In view of the discussion on the climate and demands for the reduction of CO2 levels, engine experts are playing a key role at all automotive manufacturers. What do you have in the pipeline for reducing fuel consumption?

Lückert: An outstanding example is provided by the spray-guided direct injection system in the gasoline engine, which we jointly set in motion within Daimler Research and Development. Mercedes-Benz was the first automotive manufacturer in the world to launch the system in 2006. In this combustion process, we even achieve stratified charging at a high load range, which significantly reduces fuel consumption.

By the way, by implementing this project, we have also demonstrated how technology from research and advanced development can be fully transferred to development and series production. We have also shown how close cooperation can lead to success in a comparatively short space of time.

Rau: The consistent downsizing of engines in combination with supercharging concepts is a second field in which we closely cooperate. The spray-guided direct injection system opens up new possibilities to further reduce consumption while simultaneously increasing responsiveness and engine agility — particularly in small engines. Our third concept for cutting fuel consumption is to reduce friction throughout the entire powertrain. Here, the spectrum ranges from materials research to structural aspects. Fourthly, we cooperate on improving energy management — and that includes everything from thermal management of engines to the development and optimization of accessory units such as starter generators.

Apart from gasoline direct injection and reduced fuel consumption, what are the key functions performed by your two units within Daimler Research & Development?

Rau: The two units share the same objective but have differently phased tasks. Research and advanced development both work on the same topic in the early stages of the project. Series production then incorporates the measures and prepares the technology for market launch.

Consequently, the two units initially conduct technology screenings and define the targets and areas of action for the individual contributors. In terms of content, in research/advanced development we develop technologies related to, for example, the charging, combustion or exhaust treatment processes. In addition, we work on tools and methods to improve internal combustion engines in terms of fuel consumption, emissions, driving performance and comfort. In general, in research/advanced development, we prepare innovations until they are ready for series production and then hand them over to our colleagues from development.

Lückert: However, it should be kept in mind that you can’t really consider a hand-over of this kind to be a definite dividing line where a project abruptly moves from advanced development to development and then goes into series production. The transitions between our units are blurred today. Instead of progressing in serial steps, work is conducted between units and in parallel, particularly during the transitional phases. This accelerates and intensifies the information exchange between employees should questions arise. Some colleagues also move with their part of the project, taking with them their know-how from advanced development to development. We shorten the interval between advanced development and the introduction of the series-produced component by up to 30 percent thanks to the accurate alignment of the strategy and teams. This enables us to launch innovations onto the market more rapidly than is possible using conventional processes. For example, spray-guided direct injection was ready for use in a concept car in 1998, ready for series production in 2002, and launched in series production in 2006. This may sound like a long time to outsiders, but for the development of such a fundamental innovation, it was a comparatively short period of time.

One of the current buzz words regarding fuel consumption reductions is downsizing. However, reduced cubic capacity alone is insufficient. How are you tackling this challenge?

Lückert: We require downsized engines that provide the same output as the larger engines they replace. In principle, the loss of output due to downsizing is compensated for by supercharging. However, smaller engines with turbochargers often suffer from significant turbo lag and consequent problems when driving off – and we don’t want to subject our customers to that. As a result, Mercedes-Benz decided to use engines featuring duct injection for the compressor that isn’t subject to these problems. Now, the situation has changed significantly regarding gasoline engines thanks to the introduction of spray-guided direct injection. The charge cycles in the cylinder are different and we can control them so that the disadvantages of turbochargers no longer apply in non-stationary situations. Consequently, we are working hard on new concepts with two-stage supercharging.

Does this mean that in downsized engines featuring spray-guided direct injection, the turbocharger now has advantages over the compressor supercharger?

Rau: Exactly. As the turbocharger is in principle driven by the hot flow of exhaust gas, it provides better fuel economy than the mechanically-driven compressor. The benefits can now be implemented without suffering turbo lag. However, as previously mentioned, this can only be achieved using spray-guided direct injection in combination with innovative turbocharging technology. A few years ago, the development of turbochargers was not advanced enough to meet Mercedes-Benz’ requirements when it came to downsized engines. However, we will succeed in implementing very challenging downsizing concepts thanks to multistage supercharging and further measures.

Lightweight designs (for example, the use of aluminum alloys instead of steels), also help to reduce fuel consumption and emissions. What lightweight construction potential do you see in combustion engines?

Rau: In principle, we pursue two approaches. First, as you mentioned, we substitute materials with lighter alternatives. Of course, the properties of the components may not suffer as a result and must always fulfill Mercedes-Benz’ high requirements. The second approach involves the integration of functions using structural solutions. In this respect smaller, more compact engines can serve as outstanding examples of lightweight design. However, the engine developers of all manufacturers are faced with conflicting objectives. If they downsize from six to four cylinders, the basic engine will become lighter. But the weight tends to increase due to the additional technical equipment required, for example, for supercharging, direct injection or exhaust treatment.

Lückert: This conflict of objectives is unquestionably a major challenge for the developers. They at least have to compensate for the added weight of the additional technology by modifying the basic engine. Of course, it’s even better if you can save more than you add. But we're certainly on the right track at Mercedes-Benz. On average, series-produced engines have become around ten percent lighter within two years. We hope to realize additional lightweight construction potential in the mid-term by using new materials.

Daimler launched a hybrid initiative at the 2007 IAA Motor Show. As a researcher/developer, can you describe to our readers how the hybridization of engines will change the demands made on your units?

Rau: The hybridization of the powertrain represents not only new challenges for us, but also new opportunities. In hybrid vehicles, the engine no longer has to take care of everything because some functions, such as driving off or the booster function when accelerating, can be assumed by the electric motor. In principle, in hybrid concepts, the engines can be designed differently and optimized accordingly as a result. High-consumption operating points are avoided where possible and purely electric driving can be used as an alternative. All in all, the positive characteristics of engines and electric motors complement each other very well.

Lückert: In terms of development, it is also necessary to keep the package consisting of an engine and one or two electric motors as small as possible so that it can be integrated into the vehicle. Therefore, downsizing is very important here as well. However, on this subject, I would like to particularly emphasize that our hybrid concepts are based on modular components that are deployed in different ways depending on the vehicle. These may be charging components, electrical systems, or electronic components. Once prepared for series production, the modules can be installed in individual model series according to requirements. It would not be economical to develop a separate hybrid concept for every model and would make the vehicle too expensive for many customers.

Mercedes-Benz stands not only for energy efficiency but also for comfort. Is this also an important topic for engine experts?

Lückert: Absolutely — along with driving performance, consumption, and emissions, comfort is one of the core values of our vehicles. The smooth operation of our engines is an example of what we as developers can offer our customers in terms of comfort. All four-cylinder gasoline engines in the C and E-Class feature a balancer shaft so that their smooth operation is comparable with a six-cylinder in-line engine. However, comfort is also expressed in functionality. For example, how easily can a vehicle or an engine be operated using a start/stop function?

Rau: From our perspective, noise emissions play a major role. Of course, it is best to avoid these at the source. That is why we strive to make engines quieter by developing new combustion procedures. We certainly see potential for the further reduction of combustion noise using different injection strategies. The diesel demonstrates what is possible in this area; today’s engines differ significantly from the clattering diesels of the past. My colleague Lückert and I are convinced that researchers and developers can still achieve a lot when it comes to reducing noise emissions.