Continental's clean diesel Golf.
Continental's clean diesel Golf.

Can diesel's reputation recover from VW saga?

DIESEL'S dirty reputation, which is costing sales, can be cleaned up. But will help arrive in time? "That's a very good question,” says Jose Avila of German car component giant Continental.

The company heavily modified a VW Golf diesel to show that detox is feasible. Continental's choice of car makes sense. The discovery of emissions-cheating software in VW by US researchers started the Dieselgate stink in September 2015.

Diesel is declining in popularity in Australia. To the end of June, diesel SUV sales to private buyers fell by 3700, or almost 10 per cent - and sales of diesel cars to private buyers were even worse, falling by more than 23 per cent in the same period.

Diesel cars don't sell nearly as well as diesel SUVs, so the number of lost diesel sales in this case is much smaller.

Avila believes a comeback with the consumer is possible. "It is hard to advertise or push the diesel when there is still some clean-up to do, literally,” says the engines and transmissions boss. "(By 2019) there's going to be a lot more promotion for the diesel, demonstrating you can clean it.”

Avila thinks it's too early to tell whether the erosion of diesel's market share is unstoppable. The lower CO2 emissions of diesel vehicles compared to petrol-burners remains a strong point so "it should allow for a comeback or at least a stabilisation of the market share”.

The diesel engine's problem has never been CO2. Its lower fuel consumption means lower emissions of this major greenhouse gas.

Instead the problem is NOx (oxides of nitrogen), the health-harming pollutant emitted in much smaller quantities than CO2. Dieselgate was sparked by the discovery of real-world NOx emissions far above the legal limits.

Continental's modified VW Golf was fitted with RDE (Real Driving Emissions) equipment - a miniaturised emissions testing rig that can be bolted to a car's towbar for accurate measurement of its emissions.

By 2020 the European Union will phase in RDE testing as an extra requirement, above and beyond current emissions-lab tests, and car brands will have to pass RDE tests to get the type approval that shows their products meet the legal requirements to be sold.

The modified Golf is easily able to deliver NOx emissions well below the legal limit in normal conditions. At the end of my test drive at Continental's proving ground in Germany, including stops and starts, the RDE readout screen in the car showed NOx emissions a little above half the European legal limit.

Clean diesels can be made but they won't be cheap. Continental engineers used existing technology - 48V micro-hybrid set-up, electrically heated exhaust catalyst and high-pressure fuel injection to produce a squeaky clean result but extra tech means extra costs.

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