The High Temperature Tribological Performance of Turbocharger Wastegate Materials

Engineer Looking at Computer Monitor

This article is a summary of a technical paper delivered at the IMechE 11th International Conference on Turbochargers and Turbocharging.

Tribology within Turbochargers

There are numerous tribological interfaces, commonly termed tribosystems, within a turbocharger. Some of these, such as the rotor bearing system, are lubricated and operate at temperatures less than 200 °C. The variable geometry and wastegate systems (Figures 1 & 2) are examples of high temperature tribological interfaces within a turbocharger which are subject to temperatures between 300°C and 800 °C but are not lubricated.

Figure 1 - Variable Geometry System Figure 2 - Wastegate Assembly

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Irrespective of the nature of the tribosystem, it is vital to select the appropriate combination of materials which provide the desired friction and wear behaviour for the interface. For that reason, extensive research and development is conducted on this topic in order to optimise the tribological performance of the system and to determine the reliability and durability of the components when in service.

Tribological Characterisation of High Temperature Materials used within Turbochargers

Within high temperature tribosystems such as the variable geometry and wastegate mechanisms, turbine inlet temperature significantly affects tribological performance. This is because for a given material at high temperature, the rate of oxidation and mechanical properties vary compared to when at room temperature. Therefore, materials which find use within high temperature tribosystems are usually of high cost due to their exotic chemical composition, which is required to provide oxidation stability whilst also affording sufficient mechanical properties, frictional response and wear behaviour. Recently, there has been increased focus on the development of materials that offer a cost reduction yet similar tribological performance compared to the more conventional substrates used at high temperature. As a result, extensive testing and analysis is conducted by Cummins Turbo Technologies in order to understand and validate the capabilities of such materials within turbocharger products. The friction and wear characteristics of high temperature interfaces within a turbocharger are traditionally established through component based experimentation. Using a research and development approach founded on the fundamentals of Materials Science, Cummins Turbo Technologies is able to select preferred material combinations with confidence prior to completion of considerably more expensive and time consuming component based testing.

Fundamental Approach to Tribological Characterisation of Wastegate Materials Wastegate Turbocharger

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In this research, a high temperature tribometer was employed in order to simulate the tribological interface between a wastegate shaft and bush within a turbocharger. Such simulation is highly complex and as such, it was essential that Cummins Turbo Technologies utilised their in-house expertise to ensure that the modelled tribosystem was representative of the engineering interface. The extensive knowledge and skill base of engineers at Cummins Turbo Technologies was also used to evaluate test samples from both fundamental and turbocharger-based experiments. Extensive analysis of test samples was conducted using highly complex methods in order to characterise the substrates with regards to surface topography, tribochemistry and wear. This methodology allowed Cummins Turbo Technologies to determine why particular materials and combinations of materials possessed superior performance at specific operating conditions.

A fundamental approach to characterisation of material friction and wear performance has numerous benefits: A significant reduction in cost compared to component-based testing, since test parts do not need to be in component-form Improvement in the efficiency of the product development process, since tribometer-based experimentation is an accelerated test and results can be obtained much faster than traditional component-based validation Reduction in complexity and marked improvements in data quality compared to component-based testing High Temperature Tribological Performance of Wastegate Shaft and Bush Materials Four material combinations were selected for testing based on their suitability for the application in terms of cost, corrosion behaviour and predicted tribological performance (Table 1).

Table 1 - Tribological test substrates

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All of the material combinations were subject to fundamental tribological tests which were conducted at 600 °C, 850 °C and 950 °C. The wear performance of the material combinations was determined using an optical measurement technique. Subsequently, the rationale behind why the materials provided the observed performance was determined using high resolution surface analysis techniques and the R&D expertise of Cummins Turbo Technologies in order to characterise the substrates and acquire the greatest possible data quality. Data correlation between tribometer and component-based experiments was successfully conducted in order to ensure that the fundamental tests were relevant and provided the appropriate level of data and confidence prior to conducting much more expensive and complex component-based experiments.

Overview: Materials Science at Cummins Turbo Technologies

This fundamental approach to Materials Science research and development has significantly improved the analysis-led design and testing capabilities of Cummins Turbo Technologies, resulting in the development and delivery of superior technologies to our customers. The analysis-led testing methodology provides greater data quality, improved efficiency of the product development process and reduction in cost of Materials Science research and development. Using the experimental and analytical techniques as described above, Cummins Turbo Technologies is developing high performance material combinations which address the specific requirements for light duty to high horsepower turbocharger applications.

