Are You Ready for an All-Plastic Automotive Engine?

Feb 8, 2016

By Mark Shortt, Design-2-Part Magazine

Veteran automotive innovator Matti Holtzberg is at it again, pushing the limits of automotive design in his attempt to build a race car engine that combines high performance with light weight. 

Matti Holtzberg has been down this road before, beginning more than 30 years ago and continuing throughout the intervening years. He came to prominence as an automotive innovator in the 1980s, when he and his company, Composite Castings, designed and built what is widely considered to be the world’s first composite-based race car engine, the Polimotor. Armed with an intuitive understanding of the dynamics of the internal combustion engine, Holtzberg began the Polimotor project with a goal to replace as many engine components as he could with composite parts.

“My objective was to try to learn as much as possible, combining my education in composites and mechanical engineering, to better understand the dynamics of it and what would be required of a composite or a plastic to replace metal,” said Holtzberg in a phone interview from West Palm Beach, Florida, where Composite Castings is located. “That was what I wanted to do from day one. I had made a lot of parts for Ford, and a friend of mine there said to me, ‘You’re making all these parts, Matti—why don’t you make the complete engine?’ So, I did, and used it as a basis to continue, over these years, to develop materials and processes for making engines.”

The 4-cylinder Polimotor engine, relying on a mostly composite cylinder block and a variety of Torlon parts, raced two seasons in the International Motor Sports Association’s (IMSA) Camel GT series, once earning a third-place finish at Road America. Holtzberg called it “a huge technical success, but 28 years ahead of its time,” partly because in those days, an automotive engineer would have a hard time finding someone who could help build a nylon intake manifold—a problem that would lengthen production times. That wouldn’t be the case today, he said, because a much higher level of competence in plastics and composites technology is readily accessible. Automotive companies are looking at more materials and reinforced composites manufacturing processes than ever before, and materials developers can offer an abundance of technology to help them.

“Thirty years ago, the level of engineering to support all of this work was nowhere what it is today,” Holtzberg told D2P. “If a part broke, they made it heavier or thicker—that was the mentality. But today, you orientate fibers differently, you change the molding process. It’s just a whole different world.”

Determined to strike while the iron is hot, Hertzberg is once again seeking to manufacture and test what he has designed: a next-generation, all-plastic engine for competitive automotive racing in 2016. His new project, the Polimotor 2 (P2), is a more ambitious, turbocharged update of the original engine that seeks to replace up to 10 metal parts with lighter weight components made from Solvay Specialty Polymers’ high-performance thermoplastics. The goal is to develop an all-plastic, four-cylinder, double-overhead CAM engine that weighs between 138 and 148 pounds (63-67 kg), or about 90 pounds (41 kgs) less than today’s standard production engine. Solvay, a global supplier of high-performance polymers, is one of the principal material sponsors of the project.

“I am using racing as a moving billboard to demonstrate the performance, durability, and production feasibility of these materials,” said Holtzberg. “I am not attempting to bring the P2 to market, but to apply the technology to other OEM engines, which I have started to do.”

He may finally have the wind at his back. New plastic composites and 3D printing technologies are piquing the interest of automotive designers and engineers, who are more inclined to work with Holtzberg to fulfill his once radical vision of deploying high-performance alternatives to metal materials in automotive engines. A big factor in his favor is the automotive industry’s need to meet the Corporate Average Fuel Economy (CAFÉ) standard of 54.5 miles per gallon by 2025, a mandate that’s spurring the push toward lighter weight engines and structural components. Mass savings provided by converting to an aluminum body, shock tower, or enclosure, for example, enable the use of a smaller, lighter, and more efficient engine.

“Every time you save weight throughout the vehicle, you have secondary savings in terms of the systems that actually have to drive or steer or brake, or cool, or whatever the case may be in that vehicle,” said Michael Robinet, managing director at IHS Automotive Advisory, in a phone interview. “They don’t need to be as robust because you’re literally pushing less weight through the air, and, therefore, there’s an efficiency there, and therefore, you’re able to use a smaller engine.”

3D Printing a Carbon Fiber Reinforced Fuel Intake Runner
The first version of the Polimotor engine used aluminum for the fuel intake runners, Holtzberg said, because of budget restrictions and the lack of other materials available at the time. Today, the automotive industry relies heavily on injection molded nylon for the intake runners, but even that’s beginning to change as automakers look for innovative new materials to withstand higher under-the hood temperatures and greater stress and strain on the engine. Both are consequences of the growing use of turbochargers in today’s smaller engines.

