Fuel and AdBlue contamination can spell disaster for modern engines, and one way it can occur is by simple human error. Diesel nozzles are larger in diameter than petrol, so it’s highly unlikely a mistake will be made in that direction, but putting petrol into a diesel tank is perfectly possible, and in these days of endlessly escalating fuel prices, the opportunity is greater as well – after all, there can be few of us who haven’t seen vans, small lorries and even tractor units filling up at supermarket petrol stations on occasions. AdBlue is another area of concern, especially when decanted out of cans or drums..
Putting petrol in a diesel engine can, indeed, have damaging effects, confirms Andy Mudie, engineering manager at DAF Trucks. The first instance, however, isn’t even in the cylinders themselves, but all the components in between. “Diesel as a fuel has very good lubricity, and as a result, many components are designed to utilise these lubricating properties,” Mudie points out. This lack of lubrication may not be apparent straight away, but damage may manifest itself in future, impacting heavily on the reliability of the vehicle.
“To best understand the next big issue, it is important to remind ourselves of the fundamental differences between petrol and diesel engines,” Mudie says. “A petrol engine uses a spark ignition which is timed to ensure the air-fuel mixture in the cylinder combusts at the right time.” Cylinder pressure and temperature are low until the timed spark ignites the mixture.
“In a diesel engine, there is no mixture of fuel and air in the cylinder on the compression stroke,” he continues. It is compression of the air alone which creates heat, then a timed injection of fuel causes combustion. “Due to its volatility, petrol injected into a diesel engine is likely to pre-combust on the initial injection, meaning the engine cannot run correctly. Also due to added heat, the valve seats and valves will begin to overheat or burn out, causing internal engine damage.”
If and when it is realised a misfuelling mistake has been made, the advice is very simple. “The best option in this situation would be not to start the vehicle,” Mudie says. “The tank and lines can then be drained and flushed, which would prevent most issues. If the vehicle is started and moved, it would have a detrimental impact on future reliability.”
FOOLPROOF?
A petrol/diesel misfuel is likely to be down to a simple case of distraction, and one would hope the distinctive smell alone would alert the driver relatively quickly. The same is far less true of diesel and AdBlue. The vast majority of AdBlue pumps found on forecourts and in depots use a magnet system to reduce the possibility of a mistake – unless the magnet in the filler nozzle recognises its counterpart in the AdBlue tank neck, it simply won’t dispense. But a great deal of AdBlue is bought and dispensed from 10-litre plastic bottles, which is when the problems start.
“We see a moderate number of incorrect fluids in the incorrect tanks on an annual basis. However, this is far too frequent for my liking and could be avoided,” says Iain Chapman, product quality manager at Volvo Trucks. “Ten-litre plastic containers of urea can be and are poured into the fuel tank.”
AdBlue is made up of around 32% urea, while the remaining volume is just distilled water. The urea is highly corrosive and causes rapid oxidisation of certain metals.
If a very small amount of AdBlue is poured accidentally into a fuel tank, and that tank is then filled up with diesel, the dilution should be enough that very little damage occurs. But Chapman has seen examples where 150 litres of Adblue have been put into the wrong tank, and then the truck has been run, causing huge damage and very costly repairs.
“AdBlue will destroy all soft metals, including copper, zinc, lead bearings and aluminium, as well as engine oil,” he tells us. “If large quantities are filled into the fuel tank, then damage to the expensive fuel injection system will – and does – occur. It can also damage the piston crowns,” Chapman continues. “Contaminated fuel/AdBlue mixture is injected into the cylinder at 2,400bar pressure and erodes it away, which means it then ends up in the oil.”
Over at DAF, Andy Mudie agrees. “If AdBlue was transferred through the fuel system until the engine stopped, the whole system would be damaged. Most components would begin to corrode and not work as effectively, or completely fail,” he warns. “As a lot of large-capacity engines use a fuel gallery within the main engine block, the engine block itself would also begin to corrode,” he continues. “This means that, even after the replacement of the main fuel system components, there will already have been an impact on vehicle reliability for the remainder of the vehicle’s life.”
The opposite scenario – diesel into AdBlue – is also a possibility. “Diesel can get into the AdBlue tank if the tank filter in the filler neck gets removed, which then allows a diesel nozzle to enter,” Chapman adds. “This then gets injected directly into the exhaust after-treatment system, causing emission faults and contamination of the silencer.” Fortunately, although emissions systems are designed to prevent deliberate attempts to avoid the cost of AdBlue, today’s technology will rapidly detect an accidental problem as well.
“On some of our vehicles, the issue would be picked up on key-on by the AdBlue quality sensor in the tank, which will detect a deviation,” Andy Mudie states. “On other vehicles, it would be picked up by the NOx sensors which measure the conversion after dosing. As it is an emissions-based system, a derate would be triggered,” he adds. “This encourages rectification and so hopefully limits the damage.” The latest systems now have seals which are better suited to hydrocarbon contamination, too.
PREVENTION
The ideal, of course, is for these kinds of issues to be avoided in the first place. “Operators should continually educate all of their drivers on the costly outcome of getting it wrong, and the dos and don’ts which should be observed if such mistakes are made,” Iain Chapman advises. They will also be advised during Volvo’s vehicle handover process.
“If the incorrect fluid has been filled in the incorrect tank, then the safest thing for the operator is to have the vehicle recovered into a Volvo workshop,” he points out.
“If the volume of fluid added can be accurately determined – for example, if a 10-litre plastic can of AdBlue has been added to 200 litres of diesel, then a technician can make the evaluation on site when attending,” Chapman concludes. “But remember the safest option is always the same: do not start or drive a truck with contamination.”