There are two main criteria for discussion performance at operating temperatures and performance in the chemical cocktail

Transcription

1 Turbochargers and Emissions Systems: Material Solutions to Help Downsize Engines Material Solutions Turbo, EGR System DuPont Automotive Webcast hosted by SAE International Nov. 4, 2010 Ed McBride, Technology Leader Air Induction Systems, DuPont Performance Polymers Randy White, Global Air Induction Segment Manager, DuPont Automotive Performance Polymers John Huber, Air Delivery Systems, DuPont Automotive Performance Polymers Thank you Mike -- Hello I am Ed McBride, Technology Associate for the DuPont Performance Polymers group and for the last twenty years I ve worked in the application development and technical service lab in Wilmington, Delaware focusing on the adhesive and elastomer industry My colleague Randy White and I will spend a few minutes talking the new operating conditions for hoses and ducts in turbocharged systems and then we will talk about integration opportunities. There are two main criteria for discussion performance at operating temperatures and performance in the chemical cocktail (slide 2) The two most important factors for material selection are the temperature rating and the chemical resistance. The temperature requirements for the hot side are obviously harder to meet as compared to the cold side. The sources of the chemical cocktail are the recycle streams highlighted in the diagram in the yellow circle the PCV system and the EGR system. The PCV (positive crankcase ventilation) loop recycles a combination of fuel and engine oil along with impurities back into the suction side of the turbocharger. The EGR (Exhaust Gas Recovery) loop is more complicated than what is shown here. The EGR source gas can be taken from either before or after the turbocharger or it can be based on a combination of the two. The EGR gas contains combustion by-products such as water, NOx, carbon monoxide, etc that are the source of the acids in the acid condensate. Contact: Dial DuPont First

2 The combination of the impurities in the EGR and PCV systems has significantly changed the requirements for materials throughout the turbocharger system. The next slide will focus on the temperature ratings followed by a discussion on chemical resistance. (slide 3) In this chart, the red represents materials for the hot side and the blue represents materials for the cold side. The temperature requirements for the hot and cold side have changed and will continue to change, so materials that are currently approved for the hot side may be limited for use on the cold side in the future. The chart represents three categories of materials elastomers, fibers and thermoplastics. It is important to note that each category uses different criteria for determining the heat resistance of a material. A hose uses a combination of elastomers and fibers while a molded air duct on the high pressure side is based on thermoplastics. Ducts on the suction side of the turbocharger can use either thermoplastics, elastomers or a combination of the two. As shown in the first column under elastomers, there have been recent developments that address the need for improved temperature performance over existing materials. An example of this is the AEM-HT development in the Vamac family which improved performance by about 10 degrees C over the existing AEM grades. The center column highlights fibers. Nomex meta-aramid fibers are the long standing choice for reinforcing high temperature, hot side rubber hoses. Recent developments in Kevlar para-aramid fibers have been on stronger and thinner fibers for higher rupture pressure and longer-life of cold side and lower temperature hoses. The column on the right shows thermoplastics. A recent development in this area has been the introduction of the Zytel PLUS family of nylons which have a heat resistance of about 10 to 20 C higher than the corresponding conventional nylons. (slide 4) On the chemical resistance side there has been a tremendous amount of change due to the use of the recycle systems previously discussed. Without recycle streams specifically the EGR and PCV -- the two key criteria for materials in the turbocharger system were heat resistance and oil resistance. With the introduction of recycle streams, the testing requirements for material selection are now more rigorous. Each OEM has its own requirements for material selection. Some of the key parameters include type of acid condensate mineral or organic, the length of the test, the test Contact: Dial DuPont First

3 temperature, testing in the liquid phase an/or the vapor phase, the type of engine oil, the type of fuel, etc Typical conditions for an acid condensate testing are based on an aqueous solution with a ph of about 3 where the samples are aged for one week at 90C. (slide 5) Two key tests in fluid aging are retention of physical properties and volume increase. This picture shows a sample of a tensile bar of chlorinated polyethylene (CPE) after aging for one week at 90C in an acid condensate solution with a ph of about 3. After fluid aging, the tensile sample was destroyed so the tensile test could not be conducted and therefore the CPE failed this test. (slide 6) These results from the Volume Increase test show the effect that the acid condensate can have on different elastomers. These samples have been aged for one week at 90C in a mineral acid condensate with a ph of about 3. These conditions were specified by an OEM. The Viton fluoroelastomer (FKM) samples on the left performed well in this test while the Epichlorhydrin (ECO) samples on the right had a very high swell. This slide and the previous slide show the problems that chlorinated elastomers have in acid condensates. Hoses based on chlorinated elastomers were acceptable in the past for the cold side but they may have difficulty meeting the acid condensate requirements. This is an example of how the changing chemical cocktail requirements can influence material selection. (slide 7) Tensile bars made from Hydrogenated Nitrile (HNBR) rubber were exposed to an acid condensate solution with a ph of 1 for one week at 100C while in the liquid phase. The HNBR sample did not perform well in this test and it performed only marginally better when aged in the gas phase. For comparison, an AEM (Vamac ) compound performed well in both the liquid and gas phases. Although the standard ph for acid condensates has been about 3, the trends are that the ph is decreasing as a result of more complicated recycle loops. A ph of 1 is much more aggressive than a ph of 3. The more acidic environment will influence material selection throughout the turbocharger system. Contact: Dial DuPont First

