Physics Based On-Board Exhaust-Temperature Prediction Model for Highly Efficient and Low-Emission Powertrain

Modern automotive powertrains are operated using many control devices under a wide range of environmental conditions. The exhaust temperature must be controlled within a specific range to ensure low exhaust-gas emissions and engine-component protection. In this regard, physics-based exhaust-temperature prediction models are advantageous compared with the conventional exhaust-temperature map-based model developed using engine dyno testing results. This is because physics-based models can predict exhaust-temperature behavior in conditions not measured for calibration. However, increasing the computational load to illustrate all physical phenomena in the engine air path, including combustion in the cylinder, may not fully leverage the advantages of physical models for the performance of electric control units (ECUs). This study proposes an onboard physics-based exhaust-temperature prediction model for a mass-produced engine to protect the engine exhaust system and reduce exhaust emissions. The combination of simplified combustion in the cylinder and heat transfer in the engine airpath model enables us to minimize the calculation load in the ECU and simultaneously predict the exhaust temperature. In-cylinder combustion is estimated accurately using the basic engine operation parameters, volumetric efficiency, and ignition timing. Convection heat transfer, thermal conduction, and radiation are considered in this model in a simple one-dimensional form. Results show that the predicted exhaust temperature is consistent with the measured temperature during engine dyno and vehicle testing. Even under the EV operation mode in a series hybrid system, low heat loss from the exhaust gas to the pipe wall owing to the heat transfer of natural convection is predicted accurately. Additionally, the detailed heat-transfer model accurately predicts the exhaust temperature after the engine is started in the series hybrid mode. Thus, this newly developed physical exhaust-temperature model is suitable for the engine exhaust-system protection and catalyst-activation management of our mass-produced vehicle.