The world's biggest car maker, Toyota, believes diesel-powered cars could be priced -- and regulated -- out of existence by the end of the next decade.
It sounds like an attention-grabbing swipe from the company that has produced almost two million petrol-electric hybrid vehicles before most other brands have developed their first; hybrid cars have come under continual fire from Europe's big diesel-selling brands.
However, Toyota's argument is surprisingly straightforward. By its calculations and research, the cost to make diesel engines meet increasingly stringent emissions regulations will make them more expensive to manufacture and maintain than cars with petrol-electric hybrid drivetrains.
The next big reduction in emissions limits is the Euro VI standard which, at present, is proposed to be enforced from September 2014. It targets significant reductions in the emissions of oxides of nitrogen (NOx), hydrocarbons (HC), particulate matter (PM), and carbon monoxide (CO), among others.
The chief engineer for the new Toyota Prius hybrid, Akihiko Otsuka, explained the rationale during his recent visit to Australia: "The emissions [level] for diesel is defined already for Euro VI. The NOx restrictions will be much more severe. So, Toyota thinks, based on our latest research, that the cost to manufacture a petrol-based hybrid and a diesel powerplant is basically the same. But the cost to run a hybrid will be cheaper because there is less maintenance."
He said the initial resistance from European makers towards hybrid technology has waned in recent years, with Peugeot, BMW and Mercedes-Benz all announcing hybrid plans.
"In Europe, diesel is still very popular. Hybrid is not so popular," he said. "But I'm sure hybrid will be popular in the near future."
He said even diesel hybrids would likely have more harmful emissions than petrol hybrids, in particular because of the extreme disparity in the levels of NOx.
As an example, the new MINI Cooper diesel emits 56 times more oxides of nitrogen than does a new Toyota Prius -- even though both vehicles have the same fuel economy rating of 3.9L/100km.
It is for this reason, Otsuka said, all vehicles in the Toyota range will be available with hybrid power by 2020.
Toyota Australia's corporate manager of product planning, Peter Evans, says Toyota believes diesel is a "transitional technology".
"By the time you take into account the cost of making diesel engines meet ... Euro VI emissions, they may make less economic sense," he says.
"You have the cost of urea injection, which has to be filled up by the dealer between your service intervals. Then you have a soot trap or particulate filter that has to be burned off by the dealers. Then you have a NOx reduction catalyst, then you have the cost of direct injection, and by then diesels may well price themselves out of the market.
"When you add to that the cost of diesel fuel, then the diesel equation in the longer term doesn't look all that bright."
Toyota emphasised that it would continue to offer a range of diesel engines in its 4WDs and utes until petrol electric hybrid technology was ready to fill the void.
Toyota, which is one of the biggest sellers of diesel vehicles in Australia by virtue of its strength in 4WD and commercial vehicle sales, said it would take time to make the transition to hybrid power.
"[Diesel engines] are perfect for commercial vehicles where you want the torque characteristics. But electric motors have good instant torque from low revs too."
He said the tide is turning and hybrid power is slowly gaining support in Europe.
"I think there's a gradual, unspoken acceptance around hybrid technology," he said. "Five years ago they [European and American makers] were all laughing at us but recently they're quietly acknowledging hybrid technology."
The other argument against diesel is the new generation of petrol engines that have diesel-like economy -- and much fewer emissions.
The latest range of engines in the Volkswagen Golf is one example, and the head of the company has gone on record as saying super-efficient petrol cars are the way of the future.
Interestingly, there is already an example close to home of a swing away from diesel power by a local distributor of a European brand.
The distributors of Alfa Romeo in Australia deliberately chose not to import the diesel version of its new MiTo hatch because the gains in economy were miniscule, and the price premium for the diesel engine was significant.
The most frugal version of the petrol-powered MiTo sips fuel at a rate of 6.1L/100km.
"We considered introducing the diesel MiTo but quickly dismissed it once we took into account the price premium for the diesel engine and the fact that there wasn't much of an improvement in fuel economy compared to the petrol engines," said Edward Butler, the general manager for Alfa Romeo in Australia.
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