Modeling Approach to Estimate EGR Cooler Thermal Fatigue Life

Cooled EGR continues to be a key technology to meet emission regulations, with EGR coolers performing a critical role in the EGR system. Designing EGR coolers that reliably manage thermal loads is a challenge with thermal fatigue being a top concern. The ability to estimate EGR cooler thermal fatigue life early in the product design and validation cycle allows for robust designs that meet engine component reliability requirements and customer expectations. This paper describes a process to create an EGR cooler thermal fatigue life model. Components which make up the EGR cooler have differing thermal responses, consequently conjugate transient CFD must be used to accurately model metal temperatures during heating and cooling cycles. Those metal temperatures are then imported into FEA software for structural analysis. Results from both the CFD and FEA are then used in a simplified numerical model to estimate the virtual strain of the EGR cooler. Using the virtual strain output, Rainflow cycle counting, Palmgren-Miner linear damage accumulation, along with a detailed understanding of customer duty cycles the EGR cooler thermal fatigue life is estimated. Model validation was completed by accurately estimating the number of thermal cycles to failure during component rig bench tests and on multiple customer field units.