GT-Suite Modeling of Thermal Barrier Coatings in a Multi-Cylinder Turbocharged DISI Engine for Catalyst Light-Off Delay Improvement

Catalytic converters, which are commonly used for after-treatment in SI engines, exhibit poor performance at lower temperatures. This is one of the main reasons that tailpipe emissions drastically increase during cold-start periods. Thermal inertia of turbocharger casing prolongs the catalyst warm-up time. Exhaust enthalpy management becomes crucial for a turbocharged direct injection spark ignition (DISI) engine during cold-start periods to quickly heat the catalyst and minimize cold-start emissions. Thermal barrier coatings (TBCs), because of their low thermal inertia, reach higher surface temperatures faster than metal walls, thereby blocking heat transfer and saving enthalpy for the catalyst. The TBCs applied on surfaces that exchange heat with exhaust gases can increase the enthalpy available for the catalyst warm-up. A system-level transient heat transfer study using experimental or high-fidelity simulation techniques to evaluate the TBC application on various surfaces would be expensive. In this work, a reduced-order system-level modeling methodology in GT-Suite was leveraged to evaluate TBCs on exhaust ports, manifold, and runners. A multi-cylinder turbocharged DISI engine was modeled in GT-Suite, with capability to model a layer of TBC on internal surfaces. The model was calibrated using measured data from steady state operating conditions due to lack of transient cold start data. Following the TBC analysis, a theoretical study to infer the effects of turbocharger casing heat loss on the catalyst warm-up was performed. The TBCs showed no tangible benefit in the catalyst light-off delay when applied on the combustion chamber walls but showed a 20-second faster catalyst light-off when an 800-micron thick TBC was applied on the exhaust flow path walls (exhaust ports, manifold and runners). The turbocharger casing/housing heat transfer was shown to have a considerable effect on the catalyst light-off delay. An additive benefit to the catalyst light-off delay was achieved by insulating the combustion chamber walls, the exhaust flow path walls, and the turbocharger casing together which was predicted to be 25 seconds faster than the baseline.