4 (slide 8) Most people who have studied at elastomers have seen a chart that rates elastomers on two axes. One scale is for temperature and the other is for swell in IRM903, which is a standard test oil that has a high aromatic content. At one time swell in IRM 903 oil was an indicator of the swell an elastomer would have in engine oil. This slide rates elastomers for the turbocharger system using two variables. One axis is performance in acid condensate and the other axis is performance in the newer engine oils. The new engine oils are significantly different than IRM 903. They are based on synthetic oils and they tend to be much more aliphatic. They also contain aggressive additive packages that improve fuel efficiency and the life of the oil. Testing in the oil often includes oil that has low levels of fuel. An example of recent developments in this area is the performance of Viton FKM compounds. The conventional Viton compounds do not perform well in the acid condensate because they contain metal oxides. Developments over the past several years have shown that the newer grades of Viton with improved formulations (no metal oxides) perform very well in acid condensates. (slide 9) Thank you Ed -- Hello I am Randy White, Global Segment Leader for DuPont Performance Polymers. I have worked in the automotive industry for over twenty years specializing in the air management systems. I am going to discuss the effects of EGR exposure to thermoplastics. The standard test procedure for evaluating plastics in acid condensate solution is to immerse tensile bars for a specified time and temperature. This slide shows how flexible thermoplastics from DuPont hold up against acid condensate with a ph of about 3. On the left, some of the aged test specimens show signs of blistering after the immersion. However this test is extremely harsh due to the total immersion in the solution. In an air duct application, the actual operating environment would be closer to a vapor phase. The significance of this test is to show how well these materials hold up after long term exposure in this harsh environment. Since we are looking at how flexible materials perform in the acid condensate test, I have selected the Elastic-modulus data to show how long term exposure effects these materials. The graph shows Hytrel polyester elastomer has very little change over 2000 hours of exposure. As expected, the modulus for the Zytel drops initially due to moisture absorption and then remains constant over 2000 hours. This data shows the flexible air duct materials from DuPont do not change in stiffness when exposed to acid condensate. Contact: Dial DuPont First

5 (slide 10) When we look at the performance of rigid thermoplastics from DuPont in acid condensate, the test specimens on the left show little or no degradation in appearance. One of the key material properties for rigid thermoplastics in an air duct is tensile strength. In this graph, the tensile strength once again shows the expected initial drop with nylon and then shows approximately 10% to 20% decrease over 2000 hours of immersion in liquid EGR solutions. (slide 11) The other key topic of interest as expressed by the marketplace is what are the best design solutions considering material selection, packaging, net cost and reduced weight. (slide 12) The optimal design solution will be a balance of performance, weight and cost. Many variables are important in developing the optimal air duct design solution. Selecting the best design solution means understanding all the requirements and material options to meet your needs. Typically, time, temperature and pressure are the three variables that are utilized in developing an air duct design. In order to select the right material for the application, chemical resistance also plays a critical role in the long term performance of the part. The last two key variables, engine movement and assembly have more to do with how flexible or rigid the assembly can be. If the air duct is too stiff, the part is difficult to assemble and during engine roll, the stress on the end connections can cause the part to fail or leak. Sometimes a rubber hose is used to decouple the vibrations from two different sources such as engine and chassis. (slide 13) Three different design options are shown for air ducts used in the turbocharger systems. Option 1 uses a combination of a high temperature elastomeric hoses and injection molded rigid thermoplastics made from high temperature polyamides. The combination of the two high temperature materials allows for complex shapes and good heat resistance. This approach is often used on the hot side of the turbo loop. Option 2 utilizes blow molded thermoplastic tubes and fiber reinforced elastomers. This option can be used on both the hot and cold side and gives you the opportunity to create complex routings and make it easier to assemble. Option 3 can be divided into an all plastic or all rubber solution. The all plastic option uses an integrated blow molded tube using flexible thermoplastics. This option can be Contact: Dial DuPont First

6 the most cost effective but there are limitations created by the air duct routing and assembly requirements. This approach is used mainly on the cold side. The second part of Option 3 is the all rubber solution. The main advantage of an all rubber assembly is flexibility for engine roll and assembly. This approach can be used on either the hot or cold side. (slide 14) Hello. This is Ed McBride again. Hoses are an excellent example of the integration of elastomers and fibers. The elastomer provides heat and chemical resistance while the fiber reinforcement restricts volumetric expansion and determines the rupture pressure of the hose. Just as different types of elastomers provide levels of heat and chemical resistance over time, the choice of fiber will impact the life of the hose with levels of heat and impulse pressure over time. Cold side hoses typically see a temperature that is less than 150C. Traditionally, hoses for this application have been chlorinated elastomers in combination with Kevlar aramid fiber. As mentioned earlier chlorinated elastomers degrade readily in acid condensates. Recent fiber developments for cold side hoses have permitted downsizing of the filament diameter while improving burst strength and overall hose performance. A combination of AEM and Kevlar meets performance requirements up to 160C while a combination of AEM Vamac Ultra HT and Nomex meet performance requirements up to 180C. Above 180C the recommended fiber is meta-aramid fiber such as Nomex in combination with a high temperature elastomer such as silicone or a co-extruded structure of Viton /silicone. (slide 15) Randy and I have been talking about hoses and ducts that convey air through the turbocharger system. The performance requirements around temperature and chemical resistance for these parts have changed. There are growth opportunities in this area for materials with a combination of good heat resistance and good performance in acid condensate and engine oils. The performance requirements will continue to change because the airflow systems will get more complicated in the future. As always it is very important to match up the materials used and the end use requirements. # # # The DuPont Oval Logo, DuPont, Hytrel, Kevlar, Nomex Vamac, Viton and Zytel are registered trademarks or trademarks of DuPont or its affiliates. Contact: Dial DuPont First