Methodology Development for Coolant Boiling Prediction in EGR Coolers 2019-01-1197

Coolant boiling detection is a key issue to ensure Exhaust Gas Recirculation (EGR) coolers performance and durability. Accurate boiling detection and prediction tools are thus increasingly demanded to support EGR coolers design in a context of raising requirements, mainly driven by the stringent regulations and the recent application of this technology to gasoline engines. In this scenario, a numerical tool for the detection and quantification of coolant boiling in EGR coolers has been developed. It is based on Computational Fluid Dynamic (CFD) simulations and its results have been successfully validated against experimental data obtained on a test bench fully instrumented for boiling analysis. As for the predictive tool, a mathematical model describing the EGR cooler performance, including conjugate heat transfer and sub-cooled boiling, has been developed. Then a numerical methodology to solve this model has been implemented using OpenFOAM® (open source CFD toolbox). To validate the results of such a numerical tool, experimental quantification of the coolant boiling degree was required. To this end, a boiling test bench has been fully equipped with different sensors (pressure, acoustic emission, acceleration, vision) and signal-processing procedures have been implemented. Thus, coolant boiling detection and quantification for a wide range of operating conditions (temperature, pressure and flow rate levels) covering all the range required by both gasoline and diesel engines has been collected. Accuracy and robustness of the methodology has been eventually checked for different EGR coolers operating under several operating conditions, even reaching severe boiling levels. Numerical results have been compared with experimental data gathered at the boiling test bench for the corresponding cooler and operating conditions. The results of the predictive tool are in good agreement with experimental data, proving the suitability of the numerical tool as a support tool of the design process for the next generation of heat exchangers.