Pleased to meet you: Nicolaus Otto. 
My pleasure: Rudolf Diesel.

Johannes Köbler

Bernhard Huber

Two combustion processes, two technical worlds, two Audi engineers –

Jürgen Königstedt and Ulrich Weiß discuss the strengths and perspectives of spark and compression-ignition engines.

Nicolaus Otto
Born in 1832 in Holzhausen an der Haide (Taunus), Nicolaus August Otto first pursued a commercial career. As a self-taught engineer, he built his first gaspowered engine in 1863. Nine years later, he founded the Gasmotoren-Fabrik Deutz AG close to Cologne. The engine that Otto designed in 1876 was a milestone in the development of the four-stroke principle. Nicolaus Otto died in 1891 in Cologne.

Herr Königstedt, Herr Weiß, as engineers, you are the ideal heirs to two great inventors, Nicolaus Otto and Rudolf Diesel. What impresses you most about their engine concepts?

Königstedt: I like the bandwidth of spark-ignition engines, the turbos and the naturally aspirated engines. For a large sedan like the Audi A8, a refined turbocharged engine like the 4.0 TFSI is a wonderful power unit. And in the R8, the V10 naturally aspirated engine is utterly fascinating with its sound, its responsive characteristics and its high revving. The maximum piston speeds are higher than those in Formula 1 – and in a series-production engine, too. I really can’t complain about any lack of challenge in the task.

Weiß: What consistently drives me is the fascination for the technically extreme. In addition to exceptionally low fuel consumption figures, my team and I want to give our diesel engines the passion and emotionality that conveys dynamism and sheer driving pleasure. The V6 biturbo goes a long way in this direction with its active sound generator, and the SQ5 TDI is the first S model from Audi with a diesel engine. This is an achievement that makes us extremely proud.

Audi’s TDIs are becoming increasingly sporty, and the spark-ignition engines increasingly efficient – to what extent are the two engine types converging?

Weiß: 25 years ago, the first TDI engine from Audi was the great pioneer in the automotive industry. It added dynamics and performance to the mix. Since then, the diesel has experienced even more pronounced change than the spark-ignition engine – it has improved enormously in terms of output, torque, emissions and refinement.

Königstedt: The last ten years have seen fuel consumption move very much to the forefront, having previously a secondary consideration to some extent. Our engines have to be consistently lighter and more fuel-efficient. They have to meet increasingly tough emissions standards and, at the same time, fulfill the desire for even better performance. These demands lead to conflicts of interest that can only be resolved through new technologies, such as our cylinder on demand cylinder deactivation technology in the V8 biturbos. Fuel consumption of less than ten liters per 100 km for the RS 6 Avant with an output of 412 kW (560 hp) – I would say that’s not bad.

Weiß: And precisely this is the attraction of our approach to series-production development – to harmonize all the requirements in a way that produces a complete overall package for the customer. To do this, we need enthusiasm, passion, know-how, craftsmanship and, not least, strong suppliers – although we have to push them along sometimes.

25 years ago, the first Audi TDI engine was the big pioneer in the automotive industry. It added dynamics to the mix.
Ulrich Weiß

If the engines are becoming increasingly similar, does that mean there are more shared components?

Königstedt: In terms of hardware, we can make use of synergies in non-combustion related components. By that, I mean parts like oil pumps, water pumps, sensors and interfaces for add-on parts.

Weiß: In areas such as software and thermal management, we use functionalities of a modular nature. What my colleague and I don’t anticipate at the moment, is an engine that fuses the diesel and spark-ignition combustion processes. There is also no such fuel available today, and the kind of development work that Audi conducts in the field of new fuels needs quite some time and a considerable push from society.

Over the next few years, we envisage further savings in fuel consumption for spark-ignition engines of roughly 15 percent.
Jürgen Königstedt

The 4.0 TFSI is a fascinating and powerful sports engine – it takes Audi’s downsizing strategy into the full-size class. The high-revving V8 biturbo with its aluminum cylinder block is systematically laid out for low charge cycle and flow losses, and develops its torque of up to 700 Nm quickly and from low down the rev range. Adjustable flaps in the intake channels set the incoming air into a cylindrical rotation, and optimize fill and combustion in accordance with their setting. The exhaust side of the cylinder heads is on the inside of the V, with intake on the outside. The two twin-scroll turbochargers (not shown here) are located with the intercooler inside the V between the cylinder banks – a layout that ensures short gas paths and dynamic response characteristics. The cylinder on demand system makes a major contribution to the high efficiency of the 4.0 TFSI.

