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Light my Fire

Text
Johannes Köbler

Photos
Ulrike Myrzik and Audi AG

25 Years of Vorsprung

In 1989, Audi presented its first model with a TDI engine. Since then, the technology has been an enormous success story – and the brand with the four rings continues to develop it at full speed.

Under pressure – four engineers, one resounding success

Herr Bauder, you are one of the pioneers of the TDI engine. What was it like back then, when it all began?

Bauder: The 1973 oil crisis triggered the instruction to develop an engine that was as fuel efficient as possible. It was quickly clear to us that it could only be a diesel. Following two or three years of advance development, we opted for the multi-spray process and were able to convince our system suppliers to design a pump for the purpose. At the time, the injection process was the main development driver. It wasn’t until somewhat later that the turbocharger drew even.

How many people were available to work on this?

Bauder: There were about ten of us at the time. The use of finite-element analysis was still very much in its infancy – the computer needed several days to generate a model and calculate the stiffness of a piston. The big challenge was to make the engine sellable in terms of power, torque, fuel consumption and acoustics; otherwise, it would have been a non-starter.

Weiß: We have 172 people working in diesel engine development these days, of which around one third works in the field of electronics – and that number is growing.

Baretzky: In race engine development, there are around 50 of us developing, building, stripping and analyzing the engines.

And how did things progress after the launch of the TDI in the Audi 100 in 1989?

Bauder: In many individual steps. The first were the variable turbine geometry for the turbocharger and the further development from five-cylinder to V6 with fourvalve technology; then came the common-rail systems, a little later with piezo injectors. The big challenge in the new century was exhaust-gas after treatment – we have now addressed all outstanding areas of criticism, with clean diesel incorporating catalysts and SCR systems. The TDI has now arrived at a point where it fulfills all emissions limits, including the toughest in the world.

Fröhlich: And it is on exactly this know-how that we are now building. Our next step is the storage catalyst in combination with an SCR system. This will enable us to meet the next phase of emissions legislation in Europe and the U.S. and lay a solid basis for the years to come. The next thing will be measurements under actual conditions, known as “real driving emissions”. Our current developments put us in an excellent position to address this.

Bauder: When you start with the 1989 level, pollutant emissions have dropped by 98 percent between then and now, while power output and torque have risen by between 100 and 150 percent.

The TDI men –
photo shoot at an engine test stand in Neckarsulm.

Richard Bauder (65) worked on the development of the very first TDI. From 1993 until 2012, he was in charge of Audi’s diesel engine development in Neckarsulm.

Ulrich Weiß (45) followed Bauder as head of diesel engine development. Interrupted by a brief spell with Daimler, Weiß has been with Audi since 1994.

Andreas Fröhlich (47) came to Audi in 1991. He has been lead engineer in diesel engine development since 2011.

Ulrich Baretzky (59) has been in charge of racing engine development at Audi since 1994. Since 2013, he has also been on the Supervisory Board of MAN Diesel & Turbo.

What is currently your main focus in TDI development?

Weiß: Firstly, there are the classic issues – fully variable ancillaries like oil and water pumps, reduced internal friction, new materials and new manufacturing processes. However, the steps we are taking here are getting smaller and smaller; we increasingly have to combine these things. Then we are working on the turbocharger and the Audi valvelift system (AVS), which gives us new freedoms in charge cycling and enables internal exhaust-gas recirculation. When it comes to injection, this decade will see us achieve pressures of more than 2,500 bar in production applications, which will reduce raw emissions even further. And the output per liter of 100 kW that we are striving to achieve over the next few years is highly dependent on injection pressure.

How high is the injection pressure in the TDI for the LMP1 race car?

Baretzky: Right now, it’s north of 2,800 bar – although our injection system differs from the production system only in its internals. Over the years, we have achieved more power with every 100-bar step. We are working very intensively on the issue of combustion chamber development and have found a few interesting solutions in this field, too. When you get the combustion process right, including the high injection pressures, you inevitably arrive at high ignition pressures. Emissions legislation is not really an issue – we have a particulate filter, and that’s that.

