Progetto e verifica prestazionale del cassoncino di aspirazione di un motore da competizione mediante analisi CFD = Design and CFD analysis performance evaluations of an intake manifold for motorsport application

In January 2020 a new project started in Autotecnica Motori: the development of a new V6 turbocharged spark ignition engine for motorsport application. The aim of this thesis project is to understand, by means of computational fluid dynamics simulations, which is the best intake manifold configuration for this engine. Constrained from the engine assembly, only two possible intake manifold configurations are possible: the first one with an air flow that enters in the intake manifold aligned with the axis of the engine bank, and the second one with an air flow that enters in the intake perpendicular to the engine bank. The aim is to evaluate the mass flow rate unbalance between the 3 cylinders of the same engine bank for each one of the two intake manifold geometries, and then to compare the two geometries in order to understand the configuration that, for the same pressure drop, provides the higher mass flow. Two different geometries have been produced and then analyzed by means of the open source CFD code OpenFOAM. At first, the steady-state model has been validated on an already existing intake manifold. By means of experimental test at the flow bench of Autotecnica Motori, it collected the mass flow rates for different pressure drops. Once the model has been validated, it has been transferred to the two produced geometry, that have been analyzed for each runner. For each single runner a characteristic flow rate versus pressure drop has been built: the analysis of the results is performed in terms of comparison of the characteristics of each single runner of the same intake manifold configuration, and then comparing the same runner for the two different configurations. Consequently, a transient CFD model has been produced. The transient model validation is complex: the idea is to make a comparison of the different lambda of each cylinder with the target lambda by endowing an already existing engine with lambda sensors and thermocouples on the exhaust manifold. Then it compares the percentage of variation of mass flow measured at the test bench and the percentage variation of mass flow obtained from the simulation. This procedure, in terms of a transient CFD model validation is of difficult application because the CFD model involves only the intake manifold, and this separation of the intake manifold from the whole engine system neglects causes that strongly affects the engine cylinder filling, like for example the intake ducts, the valve-train distribution system and the in-cylinder turbulence: it would be necessary to simulate the whole engine system in order to be sure to take in account all the possible factors that affects a possible unbalance. Anyway, the transient simulation has been performed on both the configurations for two fixed engine working points: the maximum torque and the maximum power. The steady-state simulation result analysis points out how the configuration with an air flow aligned with the engine bank is the best one: the flow is better aligned towards the runners and the mass flow rate are consistently higher with respect to the second solution. The transient model confirms these considerations: the solution with an air flow aligned with the engine bank axis is the most efficient one, but differently from the steady-state simulations, the transient one can perceive, for each intake manifold geometry, a bigger unbalance in terms of integral average percentage variation of mass flow.