The most powerful member of the V6 TDI family is conceived as a biturbo – the two turbochargers are arranged in series and connected by a changeover valve. At low revs, the valve is closed; the small high-pressure charger with its variable turbine geometry does most of the work, while the large low-pressure charger handles pre-compression. Upward of about 2,500 rpm, the valve begins to open and the small turbo gradually transfers the main workload to its large counterpart. In the range between 3,500 and 4,000 revs, the valve is fully open and only the large turbocharger is operating. The substantial performance of 230 kW (313 hp) and 650 Nm of torque called for far-reaching modifications to the 3.0 TDI biturbo and its peripherals. A sound actuator in the exhaust system gives the three-liter diesel a rich, sonorous tone.

Rudolf Diesel
Rudolf Christian Karl Diesel was born in 1858 in Paris. He completed his studies as an engineer in Munich in 1880. Following many years of fundamental research, he brought to life the first compressionignition engine at Maschinenfabrik Augsburg, later MAN, in 1893. Rudolf Diesel died in 1913 during a ship’s crossing from Belgium to England. His engine entered series production in a car in 1936.

What development do you anticipate in your fields over the next few years?

Weiß: A major issue for us is the exhaust aftertreatment systems necessary for the Euro 6 standard. A second field is intelligent supercharging technology, which I see as even more important than further increases in injection pressure. The electric biturbo, which is currently the subject of intense development work, will deliver a whole new level of responsiveness. Basically, there are a large number of elements in engine technology that are extremely promising, but that involve a great deal of effort. And intelligent control is gaining in importance across the board – in my department, one in three people are electronics specialists. We work with the most powerful computer systems available on the market and are having to upgrade them continuously.

Königstedt: Over the next few years, we envisage further savings in fuel consumption for spark-ignition engines of roughly 15 percent – through further Downsizing, further reductions in friction and new combustion processes. In our larger four-cylinders, dual injection is already bringing new levels of freedom, and variable compression also has some very interesting potential. In general, the competitive air is getting ever thinner. When a world-class sprinter manages 100 meters in 9.8 seconds, it takes a monumental effort to reach 9.7 seconds. It’s never easy to dash out in front.

On the subject of downsizing – how small might an Audi gasoline engine be in future?

Königstedt: Our 1.4 TFSI already runs on two cylinders at low loads thanks to COD. In principle, I would not exclude the notion of a three-cylinder, but the principle of “the fewer, the better” does not apply for us. Downsizing is not the right route in all cases, which is why we at Audi all refer to rightsizing – the principle of developing the right drive for every vehicle concept.

Ulrich Weiß (left): Born in Vaihingen/Enz, he studied Mechanical Engineering in Stuttgart. Interrupted by a stint at Daimler, he has worked for Audi since 1994. The 44 year-old is Head of Development, Diesel Engines.
Jürgen Königstedt (right): Born in Cologne, he studied Mechanical Engineering in Aachen, coming to Audi in 1996 via Volkswagen. Königstedt (51) heads up the development of spark-ignition V engines from six to ten cylinders.

If Nicolaus Otto and Rudolf Diesel were alive today – would they still be the great, ingenious inventors?

Weiß: Just like us, they would work in large teams covering many disciplines all the way through to chemistry. The spectacular strokes of genius that took place 100 years ago can no longer happen today, but there is a constant stream of new, intelligent solutions for detail problems.

Königstedt: Otto was more of a businessman than an engineer. And he was an impressive, courageous personality – an entrepreneur in the best sense of the word.

If you were to attempt to look into the more distant future, would it be the diesel or the gasoline engine that has the better hand?

Weiß: That’s a decision for our customers in combination with the policies that define consumption and emissions legislation and regulate resource management. At the moment, we are seeing a strong trend toward SUVs – in our organization, too – which tends to favor diesel engines. But in the medium term, diesel will need another market outside of Europe. We are seeing initial success in increasing its acceptance in the USA, which is something we want to build on …

Königstedt: … although the growing markets like China and India are heavily biased toward spark-ignition engines. In a few years, we might be able to offer our customers hybrid systems at only a very slight price premium. That would then favor the gasoline engine.

Herr Königstedt, Herr Weiß, do you see yourselves as partners or as rivals?

Königstedt: We are both big car guys, and each of us has huge respect for the work of the other …

Weiß: … and we are also quite happy to look over each other’s shoulders without reservation. My wedding car was an R8 Spyder that my colleagues were nice enough to lend to me

Königstedt: I spent some time recently in a diesel company car, and it wasn’t bad at all.