How high is the ignition pressure in a racing diesel?

Baretzky: We are at well over 200 bar – with the corresponding loads exerted on the crankshaft, bearings, cylinder heads and pistons. Our crankcase incorporates tensioning bolts made from high-strength steels. We don’t use any exotic materials, because we want to guarantee transfer into series production. The crankshaft and pistons are made from steel, the heads from aluminum. If you cast them right and cool them correctly, you achieve a considerable increase in strength and durability.

Engine failure is, of course, unheard-of at Audi Sport …

Baretzky: We haven’t had a single racing failure in the last 20 years. To a certain degree, our engines have it easier than the series-production units. They only have to hold up for 36 hours – although, in Le Mans, 73 percent of those are under full load. So in the end, it makes the whole thing more demanding …

Milestone –2.5 TDI from 1989 with 88 kW (120 hp) and 265 Nm of torque.

2.5 TDI

In 1989, Audi presented a technical milestone at the Frankfurt Motor Show. The five-cylinder in the Audi 100, with a displacement of 2,461 cm³, was the world’s first direct-injection turbodiesel with fully electronic management – the first TDI. The distributor-type injection pump for the two-valve engine built up to 900 bar of pressure.

The five-cylinder TDI started with 88 kW (120 hp) and 265 Nm of torque, the latter at 2,250 rpm. The brawny power delivery was a major statement. The Audi 100 2.5 TDI reached a top speed of almost 200 km/h, with average fuel consumption according to the then standard of 5.7 liters per 100 km. As of 1994, the five-cylinder was equipped with a redesigned pump and exhaustgas aftertreatment and generated 103 kW (140 hp) in the Audi A6; there was also a version available with 85 kW (115 hp).

First TDI with VTG charger from Audi – the 1.9-liter from 1995.

1.9 TDI

1991 saw Audi introduce the first fourcylinder TDI to the market. An extensive redesign followed four years later – the displacement of 1,896 cm³ now delivered a substantial 81 kW (110 hp) instead of 66 kW (90 hp). The maximum torque grew from 182 Nm to 225 Nm, available as of just 1,700 rpm and remaining constant through to 3,000 revs.

This was thanks primarily to a turbocharger with variable turbine geometry (VTG) on the exhaust side, which en- abled a smooth and spontaneous build up of torque, even at low revs. The powerful, four-cylinder TDI, whose distributor- type injector pump operated at almost 950 bar, ran in the A4, the A6 and the A3 launched in 1996.

In the early nineties, Audi took some fundamental decisions. In 1993, the brand shifted its diesel lineup completely to TDI engines. As of 1994, the five-cylinder – now with 103 kW (140 hp) – was also available with quattro permanent all-wheel drive. The TV spot featuring the question “Where’s the tank?” made the engine legendary. The Audi A6 TDI could cover up to 1,300 kilometers on one single tank of fuel.

The all-new V6 layout with four-valve technology – the 2.5 TDI.

2.5 V6 TDI

In 1997, the successor to the fivecylinder was the world’s first V6 TDI with four-valve technology. It presented solutions such as the swirl and tangential ducts in the intake and the radialpiston injector pump, which developed up to 1,850 bar pressure. From a displacement of 2,496 cm³, the V6 TDI generated 110 kW (150 hp) and a maximum of 310 Nm between 1,400 and 3200 rpm. It was used in the A4, the A6 and the A8. In its final evolution, it produced 132 kW (180 hp).

Premiere of common-rail injection – 3.3 TDI, the first V8 diesel from Audi.

3.3 TDI

3,328 cm³ liters of displacement, four overhead camshafts, 32 valves, two turbochargers with variable turbine geometry – the V8, which was introduced in the Audi A8 in 1999, was stateof- the-art. Its crankcase was made from high-strength and lightweight vermicular graphite cast iron; the charge air and the recirculated exhaust were water cooled. A common-rail system – new at Audi – injected the fuel at a pressure of 1,350 bar.

With 165 kW (225 hp) and 480 Nm of torque, the V8 TDI was a highly cultivated and refined drive. Its top speed of 242 km/h opened up a whole new dimension.

