tanks as an extra precaution.

"The mines are extremely sensitive to the dangers of diesel contamination," he says, "and monitor fuel quality constantly. Transporters should emulate this practice. We see contamination creeping in because of poor filling habits. It is not uncommon for diesel to pass through three tankers before it gets into the truck. Often, it is third party distributors carrying the fuel who may run mixed loads in a single tanker. If not adequately cleaned after each load, contamination will occur."

Lategan cites the practice of using a dipstick to measure tank volumes as another potential cause of contamination. "Those dipsticks stand out in the open and are often dirty. If not cleaned before every dip they will contribute to the build-up of slurry and sludge in the tank."

Hello computer.

Turbo injector units are analysed and configured using advanced technology at DPA Diesel.

Clean the tanker between loads to prevent contamination of product.

Diesel vigilance
With the diesel logistics chain encompassing any number of parties, truckers need to have policies and procedures in place to manage the flow of diesel into their engines. Besides testing kits and well-maintained filters, personnel responsible for filling the bowsers and trucks need to do so in a manner that guarantees zero entry of dust. It is recommended that standing trucks should have full fuel tanks to avoid condensation build-up.

OEMs have recognised the need for primary and secondary fuel filters spec'd for SA conditions, as well as the necessity to have adequate water separation devices fitted to the fuel line. SANS (SABS) now has a specification for contamination in diesel, making it easier to avoid spoiled product.

The bottom line is, you can't be too careful when it comes to the lifeblood of a modern truck. If there's dirt in its 'veins', it will have a 'heart attack'.

Volvo’s DME-powered truck uses EGR (exhaust gas recirculation) and a catalytic converter to almost eradicate particulate matter, NOx and carbon dioxide emissions.

The quest for cleaner burning trucks is not the sole domain of oil companies. OEMs have, for many years, been investing in the development of engines that run on alternative fuels, capable of near-zero emissions and improved efficiency.

Volvo is one example, unveiling a second-generation 'green' truck in mid 2005. The vehicle, a conventional diesel Volvo FM model, is fitted with a modified fuel line adapted for a bio-fuel called DME (dimethyl ether), a gas that converts to liquid when compressed.

DME is derived from a number of renewable resources (like black liquor, a by-product of the production of paper pulp) as well as fossil fuels and is purported to release almost no harmful emissions. Volvo states that emission levels from the DME truck are lower than Euro 5 standards.

The DME engine combusts at much lower pressures than a conventional diesel engine but also uses a common-rail injector unit. DME has a lower viscosity and lubricity than diesel and therefore special sealing materials were needed for the engine as well as lubricating additives. Watch out OPEC.