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One-dimensional (1-D) unsteady gas dynamic models of a number of common muffler (or silencer) elements have been incorporated into a1-D simulation code to predict the impact of the muffler on the gas dynamics within the overall system and the radiated Sound Pressure Level (SPL) noise spectrum in free-space. Correlation with measured data has been achieved using a Single-Pulse rig for detailed unsteady gas dynamic analysis and a Rotary-Valve rig in conjunction with an anechoic chamber for noise spectra analysis. The results obtained show good agreement both gas dynamically and acoustically. The incorporation of these models into a full 1-D engine simulation code should facilitate the rapid assessment of various muffler designs prior to prototype manufacture and testing.

This paper reports on the experimental evaluation of certain aspects concerning the mathematical modelling of pressure wave propagation in engine ducting. A particular aspect is the coefficient of discharge of the various ports, valves or apertures of the ducting connected to the cylinder of an engine or to the atmosphere. The traditional method for the deduction of the coefficients of discharge employs steady flow experimentation. While the traditional experimental method may well be totally adequate, it is postulated in this paper that the traditional theoretical approach to the deduction of the discharge coefficient from the measured data leads to serious inaccuracies if incorporated within an engine simulation by computer. An accurate theoretical method for the calculation of the discharge coefficient from measured data is proposed.

A three dimensional computational fluid dynamics program is used to simulate theoretically the scavenging process in the loop-scavenged two-stroke cycle engine. The theoretical calculation uses the k - ε turbulence model and all calculations are confined to the in-cylinder region. The calculation geometry is oriented towards five actual engine cylinders which have been tested under firing conditions for the normal performance characteristics of power, torque, and specific fuel consumption. The same five engine cylinders have also been experimentally tested on a single-cycle gas testing rig for their scavenging efficiency - scavenge ratio characteristics. The ranking of the cylinders in order of merit in terms of scavenging efficiency by both the rig and the theoretical calculations is shown to be in good agreement with the evidence provided by the actual firing engine test results.