Compact, powerful and highly efficient – the 1.2 TDI with the automated manual transmission.

1.2 TDI

In 2001, Audi set a new best in the subcompact class – the A2 1.2 TDI achieved an average fuel consumption of 2.99 liters per 100 km (81 grams of CO₂ per km). It was the first and, so far, the only three-liter car in the world with five doors. Its design adhered strictly to the demands of the wind tunnel, resulting in a cd figure of 0.25. Thanks to the aluminum bodyshell, it had a curb weight of 855 kilograms.

Beneath the hood of the 3.83-meter Audi A2 1.2 TDI was a three-cylinder diesel with a displacement of 1,191 cm³. Derived from the 1.4 TDI, it produced 45 kW (61 hp) and maximum torque of 140 Nm from 1,800 to 2,400 rpm. The small two-valve engine used a VTG turbocharger and pump-jet injection that developed 2,050 bar pressure. A start/stop system switched off the engine when the car was at a standstill, while a five-speed automated manual transmission sent the drive to the front wheels.

High achiever – the 3.0 TDI in Audi’s new V-engine layout.

3.0 TDI

The 3.0 TDI, which debuted in 2004, was the first member of Audi’s new V-engine family with a common 90-degree V-angle, 90 millimeter cylinder spacing and chain drive at the back. Like all large Audi diesels, it had a stiff, lightweight block made from vermicular graphite cast iron, with a particulate filter to clean the exhaust.

Also new, were the inline piezo injectors, which could inject tiny amounts of fuel and open and close extremely quickly to realize multiple fuel injections. This enabled them to deliver a finely modulated increase in pressure to a maximum of 1,600 bar and a combustion process that ensured quiet engine acoustics. Over the years that followed, Audi converted its entire diesel-engine lineup to piezo technology.

The three-liter TDI came initially in three variants; they generated 150 kW (240 hp), 165 kW (224 hp) and 171 kW (233 hp). In the space of just a few years, it was being used extensively across the model range. Audi launched its second generation in 2009.

AdBlue injection – nitrogen oxide is split into nitrogen and water.

3.0 TDI clean diesel

In response to increasingly strict exhaust regulations, Audi launched “clean diesel” technology in 2009. The 3.0 TDI clean diesel was equipped with a common-rail system with 2,000 bar pressure and a new kind of combustion chamber sensor. The fine spray and the precise combustion of the fuel ensured low raw emissions.

In the exhaust line, an SCR catalyst reduced the remaining nitrogen oxides. The injected liquid additive AdBlue broke up in the hot exhaust to create ammonia, which split the nitrogen oxides into nitrogen and water.

Powerhouse – the two chargers on the 3.0 TDI biturbo cooperate with one another via a switching valve.

3.0 TDI Biturbo

The V6 diesel range is crowned by the biturbo version, which appeared in 2011. Compared with the monoturbo, many details of the biturbo have been modified. Following its most recent redesign, the clean diesel delivers 235 kW (320 hp) and 650 Nm of torque. A switching valve between the small and large charger manages the boost; a sound actuator inside the exhaust system gives the diesel engine a rich, deep tone.

Multi-faceted – the 2.0 TDI is in many Audi models, ranging all the way to the business class.

2.0 TDI clean diesel

The 2.0 TDI is the bestseller in the Audi lineup – from the A1 to the A6, it is in many of the company’s model lines, with up to 140 kW (190 hp) of output and 380 Nm of torque. In its newest, Euro 6 versions, the fourcylinder diesel boasts an array of compelling technical details, like an integrated valve drive module complete with adjustable intake camshaft, two balancer shafts in the crankcase, flexible thermal management, a common-rail system with 2,000 bar pressure and a high and low-pressure exhaust-gas recirculation system.

Torque colossus – Between 2,500 and 2,750 rpm, the V8 TDI sends a whopping 850 Nm to the crankshaft.

