MME419 EXECUTIVE SUMMARY APRIL 9, 2007 FACULTY ADVISOR: DR. ROI GURKA

Noise Reduction and Automotive Muffler Design

By Benjamin Higgs, Ryan Rupke

The primary goal of this project is to develop a muffler system to meet the demanding needs of a Formula SAE prototype race car. This development must adhere to the FSAE standards as they relate to noise control. In order to fully understand the problem definition, a comprehensive study of sound properties is completed. This research elaborates on sound waves and how they may be reflected, diffracted or absorbed or actively cancelled using constructive interference. Reflection and diffraction properties represent destructive interference and depend on the angles at which they hit an object. Absorption, also a form of destructive interference, relates to the material that the sound wave comes in contact with. Constructive interference occurs when a second sound source is placed 180° out of phase from the first source. The source of noise that a muffler must attenuate is the result of combustion from the engine. Several of the more common mufflers are described in detail. These mufflers include reflective, glass pack, Hedman Hedder, and Aero Turbine mufflers. A reflective muffler is excellent at attenuating sound, but is very restrictive in nature. On the other hand a glass pack muffler is sufficient at attenuating sound at higher engine speeds, but allows for much more air flow through the system. This relieves the engine of any undue pressure, allowing it to perform to its potential. A set of muffler concepts are devised and then eliminated through a series of evaluations based on the needs and wants of the FSAE team. The resulting choice of muffler is a glass pack design due to its simple yet effective nature. Baseline tests in sound attenuation, frequency, and flow rate are completed on the 2006 muffler and a straight pipe for comparison purposes. Muffler models are constructed in a computer program. Simulations are then executed to distinguish which model most effective at attenuating sound at the specified frequency of 5000Hz. As a result, a more accurate prototype is constructed. A final prototype is constructed with the aid of CAD software. Final materials include a carbon fibre outer shell, aluminum end caps and a stainless steel inner core with fibreglass insulation. The aluminum end caps allow for resistivity to exhaust gas heat. Stainless steel is strong and also resistive to heat. Titanium is preferred, but it is too expensive for the purposes of this project. All components add to the weight reduction in the 2007 muffler. The final weight of the muffler is 1899g, a 1535g (45%) savings from the 2006 model. An expected increase in flow rate and sound attenuation allows for some freedom to work with when fabricating the 2008 muffler.