► Bentley Bentayga Diesel is launched
► It's Crewe's first-ever oil-burner
► Uses Audi-style triple charging
Bentley has introduced its first diesel in its mould-breaking Bentayga SUV and, as you might expect from a company that prides itself on effortless performance, the 4.0-litre V8 doesn’t disappoint.
A total of 429bhp and 664lb ft of torque from just 1000rpm combine to make the Bentayga the world’s quickest diesel SUV – with the 0-62mph sprint being dispatched in just 4.8 seconds. Flat out, it’ll hit 168mph.
The oil-burning Bentayga also boasts the brand’s lowest CO2 rating, at 210g/km, and is claimed to average 35.8mpg. That grants it an overall range approaching 620 miles, thanks in part to its large 17-gallon fuel tank.
Bentley Bentayga Diesel review: we drive the new oil-burning crossover
Bentley diesel: two turbos and a compressor
This combination is key to that prodigious torque figure and the impressive acceleration times quoted by Crewe. Adopting 48 volts for its active roll bar technology allows Bentley to apply it to other vehicle functions – in this case a 7kW e-compressor that spins up to 70,000rpm in 250 milliseconds from start. This forces air into both banks of the V8, leading to a prompt response and an increase in its exhaust gas output, which helps spool the first turbocharger quickly.
The clever bit is that the engineering team has utilised the same cylinder deactivation technology employed in the petrol V8 to close off one exhaust valve per cylinder. There are two exhaust valves per cylinder, but each supplies a different turbo. At low speeds the exhaust valve supplying the second turbocharged is closed, increasing the exhaust gas flowing into the first turbo – allowing it to quickly and smoothly take over from the e-booster beyond engine speeds of about 1500rpm.
As engine speed increases the cam slides across, opening the second exhaust valve to feed the ‘passive’ turbocharger, which comes on boost from about 2700rpm to the redline.
It sounds fiendishly complex...
It is. And packaging it all within the tight confines of the vee must have kept engineers awake at night, but going by the brief passenger ride with Bentley’s engineering director, Ralf Frech, at the helm the continuous surge of torque that is such a part of Bentley’s DNA isn’t missing from the latest addition to the Bentayga family.
Keeping emissions under control are, effectively, four after-treatment systems built into two exhausts: a NOx trap that doubles as a regular oxidation catalyst, urea injection which acts as a SCR, and a particulate filter to trap more diesely nasties.
Heavily revised calibration for the ZF eight-speed auto ensures the diesel V8 performs as well off-road as its W12 sibling, according to Bentley engineers.
In bed with Audi – again!
As with the petrol V8, the engine is a joint development with other brands within the Volkswagen empire, principally Audi. 'Paul Williams [Bentley’s director of powertrain development] team was involved from the concept stage onwards,' Frech told CAR. 'So the base engine was done with Audi but the calibration, inlet manifolds, exhaust and emissions development are all unique to Bentley.'
Despite the furore over VW’s dieselgate emissions scandal, Frech believes diesels have a long-term future in this class of vehicle, even compared with plug-in hybrids which are a magnitude of cost higher, though he concedes that some city-drivers might want a hybrid in the future.
And it costs?
The new Bentley Bentayga Diesel is priced at £135,800 in the UK, or about £30k less than an entry-level W12; for that, owners also get a new black radiator mesh, a diesel badge and twin quad tail pipes to mark out the derv crossover.
Buyers can opt for split-colour leather seat and door trims and liquid amber veneer (pictured above), the first new Bentley timber trim in five years.
With sales already ahead of this year’s 3600 target, Bentley expects to sell closer to 5500 Bentaygas before the end of 2016. It forecasts that in 2017 diesel variants will account for half of all its sales in the UK, Europe, South Africa and Australia - whilst also attracting younger buyers into the Bentley fold.
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