Analysis of Pulsating Phenomena in the Intake Manifold of an Internal Combustion Engine Using the Acoustic Theory

The air flow in intake manifolds is largely influenced by the pulsating phenomena generated by the interaction between the alternative movement of valves and pistons and also by the geometry of its components. It is possible to increase the amount of air entering the internal combustion engine if the frequency of these pressure pulses are tuned to the its intake system’s natural frequency. Elements such as Helmholtz resonators, plenum and runners change the system’s natural frequency and make it possible to increase the volumetric efficiency curve over a wide speed range. In this work, analytical expressions were developed using the Transfer Matrix Method (TMM) and Lumped-parameter Model (LPM) acoustic theories in order to determine the system’s natural frequency. Numerical results were obtained using a one-dimensional computational code based on the Characteristics Method. Experimental tests in non-stationary condition were performed using a flow test bench equipped with a four-cylinder engine, running with only two intake valves from cylinders two and four. The numerical and experimental results were compared and a good agreement between the data were observed, thus confirming the numerical code's capacity to reproduce this type of flow. The results have shown that the natural frequency is important to understand the behavior of the pressure and mass flow rate curves. The insertion of resonators increased the mass flow rate by up to 40.52%. Moreover, they were not limited only to the point of natural frequency, but to a wide frequency range. Quality factor results of up to 26.3% (at 1600 rpm) for the single-chamber resonator and 32.8% (at 2000 rpm) for the double-chamber resonator show that the resonators acted in the intake manifold system in order to diminish the pulsating flow effects and consequently maximizing the mass flow rate curve.