Commercial engines and biodiesel: A study in sealing

As agricultural, construction, heavy- and light-duty vehicle manufacturers increase their use of biodiesel fuels, components used to seal engines and transmissions against contamination and leaks must be made of validated elastomeric materials that can withstand unique operating conditions and fuel blends, but research on the impacts of biodiesel on those components did not exist until recently.

Joseph Walker, global director, Advanced Materials Development for Freudenberg-NOK Sealing Technologies, recently unveiled results of an extensive company study that analyzed how biodiesel engine-oil dilutions impact common sealing elastomers. The study was launched in response to published accounts highlighting concerns associated with oil-diluted, biodiesel fuel in heavy machinery.

“We realized we needed to understand how biodiesel fuel-oil blends are impacting our business of materials, seals, and other rubber components,” Walker says. “As a global materials expert, if we can’t advise our customers about biodiesel sealing matters, who can? This is the first time a company has studied the effects of biodiesel fuel-oil on the short- and long-term performance of different materials and sealing elements.”

This latest study is an extension of previous research projects Freudenberg-NOK has undertaken since 2009 to examine the impact that alternative fuels have on engine and transmission rubber components. The company began its research by exploring the effects ethanol would have on various rubber materials. In 2008, the company expanded its research by exploring the impact that various blends of methanol have on seals and gaskets.

As global environmental legislation and energy conservation initiatives began to have an increasing impact on commercial vehicles, construction and agricultural equipment, and even light-duty trucks, Freudenberg-NOK engineers realized customers were turning to biodiesel fuels as alternatives to other commercially available fuels and new research was necessary.

“As large earth-moving equipment and other heavy machinery becomes cleaner through the use of advanced particulate filters and catalyst regenerative systems, engine manufacturers are going to experience motor oil contamination in their engines from fuel – mainly through late cylinder injection times,” Walker explains. “Biodiesel fuels have a much higher boiling point, and the fuel is miscible with the engine oil. This means more fuel remains in the oil during use, and this diluted oil mixture impacts engine and component operation. As a result, there was a large need to study how our static and dynamic seals would behave in diluted engine oil.”

Freudenberg-NOK’s comprehensive study was designed to close this information gap. The study that tested the effects of biodiesel fuel-oil-diluted mixtures on 15 common sealing materials including silicones, fluorosilicones, polyacrylate polymers, acrylonitrile (ACN) materials, ethylene acrylic elastomers (AEM), fluorocarbon rubbers (FKM), and hydrogenated nitrile butadiene rubber (HNBR).

“We realized that if we understood how these biodiesel fuel-oil mixtures impacted elastomeric materials, we could determine which ones would perform best and longest for our customers and allow them to improve engine design as well as mitigate any possible customer dissatisfaction,” Walker says. “And the dilution of the engine oil with biodiesel fuel does have pronounced effects on both lubricant and seal life.”
 

Biodiesel material testing, results

Freudenberg-NOK engineers set a performance baseline, immersed the materials in biodiesel fuel-oil blends, and then tested for retention of specific seal properties as well as dimensional stability. Testing was conducted at 150°C with immersion times of 504 hours and 1,008 hours using purchased commercial-grade biodiesels. The study tested the effects that biodiesel has on the given material’s hardness, modulus, tensile strength, elongation, and volume.

The compounds were constructed using known compounding techniques for fuel and biofuel systems – for example, the elimination of metal oxides. The temperature of 150°C comes from the typical temperatures being seen in the oil sumps for various engines. Sample data for changes in modulus are shown after 1,008 hours of exposure (table at top).

In testing the effects of biodiesel engine oil dilution on various elastomeric material properties, the Freudenberg-NOK study revealed that certain grades of elastomers – specifically those with molecular architectures that uniquely crosslink with organic peroxides – offer the strongest sealing solutions when used in systems that run on biodiesel blends.

Freudenberg-NOK further found that B20 diluted oil tends to be more aggressive in attacking the structure of some elastomeric materials, increasing the likelihood that components made from these materials could be compromised and fail prematurely.

Data from the Freudenberg-NOK study revealed that increasing the fluorine content in various types of fluoroelastomers (FKMs) did not produce improved property retention in all cases. Further, FKM types 2, 3, and 5 performed best when subjected to various biodiesel fuel-oil blends. FKM types 2, 3, and 5 are all cured using perioxide crosslinking mechanisms.

Additionally, Freudenberg-NOK’s research revealed that Type 1 FKMs, which rely upon a bis-phenol AF cure system, show greatest adverse impact.

Walker and his team also analyzed the impact that biodiesel fuel-oil blends have on non-FKM component systems. Data indicate that fluorosilicone (FVMQ) presents itself as an alternative to some FKM types and to highly saturated HNBR. However, as with any application, the specific part function needs to be evaluated. For example, FVMQ may function satisfactory for a static seal but not for a dynamic seal.

The Freudenberg-NOK study found that fully saturated HNBR systems – those with residual double bonds less than 1% – performed well in testing. It also found that high temperature ACN (HT-ACM) material systems could be considered for use in a biodiesel fuel oil environment in select applications.

“By benchmarking different polymer architectures and how new fuels affect them, Freudenberg-NOK has a strategic advantage that helps our customers operate in today’s changing environments,” Walker says.

He adds that the analysis is particularly important to customers in the construction, agriculture, and heavy-equipment industries because those machines are operated for long periods between maintenance cycles.

“We can offer customers elastomeric seals that have been specifically engineered and validated to operate flawlessly in a biodiesel fuel environment. Our customers can be assured that their machinery will experience fewer mechanical failures and downtime due to seal issues,” he concludes.

Freudenberg-NOK Sealing Technologies
www.fnst.com

For additional information or to learn more about the study, contact Joseph Walker at joe.walker@fnst.com.