The Polimotor 2 composite-based engine, based on the Ford 2.0 liter Duratec engine, has already achieved a breakthrough of sorts with the rapid and successful fabrication of a 3D printed, carbon-fiber reinforced polymer fuel intake runner for test purposes. Intake runners are found in racing and production-scale cars, and are typically integrated with an engine’s plenum, a pressurized chamber that uniformly distributes air flow between an engine’s air inlet and its cylinders. The performance of the intake, which injects fuel into the air stream just as it enters the engine, has a direct influence on the engine’s horsepower.

Arevo Labs, based in Santa Clara, California, employed its Reinforced Filament Fusion process to quickly produce the fuel intake runner using a custom-formulated, reinforced grade of Solvay’s KetaSpire® KT-820 PEEK. The material, reinforced by a 10 percent carbon fiber loading, resists chemical degradation by ethanol-based fuels and is able to withstand higher temperatures than nylon. Reliable mechanical performance at continuous-use temperatures up to 240°C (464°F) made the material well-suited for use in the Polimotor 2, where the fuel intake runner is reported to encounter temperatures reaching 150°C (302°F) near the pistons in the intake port. By using the carbon fiber-reinforced material, the team was also able to reduce the intake runner’s weight by 50 percent versus the original aluminum part.

“This is a real first,” said Holtzberg. “Nobody has ever printed real carbon. Everybody else has carbon powder mixed in with a polymer, but this has significant aspect ratio to it—length times diameter and height versus diameter—and the use of PEEK. What Solvay brought to the table here is a really exciting technology. This is a very high melt temperature resin. Nylon has been adequate, but the demands of future engines and higher engine temperatures will require high temperature resistant materials. 3D printed PEEK solved our need for rapid high temperature-resistant composite runners for testing.”

Arevo’s technology forms complex shapes by bonding polymer filaments on top of or alongside each other in successive stages. It can, therefore, quickly convert digital designs into functional parts without the time or cost required to first build a molding tool and prototype. One of the factors that separates the company’s Reinforced Filament Fusion platform, however, is its unique ability to print with reinforced PEEK polymers. The platform makes use of Arevo’s process control software to help optimize the mechanical properties of printed parts.

Although the strength of carbon fiber can surpass the strength of metal, the plastics industry’s dream of making plastic parts that can replace metal parts has not been fully realized with conventional manufacturing technologies. One reason is that current manufacturing processes, such as injection molding or machining, lack the ability to control carbon fiber orientation in a way that would optimize the mechanical properties of the part, said Hemant Bheda, CEO of Arevo Labs.

“Carbon fibers are very strong, but they’re only strong in one direction, whereas metals are obviously strong in all the directions,” Bheda said in a phone interview. “We call this an anisotropic behavior of the material. If you only get strength in one particular direction, then the challenge is, when you construct a part, to orient the carbon fiber in the direction where you want the ultimate strength. Now, with additive manufacturing, we have complete control of the orientation for the very first time.”

Arevo is able to control the carbon fiber orientation through its software, which creates smart toolpaths that align the fibers in a way that optimizes mechanical properties. “This is the key to making parts that are strong and can possibly replace metal parts,” said Bheda. “We joke that we are wrapping software around the molecules—the material molecules.”

The company uses additive finite element analysis (AFEA) to predict part strength based on fiber orientation. “The whole combination—the material formulation with carbon fiber; the process that enables the printing of parts using such reinforced materials; and the software that can create smart toolpaths—we call Reinforced Filament Fusion Technology,” said Bheda. “It is a combination of material formulations, deposition process, and software collaborating to make the lightest, strongest part at the lowest possible cost.”

A Whole New Range of Possibilities
When Holtzberg was working on the first Polimotor engine in the 1980s, neither 3D printing nor Solvay’s PEEK polymer technology were available for use. Now, their convergence is opening up “a whole new range of possibilities” for automakers who are seeking lighter, high-performing alternatives to metal, according to Brian Baleno, global automotive business development manager at Solvay Specialty Polymers, Alpharetta, Georgia.

“At the time of Polimotor 1 in the 1980s, Matti was really only working with a material or two in terms of thermoplastics,” Baleno said in a phone interview. “Now, there are materials like Amodel PPA, AvaSpire, PAEK, KetaSpire PEEK, and Radel PPSU, and you see these throughout the engine. These materials are really enablers, allowing for lightweighting and high performance at elevated temperature, with the chemical resistance you need in engine components.”

