A Methodology for Modeling the Cat-Heating Transient Phase in a Turbocharged Direct Injection Spark Ignition Engine

This paper presents the modeling of the transient phase of catalyst heating on a high-performance turbocharged spark ignition engine with the aim to accurately predict the exhaust thermal energy available at the catalyst inlet and to provide a “virtual test rig” to assess different design and calibration options.The entire transient phase, starting from the engine cranking until the catalyst warm-up is completed, was taken into account in the simulation, and the model was validated using a wide data-set of experimental tests.The first step of the modeling activity was the combustion analysis during the transient phase: the burn rate was evaluated on the basis of experimental in-cylinder pressure data, considering both cycle-to-cycle and cylinder-to-cylinder variations.Then, as far as the exhaust temperatures are concerned, a detailed model of the thermocouples was implemented to replicate the physical behavior of the sensors during the warm-up and to compare the simulated temperatures with the measured ones.Finally, a complete analysis of the energy balance during the transient was carried out: the thermal power available to the catalyst inlet was obtained from a complete analysis of power losses (i.e. friction and pumping losses, in-cylinder heat transfer, engine block and engine coolant heating, exhaust manifold heat transfer, etc.).In conclusion, the proposed methodology allows to reliably simulate in details the Cat-Heating transient, showing a valuable potential in driving the main design and calibration choices during the engine development process.