Materials that Withstand Today’s Hotter Running Engine Systems

Engine downsizing, lightweighting, turbocharging, direct injection, and exhaust gas recirculation are all responses to the drive for greater fuel economy, higher engine efficiency and lower CO2 emissions. But these advances come at a price.

They generate more heat, and involve more aggressive gases, fluids, and acidic gas/air mixtures, often under high pressure. Many traditional materials of construction can no longer perform in the much hotter, confined and stressed environments created by the modern engine.

DuPont offers the industry's broadest range of plastics and elastomers for key air management applications including air intake manifolds and gaskets, air ducts, turbocharger hoses and resonators, exhaust gas recirculation seals, hoses, valves, bushings, and sensor seals.

Elastomers and Plastics Solutions in Air Management
Air management systems integrate many components, including the turbocharger, resonator, intercooler, air intake manifold, exhaust gas recirculation and closed positive crankcase ventilation systems with air ducts, hoses, seals, gaskets, bushings and membranes to connect and seal these components.

These vital components require exceptional materials to withstand the high mechanical stresses, extremes of heat and cold and aggressive chemical environments for the lifetime of the vehicle. They must also be sustainably produced, and help automakers meet ever more stringent global evaporative emissions legislation - including US PZEV Phase III, LEV II, and Euro 5 and 6 - by demonstrating low to zero permeability to engine gases and fluids.

DuPont: A Key Partner for the Auto Industry
DuPont is currently the only company able to supply one-stop rubber and plastic solutions for many key air management components like air ducts, integrating from one side DuPont™ Vamac® AEM acrylic rubbers and DuPont™ Viton® fluoroelastomers, often reinforced by DuPont™ Kevlar® para-aramid fiber or DuPont™ Nomex® meta-aramid fiber, and from the other side the stiffer DuPont™ Zytel® PA66 and PPA resins and the softest DuPont™ Hytrel® TPC-ET thermoplastic polyester into welded, injection or blow-molded parts that can save up to 50% in weight, and over 20% in cost compared with metal parts.

The company is also at the forefront of materials development and testing to resist acid condensates in exhaust gas recirculation (EGR) systems, with the objective of helping OEMs reduce weight, and meet legislation requiring particulates and CO2 emissions reduction. DPP has become a key supplier to the auto industry OEMs, providing elastomer and resin solutions in air management.

Following is a review of the DuPont products best suited to key air management system components. For a deeper look at the solutions portfolio, click here.

Turbocharger Hoses
Today's trend to smaller, more fuel efficient and higher performing engines owes much to turbocharging. The latest turbocharged engines, both diesel and gasoline, deliver superior performance and transform more of the fuel energy into power than normally aspirated engines.

With increases in engine power and performance come big hikes in temperatures and pressures. Turbocharged diesel engines expose hot side turbo hoses to higher temperatures above 165°C up to 220°C and pressures of 2.5 bars. And the trend towards higher compressed air pressure is expected to lead to even higher operating environments in the next few years.

This temperature evolution is causing turbo hose manufacturers to switch to higher performing elastomers. Traditional CM, CR, ECO or NBR/CR materials have been rapidly displaced by standard AEM, HT-AEM and HT-ACM. However, even these polymers fail at continuous exposure above 185°C.

High performance specialty fluoroelastomers like Viton® can withstand temperatures up to 230°C in aggressive engine oils for the lifetime of the vehicle. DPP has developed a range of formulations based on Viton® elastomers for FKM/silicone turbocharger hoses that combine excellent extrusion properties and processability with optimum balances of heat and oil aging resistance, as well as low temperature flexibility and opportunities for silicone adhesion.

Major Success for DuPont™ Vamac® Elastomers
The turbo revolution is also becoming a major success story for high temperature Vamac® HT AEM— a key material of construction for turbocharger hoses, particularly in replacement of silicone rubber (VMQ) and polyacrylic (ACM).

Vamac® elastomer is specified for turbocharger hoses for continuous temperatures as high at 175°C, peaking as high as 190°C.

Fiat is using HT-AEM including new Vamac® Ultra HT (=VMX 3038) for the class F (continuous temperature = 170°C) of their new turbo hose material specification Fiat 9.02132/01.

Turbo Air Ducts and Short Connectors
Air ducts operate in a hot and stressful environment involving heat, pressure/vacuum, engine oil and blow-by-gases - conditions that can induce rapid heat aging in many plastic and rubber materials.

Specific grades of Hytrel®, Vamac®, Viton® and Zytel® are available for turbo air duct components. The selection of product and type depends on function and operating conditions. For example, is the duct positioned on the hot or cold side of the intercooler? What degree of flexibility is required? Will it integrate with other materials? Our global team of technical development experts help OEMs select and develop the best solution for a specific application.

Mahle and BMW Specify Air Duct of DuPont™ Hytrel® Polyester Elastomer to Reduce Weight and Cost
Stiff yet elastic DuPont™ Hytrel® HTR4275 is being used in a new two-component air duct from system supplier Mahle of Stuttgart, Germany, that connects the intercooler and throttle body of BMW’s three liter, six cylinder twin-turbo engine.

Reducing the part to just two basic components has led to lower weight, more efficient production and assembly, and a significant cost advantage over the earlier model of glass-fiber reinforced nylon and elastomers. Used on the cold side of the engine, the innovative air duct consisting of two Hytrel® sections is one of the first mono-material solutions of its kind in Germany.

Charge Air Coolers
Charge air coolers, also known as intercoolers, cool engine air from the turbocharger before it enters the engine. Components in this unit must accommodate wide temperature variations, hot air under pressure, vibration and mechanical stresses.

