A Comprehensive Method for the Characterization of Engine Heat Rejection

New SI engine generations are characterized by a simultaneous reduction of engine displacement and an increase of brake power. Such conflicting targets are achieved through the adoption of several techniques such as turbocharging, direct fuel injection, variable valve timing and variable port lengths. This design approach, called “down-sizing”, leads to a marked increase in the thermal loads acting on the engine components, in particular on those facing the combustion chamber. Hence, an accurate evaluation of the thermal field is of primary importance in order to avoid mechanical failures. Moreover, the correct evaluation of the temperature distribution improves the prediction of pointwise abnormal combustion onset.

The presentation proposes a fully integrated STAR-CCM+®/STAR-CD® methodology developed by the authors for the prediction of the engine thermal field, which is applied to different high performance turbo-charged DISI engines: the methodology employs STAR-CD in-cylinder 3D-CFD combustion simulations and STAR-CCM+ CHT (Conjugate Heat Transfer)  simulations of the whole engine, inclusive of both the solid components and the coolant circuit.

In-cylinder analyses are used as thermal boundary conditions for the CHT simulations, which are in turn a fundamental benchmark to evaluate the accuracy of the combustion heat flux estimation by means of a combination of global engine thermal survey and local temperature measurements.

This integrated approach allows a preliminary evaluation of some consolidated heat transfer models in order to evaluate the accuracy of the predicted gas-to-wall heat fluxes. A modified heat transfer model is then proposed, critically motivated and applied to the specific engine conditions under investigations in order to match both the target thermal balance and the point-wise temperature distribution. The proposed model strongly improves the predictive capability of the combined in-cylinder/CHT methodology in terms of both global thermal balance and pointwise temperature distribution for both the investigated engines.

Session Time Slot(s): 
03/07/2016 - 17:05-03/07/2016 - 17:30
Hilton Grand Ballroom
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