Baleno called the ability to 3D print the carbon fiber-filled PEEK fuel intake runner “phenomenal.” One reason is that KetaSpire PEEK, unlike a commodity material, is at the very top of the performance pyramid for its ability to resist chemicals, high temperatures, fatigue and wear. “It’s a lot different from 3D printing a toy, for example, out of commodity plastic,” he noted. Even more surprising, he added, is the ability to 3D print a part that incorporates the true benefits of carbon fiber in the polymer.

“Printing with a carbon fiber and getting fiber alignment within the part—that’s extremely impressive,” he said. “The 3D printed, carbon fiber-filled PEEK runner is new, it’s novel, and it’s innovative, and the more aware of this technology that automotive designers become, the greater the design flexibility they’ll have in their designs. It can also really accelerate their path to market.”

Holtzberg’s program will use Solvay’s advanced polymer technology to develop up to ten additional engine parts, including a water pump, water inlet/outlet, throttle body, fuel rail, and other high-performance components, according to Solvay. Among the materials targeted for use are Solvay’s Amodel® polyphthalamide (PPA), AvaSpire® polyaryletherketone (PAEK), Radel® polyphenylsulfone (PPSU), Ryton® polyphenylene sulfide (PPS), Torlon® polyamide-imide (PAI), and Tecnoflon® VPL fluoroelastomers. Besides the fuel intake runner, the Polimotor 2 team is also enlisting Solvay’s materials to fabricate a cam sprocket, a 3D printed plenum chamber, and an oil scavenger line for the engine’s dry sump modular oil pump system.

Polimotor 2 selected Solvay’s 30 percent carbon fiber-reinforced Torlon® 7130 PAI (polyamide-imide) to mold the engine’s spur tooth cam sprockets. The material replaced conventional metal to deliver a mechanically strong, but extremely lightweight part with high fatigue resistance. Allegheny Performance Plastics, a Leetsdale, Pennsylvania-based manufacturer of custom injection molded parts and an experienced processor of high-performance thermoplastics, injection molded the net shape. Gates Corp., a manufacturer of power transmission belts and fluid power products, provided final machining to produce a spur tooth design that is said to reduce wear and optimize transfer of transmission torque between the sprocket and the belt. The Polimotor 2 engine will incorporate two 4-inch (102mm) diameter sprockets and one 2-inch (51mm) diameter sprocket in its valve train drive system, according to Solvay.

Cam sprockets, typically made of sintered steel, aluminum, or thermoset phenolic polymers, are attached to one end of the cam shaft in the engine. Along with the timing belt, they help maintain timing between the cam shaft and crankshaft. Their reliability in delivering precise timing control is essential to maintaining optimal engine performance.

Commenting on the molding of the cam sprocket, Greg Shoup, division president ofAllegheny Performance Plastics, told D2P that Torlon, in general, requires specialized injection molding equipment, peripheral equipment, and an extended post molding curing process.

“Torlon 7130 has a very high melt viscosity that requires high machine pressures to properly pack the part out,” he said in an email. “The parts are required to be free from voids and cracks, which is verified by x-ray. This was a challenge due to the large thick cross section. The tool had to be built with a very large diaphragm gate to fill the thick cross section properly, and the large diaphragm gate had to be removed from the ID via a secondary machining process.”

Fraser Lacy, senior engineering specialist at Gates Corp., Rochester Hills, Michigan, said in a phone interview that the cam sprockets would normally be produced by sintering, hob cutting, or wire cutting.

“In this case, we used the Solvay material, and it worked really well. We were really pleased with the dimensional stability of it, and we were pleased with the finish that we obtained from the prototype part that we had. It came out really well—no problem with tearing or jumping out, or breaking.”

Then, and Now
When Holtzberg began work on the original Polimotor, he wasn’t motivated by the same pressures to reduce engine weight that exist today.

“I think I was just intrigued by the fact that you could make something differently from the way it had been made,” he said. “That was the challenge. In those days, everybody thought something as simple as a valve cover had to be made out of steel, and a wheel had to be made out of steel, and intake manifolds had to be made out of iron. That just didn’t make any sense to me, so it was somewhat of an intellectual and technical challenge. I’ve been fascinated with engines all my life, and just saw an opportunity to do something a little differently.”

