Analytical And Experimental Studies On Effect Of Bends In Engine Manifolds On The Gas Exchange Phenomena

Abstract

Factors which influence the gas?exchange processes are numerous and inter?related in a complex manner. In the analytical formulations proposed by earlier investigators to examine gas?exchange phenomena, the inlet and exhaust manifolds have been considered as straight pipes. However, bends in the intake and exhaust manifolds are a practical necessity, especially in multicylinder engines. The effect of bends in the intake and exhaust manifolds on the gas?exchange phenomena is one factor which has not received much attention. In this thesis, an attempt is made to study the gas?flow behaviour in pipes and engine manifolds with bends. Based on an analysis of the flow through a pipe with a bend, it is shown that the wave phenomena-assuming compressible, one?dimensional, isentropic, unsteady flow-can be analysed provided the dynamic pressure variations through the bend are known. A correlation for the dynamic bend loss factor is proposed, based on experiments conducted on a step pressure?wave generator test apparatus. It is observed from the correlation that the bend factor K=?P/(12?V2)K = \Delta P / \left(\frac{1}{2} \rho V^2\right)K=?P/(21??V2) is a function of pressure ratio up to a value of around 2.0 and remains constant thereafter. With sharp bends (i.e., bends with radius?of?bend to pipe?diameter ratio R/D<2.5R/D < 2.5R/D<2.5), the bend?loss factor increases as the R/DR/DR/D ratio decreases. Pipes with an R/DR/DR/D ratio greater than 2.5 behave almost like a straight pipe. The bend?loss correlation proposed in this study has been used along with a computer code developed by Benson to examine the gas?exchange processes in a compression?ignition engine. Based on a comparison of the experimental and predicted results, it is concluded that the proposed bend?loss correlation, along with Benson抯 code, provides a satisfactory analytical tool in the design optimisation of gas?exchange phenomena in compression?ignition engines.