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.
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.
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.
The cylinder on demand (COD) system in the turbocharged V8 deactivates four of the eight cylinders under low and medium load by shutting the valves and deactivating injection and ignition. The 4.0 TFSI operates as a four-cylinder until the driver steps firmly on the gas pedal.
The operating points shift to higher loads in the active cylinders, which raises efficiency. It all takes place so smoothly and quickly that the switchover is barely perceptible. COD technology reduces consumption in the NEDC by around 5 percent.
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.
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.
Source: Audi Dialoge Technologie Magazin
Text: Johannes Köbler
Photos: Bernhard Huber