A Simulation Method for the Calculation of Water Condensation inside Charge Air Coolers

The automotive industry uses supercharging in combination with various EGR strategies to meet the increasing demand for Diesel engines with high efficiency and low engine emissions. The charge air is heated by the EGR and the compression in the turbocharger to such an extent that high NOx emissions and a reduction in engine performance occurs. For this reason, the charge air cooler cools down the charge air before it enters the air intake manifold. In case of low pressure EGR, the charge air possesses a high moisture content and under certain operating conditions an accumulation of condensate takes place within the charge air cooler. During demanding engine loads, the condensate is entrained from the charge air cooler into the combustion chamber, resulting in misfiring or severe engine damage. In order to be able to take appropriate countermeasures, it is necessary to investigate the basic physical mechanisms under which condensation occurs and to simulate them using an appropriate condensation model. This paper presents a simulation method for calculating the accumulated condensate and the condensate mass flow inside charge air coolers using a numerical approach based on the boundary layer theory for the case of heat and mass transfer analogy over a flat plate with surface suction. The solution routine is embedded as a user code in the simulation software Star-CCM+ and one single duct of the charge air cooler is modeled applying the porous media model. Different operating states are simulated, and the numerical results are compared to own experimental results. The results show good agreement between experiments and simulations and the relevant quantities such as accumulated condensate and condensate mass flow are matching well.