In the future, emissions aftertreatment systems will be challenged to continually adapt to a number of key trends, including increasingly stringent regulatory requirements, changing engine strategies, and consumer preferences—particularly for improved fuel efficiency, but also for aesthetic considerations such as vehicle sound. State-of-the-art engineering skill as well as strong expertise in the basic sciences will be fundamental to developing technologies and products that address these trends. Moreover, as emissions control solutions become more complex and their components function interdependently, expertise in systems integration will become even more essential.
Integrating mechatronics and software into a range of emissions control components and systems is one way Tenneco is working to meet the challenge of delivering innovative, cost-effective and adaptable systems for our customers.
For example, Tenneco’s XNOx SCR technology is a comprehensive and adaptable DEF solution capable of delivering greater than 95% NOx conversion efficiency to ensure our customers are ready to meet the world’s increasingly stringent NOx emissions standards and performance goals. The system is comprised of an adaptable model-based controller; a patented return flow style injector; fluid delivery components including a pump, filter, and pressure sensor; and ancillary parts such as tanks, lines, and sensors.
The electronic controller drives the system, with software that predicts engine out NOx and accounts for ammonia storage and the degradation of the catalyst over time. It dynamically translates engine data to ensure that the fluid delivery system and injector precisely disperse accurate amounts of urea to achieve desired emission levels across operating conditions while minimizing backpressure and costs.
Electrification and selective cylinder deactivation are examples of engine strategies used to improve fuel economy and that can significantly alter the acoustic properties of the vehicle’s engine and exhaust system. Tenneco has several new solutions incorporating mechatronic technology to help deliver an exhaust tone that supports a vehicle’s brand image and meets consumer expectations, while supporting the overall fuel efficiency goals.
Tenneco’s Signature Sound System is an acoustic technology that can produce custom-designed exhaust tones, ranging from sporty to comfort. The system combines an audio controller and amplifier module with an integrated loudspeaker, controlled by a proprietary, programmable electronic signal processing system, to produce the desired signature sound characteristic.
For engines incorporating cylinder deactivation, electronically controlled exhaust valves provide a compact, lightweight, and cost-effective solution for precise sound design and noise control, as well as adaptive exhaust control when operating in fuel-saving mode. Tenneco offers the only electronic acoustic valve in the market with a unique safety feature, where in the event of a power failure, the valve opens automatically via a return spring, preventing any engine damage. The valve is available in an additional configuration, allowing variable backpressure to complement cylinder deactivation systems. Tenneco debuted its electronic valve in the passenger car market on the all-new 2014 Chevrolet Corvette Stingray, and this technology has potential applications in a number of other market segments, including commercial vehicle and off-highway.
Tenneco is also developing other technologies to convert waste exhaust heat to useful energy. In a typical internal combustion engine, only about 30% of the fuel energy is used to propel the vehicle, with a significant portion lost in the form of waste heat in the exhaust system. In the most basic form, wasted heat can be recovered with mechatronic heat exchangers to aid in improving cold start performance of engines and drivetrains. Tenneco’s Thermoelectric Generator (TEG) is designed to convert a portion of that lost energy to electrical power that can be distributed to the vehicle’s electrical systems. The company is currently partnering with a DOE-sponsored industry consortium of suppliers and vehicle manufacturers to optimize the design, validation, and testing of TEGs for light vehicles. Improving the capabilities of the TEG in coming years will further the progress made by OEMs in reducing emissions and improving fuel economy. That progress is vital as engines continue to operate at higher temperatures with greater loads.
Another example currently under development is an exhaust heat recovery system based on the Rankine cycle. This technology has the potential to be an effective method for meeting the requirements of future regulations for carbon dioxide emissions control as well as improved fuel efficiency to help reduce vehicle operating expenses. The Rankine cycle is a well-known principle already used in stationary applications such as power generation.
In mobile applications, especially in the field of light- and heavy-duty vehicles, the same thermodynamic principle applies, with engine exhaust gas serving as the heat source. After passing through the aftertreatment module the exhaust gas is sent to a heat exchanger, evaporating a pressurized working media. Afterwards, this media is expanded (e.g., in a piston- or turbine-type expander) and cooled down to repeat the process. The energy from the expander can be used to provide torque to the vehicle crankshaft, to drive a generator to provide electric power for the vehicle’s accessories, or both, depending on customer needs.
Tenneco expects that vehicles could employ Rankine-based systems by the end of this decade. The company is currently in the process of integrating key components into a complete aftertreatment module, ensuring that the technology works efficiently with the vehicle’s aftertreatment module as well as the entire emissions control system. Tenneco believes this approach will satisfy coming carbon dioxide emission controls as well as improve vehicle efficiency. For example, a Class 8 truck could expect fuel efficiency improvements of up to 5% in typical use.
In the future, regulatory requirements and changing consumer expectations will continue to drive more complex, sophisticated and efficient emissions control products. By combining traditional engineering skills with greater scientific knowledge of the combustion process, and an increasing focus on the integration of mechanical and electronic systems, the industry will be ready to provide products to meet these needs in the decades ahead.
Tim Jackson, Executive Vice President-Technology, Strategy and Business Development, Tenneco, wrote this article for SAE Off-Highway Engineering.