Relation between Inlet Valve Closing Angle and Volumetric Efficiency of a Four-Stroke Engine

Abstract

A study was made to find an indicative factor of the optimum closing angle of an inlet valve for an engine system without intake and exhaust pipe effects. From analytical discussion, the authors derived as this factor the nominal Mach number of incompressible fluid flow through a mean effective valve area into a cylinder due to piston motion at its mean speed. This factor coincides with"Inlet-Valve Mach Index"adopted by C.F.Taylor for estimation of volumetric efficiency. Examination of the computed result of the weight of charge air for a variety of valve lifts and closing angles at motoring has shown that this nominal Mach number defines the relation between volumetric efficiency and valve closing angle. A series of experiments were then made to measure volumetric efficiency under various valve lifts and closing angles at motoring by means of the hydraulic tappet with a leak hole as presented in the previous paper. The results verified the theoretical prediction with rather small errors.