Technical Superiority: High-Tech Diesel Engines from Audi

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January 7, 2007

Source: Audi AG

The new V12 TDI with its supreme performance is a trademark Audi engine. Ever since it first invented the TDI engine 18 years ago, the brand has played a pivotal role in advancing technology in this field. Diesel engines from Audi are powerful, efficient and smooth, and they have demonstrated their superiority both on the road and the racetrack.

368 kW/500 bhp – the new V12 TDI engine in the Audi Q7 is a veritable pageant of technology and represents the new pinnacle of passenger car diesel development. The twelve-cylinder power unit provides unquestionable proof of the pre-eminent technological expertise at Audi. 18 years after the Ingolstadt brand invented the modern-day TDI engine, it is presenting it in an all-new high-tech, range-topping guise.

The wide-ranging pool of know-how at Audi is also plainly in evidence in the brand’s other large diesel engines which likewise succeed in fusing sheer power with excellent efficiency. The two V6 TDI units summon 132 kW/180 bhp and 171 kW/233 bhp respectively from their capacities of 2.7 and 3.0 litres, with the V8 TDI drawing 240 kW/326 bhp from its 4.2 litres. The TDI engines from Audi are full of power and torque, yet they are also efficient and economical, as well as being quiet and smooth.

TDI engines are full of power

The three-litre TDI unit propels a variety of Audi models, ranging from the mid-size A4 up to the Audi Q7 high-performance SUV. Its 171 kW/233 bhp equates to an output of 57.6 kW/77.9 bhp per litre – a figure which up until just a few years ago was unprecedented outside of the sports car faction. In all of the models it is fitted in, the 3.0 TDI drives all four wheels via the quattro permanent four-wheel drive system, yet another Audi technology whose tremendous potential for motoring pleasure and driving safety underscores the brand’s sporty essence.

The three-litre diesel engine ensures dynamic performance. It powers the Audi A8 luxury saloon, for example, to a majestic top speed of 243 km/h and from nought to 100 km/h in just 7.8 seconds. Yet more evidence of the Audi brand’s exclusive expertise can be found in the A8 3.0 TDI quattro: its body tips the scales at a mere 222 kilograms thanks to its state-of-the-art Audi Space Frame (ASF). ASF reverses the weight spiral. Recently, Audi received the European Body Car Award for the TT body with its hybrid construction that makes intelligent use of aluminium combined with steel.

TDI engines are full of torque

The great strength of all diesel engines from Audi is their immense torque. The pulling power of diesel engines clearly surpasses that of comparable petrol units. What’s more, their power is on tap at very low revs, just above idling speed in fact – meaning that the driver merely has to coax the accelerator pedal for a smooth yet persistent build-up of thrust. Consequently, the pulling power is there whenever it is needed, making for a composed and relaxed driving style.

Built in the vein of a classic American small block, the three-litre V6 transmits as much as 500 Nm of torque to the crankshaft at engine speeds as low down as 1,400 – 1,500 rpm. The diesel powerplant generates an exceptional 168.5 Nm for each litre of capacity.

TDI engines are efficient and economical

Diesel engines make more efficient use of the energy contained in the fuel they run on than petrol engines do. Audi has played a decisive role in the development of the many different solutions that have been devised to capitalise on this fundamental principle of physics – four-valve-per-cylinder technology for an optimum cylinder charge in any operating situation is just one example, as is the principle of variable turbine geometry used in turbochargers.

The A8 is a saloon of stately proportions, measuring 5.06 metres in length, but even in such a large car the 3.0 TDI demonstrates astounding restraint in terms of fuel consumption. On the EU driving cycle, it limits itself to an average of 8.5 litres per 100 km, while the 2.7 TDI in the Audi A4 is even more frugal, burning just 6.7 l/100 km.

Such high efficiency heralds more than just financial benefits for drivers, especially on long journeys: thanks to the 90-litre tank capacity, motorists adopting a relaxed driving style can cover far in excess of 1,000 km between refuelling stops – not only does this cut costs, it saves time and nerves too.

TDI engines are quiet and smooth

The sound from Audi’s latest direct-injection diesel units is barely perceptible to passengers’ ears, as they run every bit as quietly as their petrol counterparts. This is partly down to the extensive development work carried out by the acoustic engineers at Audi. Carefully positioned finning on the cylinder blocks nips vibrations in the bud, while all of the potential paths via which vibrations could be transmitted into the interior have been eliminated from the engine mountings and bodyshell.

One of the key advances can be attributed to the common-rail technology, as it virtually gives the control unit free rein over the injection of fuel, which can take place up to five times during each power stroke. The pilot injection phases take place well in advance of the main injection to produce a more gradual pressure build-up for smoother combustion. The innovative piezoelectric injectors used by Audi in its large diesel engines heighten this effect with their extremely fast, high-precision actuation, finally putting an end to the harsh knocking and metallic rattling sounds normally heard at partial throttle.

Audi – drawing on a wealth of TDI expertise

The engine unveiled by Audi at the Frankfurt Motor Show in the late summer of 1989 was nothing less than an absolute sensation: exhibited in the Audi 100, the five-cylinder turbodiesel mustered 88 kW/120 bhp and 265 Nm of torque from its capacity of 2.5 litres. It was the first ever passenger car diesel engine to feature direct injection and fully electronic management – in short, the world’s first TDI.

