Pressure waves in the inlet and exhaust manifolds: the effects on engine performance

Carmine Maria de Sanctis¹; Waldyr Luiz Ribeiro Gallo²

¹ Istituto Politecnico di Torino (Italy); ² Departamento de Energia - FEM - UNICAMP

doi:10.20906/CPS/COB-2015-0795

Resumo

The wave phenomena in the intake and exhaust manifolds affect the residual gas fraction inside the cylinder, the volumetric efficiency and the indicated performance of an internal combustion engine. These pressure waves, which can be described as changes in the pressure propagating in space and time, are created in the inlet and exhaust manifolds in response to sudden changes of speed of the gaseous mass in motion due to the pulsed operation of the engine valves. When the pressure waves formed in the inlet manifold have a frequency such that a maximum or a minimum are reached at the entrance of the cylinder shortly before the closing of the valve, it occurs, respectively, an increase or a decrease in the volumetric efficiency. At the exhaust manifold, the influence of the pressure waves is expressed in an opposite way. Extensive experimental research has been done to achieve a "tuning" of these pressure waves to increase the engine performance, always taking into account the real geometry of the intake and exhaust manifolds. The objective of this work is to present an analysis of the effect of the pressure waves on the indicated performance of a spark-ignited engine and how a variable valve system can be useful to take advantage of these waves, both for intake and exhaust systems. A thermodynamic simulation model was employed, together with a camless variable valve system, to explore the effects of the wave phenomena on the indicated performance of the engine. Since real wave data was not available, a typical wave pattern was used. Three engine speeds were analyzed, and the effect of engine speed on the wave amplitudes was taken into account. The algorithm successfully showed the changes on the engine's performance related to the variation of several parameters: the valve timing, the valve lift model and the profile of the wave pressure applied to the manifolds. Aided by the algorithm, an optimal condition of volumetric efficiency was obtained choosing the best valve lift model and adjusting the valve timi

Palavras-chave: Spark-ignition engines; Pressure waves in manifolds; Variable valve timing; Camless valve actuation; Volumetric efficiency