Computer tools are providing engineers at Eberspaecher with meticulous methods for developing new exhaust system technology that will meet upcoming heavy truck diesel emissions law.
Eberspaecher's approach entails combining current technologies—diesel oxidation catalyst and diesel particulate filter—with new selective catalytic reduction (SCR) technology in the same system. The combined diesel aftertreatment system, which can reduce nitrogen-oxides and particulate matter emissions by about 90%, would meet U.S. EPA 2010 regulations for commercial on-highway vehicles.
In developing the combined diesel aftertreatment emissions system for heavy trucks, Eberspaecher engineers relied on FEA and CFD tools to validate system design and functional performance. "No new tools were necessarily developed, but some new methods were," explained Martin Romzek, Vice President of Development for Eberspaecher North America.
As an example, generating conjugate heat transfer calculations in CFD was done for the purpose of predicting the temperature environment for various components during high-temperature regeneration cycles. "This calculation method was used to make fundamental decisions on various materials before parts were ever built. Some testing has been conducted to verify the results, but all design decisions were made with the guidance of this analysis," explained Romzek, responsible for the company's Advanced Engineering (Acoustic, Durability, and Thermodynamics–Simulation and Test) and Prototyping departments.
CFD also played a vital role in creating the basic system concept. "CFD was used extensively to tune the systems for proper flow path geometry, mass flow distribution, and system backpressure. These are standard calculations, but due to the size and complexity of these systems, it is literally impossible to study individual component functions separately," noted Romzek. Using CFD for urea flow distribution and conjugate heat transfer calculations is a bit unusual. "Each of these calculations are fairly new methods and both have very complex inputs, but in our programs both tools were essential in laying out the foundation of the design prior to building any parts," Romzek noted.
FEA helped engineers determine the system layout, architecture, and materials designations. "The trick was to develop large, integrated systems that not only demonstrated acceptable mechanical durability behavior but also would ensure thermal stress capability over the life of the thermal cycling to regeneration temperatures. At times these two challenges were opposed, but by reciprocating the two FEA calculations of mechanical stress and thermal stress and by working closely with the CAD team, creative design solutions were realized with literally no testing involved. Testing was conducted simply as a final validation check mark," Romzek explained.
Testing did not follow a conventional path. "In a typical automotive system, we perform mechanical durability design validation testing on literally each and every component—i.e. each converter and each muffler, even the pipe/flange/hanger joints—within the system. Since these very complex commercial vehicle systems are fully integrated, there are no isolated/standalone components like a muffler or a converter to validate individually," noted Romzek. Simply put: the scale and pace of this commercial vehicle development program rendered "trial and error" testing unfeasible. "The only solution to test mechanical durability of the system is to (test) entire systems on a key-life/full system rig test. Also, these systems must be validated to 500,000 mi, not 100,000 mi like automotive," noted Romzek.
Many of the tools and methods being used to develop the combined diesel aftertreatment system for heavy trucks are a carryover from the company's automotive business. "These tools are used in automotive, but there are also extensive component tests run to compare and contrast results and, ultimately, help refine the tools. The big difference in this commercial vehicle development process is that due to the complexity, size, and integrated construction, these tools had to be in some cases 100% relied upon to make design decisions. Testing of these components is only possible as a final validation, not for 'trial and error' verification testing," Romzek noted.