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- Experimental Analysis of the Discharge and Flow Coefficients of a Multivalve Internal Combustion EnginePublication . Henriques, Simão Tiago Livramento; Brojo, Francisco Miguel Ribeiro ProençaThe search for newer ways to reduce emissions and fossil fuel consumption worldwide has be- come more urgent than ever since climate change was identified as the main challenge of the current century. Internal Combustion Engines (ICEs) are responsible for a large portion of emis- sions and, for this reason, a constant search for engine efficiency improvement has been made. The key to achieve an improved engine performance might be lying in the study of the airflow across the intake system since several factors and phenomena which considerably limit engine breathing and efficiency are identified. Being the major inlet flow restriction, the port-valve assembly plays an important role in allowing the airflow to be drawn into the cylinder. In order to measure how efficient the induction process is, discharge and flow coefficients are defined and investigated under different intake conditions. In this sense, an experimental investigation aiming at the study of the fluid dynamic efficiency of a multi-valve Spark-Ignition (SI) engine during the induction stroke was carried out at the Propulsion laboratory of the University of Beira Interior (UBI). To this purpose, the effect of adding a throttle body to the inlet system and de- activating one inlet valve are analysed under static and dynamic conditions. Four throttle plate angles: 30, 50, 70, and 90º were tested along with an inlet configuration without a throttle plate. The experimental tests were conducted at a steady/unsteady flow rig in terms of dimensionless discharge and flow coefficients, in order to understand if the dynamic performance of the port- valve assembly can be predicted through steady discharge and flow coefficients. Throughout the tests, the pressure drop was kept constant at 13 kPa and the valve lift varied from 0.5 mm to 8.4 mm. During each measurement, the air mass flow, inlet temperature, valve upstream pressure and cylinder pressure are registered. The investigation highlights the influence of valve lift on engine breathing. Moreover, it demonstrates that adding a throttle body into the inlet system will result in reduced engine breathability in comparison to a configuration without a throttle plate. This study also indicates that deactivating one inlet valve, in multi-valve engines, leads to higher discharge coefficients, while the conventional configuration results in higher flow co- efficients. The impact of the camshaft velocity on engine breathing is evaluated in terms of mean discharge and flow coefficients. The research shows that the discharge and flow coeffi- cients decrease slightly as the camshaft velocity increases. Overall, a good agreement between static and dynamic results was achieved, proving that steady coefficients can predict with good accuracy the unsteady behaviour of the intake port and valve.