Cummins Office Building

Cummins Inc.

Cummins is a global power leader that designs, manufactures, sells and services diesel and alternative fuel engines from 2.8 to 95 liters, diesel and alternative-fueled electrical generator sets from 2.5 to 3,500 kW, as well as related components and technology. Cummins serves its customers through its network of 600 company-owned and independent distributor facilities and more than 7,200 dealer locations in over 190 countries and territories.

Cummins continuing to supply critical filtration material for personal protective equipment

Cummins Filter Media
To date, Cummins has provided more than 14 tons of its filtration media to mask manufacturers across the globe.

In this Q&A, Amy Davis, Vice President of Cummins Filtration, shares an update on the company's progress to provide filter media to mask manufacturers around the globe. 

As the world began to grapple with COVID-19, employees at Cummins were working on innovative solutions to help supply PPE that was in high demand. On April 6, Cummins announced plans to use their filter technology to supply critical materials for N95 respirator masks, an essential piece of personal protective equipment for front-line healthcare workers.

Following the N95 announcement, on April 14, Cummins announced an additional partnership with 3M, which would include the utilization of equipment typically used for producing diesel engine filters to manufacture high-efficiency particulate filters for use in 3M’s powered air purifying respirators (PAPRs).

To date, Cummins has provided more than 14 tons of its filtration media to mask manufacturers across the globe, which has been used to produce more than eight million masks. Amy Davis, Vice President of Cummins Filtration, recently shared an update on the company’s progress to date.

Cummins Filter Media -  Covid - By the Numbers - 1
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Q: First, can you share more about the Cummins Filtration business and your core products?

DAVIS: Our core expertise is designing, manufacturing and selling air, fuel, hydraulic and lube filtration, as well as chemical technology products for diesel and gas-powered equipment around the world. 

Q: How did Cummins Filtration get involved in supplying media for masks?

DAVIS: The need for masks, especially N95 respirator masks, skyrocketed in March and April in response to the COVID-19 pandemic. We learned that many of the world’s leading mask manufacturers needed the critical materials to assemble masks and were struggling to meet demand. We realized that the NanoNet® and NanoForce® Media technology typically found in filtration products for diesel engines could also be used in surgical masks and N95 respirator masks worn by healthcare professionals to help stop the spread of COVID-19. Once we made that connection, we began exploring partnerships to apply the filter material to masks. 

 

Cummins Filter Media - Covid - By the Numbers - 2

Q: How has Cummins been able to partner with 3M in an additional effort to meet the surge in demand for PPE due to the COVID-19 outbreak?

DAVIS: We needed to move fast and saw an opportunity to use our existing workforce at our Neillsville, Wisconsin facility to meet this demand. We acquired, commissioned and tested a new pleater in a matter of weeks and have already produced more than 41,000 filters for 3M’s PAPRs since mid-April. Internally, we talk a lot about employee empowerment and decision making and this project is a testament to our employees’ ability to adapt quickly to fill an important supply void in a totally different market. 

Q: What has the response been like from mask manufacturers?

DAVIS: Demand has been strong – in fact, it’s getting to the point where demand will exceed our capacity. Seeing so many organizations inquire about the media reinforced how critical the need for masks was globally. We’ve talked with Universities, health care systems, other automotive companies and mask manufacturers large and small about our media. To date, we’ve supplied 6 tons of the complete composite multilayer media that can be used in N95 masks, and we’ve shipped 8 tons of a simpler polypropylene media that can be used in surgical masks. 

 

Cummins Filter Media - Covid - By the numbers - 3

Q: Do you plan on selling media for masks long-term, or is this a temporary measure to respond to the COVID-19 pandemic?

DAVIS: We’ve added manufacturing capacity and capability to our plants and plan on continuing to supply media for masks as long as there is demand and a need to protect our communities from COVID-19.  

Q: What has been the most interesting thing about this project for you?

DAVIS: Our employees always want to help, and it wasn’t a surprise when they demonstrated how quickly we could pivot from supplying filters for diesel engines to supplying the media that is critical to manufacturing medical PPE. It only took us one month to go from concept to production on this project! Cummins Filtration employees across the globe have taken immense pride in being part of the solution to help our communities, and the entire initiative is a great example of how Cummins embodies our mission of making people’s lives better by powering a more prosperous world.

Cummins Office Building

Cummins Inc.

