Design of Expansion Chamber Mufflers Incorporating 3-D Effects* A.D. Sahasrabudhe Department of Mechanical Engineering; North Eastern Regional Institute of Science and Technology; Itanagar- 791 100; India M.L. Munjal Department of Mechanical Engineerinff Indian Institute of Science; Bangalore-560 012; India S. Anantha Ramu Department of Civil Engineering; Indian Institute of Science; India *Received: 21 November 1989; revised: 4 November 1991 Advancements in the analysis and design of complex mufflers for the commercial automotive exhaust systems incorporating three-dimensional (3-D) or higher order mode effects have long been anticipated. In this paper, design curves obtained by making use of 3-D finite element analysis are presented for the reactive expansion chamber mufflers of the simple and extended-tube type with stationary medium. Some useful design guidelines are also provided for achieving optimal performance. Nomenda~re b width of a reetmNnlar duet co local sound speed d diameter of the tube f frequency, Hz H semi-major axis of an ellipse h height of a rectangular duct k wavenumber, 2nf/e o 1 length of the tube m area expansion ratio r radius of the tube TL transmission loss ~x diameter expansion ratio [3 length to diameter ratio o offset radial distance wavelength, e,/f 0 relative angle between inlet/outlet tubes Introduction The expansion chamber is one of the most basic types of si- lencing elements used in intake and exhaust systems. A simple expansion chamber muffler consists of an inlet tube, an expan- sion chamber and an outlet tube (see Fig. I). An extended-tube expansion chamber muffler differs from tile simple expansion chamber muffler in that tile inlet and outlet tubes are extended into the chamber, as shown in Fig. 2. The location of the inlet and outlet tubes can be either coaxial with the expansion cham- ber (called a concentric expansion chamber), or offset from the center of the chamber (known as an offset expansion chamber). The cross-section of the chamber can be either rectangular, cir- cular or elliptical in shape. Rectangular expansion chambers are generally used in air-conditioning duct networks, while cir- cular or elliptical expansion chambers are found mostly in en- gine exhaust mufflers. The expansion chamber was analytically modelled by Davis, et el., in the early 1950~ for plane wave propagation assuming linear waves in a stationary medium. 1 Their analysis revealed Volume 38/Numberi 27