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Diesel vs Hybrid

POSTED BY admin ON 03 April 2012

A Hummer H1 has a lower life-cycle energy cost than a Toyota Prius hybrid.
A Toyota Prius takes more energy to build than a Hummer H3 and is therefore not as environmentally friendly as Toyota claims, so says market research agency CNW Marketing.

CNW Marketing’s “Dust to Dust” report in 2007 was the origin of a highly circulated myth that critics of hybrids still perpetuate.

In truth, CNW’s claim was quickly debunked by those in the know. The most obvious flaw was a clearly biased assumption on the total distance travelled over the vehicle’s lifetime. CNW assumed a Hummer H1 will travel over 609,000km in its lifetime, while the Prius will cover only 175,000km.

CNW’s argument was that the Hummer will last longer, which was clearly an unsubstantiated claim.

In fact, all over the world, Toyota Prii (plural of a Prius) are driven almost non-stop daily by taxi drivers. An Australian taxi company with a fleet of 32 Toyota Prii (plural of Prius) had only a single case of hybrid battery replacement, after 500,000 km. The highest recorded mileage for a Toyota Prius is over 550,000 km with no failure on the hybrid system.

Prius taxi in Switzerland

Prius taxi in Hong Kong

As expected, independent, peer-reviewed academic studies show the Toyota Prius have a far lower life-cycle energy cost.

A hybrid is not environmentally friendly once battery production is taken into account
Production of batteries and electric motors require intensive mining of rare earth metals, including nickel, lithium and neodymium. Like all mineral extraction, there will be significant environmental impact.

However, the same argument also applies to extraction of crude oil. But unlike oil, batteries can be recycled. Oil is a single use resource and once burnt, cannot be recovered.
Oil is a diminishing resource and there is no argument about that. Batteries however, can be recycled many times over.

Even without recycling, hybrid batteries that are past their automotive service life are still powerful enough for secondary uses. They can be used as an emergency back-up power for homes and offices while some power generation companies are evaluating their use as a buffer energy storage in power plants to meet peak demand.

Diesels are more economical and provide higher mileage than hybrids.
That is true. A VW Golf BlueMotion TDI, for example, consumes only 3.8 litres per 100 km, significantly better than many hybrids.

However, keep in mind that in a free market, diesel is often more expensive than petrol. In Britain for example, premium diesel for passenger cars retail at 155p (RM7.55) per litre versus 140p (RM6.83) per litre for regular unleaded petrol.

In the Malaysian context where diesel is subsidised more than petrol, total gains can be quite significant. However. because of our lower quality Euro 2M diesel, there aren’t many model choices available.

Diesel engines have a higher compression ratio and the engine block needs to be built with stronger materials. Thus diesel engines cost more to produce. Again, taking the example in Britain, a VW Polo BlueMotion TDI is the second most expensive variant after the Polo GTI.

To remain legal in the latest Euro5 emission standard, diesel engines now require exhaust gas treatment (urea based Selective Catalytic Reduction or SCR) and a particulate filter. Both items require periodic maintenance and the urea tank needs to be topped up regularly. So there are added maintenance cost associated to a diesel.

The only clean diesel engine that does not require SCR is Mazda’s SkyActiv-D engine.
Having said that, there are many satisfied Malaysian owners of BMW 320d and 520d diesel. Nasim is also considering to introduce Peugeot’s famed HDi diesel powered models in Malaysia.

Diesels are more environmentally friendly because they use less fuel
Not necessarily. The nature of how a diesel engine works also means NOx and particulate matter (soot) emission are significantly higher.

In Malaysia, most European clean diesel engines are running with their PM filter removed to accommodate our lower quality Euro2M diesel. Clearly the environmental friendly argument does not apply in Malaysia.

When the new Euro6 emission standard is enforced in the EU by 2014, it will be even more difficult for diesels to remain legal. Many European manufacturers admit that further development of diesel engines will be limited and this is the reason why VW and the PSA Group, both strong advocates of diesels, are gradually moving into petrol-electric hybrids and diesel-electric hybrids.

Peugeot 3008 Hybrid4 - world's first production diesel-electric hybrid passenger car

What about diesel-hybrids?

Diesel engines are between 5 and 10 per cent more efficient than a petrol equivalent. The idea improving an already very economical diesel engine with a hybrid set-up is attractive.

But there are several challenges to this. Firstly, a diesel engine is in itself a higher cost item. Hybrid components are very complex to design and costly to build. Combining two high cost components in the hope of lowering fuel expenses is not a very attractive proposition to many carmakers. This is the reason why both Toyota and Honda, the current leaders in hybrid technology, have shown little interest in diesel-electric hybrids.

Then there is the driving experience. One of the key challenges in designing hybrid vehicles is to maintain a smooth transition between engine power and battery power. The higher NVH characteristic of a diesel engine makes this task a lot harder, requiring even further high cost engineering solutions.

Still, the PSA Group is confident that its concept is workable. The Peugeot 3008 Hybrid4 is the world’s first production diesel hybrid car, followed by the 508 RXH.

This is a continuation from our quarterly review series centre spread story Going Beyond Hybrids. This article first appeared in March-28’s edition of CBT Quarterly Review.

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