4.2 TDI clean diesel

The big strength of the eight-cylinder diesel that Audi offers in the A8 and Q7 is its mighty torque – 850 Nm in the latest evolution. Thanks to the VTG turbocharger, which produces up to 1.7 bar of relative charge pressure, the build-up of power begins from the very lowest end of the rev range. This, as well as the engine’s extremely smooth running characteristics, enables engine speeds of around 800 rpm, which leads to considerably lower fuel consumption.

In the Audi A8, the V8 TDI generates 283 kW (385 hp), making the luxury sedan move like a sports car. The sprint from zero to 100 km/h is over in 4.7 seconds (A8 L: 4.9 seconds), while the top speed of 250 km/h is a mere formality.

“The instruction was to develop an engine that was as fuel-efficient as possible. It was quickly clear to us that it could only be a diesel.”
Richard Bauder

Where are the areas of commonality between the racing engine and the series-production TDI?

Baretzky: There are none in the engines themselves, but in the development of new concepts. In motorsport, we have the freedom to pursue new avenues and to try out new ideas in a way that isn’t possible in series development. From a technical standpoint, what’s possible for us will also work there.

Weiß: We’re very happy to accept this support. Motorsport motivates our production suppliers; it helps them and us to understand where possible routes could take us. This opens a great many doors when it comes to sporty diesel engines. The success at Le Mans shows the potential of this idea.

How much fuel does the racing diesel consume?

Baretzky: Compared with the twelve-cylinder from 2006, we reduced fuel consumption with the 3.7-liter V6 TDI by 21 percent, while at the same time increasing the lap times in Le Mans by around 15 seconds. Starting from this low basis, we managed to lower the consumption for 2014, in light of the new efficiency regulations, by a further 25 percent. The reduction in fuel consumption, too, is ultimately based on higher pressure, higher temperatures and better mixture formation. What binds us with our colleagues in series development is specific fuel consumption – the requirement to extract an ever-increasing amount of power from each drop of fuel.

Herr Weiß, Herr Fröhlich, how will the fuel consumption of Audi’s series-production TDIs develop in future?

Weiß: Last year, we finished first among the premium manufacturers in fleet figures, with 142 grams of CO₂ per km. We are working hard to achieve the 95-gram target for 2020 and are feeling very positive about it.

Fröhlich: A reduction in fuel consumption of 15 percent by 2020 is surely possible through engine-based measures alone. Electrification will increase this figure considerably.

Weiß: This is where the future is just beginning! The first hybridization step for the TDI is the electric auxiliary drive for the turbocharger. This will give us considerable improvement in the dynamic transition characteristics, i.e. engine responsiveness. We could well envisage the electric biturbo for all of our engines.

Baretzky: In Le Mans this year, we will again be using a further developed MGU – a Motor Generator Unit with a flywheel accumulator – as a temporary drive for the front wheels. The driver feels this when accelerating from lower revs. But, compared with the energy that the TDI delivers per lap, it’s a very modest contributor. Incidentally, our turbocharger generates 2.8 to 3.0 bar of absolute charge pressure, which isn’t that much more than in a production car. There are actually similarities in one or two technical areas.

“What binds us with our colleagues in series development is the requirement to extract an everincreasing amount of power from each drop of fuel. In motorsport, we have the freedom to pursue new avenues and to try out new ideas. From a technical standpoint, what’s possible for us will also work in series production.”
Ulrich Baretzky

Fröhlich: Besides the electric biturbo, we also have a few more concepts up our sleeves. We have conceived a matrix of hybridization variants and scalable electric motors, which we are currently implementing at a fast pace.

Weiß: Here in Neckarsulm, of course, we develop the V diesel engines for all of Audi’s larger models. It’s here, in particular, that hybridization has great deal of appeal. As a customer, you can use the TDI for distance driving and, in the city, where the drive is subject to lower loads, you can drive electrically with zero local emissions. Naturally, the financial implications, complexity and weight all increase. We are, after all, putting two complete drivelines into the car. We have to find the right balance in order to bring maximum benefit to the customer.

Does this mean that downsizing at any price is not the way forward?

Weiß: A few of our competitors are going completely in this direction, and small engines are very good for fuel consumption on the approval cycles. However, this does not always transfer to real-life customer consumption, which is why we have opted for rightsizing – the right engine size for each respective vehicle size.