The beefy power of the five-cylinder drive unit redefined standards in the diesel segment when it went into series production in 1990. And Audi has been consolidating its head start ever since with one new development after another.

1991 marked the debut of a four-cylinder TDI model which extracted 66 kW (90 bhp) and 182 Nm from its capacity of 1.9 litres. Four years later its output was upped to 81 kW/110 bhp, thanks partly to the inclusion of a brand new turbocharger with turbine vanes that could be adjusted flexibly to match current requirements. The advertising slogan “Where’s the tank?” made the TDI’s proverbial economy and its tremendous operating range famous in Germany – the 66 kW/90 bhp variant of the 1.9 TDI made do with a mere 5.1 l/100 km in the Audi A4.

The five-cylinder engine’s output was uprated to 103 kW/140 bhp in 1994; coupled to a six-speed gearshift and optional four-wheel drive, it advanced to the status of the first TDI quattro. With vital statistics reading 290 Nm of torque at 1,900 rpm, a top speed of 208 km/h, 9.9 seconds for the 0-100 km/h dash and a Euromix fuel consumption of 6.0 l/100 km, it set a new benchmark for sporty touring saloons to measure themselves by.

The world’s first V6 TDI passenger car engine followed in 1997. Fitted with a four-valve cylinder head – yet another major innovation on the TDI front – it had an output of 110 kW/150 bhp. Audi premiered its first diesel engine with the pioneering common-rail injection system in 1999 when it unveiled the 165 kW/225 bhp V8 TDI. The very same technology is employed by the current family of V diesel engines, ranging from the 2.7 V6 TDI and the 3.0 V6 TDI to the 4.2 V8 TDI and finally the new six-litre V12 TDI.

For 18 years now, Audi has been harnessing all of the innovative flair it has amassed in this field to constantly push back the limits of what is possible. The TDI engines have been pivotal in the Audi brand’s rise to the rank of sporty premium manufacturer; today, every second Audi that is sold worldwide has a diesel engine under the bonnet. The TDI engines have enjoyed an unparalleled triumph – and the success story is set to continue apace.

TDI on the racetrack: a quiet, efficient, dominating force

Initially, even the drivers could not believe their ears – seasoned professionals of the likes of Tom Kristensen and Frank Biela suddenly had to change their habits. Previously, they had used the engine noise emanating from their open sports cars as an important yardstick – and now the engine noise faded out altogether above a certain speed, so quiet was the V12 TDI in the new R10.

The V12 diesel race car from Audi has taken motorsport into a whole new era. Designed in accordance with the regulations that govern the Le Mans 24 Hours, the 5.5-litre TDI racing engine is a cut above the rest. With its prodigious torque of over 1,100 Nm, it comfortably outperforms any petrol model. At its rated engine speed, over 478 kW/650 bhp is on tap – translating into a top speed in the region of 330 km/h.

A further forte of the V12 TDI is its low fuel consumption. Measured against its already extremely efficient predecessor, the R8 with petrol direct injection, the R10 TDI burned considerably less fuel at Le Mans. This was despite the fact that the diesel was unable to make the very most of its strengths on the Sarthe circuit with its long straights and a full throttle ratio approaching the 75 percent mark.

The high range was crucial to victory

The high range and the resulting reduction in the number of refuelling stops proved to be a crucial factor in the victory at the classic 24 Hours. Frank Biela (Germany), Emanuele Pirro (Italy) and Marco Werner (Germany) only had to call in at the pits 27 times in their car with start number 8. They completed 380 laps – 5,187 km – at an average speed of 215.409 km/h.

Spurred on by its triumph at Le Mans, Audi went on to achieve something that no other manufacturer had before it – the R10 TDI won all eight of the races it competed in over the course of the 2006 season. The sequence of victories spanned the breadth of the United States, starting in March at the 12 Hours of Sebring in Florida and culminating at Laguna Seca in California in October.

In the American Le Mans Series, Scotsman Allan McNish together with Dindo Capello from Italy emerged as the overall champions of the large LMP1 category long before the season had drawn to a close. With a total of 23 wins under his belt, Capello is the most successful ALMS driver of all time. Audi also took the constructors title in the large LMP1 category by a substantial margin after racking up 215 points ahead of Lola in second on 160 points.

A panel of judges from the British magazine “Race Engine Technology” voted the V12 TDI in the Audi R10 TDI “Race Engine of the Year 2006” and “Alternative Race Engine of the Year”. The engine’s design engineer Ulrich Baretzky, Head of Engine Technology at Audi Sport, and the Head of Audi Motorsport Dr. Wolfgang Ullrich perceive the V12 TDI as a perfect illustration of motorsport and series production cooperating closely with one another.

Transfer between motorsport and series production

“We can avail ourselves of the expertise and test facilities of our colleagues in series development,” remarks Dr. Ullrich. The know-how flows both ways though, with technological highlights from the racetrack often injecting vital new stimulus into series development.

Audi performed a similar technology transfer back in the late 1980s. At that time, the touring cars from Ingolstadt were dominating the TransAm and IMSA races thanks to their quattro drive and turbocharged petrol engines that generated in excess of 700 bhp in some cases. 20 years on, large-scale series development is once again reaping the benefits of motorsport technology.

The data and the performance and fuel consumption figures stated here refer to the model range offered for sale in Germany. Subject to amendment; errors and omissions excepted.


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