Effects of Engine Speed on the Performance at Extreme Vehicle Driving Conditions 2019-36-0297

Nowadays, improvements in engine fuel economy and reduction in pollutant emissions have been much discussed. Downsizing and downspeeding are methods widely used in the automotive market, used to increase internal combustion engine efficiency. Fuel consumption is commonly measured through a specific cycle that could differ between countries. Federal Test Procedure (FTP-75) for Latin America and New European Driving Cycle (NEDC) for Europe are some examples. These cycles include normal driving conditions, low vehicle load and mild environmental conditions. The style of gear shifting is one of the main factors affecting fuel efficiency and performance of motor vehicles. At extreme diving conditions, parameters like coolant and air charge temperature could reach limit durability values of the system. In order to avoid knocking and maintain structural reliability, it becomes mandatory to control the engine speed. An increase in engine speed reduces engine load requirements and thus, turbocharger loads. Lower turbocharger requirements reduce ACT and, consequently, reduce knocking. This process allows an advanced ignition timing, enabling more chamber pressure and improving fuel conversion efficiency. However, a higher engine speed also increases friction losses and combustion frequency, lowering the generated torque and tending to decrease engine efficiency. It is interesting to note parameters that affect positively and negatively at the same time, depending on the point of view. The present paper aims to analyze the performance and fuel consumption of a turbocharged engine working under extreme driving conditions, simulating a CVT transmission behavior at various speeds. The evaluated vehicle parameters are: power, coolant temperature, ACT and brake specific fuel consumption (BSFC).