Fröhlich: We are still active in the eight-cylinder segment and continuing our development work there. If our customers want to drive a powerful V8 TDI, then that’s what they’ll get in future, too. And the end of the day, the key factor is acceptance, i.e. the market.

Weiß: The biturbo TDI, including the one in the SQ5 TDI, is a great success for Audi and a new door opener. We are proud of the first S-emblem on a diesel and also of its sporty sound. We have been working on this issue for a long time to ensure that our engines are perceived more emotionally, despite the many catalysts, which absorb the sound. The emotionality and the driving fun of a diesel have many facets, not least the high torque at low revs.

Does the future of the TDI lie in its sporting credentials?

Weiß: Now that we have addressed the tasks set by emissions legislation, we can once again concentrate fully on the dynamics and efficiency of the diesel engine. We will further expand the assets of economy and efficiency bestowed upon the TDI by Richard Bauder. At the same time, we are working on the strengths covered by Ulrich Baretzky in motorsport – dynamics and emotionality.

Bauder: If you further reduce emissions and consumption while continuing to increase performance, the diesel will become even more competitive …

Baretzky: … and when you see how fast it has developed in the last 25 years, I believe it still has the largest part of its future ahead of it.

Weiß: In order to grow the diesel engine further, we need new markets. And this calls for stable and predictable legislation. China, of course, is of major interest to us, but we have the problem there of variable fuel quality in rural areas. For Europe, we are pursuing another fuel issue – sustainably produced Audi e-diesel, which we are testing in our engines. It’s a suitable piece in the puzzle of the future. Like every new technology, it will have its breakthrough when the time is right.

“Now that we have ad- dressed the tasks set by emissions legislation, we can once again concentrate fully on the dynamics and efficiency of the diesel engine. There are many facets of dynamics and emotionality in a TDI.”
Ulrich Weiß

“A reduction in fuel consumption of 15 percent by 2020 is surely possible through engine-based measures alone. Electrification, for which we have developed a whole matrix of solutions, will increase this figure considerably.”
Andreas Fröhlich

2014 – 3.0 TDI clean diesel

3.0 TDI clean diesel Technical Data
Bore / stroke 83.0 / 91.4 mm
Displacement 2,967 cm³
Cylinder spacing 90.0 mm
Power 200 kW (272 hp) @ 4,000 rpm
Specific power 67.4 kW (91.7 hp) per liter of displacement
Torque up to 600 Nm from 1,500 to 3,000 rpm
Compression 16.0 : 1
Weight 192 kg

For the 25th anniversary of TDI technology, Audi has once more fundamentally redesigned the 3.0 TDI – in its latest evolution, the V6 diesel is even cleaner, more efficient and more powerful. In the top version, the monoturbo generates 200 kW (272 hp) and sends up to 600 Nm to the crankshaft from 1,500 to 3,000 rpm. It undercuts its predecessor in fuel consumption by a good ten percent.

The new three-liter diesel boasts fascinating high-end solutions in all technical areas. The pistons are supplied with cooling oil via cast-in ring channels, while new coatings on the rings and pins ensure minimal friction. The weight-optimized crankcase is made from high-strength vermicular graphite cast iron and the newly conceived cylinder heads have separate coolingwater circuits; the cylinder-head water jackets are split into two, in order to lower pressure losses. The oil pump is fully variable. The turbocharger and exhaust manifold have also been modified, while the common-rail injection system develops 2,000 bar of system pressure.

Designed to meet the limits of the Euro 6 standard, the 3.0 TDI bears the adjunct “clean diesel”. In the interests of rapid start-up, the exhaust aftertreatment components are positioned as closely as possible to the rear of the engine. The oxidation catalyst lies coaxially downstream of the turbocharger’s turbine outlet. Direct behind it is the diesel particulate filter; its filter walls are covered in a coating that converts nitrogen oxides in the exhaust using the SCR process (selective catalytic reduction). A metering module injects the necessary AdBlue additive.

