As cars get increasingly complex, computer simulation becomes an ever more important tool in making engineering design decisions. The interactions between the various subsystems mean that finding the optimum combination just keeps getting more difficult. Testing all those mixes with hardware is enormously expensive and time consuming, so carmakers are producing mathematical models that allow them to vary parameters and run through thousands of combinations in a fraction of the time. Once they get a few combinations that look like a good system, they can then build a more limited set of test parts for hardware testing.

Mercedes-Benz has made extensive use of mathematical modeling in developing the Bluetec diesel emission control systems. When developing models, it's hard to factor in all the variables that can happen in the real world. As a result, when the technology first started being used extensively in the late '80s, certain elements had to be ignored, which limited the accuracy of the models. The power of modern computers has made more complete models more practical, something that is critical when developing hardware and controls for things like fuel and exhaust systems. In the case of Bluetec, it was important for Mercedes to optimize the consumption of urea to minimize maintenance requirements, as well as NOx emissions.

[Source: Mercedes-Benz]

A clean bill of health - Reducing emissions with simulation technology
  • Reducing emissions with simulation technology
  • Attaining greater maturity of development
  • E 300 BLUETEC on the European market
Stuttgart – Constantly improving fuel injection, combustion and exhaust gas aftertreatment in engine development: the researchers at Daimler AG are pursuing this objective with sophisticated simulation technology. Their aim is to reduce fuel consumption even further, while at the same time complying with increasingly stringent emission limits for nitrogen oxides and particulates. By means of model calculations in combination with real-life tests, a higher degree of development maturity can be reached at an earlier stage. For example, the environment-friendly BLUETEC diesel technology – after the positive experience gained on the U.S. market – is also available in Europe.
Theory and practice
For a number of years, the Daimler researchers have already been carrying out simulations for the design of exhaust gas units and their optimisation: although indispensable, the conventional measurements on the test rig are time-consuming and expensive. Moreover, in view of its large number of components, the complex overall system comprising engine and exhaust gas aftertreatment unit can only be efficiently optimised by means of modelling.
It is the link between simulation and measurement that makes new, state-of-the-art exhaust gas aftertreatment systems such as BLUETEC at all possible. This modular concept initially involves reducing nitrogen oxide levels by means of engine optimisation measures; these are supplemented by an intelligent exhaust gas aftertreatment system that operates without additional service fluids and reduces further emissions.
The clean diesel engine
In the case of the diesel engine, the experts are focussing their attention above all on the emission of nitrogen oxides and particulates. Future exhaust systems, for instance, will as a rule combine filters and catalytic converters, whereby interaction between the individual components must be taken into account. These components also communicate once more with the combustion process within the engine: the exhaust system, for example, informs the engine when the particulate filter is full, and the engine in turn must react accordingly.
Individually calculated, reaching the goal together
Daimler AG's researchers take these complicated interactions into ac-count in their simulations. They are on the one hand developing models for individual components such as the three-way catalytic converter, oxidation, SCR and NOx storage catalytic converters, and the particulate filter. These models are founded on physical and chemical processes.
In order to ultimately integrate these individual models into an overall system, the specialists at Daimler have also developed a so-called simulation environment. On this basis, they can assemble the various components into a modular system. This ensures user-friendly handling. Researchers and development experts can now jointly ascertain the most favourable configuration of individual components in each case for engine optimisation and plan their work accordingly.
Prior assessment
The researchers' calculations help answer some highly diverse questions: what temperatures prevail before and after exhaust gas after-treatment, and what are the nitrogen oxide levels? What values are modified when a larger catalytic converter is used? Is the temperature window optimal? Are the pipes of the right length?
Once several test cycles have been completed, the data become available for preliminary optimisation. The design of the overall system and of the individual components is initially assessed by means of simulation; the real-life tests on the test rig can then be strategically initiated.
This perfect match of theory and practice greatly enhances the degree of maturity in development. With the benefit of these findings, the experts are now in a position to develop the best possible operation strategy at an early stage, in order to gradually optimise the engine. E 300 BLUETEC, which is available on the European market, is thus a prime example of modern diesel technology – clean and efficient.

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