Many of Solvay’s materials that are currently being used to make parts for Polimotor 2 weren’t available in those days, and many parts—such as the plenum chamber, intake manifold, oil pump, and water pump—were still being made of metal and, sometimes, heavy metals. The impellers on the water pumps were made of iron, Holtzberg said. Because making parts out of metal was the predominant mindset then, there were challenges to doing things a different way.

“I was really focusing more of my attention on the moving parts, as opposed to the stationary parts,” Holtzberg said. “Stationary parts were not a challenge—we designed those out of a particular material that worked right away, and never had an engine failure in testing. But making the higher stressed, higher temperature stress and physically stressed parts—the reciprocating and rotating parts of an engine—were a real technical challenge, and that’s what I enjoy doing.”

Fast forward 30-plus years, and Holtzberg now uses different words to describe the tasks required to build an all-composite engine today.

“I don’t think of them as technical challenges,” he explained. “We’re evaluating newer, stronger, lighter materials for the engine itself, and we’re looking at materials that were not in existence [during the first Polimotor project]. When I did the Polimotor, Torlon was the only high performance, injection moldable thermoplastic. But now, there must be 10 times more materials out there today, just off the top of my head.

“We’re learning which is the right material to use, and where,” Holtzberg continued. “Solvay has some very interesting prototype manufacturing processes that we’re using to evaluate, so I don’t see any real technical challenges.”

Reason for Optimism
Although customer acceptance remains an obstacle to the wider use of composites in automotive manufacturing, knowledge of the materials on the part of automotive engineers continues to increase, and Holtzberg is optimistic that composites technology will have a bright future in OEM engines going forward. He’s been designing an engine block for a leading European automaker, and is seeing “tremendous response” from OEMs all over the world as they continue to learn the benefits that plastic parts manufacturing processes bring to engine components.

“They’re very interested in what we are doing,” he told D2P. “Cost is still an issue. But as the OEM uses injection molding instead of sand casting metal, or even die casting metal, they’re rapidly learning the benefits of making something out of plastic. When I’d go to an automotive company years ago, they had no idea what you were talking about. Today, they think they know more than you. Everybody’s skiing on composite skis, and playing tennis with composite rackets, or golfing with composite clubs, and everyone is just so much more aware of what composites can do. Everybody’s accepting the technology much better than they did.”

At the same time, Holtzberg acknowledges the difficulties that he’s up against. “It’s hard to sell an automotive engineer anything because there are just so many other variables that need to be considered. You know, how do they manufacture it, what’s the consistency of the part? But when you see composite parts on airplanes, I think that tells you the most.”

Does the Polimotor have what it takes to make it in the consumer market? Anthony Schiavo, research associate at Lux Research and a member of the company’s advanced materials team, cautions against making a hasty judgement.

“I think instinct is to say, ‘No way, this is some F-1 technology,” he said in a phone interview, referring to the long time that it took for composites to come to automotive use after being launched on the F-1 rocket engine. “So if you look at it that way, it’s easy to say that it’s going to take a really long time to come to consumer vehicles. I think that’s the easy thing to say, but I’m not sure that that really captures the full scope of what’s happening. Because with electrification, you’re going to be able to put a smaller and smaller engine into your car because it’s going to be doing less and less of the heavy lifting of actually moving the vehicle around. It’s going to be increasingly in a supporting role, and the requirements for the engine are going to be reduced. So that’s one thing.

“The second thing is, at the same time, we’re seeing a huge increase in what I’ll broadly call ‘digital manufacturing.’ This is our ability to simulate composites, especially, and our ability, with things like 3D printing, to make really complex designs. The cooling that is going to have to go into this polymer engine is going to be really complex, to make sure that it doesn’t melt or have any other sort of issue. So a polymer engine is really going to be tricky, but our ability to manufacture very complex geometries is getting a lot better, even with composites, because we’re now having an increasing amount of 3D printing of composites.

“It’s still going to be a long-term prospect, but I could see having some play 15 years down the road, maybe. You’re not going to be building that Chevy small block out of plastic, right? That’s the wrong way to think about it. You’re going to be building some kind of secondary support engine and you’re going to have a better way of manufacturing it. You probably won’t be 3D printing it, but you might be 3D printing the injection mold that lets you make a really complex shape in a more cost-effective way.

“You’ll also have the tools to run and test all of that, making sure that the cooling works before you have to start building any engines. There are going to be a lot of tools in the future that we just don’t have today, or are just starting to improve today. So if you think about all those tools that we’ll have in the future, I think it’s actually better positioned for the consumer market than it might seem on first glance.”