The new 3.0 TDI clean diesel

1 Throttle valve
2 Swirl flap in intake manifold
3 Common-rail injector
4 Common-rail high-pressure pump
5 Drive gear for high-pressure pump
6 Roller cam follower
7 Assembled hollow camshaft
8 Camshaft gears
9 Idler gear for camshaft drive
10 Aluminum pistons with cooling channel and DLC-coated piston pins
11 Balancer-shaft drive gear
12 Bearing frame
13 Crankcase in vermicular graphite cast iron
14 Cooler for exhaust-gas recirculation system
15 Exhaust-gas recirculation take-off
16 Turbocharger with variable turbine geometry
17 Turbocharger housing insulation

Newly developed – the cylinder head of the 3.0 TDI with camshaft drive gears.

Cylinder head
The new packaging of the exhaustaftertreatment components led to modifications in the chain drive on the 3.0 TDI. The oil/vacuum pump and the high-pressure pump in the commonrail system were given separate drives. In the camshaft drive arrangement, gear sets and idler gears running on sophisticated needle-roller bearings replaced the big chain wheels. Designed as assembled hollow shafts, the camshafts are particularly lightweight. They actuate the valves via extremely stiff roller cam followers.

Additional pressure –
the new charger (red) uses an electric drive to compress the air.

Efficiency hero –
the Audi A3 ultra emits an average of no more than 85 grams per CO₂ per kilometer.

3.0 TDI with electric biturbo
Audi is working intensively on the diesel engine with a completely new technology known as electric biturbo. The turbocharger works in tandem with an additional, electrically driven compressor. Instead of a turbine rotor, it incorporates a small electric motor that accelerates the compressor rotor to extremely high revs in a very short space of time. The electric charger is connected downstream of the intercooler and is bypassed in most operating situations. When very low revs mean there is little energy in the exhaust, the bypass flap closes and the electric charger is activated. The new technology enables a previously unheardof level of power build up at very low revs or when pulling away from a standstill – making the 3.0 TDI even sportier.

Audi A3 ultra
3.2 liters of fuel per 100 km, a CO₂ equivalent of 85 grams per km – the Audi A3 ultra is the most efficient model in the Audi lineup. It is driven by the 1.6 TDI, which has been systematically designed for minimal friction. The 81 kW (110 hp) and 250 Nm of torque flow through a six-speed manual transmission to the front wheels, giving the three-door, which has a curb weight of just 1,205 kilograms, extremely agile performance. Audi is gradually expanding its ultra range – which will soon consist of 13 models.

25 Years of TDI: The Success Story
This year sees Audi celebrate a very special anniversary – the 25th birthday of the TDI. In fall 1989, the Audi 100 2.5 TDI first appeared at the Frankfurt Motor Show; it presented the first turbodiesel engine with direct injection and fully electronic control. Since then, the brand with the four rings has expanded its leadership ever further, setting many more milestones along the way.

Since 1989, TDI technology has helped the diesel engine soar to previously unimaginable technical heights and become an overwhelming market success. Development began in 1989 with an injection pressure of 900 bar. In many engines, this figure now stands at 2,000 bar. Based on displacement, the power and torque of the TDI has increased over the 25 years by more than 100 percent, while pollutant emissions have fallen by 98 percent.

To date, Audi has produced around 7.5 million cars with TDI engines – 600,000 of them in 2013 alone. They contributed significantly toward the brand with the four rings achieving the lowest fleet fuel consumption of all German premium manufacturers. The TDIs offered by Audi today are highly efficient and clean, cultivated, comfortable and powerful. Aside from the R8, they are in all model ranges. The lineup stretches from 1.6 to 4.2 liters of displacement and from 66 kW (90 hp) to 283 kW (382 hp).

25 years after the market launch of the first TDI, Audi continues to extend its lead. The extensively redesigned 3.0 TDI clean diesel sets a new milestone – in future, the electric biturbo will make the TDI even sportier and more emotional. In parallel, Audi is working hard on the electrification of its drivelines. When it comes to fuels, the brand stands firmly behind sustainably produced Audi e-diesel. Audi’s TDI engine can look back at an impressive success story – and forward to a great future.