Cummins is a global power leader that designs, manufactures, sells and services diesel and alternative fuel engines from 2.8 to 95 liters, diesel and alternative-fueled electrical generator sets from 2.5 to 3,500 kW, as well as related components and technology. Cummins serves its customers through its network of 600 company-owned and independent distributor facilities and more than 7,200 dealer locations in over 190 countries and territories.

Counterfeit turbos turn dream cruise into a nightmare

Rick Renfroe spent years diligently planning for a dream cruise. Little did he know, he had been deceived by counterfeit parts that were going to cause his trip to go horribly wrong.

Rick Renfroe had been planning a cruise to Key West and the Bahamas for well over a decade. The day he finally got his keys to a Sundancer 440 with twin Cummins diesels, that dream was on its way to becoming a reality.

No stone was left unturned in his boating preparations. Every mechanical element was checked and tested ahead of time, and if there were any doubts about a part’s reliability, it was replaced. 

This included the Holset® turbochargers mounted to the Cummins 6BTA5.9-M2 engines. Right before the big trip, Renfroe was wrapping up months of trouble-free performance sea trials when smoke started to appear from the port engine. 

Rather than taking any risks, Renfroe and his diesel mechanic decided to replace the turbochargers in both engines. 

The Start of a Vicious Cycle 

Counterfeit TurboThe local marina did not have the correct turbo model in stock, so Renfroe searched online and found a dealer in Atlanta, 600 miles (965 km) away, that did. With the trip fast approaching, he quickly drove to Atlanta to pick up the turbos and brought them back to be installed immediately by his trusted technician. 

The new HX40M turbos were advertised as “genuine Holset.” They looked right. They fit right. However, when the owner fired up the engines for a shake-down cruise in nearby waters, it took less than two minutes for the turbo on the port engine to have a significant failure. 

Assuming a manufacturing defect was the issue, Renfroe got back in his car, drove to Atlanta and exchanged it for another unit. He shrugged it off as an anomaly. Little did he know, this was only the beginning of his troubles. 

With the second replacement turbo installed, the family embarked on the first leg of the journey. All was going according to plan, and they spent a delightful week cruising the Bahamas and back to Key West. They started up the western coast of Florida, and just as they were leaving a fuel stop in Venice, the turbo on the starboard engine died, forcing them to idle for 14 miles (about 23km) to the nearest marina. 

A postmortem on the turbo revealed a seal failure and oil leak in the turbo, which caused the shaft to snap. The family rented a car to get home and a slip for their boat. Renfroe once again drove back to the dealer who sold him the first three units to get yet another replacement. Finally, back at his home port, Renfroe noticed oil seeping out of the housing. Fed up, he sent the turbos to Holset, where it was discovered the entire lot of turbos were counterfeit.

Hurricane Michael 

An ugly situation took a disastrous turn when Hurricane Michael suddenly started bearing straight down at the port. With no turbo on one side, there was no way to escape the hurricane’s path in time. Renfroe had no other choice but to remain docked and hope for the best. Unfortunately, the entire Panama City Marina took a direct hit and was completely destroyed – including Renfroe’s Sundancer 440. 

Hurricane Michael
During Hurricane Michael, the entire Panama City Marina took a direct hit and was completely destroyed - including Renfroe's Sundancer 440. 

Despite the situation, Renfroe appreciated the Holset team that made every effort to remedy the situation once they were contacted. He learned firsthand that to be absolutely positive you are getting a Genuine Holset turbocharger, with Holset reliability, durability and performance, you must always buy from an authorized Holset distributor. 

To learn more about Genuine Holset turbochargers and parts, visit Holset.com to find your local authorized Holset distributor
 

Cummins Office Building

Cummins Inc.

Cummins is a global power leader that designs, manufactures, sells and services diesel and alternative fuel engines from 2.8 to 95 liters, diesel and alternative-fueled electrical generator sets from 2.5 to 3,500 kW, as well as related components and technology. Cummins serves its customers through its network of 600 company-owned and independent distributor facilities and more than 7,200 dealer locations in over 190 countries and territories.

Cummins Turbo Technologies launches exhaust throttle valve

Cummins Exhaust Throttle Valve - ETV

A new Exhaust Throttle Valve (ETV) for aftertreatment thermal management and exhaust braking has been developed by Cummins Turbo Technologies (CTT). ETV helps engine manufacturers meet stringent emission requirements.

