Abstract

Abstract The application of turbocharging is still a crucial aspect, especially in hydrogen engines where ultra-lean combustion is required, to mitigate abnormal combustion and NOx formation. The adoption of advanced turbocharging systems results in an increased complexity of the engine intake and exhaust circuits and requires a proper design to optimize unsteady flow phenomena. Therefore, it is essential to understand the performance of the single elements of the turbocharging circuit and their interactions when coupled. A specific test rig for components of propulsion system is operating at the University of Genoa, where investigations under steady, transient and pulsating flow conditions can be performed. This study presents the results of experimental investigations conducted under unsteady flow conditions on the exhaust manifold of an internal combustion engine, specifically examining unsteady phenomena in the turbine inlet circuit. The pulsating flow is generated by a motor-driven cylinder head. Pressure signals recorded in different sections of the exhaust circuit located in the inlet and outlet turbine circuit are analysed in detail, quantifying also the effects of flow unsteadiness using parameters proposed in the open literature. In particular in the following article, the degree of instability, the Strouhal number and the reduced frequency are considered to quantify the impact of unsteady phenomena within the system for the considered lengths. Understanding the unsteadiness within engine circuits is crucial for determining the appropriate modeling approach for system simulation. This work highlights that a quasi-steady flow model is appropriate for modeling individual branches for the exhaust manifold, while a wave action model is necessary for the entire exhaust circuit.

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