The emissions limits of CO2 for vehicles are becoming more stringent with the aim of reducing greenhouse gas emissions and improve fuel economy. The New European Driving Cycle (NEDC) is adopted to measure emissions for all new internal combustion engines in the European Union, and it is performed on cold vehicle, starting at a temperature of 22°C ± 2°C. Consequently, the cold-start efficiency of internal combustion engine is becoming of predominant interest.
Since at cold start the lubricant oil viscosity is higher than at the target operating temperature, the consequently higher energy losses due to increased frictions can substantially affect the emission cycle results in terms of fuel consumption and CO2 emissions.
A suitable thermal management system, such as an exhaust-to-oil heat exchanger, could help to raise the oil temperature more quickly. To evaluate CO2 emissions and the benefits deriving from thermal management devices, an integrated model of the engine under consideration has been developed in GT-SUITE. The model is characterized by the integration of engine performance, vehicle, cooling system, lubricant system and friction sub-models.
In particular, a friction sub-model has been developed in this work, by extending the Chen-Flynn engine friction model to take into account the actual oil temperature. The calibration of the thermal and friction sub-models has been done by defining a methodology based on few simple engine tests on a dynamometric bench. The tool, once calibrated and verified, can be used to predict the efficiency of different thermal management devices and strategies during engine warm-up and in different driving cycles.