"With more than 60 years of experience in engine air handling innovation, CTT is uniquely positioned to integrate ETV with engine systems that provide customers with a complete system level solution. Cummins’ knowledge of air handling systems combined with experience in control systems technology has achieved a cost effective, high performing ETV to meet the needs of our customers," commented Matt Franklin, Director – Product Management & Marketing.

Initially, the launch of the ETV was developed for medium-duty engine applications in India and China, and has since grown to Brazil, Europe and Mexico. ETV applications include on-highway truck, transit bus, refuse and tipper trucks. 

The ETV not only helps engine manufacturers meet stringent emission requirements, but also offers flexible design needs. Cummins’ Original Equipment Manufacturers (OEM) have options to configure the product with heat shields, coolant fittings and locator features. Bespoke ETV products can be designed with customized flap diameter for tailored pressure control and unique end connections for easy integration. These flexible design offerings help OEM’s meet their packaging and performance requirements. 

"We have validated the product extensively on more than 130 applications with five different engine families. At the end of 2019, the total field mileage accumulation exceeded ten million kilometers - equivalent to circling the earth 250 times. The extensive engine and vehicle validation pursued by CTT has ensured a reliable and durable product," explained Brett Fathauer, Executive Director, Research & Engineering. 

A modular service strategy was also put in place to allow selected components to be serviced, rather than replacing the entire ETV. Thus, lowering the total cost of ownership. Additionally, CTT has leveraged its global supply chain to minimize product costs and support global market needs. The ETV is currently in production and is available now for customers.
 

Cummins Turbo Technologies News

Stay up to speed on the latest turbocharger technology by signing up for the Cummins Turbo Technologies quarterly newsletter.

Cummins Office Building

Cummins Inc.

Cummins is a global power leader that designs, manufactures, sells and services diesel and alternative fuel engines from 2.8 to 95 liters, diesel and alternative-fueled electrical generator sets from 2.5 to 3,500 kW, as well as related components and technology. Cummins serves its customers through its network of 600 company-owned and independent distributor facilities and more than 7,200 dealer locations in over 190 countries and territories.

Cummins Turbo Technologies breathes new life into the HE600 Holset Turbocharger

Cummins Holset HE600WG Turbocharger
Cummins Turbo Technologies (CTT) has revitalized the HE600 Turbocharger (pictured) platform

With an all-new compressor stage and turbine housing, the HE600 Holset Turbocharger from Cummins Turbo Technologies (CTT) offers a class-leading product for its customers. 

Strengthening its product catalogue, CTT has revitalized the HE600 platform by delivering significant improvements on performance and durability. By combining years of engineering experience in turbine wheel and impeller design, overall turbocharger efficiency has increased more than four percent while offering a product that is more robust.

"We have used advanced aerodynamic techniques to design a new impeller and compressor housing that offers up to five percent higher efficiency in the flow range of our key customer applications. In addition, a new turbine stage was developed and designed with the benefit of analysis tools that enhance performance, while still optimizing thermal stress and improving fatigue life," explained Charles King-Cox, Compressor and Turbine Stage Director for Cummins Turbo Technologies.

The performance results of the upgraded HE600 have been met with enthusiasm from customers in both on-highway and off-highway applications who describe the Holset product as "class leading."

The turbochargers have increased the flow range to have an overlap with the larger HE800 series. Customers using HE800 can now switch to a more compact HE600 that has increased map-width, higher performance and improved durability to help meet downsizing requirements to save on costs. 

Aerodynamic efficiency is a critical element of turbocharger design and the team at CTT has used the latest design practices to ensure the new product beats the competition and drives value for customers. 

The new product design incorporates aerodynamic efficiency, surpassing the competition with high efficiency and durability. Production for the new HE600 will begin in 2020 and cater to a wide range of customer applications, including on-highway trucks, generators, industrial markets and marine markets. 

"We are continuously working to improve our product line - and the HE600 is no different. This product will exceed performance expectations and provide increased value for our customers across the globe," commented Matt Franklin, Director - Product Management and Marketing at Cummins Turbo Technologies.
 

Cummins Turbo Technologies News

Stay up to speed on the latest turbocharger technology by signing up for the Cummins Turbo Technologies quarterly newsletter.

Cummins Office Building

Cummins Inc.

Cummins is a global power leader that designs, manufactures, sells and services diesel and alternative fuel engines from 2.8 to 95 liters, diesel and alternative-fueled electrical generator sets from 2.5 to 3,500 kW, as well as related components and technology. Cummins serves its customers through its network of 600 company-owned and independent distributor facilities and more than 7,200 dealer locations in over 190 countries and territories.

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