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Diesel technology continues to develop

Diesel's popularity on a global basis far outstrips that of electrically powered vehicles, even including hybrids.

  • Audi_RS5_TDI_electric_turbo

COPENHAGEN, DENMARK — Given all the attention electric vehicles are getting these days, one could be forgiven for believing that the internal combustion (IC) engine as an automotive power plant is already dead.

It’s not. In fact, the most popular alternative to the gasoline IC engine isn’t electric, it’s the diesel IC engine.

Diesel’s popularity on a global basis far outstrips that of electrically powered vehicles, even including hybrids. On a comparative basis, battery-only EVs have made barely a blip in the marketplace.

There is no doubt that further electrification of vehicles is inevitable.

But it’s likely to occur in a variety of ways that go beyond simply driving the wheels with an electric motor — a point Audi made here this week at an event celebrating 25 years of TDI diesel engines.

TDI technology, which is shared among Volkswagen Group brands, including Audi, encompasses three core components — turbocharging, direct injection and a high-pressure common rail fuel system.

When Audi introduced TDI in its 100 sedan at the Frankfurt auto show 25 years ago, it marked a paradigm shift both in how diesels performed and in how they were perceived.

Before that turning point, diesels were seen as better suited to heavy duty industrial applications — stationary power plants or engines in ships, construction equipment and transport trucks — than to high-revving passenger car use.

They produced tremendous levels of torque but at relatively low speeds and within a small peak power band.

The TDI engine maintained the key strengths — high torque output and exceptional efficiency — but added the ability to deliver them over a broad speed range, similar to that of gasoline engines.

In short, it was the technology incorporated in TDI that made diesels truly desirable for application in passenger cars, and later in utility vehicles.

They performed as well as gasoline engines in most respects — better in some, such as initial acceleration at low speed — and consumed significantly less fuel in the process.

That introduction was just the starting point, however, for TDI engines have continued to evolve through their 25-year history, becoming ever more powerful and fuel efficient, as well as quieter and much, much cleaner. Of necessity, they now meet the same emissions requirements as gasoline engines.

At this event, Audi revealed details of the latest edition to its TDI lineup: a redesigned 3.0-litre V6 that will debut in the A7. In base form, Audi says, it is 13 per cent more fuel efficient than its already fuel-thrifty predecessor.

The 3.0-litre comes in three forms: a base model with a single turbo, a higher-efficiency Ultra version and a higher-performance bi-turbo. Demonstrating the versatility of the concept, the power outputs for the three variants are 272, 218 and 326 horsepower respectively, with corresponding torque plateaus of 429, 295 and 479 lb.-ft. — something to suit every purpose.

Rather than using a separate turbocharger for each cylinder bank, as is sometimes done in twin-turbo gasoline engines, the biturbo employs turbos of different size in a best-of-both arrangement.

At low speeds, when the exhaust airflow through the bigger turbo is low and provides little boost, it is rerouted through the smaller one, which spins faster, ramping up pressure more quickly. At higher speeds, the exhaust pathway to the bigger turbo opens as well.

It’s an effective way to combat the dreaded turbo lag on initial acceleration — once the bane of turbocharged engines, gasoline or diesel. In the A7 I drove, there simply was no perceptible lag.

That said, Audi has taken a further step, in concept form, by installing an electric motor to spin up the smaller turbo even before exhaust gases can do so. I had a chance to test an RS5 Coupe concept fitted with that engine on a track and it blasted off the line with the kind of kick in the back I associated with the muscle cars of my youth.

That’s one way to add electrification to a vehicle. Another, of course, is hybridization and Audi made it clear that there will be diesel hybrids, including plug-in hybrids, in its future. The company has already honed its expertise on that combination with its Le Mans winning race cars.

It’s a logical progression. If diesels are the most efficient form of conventional IC engines, which they are, it simply makes sense to use them as the IC half of a hybrid powertrain.

Whether on their own or in a hybrid configuration, diesel engines will continue to develop and are likely to play a major role as an automotive power plant well into the future.

Travel for freelance writer Gerry Malloy was provided by the manufacturer. Email: [email protected]

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