Developing durable thermoplastics for IC engines

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Auto makers are looking to improve performance with smaller engines that squeeze more power out of every last cubic centimeter, and at the same time they are looking to reduce weight wherever they can – all at a competitive cost.

Injection moldable high-performance thermoplastics often enable components to be realized with optimized lightweight designs and price/performance ratios much better than with metals.

The most commonly used thermoplastics for engine components are polyamides (PA). A typical example is the air intake manifold (AIM). Glass fiber-reinforced polyamides have been used to make AIMs for some 30 years. For virtually all of that time, they have been made in so-called ‘standard’ polyamides, PA6 and PA66, reinforced with glass fibers.

These materials have excellent mechanical properties, as well as very good resistance to the types of oils and chemicals found under the bonnet. They also have quite good thermal properties: they can be used in environments where the constant used temperature is around 180-200°C for shorter term. But their temperature resistance is not sufficient if parts need to pass accelerated aging tests lasting 3,000 hours.

Charge air cooler

So with turbocharged engines increasingly common, they may not be good enough. Not only do turbochargers use hot exhaust gases to drive the turbine that pushes more air into the cylinders, but the rapid compression of the air causes its temperature to rise considerably. So wherever you look, it’s hot.

Also to be considered is the continuing evolution of the turbocharger. More or less all turbocharged engines now incorporate charge air coolers (CACs) between the turbocharger and the AIM.

In such engine designs, the need for extra-high thermal resistance is even more urgent than ever. The air temperature reaching the CAC from the turbocharger can be as high as 230°C in continuous use, with peaks up to 260°C in high-pressure pulses.

Full integration

Together with air-to-air CAC systems, OEMs have also developed liquid-cooled types, which can be integrated fully into the manifold. An integrated CAC/AIM delivers still higher efficiency, since the design has a lower air duct length and improves engine responsiveness by reducing pressure losses.

All-plastic AIMs with integrated liquid-cooled CACs achieve a giant step forward in reducing weight, improving engine responsiveness and minimizing turbo lag, yet they require a great deal more from the plastics materials used to create them.

Air intake manifold

Integrating the cooler into the AIM drastically changes the geometry of the manifold in a way that could cause a loss of stiffness and strength, which are critical at higher temperatures.

The new geometry also requires materials with high weldability and weld line-aging resistance to maintain the part’s integrity. At the same time, the material must withstand exhaust gas recirculation (EGR) and blow-by.

A hybrid sports car introduced last year, that is powered by an electric motor combined with a powerful turbocharged 1.5-liter gas engine, features the world’s first high-heat plastic AIM with integrated liquid-cooled CAC.

Heat resistance technology

This new injection-molded AIM/CAC is made in a modified form of DSM’s Stanyl polyamide 46, a polyamide with inherently better thermal properties than standard polyamides; the grade is Stanyl Diablo OCD2100. It contains 40% glass fiber reinforcement, as well as specially developed and patented heat stabilizer technology from DSM – Diablo.

When a part made with a polyamide incorporating Diablo technology is put in a high-temperature environment, micro-cracks will appear on the surface that lead to degradation that penetrates to the core of the part. The Diablo technology protects the surface, preventing the micro-cracks from appearing.

The stabilization technology provides a significant improvement in thermal resistance that can be used in numerous air management components located around the engine – hot charge air ducts, mixing tubes and resonators, for example.

Looking to the future

DSM is already working on the next generation of Diablo technology. “DSM will aim to combine higher long-term behavior with even better chemical resistance,” said Willy Sour, product development specialist. “When an auto maker asks for both high heat performance of 250°C and extremely good chemical resistance, we will be able to meet that requirement.”

The company is also active in the development of Diablo polyamide grades for blow molding. One such grade, Stanyl Diablo OCD2305BM, was launched two years ago. “At that time the market was not fully ready for such a high-performing grade, but the situation is changing,” says Kurt Maschke, global segment manager, Air/Fuel. “We have identified a gap in our portfolio between the standard blow molding grade, Akulon K240HGP3, and Stanyl Diablo OCD2305BM, and we are currently working to close this gap. “You can expect the launch of a new Diablo blow molding grade during 2016.”

February 17, 2016

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About Author

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Dean has been with UKi Media & Events for over a decade, having previously cut his journalistic teeth writing and editing for various automotive and engineering titles. He combines extensive knowledge of all things automotive with a passion for driving, and experience testing countless new vehicles, engines and technologies around the world. As well as his role as editor-in-chief across a range of UKi's media titles, he is also co-chair of the judging panel of the International Engine of the Year Awards.

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