DuPont™ Zytel® glass reinforced nylon 66, Zytel® HTN and Zytel® PLUS nylon resin are proving ideal candidates for this demanding air management application, enabling weight and cost reduction in replacement of traditional materials.

New DuPont™ Zytel® PLUS nylon resin helps reduce weight and cost in charge air coolers, exhaust mufflers, turbo air ducts, engine mounts, resonators, cylinder head covers, oil pans, EGR coolers, oil modules, thermostats, transmission components and radiator end tanks, while maintaining excellent performance levels much longer than traditional nylon despite exposure to hot oil, hot air, calcium chloride and other aggressive automotive chemicals.

Vamac® is often used for intercooler seals, while Viton® has been specified for more severe technical requirements.

EGR valve bushings of Vespel® at Gustav Wahler

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EGR Seals, Hoses, Valves, Bushings and Gaskets
EGR systems, designed to reduce oxides of nitrogen (NOx) from exhaust emissions, recirculate already combusted exhaust back into the air intake to dilute the incoming air/fuel mixture, thus reducing combustion temperatures well below the 1300+°C peak at which NOx is formed. However, recycling exhaust gases back into the engine results in gas compositions that are very aggressive to many sealing elastomers.

Vamac® ethylene acrylic elastomers and Viton® fluoroelastomers are at the forefront of developments in flexible hoses and hose-end seals, providing long-term temperature and acid resistance for these key EGR applications.  

Vamac® provides a cost-effective EGR hose and sealing solution at peak temperatures up to 150°C, while Viton® can be considered the primary candidate for highly concentrated acid environments at peak temperatures up to 225°C.

EGR Valve Bushings of DuPont™ Vespel® Parts at Gustav Wahler
In rigid EGR applications, valve bushings of Vespel® TP polyimide have replaced metal components because of its stiffness, tensile strength, and resistance to friction, wear and hot exhaust gases at temperatures up to 220°C. The valve bushings, made by Gustav Wahler GmbH and Co. KG of Esslingen, Germany, for an EGR system used in four and six-cylinder stratified-charged petrol engines, position and guide the cylindrical operating rods of EGR slip-in valves, supporting their smooth operation during millions of openings and closings.

Low wear, low friction injection molded bushings of Vespel® TP polyimide for EGR valves manufactured by Gustav Wahler for four and six cylinder petrol engines, offer increased design freedom, reduced weight, elimination of contact corrosion and increased resistance to aggressive exhaust gases when compared to similar metal bushings.  

Turbocharger Resonators
Turbocharger resonators act as mufflers to reduce the pulsating turbo whine from the turbocharger and change the frequency of the sound to a lower, more pleasant register. Resonators operate under high pressure and temperature, conditions suited to Zytel® HTN PPA.

Zytel® HTN has been specified for a hot turbocharger resonator housing developed and molded by Umfotec GmbH, and fitted as standard equipment to 1.6 and 2.0 liter turbo-diesel engines produced by a major German OEM.

Sensor Seals
Oxygen sensor (or lambda sensor) seals play a key role in engine performance and pollution reduction by monitoring the level of oxygen in the exhaust so the air/fuel mixture can be regulated to reduce emissions. The unit is mounted in or near the exhaust manifold downpipe ahead of the catalytic converter and is exposed to hot, aggressive exhaust gases.

Viton® fluoroelastomers - and sometimes DuPont™ Kalrez® perfluoroelastomer parts - are used for oxygen sensor seals because of the requirements: excellent long-term sealing performance coupled with resistance to hot exhaust gases and temperatures over 225°C to 300°C.

Air Intake Manifolds and Gaskets
The air intake manifold (AIM) distributes air into the cylinders of a direct injection engine, or an air/fuel mix in a non direct-injection engine. It is an increasingly difficult sealing challenge for the automotive designer in view of more stringent emissions requirements, demands for longer fuel system life, higher engine temperatures and new manifold materials. AIM units were typically made of aluminum or cast iron, but the trend is to plastics and elastomeric sealing.

DuPont™ Viton® AL, the fluoroelastomer type best suited for AIM gaskets, excels in low permeability far surpassing that of HNBR, VMQ (silicone) and FVMQ (fluorosilicone), and compression set resistance, ensuring long-term retention of sealing forces. It offers the lowest permeability to fuel of all elastomers used commercially, in compliance with LEVII and PZEV emissions regulations.

DuPont™ Viton® GAL-S and Viton® GLT-S are the fluoroelastomers of choice for better low temperature performance, and especially for higher resistance to aggressive biodiesel and acid exhaust gas fumes recirculating in the air intake manifold via the EGR high pressure loop.

AIM gaskets and O-rings of Viton® offer the lowest permeability to fuel of all elastomers used commercially, in compliance with LEVII and PZEV emissions regulations, and enable simplified AIM constructions.

AIM seals made of Viton® remain resilient and retain sealing force over a temperature range from -40°C to +230°C even during exposure to hot air, gasoline and diesel fuels, including blends with methanol, ethanol and oxygen-containing additives. Retention of sealing force at very low temperatures (-40°C) helps prevent air in-leakage.

More Than 100 Materials and Families
DuPont Automotive offers more than 100 materials and products to the global automotive industry and through its global applications network is committed to delivering cost-effective solutions to help reduce vehicle weight for better fuel economy and CO2 emissions reductions, to integrate part functionality to simplify assembly and eliminate cost, and help bring invention to market quickly, cost effectively.