The search for cleaner heavy-truck engines will soon see drivers asked to fill up with urea - the chemical compound present in urine - alongside their regular diesel fuel.
The chemical is the European manufacturers' answer to rules coming into force in 2007 to stop heavy trucks spewing out toxic smog-forming nitrogen oxides and soot, linked to more than 200,000 deaths a year. Catalytic converters supplied with urea can cut out more than 60 per cent of the pollutant from the cleanest engines now available.
It sounds like good news for all: truck operators will see fuel costs fall by more than the cost of the chemical, while polluted parts of Europe should benefit from a drop in dirty diesel engine fumes. After treatment, almost all the nitrogen oxide in the exhaust is turned into harmless nitrogen and water.
But doubts are being raised about whether the solution of urea required - dubbed AdBlue by truckmakers in a triumph of marketing over reality - will be available on time. Even where it is available, it's not clear that drivers will want to pay for the extra 1.5 to 2 per cent to already high fuel costs.
Leif Johansson, chief executive of Volvo, Europe's second-biggest truckmaker, warned the European Commission last week that, without legal changes forcing drivers to fill up, many of the new lorries would be dirtier than current ones.
"There is a problem on the side of the oil companies," says Dietrich Müller, who is leading the launch of the new trucks in Europe at Daimler. "We need a distribution network there."
The first trucks equipped with the new system are due to go on sale this autumn. Müller expects them to be bought by freight companies making heavy use of toll roads in Germany and the Netherlands, where discounts for trucks using the new technology will be available well before the start date of the new rules in three years.
Johansson said it was impossible to estimate how many drivers would try to save cash by not using urea, but "it could be pretty heavy." By comparison, when cleaner engine rules came in in the US two years ago - making them less efficient, but not involving fuel changes - up to a quarter of truck companies ordered extra vehicles early to get the older engines that were cheaper to run.
US regulators have already indicated that they are not ready to accept the new system, known as selective catalytic reduction (SCR), because they can see no way of forcing drivers to use the urea.
The new emissions regulations come into effect in 2007, and can be met by another system - being adopted for the US - known as exhaust gas recirculation (EGR). But EGR makes engines less efficient and needs filters to catch soot, further increasing fuel consumption. It would also be very expensive to make engines meet the further tightening of emissions rules due for 2009 in Europe and 2010 in the US.
"It makes no economic sense" to use EGR for the 2009 rules, says Amsgar Schäfer, head of engine technical development for the regulations at DaimlerChrysler, the world's largest truckmaker.
European regulators are exploring the possibility of enforcing the rules by restricting what trucks can do if the urea tank is not filled. Ideas include a low speed limit - "limp-home mode" - or a limit on how many times the engine can be started. Manufacturers are opposed to such moves. "If the driver is in Kazakhstan and he has to come back at 40km an hour that would be a very long journey," says Schäfer.
Some truckmakers fear that, without central rule-making, drivers face complex or even contradictory laws on filling the urea tank in different member-states, while passing 25 separate national laws could also take a long time.
However, Daimler expects strong enforcement in Germany, which sits across several vital north-south and east-west transport links in the EU, to force most large trucking companies to run their vehicles cleanly.
But the problem of enforcement should go away in 2009, both officials and truckmakers hope. Detectors are then due to be installed on board to record engine pollution levels.
This has also raised hopes among the manufacturers that US regulators could be persuaded to allow the urea system - not least because they can find no other financially feasible way of meeting the next generation of pollution requirements.
A dirty image haunts US diesel
Ask an American driver about diesel and he or she will probably recall the clouds of black smoke which used to belch out of the back of the poorly designed late-1980s diesel cars. Mercedes-Benz is trying to overcome this negative image by bringing modern European diesel E320 cars to the US.
The sales pitch is simple – the cars are up to 30 per cent more fuel-efficient than petrol vehicles, while high torque gives them better towing ability and a faster start on the short freeway entry ramps. But sales remain tiny: just 3,000 this year. Only one other company, Volkswagen, sells diesel cars in any numbers in the US. Its sales also remain tiny compared with the 16.8m petrol cars and light trucks sold in the US last year.
New light vehicle emissions rules coming in 2007 will mean even the cleanest of today’s diesels can’t be sold in the US. A problem is the cost of the system. "Probably this can’t be a business case in the near term," says Hans Schulte, chief engineer for diesel research and advanced engineering at Ford. "It’s really a fuel price issue. If the US had the same prices as Europe and the rest of the world, a diesel market would have developed long ago."
If EU regulators, under pressure from Germany, adopt equally strict standards for cars in 2010, urea might become a standard second fill-up for European diesel drivers. In this case, says Schulte, it would probably be introduced in the US too, as no extra development cash would be needed.