Like a fish out of water

Mercedes-Benz is using the tropical boxfish as a model for a fuel-thrifty concept car, saying the creature is an "aerodynamic ideal".

The project is known as the "bionic car study", and a working model will be unveiled at an innovation symposium hosted by Benz parent DaimlerChrysler in Washington DC.

The luxury carmaker says the study has achieved outstanding results for fuel consumption and exhaust emissions.

Mercedes-Benz researchers say despite its boxy, cube-shaped body, the boxfish is "outstandingly streamlined and therefore represents an aerodynamic ideal".

The concept car achieved a ground-breaking wind drag coefficient of just 0.06 in tests.

Engineers first created a 1:4 clay model based on the boxfish. Tests in a wind tunnel produced a drag-coefficient - wind resistance factor - of 0.095, a previously unprecedented value in automotive engineering, says the company.

The boxfish is also a prime example of rigidity and light weight. Its skin consists of hexagonal, bony plates which provide maximum strength with minimal weight and protect the animal from injury.

Mercedes-Benz researchers examined the bionic structure and transferred its principle to the study using a process based on the principles of bone formation. The bionic design provides around a 40 per cent improvement in the strength of door panels than would be possible with conventional designs.

If the entire bodyshell is designed on the same bionic principle, researchers say the total weight is reduced by around one third, with undiminished strength and crash safety.

The findings were used in the development of the working bionic car, a four-seater just over 4m long with a drag-coefficient of 0.19. The C-Class Mercedes-Benz sedan is rated at 0.26.

Mercedes-Benz says the streamlined design, powered by a 103kW (140bhp) high-tech, cleaner-burning diesel engine, uses 20 per cent less fuel and emits 80 per cent lower exhaust emissions. At a constant speed of 90km/h the direct-injection diesel unit consumes only 2.8 litres/100km, or around 80mpg, says the carmaker.

The aim of the concept is to push out the design envelope and to introduce new diesel technology, called "Adblue", an aqueous urea solution which is sprayed into the exhaust system in precisely metered quantities, depending on the engine operating status. This converts the nitrogen oxides into harmless nitrogen and water, says the carmaker.

The reservoir for the urea fluid is in the spare wheel recess of the concept car, and its capacity is sufficient for a mileage corresponding to the service interval for a current Mercedes-Benz diesel model.