Demonstration model of the experimental engine with lightweight cylinder casing being presented at the Hannover Messe. Click to enlarge.

Carmakers have been relying on aluminum to reduce the weight of engine components such as the cylinder block. Although the use of fiber-reinforced plastics to achieve further weight savings could seem to be an obvious solution, there are numerous technical challenges involved because the materials used have to be able to withstand extreme temperatures, high pressure and vibrations without suffering damage.

Plastics have been recognized as possessing these qualities since the 1980s, but at that time it was only possible to produce this type of part in a small volume and by investing a lot of effort in the form of manual labor—a non-starter for the automotive industry, in which cylinder blocks are mass-produced in millions of units.

To ensure that their engine would be sufficiently robust, the research team first looked at the engine design and identified the areas subject to high thermal and mechanical loads. In these areas, they used metal inserts to strengthen thee wear resistance, said Berg.

One example is the cylinder liner, inside which the piston moves up and down millions of times during the life of the vehicle. The researchers also modified the geometry of these parts to ensure that the plastic is exposed to as little heat as possible.

The characteristics of the plastic material also play an important role—the plastic must be sufficiently hard and rigid, and resistant to oil, gasoline and glycol in the cooling water. It must also demonstrate good adherence to the metal inserts and not have a higher thermal expansion coefficient than the metal, else the inserts would separate from the substrate.

Berg’s team used a glass-fiber-reinforced phenolic composite developed by SBHPP, which fulfills all of these requirements and comprises 55% fibers and 45% resin. A lighter-weight but more expensive alternative is to use a carbon-fiber-reinforced composite—the choice depends on whether the carmaker wishes to optimize the engine in terms of costs or in terms of weight.

The researchers produce these components from granulated thermoset plastics using an injection molding process. The melted composite material, in which the glass fibers are already mixed with the resin, hardens in the mold into which it was injected.

The scientists analyzed the process using computer simulations to determine the best method of injecting the material in order to optimize the performance of the finished product. The process is compatible with mass production scenarios and the manufacturing costs are significantly lower than those for aluminum engine parts, not least because it eliminates numerous finishing operations.

A prototype of this engine will be presented at this year’s Hannover Messe, which takes place 13-17 April. Test runs of the new engine have been completed successfully.

In addition to delivering the ame performance as conventionally built engines, the Fraunhofer engine offers further advantages such as lower running noise as against engines relying exclusively on metal parts, said Berg. Initial data also indicates that the amount of heat radiated to the environment is lower than that generated by aluminum-based engines.

The team intends to take its research further by developing a multi-cylinder plastics-based engine, including the crankshaft bearings.