NOx Reduction: Part 2 of a 3-part series
Improving EGR and SCR NOx reduction systems
Nitrogen oxide (NOx) gas, formed from the reaction of nitrogen and oxygen during combustion, is a significant and undesirable air pollutant, especially in cities where motor traffic is heavy. Progressive global emissions standards are setting limits for NOx that challenge the auto industry to raise the effectiveness of deNOx systems.
Euro 6 standards in 2014 will apply a 0.060 g/km cap on NOx emissions for gasoline passenger cars and 0.180 for diesel, and Japan Step 6 will regulate in parallel. In the United States, the Environmental Protection Agency (EPA) and the California Air Resources Board (CARB) already apply a 0.05 g/km gasoline NOx limit.
For diesel passenger cars, the evolution in NOx reduction regulation since Euro 1, US Tier 1 and Japan Step 1 emissions standards in 1992 has been particularly dramatic. Over the period 1992 to 2014-2015, automakers will have been required to reduce NOx emissions by 83%, 89% and 92% respectively. No small task.
NOx reducing systems
The auto industry is applying numerous technologies to tackle the challenge of NOx reduction—and key among these are exhaust gas recirculation (EGR) and selective catalytic reduction (SCR) systems.
EGR systems 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. Most modern engines now require EGR systems in order to meet emissions standards.
SCR systems convert NOx into nitrogen and water by injecting urea through a catalyst into the diesel engine exhaust stream, where it is expelled through the tailpipe. SCR technology can reduce NOx emissions by up to 90%, and can be combined with a diesel particulate filter (DPF) to reduce emissions further.
Solutions to reduce NOx via material technology
EGR and SCR systems create high temperatures, pressures and chemically aggressive gas compositions that require ultra high performance plastics and elastomers for ducting, hoses, seals and other components. The aqueous urea (such as AdBlue®*) used in SCR systems is also corrosive to many materials.
DuPont Performance Polymers is actively engaged with automakers to develop plastics and elastomers that will withstand these operating environments, provide system-lifetime service in EGR and SCR applications, and help raise system efficiency.
Plastics for NOx reducing systems
DuPont offers innovative plastics solutions for low-emission, fuel-efficient vehicles (homologated for SCR/urea/AdBlue®), including:
DuPont™ Hytrel® TPC-ET thermoplastic elastomer provides the flexibility of rubber, the strength of plastic and the processibility of thermoplastics. Hytrel® is used for EGR and SCR applications, including air induction systems, seals, valves, reinforced hose and bearings.
DuPont™ Zytel® HTN and Zytel® PLUS high temperature resins retain stiffness, strength and rugged mechanical properties under long-term exposure to high temperatures, pressures, vibration and aggressive exhaust gases, and are widely specified for many EGR, SCR, turbocharger and other engine air and exhaust management system components.
DuPont™ Vespel® polyimide parts have replaced metals in EGR systems and turbochargers—providing stiffness, tensile strength and resistance to friction, wear and hot exhaust gases at temperatures up to 220°C.
DuPont™ Teflon® brand fluoropolymers can play a critical role in enabling oxygen sensors in automotive fuel systems, enhancing engine control in a way that saves up to 15 percent of fuel and allows for up to 95 percent reduction in NOx emissions.
Elastomers for NOx reducing systems
DuPont offers innovative elastomer solutions for low-emission, fuel-efficient vehicles (homologated for SCR/urea/AdBlue®), including:
DuPont™ Vamac® Ultra ethylene acrylic elastomers (AEM) provide cost-effective flexible hose and sealing solutions for aggressive EGR environments at peak temperatures up to 150°C.
DuPont™ Viton® fluoroelastomers provide long-term temperature and chemical resistance in flexible hoses and hose-end seals exposed to concentrated acid environments at peak temperatures up to 225°C in EGR systems.
Why lighter is better—with plastics
Look out for the third article about DuPont technologies for CO2 reduction, “Why lighter is better—with plastics,” appearing in the next issue of AutoFocus, online later in 2013. For more information about products and technologies from DuPont for automotive, visit DuPont Automotive.
Missed CO2 Reduction: Part 1? Read it here:
DuPont innovation: Speeding the way to higher engine and fuel efficiency & lower CO2 emissions
* AdBlue® is a registered trademark of the German Association of the Automobile Industry (Verband der Automobilindustrie - VDA).
**TurboBoss™ is a trademark of Veyance Technologies, Inc.