Ottimizzazione delle prestazioni di un motore motociclistico tramite valvola parzializzatrice allo scarico

The study finds out aspects of unsteady fluid dynamics in internal combustion engine motorcycle. The pressure waves that arise from intake and exhaust manifolds of an engine have been investigated. In order to improve the performance of the engine, its volumetric efficiency has been increased, using a device able to maintain the same geometry of exhaust manifolds but also to change the configuration in function of the revolution number and the power of the engine. Using a simulation of the CFD Fluent code, it is possible to display at wich speed intake valves open and exhaust valves close simultaneously with the incoming depressure wave. The reaction of the exhaust manifolds at pressure impulse, the natural frequency and vibration modes have been investigated. In this way it is possible to determine at wich speed the exhaust manifolds improve the volumetric efficiency. In order to obtain truthful results of the funcioning of the exhaust manifold engine with a throttle valve, I use the monodimensional Lotus Engine code. The succes of the 1D simulatiuon tests encuraged to execute an exhaust manifold with a trottle valve included. The sperimental studies confirmed the results of the 1D simulation, so the engine torque and power had been improved at low-medium number of revolution.