The Quest for the Plastic Engine
Back in the day, engines were the exclusive domain of cast iron and steel. But, during the past decade, more lightweight materials, such as aluminum and hard thermoplastics, have been slowly creeping under the hood. The Holy Grail, an engine made almost entirely out of plastic, is finally close to reality.
A team of engineers in Florida has been developing a functional engine with plastic and carbon-fiber composite components. When it debuts this summer, the revolutionary Polimotor 2 will be 33 percent lighter than a traditional engine. It’s the brainchild of Matti Holtzberg, president of Composite Castings LLC.
“Our goal is to demonstrate the durability and performance of a plastic engine by using the latest in thermoplastics technology,” says Holtzberg. “At the same time, we want to showcase CO2 reduction technologies, such as turbocharging and electronic water pumps.
“There is growing interest in our engine from several large automakers,” claims Holtzberg. “Range-extending technology may be one of the first areas of commercial use.”
According to Holtzberg, a plastic engine offers numerous benefits, such as corrosion resistance, less noise and vibration, and lower weight.
“In addition, manufacturing costs are much lower and cleaner, because machining, heat treatment and other traditional production processes are almost completely eliminated,” explains Holtzberg, who has updated an engine he originally developed back in the 1980s.
The next-generation Polimotor 2 engine features a four-cylinder layout with a double overhead camshaft design. The two-liter turbocharged engine will produce up to 350 hp at 7,000 rpm.
It will weigh 140 pounds, which is 90 pounds less than a similar metal engine. The original Polimotor 1 engine weighed 168 pounds (it used aluminum pistons, a steel crankshaft and steel rods).
To produce components for the new engine, Holtzberg is working with suppliers such as AGY Holding Corp. (a producer of glass fibers) and Solvay Specialty Polymers (a producer of materials such as polyphenylene sulfides and fluoroelastomers). The goal is to eventually use carbon-fiber composite parts, which would make Polimotor 2 up to 48 percent lighter than a traditional engine.
According to Holtzberg, the new polymer chemistries used in Polimotor 2 were not available 30 years ago, including polyether ether ketone (PEEK), polyphenylsulfone and polyphthalamide (PPA).
Many metal parts have been replaced with plastic, including cam sprockets (polyamide-imide), the oil scavenger line (PEEK) and the water inlet-outlet fixture (PPA). Other plastic engine parts include the oil pump, throttle body and water pump.
"Each component has its own unique set of challenges, but the fuel rail has been the most difficult to produce," says Holtzberg. "The 19-inch-long plastic injection-molded part is made from a polyphenylene sulfide alloy grade that's reinforced with 40 percent glass fiber. It was challenging to build because of the dimensional requirements."
In addition to using new materials, Holtzberg and his colleagues are harnessing new production technologies that didn’t exist 30 years ago, such as additive manufacturing. The engineers used 3D printing to produce a variety of parts, including the air intake plenum, which is made out of polyamide, and the air intake runner, which is made from PEEK.
The air intake plenum chamber was fabricated with selective laser sintering. According to Holtzberg, the plenum in the Polimotor 2 will encounter lower temperatures than in a conventional metal turbocharged engine (150 to 200 F vs. 250 F), due to the low thermal conductivity of the engine’s plastic composition.
The air intake runner was produced with reinforced filament fusion technology. “The intake runners in the original Polimotor engine were made from aluminum, but today the automotive industry relies almost entirely on injection-molded nylon,” says Holtzberg. “Replacement of the original aluminum runner with PEEK reduced the part’s weight by 50 percent.”
Polimotor 2 features a compression-molded engine block. Epoxies and other types of adhesives are used to assemble a variety of the components.
"The more weight we can take out, there's less stress on joints and seals," says Holtzberg. "There's been tremendous progress made in adhesives over the last three decades. In fact, I see a day in the near future when cylinder heads will be bonded onto engine blocks."
Later this year, the Polimotor 2 engine will be installed in a race car. If testing proves successful, it could make its on-track debut at a 10-hour endurance race in Georgia this fall.
In the spring, Holtzberg plans to compete at Daytona, Sebring and other road racing circuits. Ultimately, he hopes to participate in the LeMans 24-hour race in 2017 or 2018.
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