A SIMPLE NOVEL METHOD FOR DIRECT EVALUATION OF THE ACOUSTIC SOURCE IMPEDANCE OF THE EXHAUST SYSTEM OF A SINGLE CYLINDER ENGINE

摘要

In this paper, a novel method is proposed for direct evaluation of the engine source impedance, making use of the values of the in-cylinder pressure and temperature at the time of the exhaust valve/port opening (blow-down condition). The source impedance just downstream of the valve throat is the sum of the cylinder compliance and valve impedance (resistance and inertance). The cylinder compliance and valve impedance both vary with respect to crank angle. Therefore, source impedance is estimated by taking the reciprocal of the crank-angle-area-weighted average of the admittance of the source while exhaust valve is open, where at every crank angle step the instantaneous cylinder volume is taken for estimation of the compliance of cylinder and the instantaneous valve flow area and mass flow rate for the valve impedance. The source impedance of a single cylinder engine is estimated at different engine speeds and it is shown that the little variations in it due to different engine speeds do not matter for the insertion loss estimation. Further a simple, albeit approximate, parametric expression of source impedance is derived in terms of cylinder capacity for ready reference of the muffler designers.