Muffler

A muffler is noise-cancellation equipment used with an automobile's exhaust system. The internal combustion engines that power automobiles generate high noise levels. Most of this noise is caused by the alternating waves of high and low air pressure that enter the exhaust system in bursts when the vehicle's engine is running. To reduce this noise to acceptable levels, automotive engineers developed mufflers.

Mufflers work by reflecting the sound waves introduced to the exhaust system by pressurized air bursts in such a way that they partially cancel themselves out. Two main muffler subtypes are used in modern vehicles: vector mufflers, which are usually found in large diesel-powered freight trucks, and spiral baffler mufflers, which are used in regular passenger vehicles. While original equipment manufacturer (OEM) mufflers are standard components of commercially produced automobiles, some consumers prefer to install aftermarket mufflers for performance reasons.

Brief History

The early development of automobile noise-cancellation technologies is usually credited to the American inventors Milton O. Reeves and Hiram Percy Maxim. Reeves and Maxim developed rudimentary mufflers independently of one another during the late nineteenth and early twentieth centuries.

Reeves worked through his family business, the Columbus, Indiana-based Reeves Pulley Company, where he built what is thought to be the automotive industry's first double muffler system in 1896. Reeves patented his invention the following year, and although it was designed specifically for two-wheeled motorcycles, the Reeves muffler system was soon adapted for four-wheel automobiles.

Maxim was a well-known scientist and inventor during his lifetime, and he became one of the most prominent acoustic technology specialists of his era. In addition to building mufflers for gasoline and diesel engines during the first decade of the twentieth century, Maxim also developed silencers and noise abatement devices for air compressors, air conditioners, and firearms.

Modern automobile mufflers are largely based on the work of the French-born mechanical engineer Eugene Houdry. Houdry is credited with pioneering the technology used in automotive catalytic converters, which help reduce the toxic elements of automobile exhaust by using catalysis to trigger oxidation-reduction redox reactions. Redox reactions turn toxic vehicle exhaust vapors into less harmful substances, thus helping control the pollutant levels released by automobiles. Catalytic mufflers based on technologies created by Houdry were first patented in 1962. These designs incorporated mufflers into vehicle exhaust systems alongside catalytic converters, and they continue to form the basis of the muffler technologies used today.

One noteworthy recent development is the increased use of variable flow muffler technologies. Variable flow mufflers use a system of valves that automatically adjust as engine speed, measured in revolutions per minute (RPM), goes up or down. This solves a long-standing engineering challenge, as mufflers were previously unable to cancel noise equally at all engine speeds. High-tech electronic mufflers that use a combination of microphones and audio transducers to detect and cancel out unwanted engine noise are another relative newcomer.

Topic Today

Modern mufflers are positioned so they line up with a vehicle's exhaust pipes, and are usually placed at or near the end of the exhaust pipes, where emissions are released. This positioning allows the muffler to capture and cancel out the greatest possible percentage of the noisy pressurized air bursts forced into the exhaust system by engine operation. Most mufflers use contoured noise mitigation structures known as baffles to bounce these incoming sound waves around the interior of the muffler. This bouncing action creates opposing waves of sound that partially cancel out the original sound waves and thus greatly reduce the amount of noise released by engine operation.

While the theory behind this technology is relatively straightforward, muffler baffles must be intricately designed and strategically placed to achieve their intended effect. The work done by muffler engineers is often likened to the tuning of a musical instrument or the carefully designed acoustic properties of a concert amphitheater.

In general, the more power an engine has, the more noise it will create. Thus, various specific muffler subtypes have been developed for use in specific vehicles. Large diesel freight trucks and high-performance automobiles with very powerful engines usually have vector mufflers, which contain an intricate and extensive collection of concentric cones and angled baffles. Regular passenger vehicles are typically equipped with spiral baffle mufflers, which have a comparatively less complex system of conical baffles that achieve levels of noise mitigation appropriate for smaller and less powerful engines. A third type of muffler known as the aero turbine muffler is less common. Aero turbine mufflers use vacuum-powered negative back pressure to draw exhaust out from the chamber of the combustion cylinder, thus reducing the noisy effects of engine-generated pressurized air bursts.

Newer muffler types, including variable flow mufflers and electronic mufflers, expand on these foundational design principles in innovative ways. Variable flow mufflers excel at canceling out noise at all engine speeds, using a network of automatically controlled valves that open and close depending on how quickly the engine is revolving. Their development marked an effective solution to one of the most enduring challenges of muffler design, which stems from the fact that engines generate more noise when they run more quickly. Previous muffler designs were only able to cancel out engine noise at a single, inflexible level, and were not able to mitigate the noise generated by a fast-running engine as well as they could quiet a slower-running engine.

Rather than the traditional baffles, electronic mufflers use an interconnected system of microphones and audio transducers to cancel out engine noise with a high degree of precision. The microphones are connected to signal generators and are positioned to detect incoming engine noise. When noise is detected, the signal generator is triggered and the audio transducers create acoustic signals that neutralize engine noise.

Bibliography

"Catalytic Muffler." Google Patents, www.google.com.gt/patents/US3061416. Accessed 5 June 2017.

"Electronic Muffler." Google Patents, www.google.com/patents/US5457749. Accessed 5 June 2017.

Ermann, Michael. Architectural Acoustics Illustrated. John Wiley & Sons, 2015, p. 221.

"Eugene Houdry." Chemical Heritage Foundation, 11 Sept. 2015, www.chemheritage.org/historical-profile/eugene-houdry. Accessed 5 June 2017.

Mamilla, Venkata Ramesh, et al. "Design and Analysis of an Automobile Exhaust Muffler." Industrial and Systems Engineering, vol. 1, no. 1, 2016, pp. 10–15.

Marinaro, Michael. "A Diversified Mind: Hiram Percy Maxim." Connecticut History, connecticuthistory.org/hiram-percy-maxim/. Accessed 5 June 2017.

Nice, Karim. "How Mufflers Work." HowStuffWorks.com, 19 Feb. 2001, auto.howstuffworks.com/muffler.htm. Accessed 5 June 2017.

"Reeves Pulley Company Collection, 1896–1969." Indiana History, www.indianahistory.org/our-collections/collection-guides/reeves-pulley-company-collection-1896-1969.pdf. Accessed 5 June 2017.

"Understanding Muffler Design and Sound Absorption Strategies." Street Muscle Magazine, 11 Mar. 2014, www.streetmusclemag.com/tech-stories/exhaust/understanding-muffler-design-and-sound-absorption-strategies/. Accessed 5 June 2017.