Study tests new muffler technology for American auto industry

November 19, 2003

COLUMBUS, Ohio - A study of muffler technology at Ohio State University is giving American automakers new options for designing quieter cars.

Engineers here have tested a promising new muffler design that utilizes glass fiber, and are developing the computational tools manufacturers will need to optimize the design.

The new design can often silence auto noise just as well as a typical muffler, but it can be lighter, less prone to corrosion, and help engines work more efficiently.

Ahmet Selamet, professor of mechanical engineering and head of the Flow, Engine, and Acoustics Research Laboratories at Ohio State's Center for Automotive Research and Intelligent Transportation, gave an overview of his recent work November 19 at the American Society of Mechanical Engineers meeting in Washington, DC.

For more than a decade, Selamet and his colleagues have developed computer-based tools and specialized equipment for improving auto exhaust systems. The challenge, he said, is to control noise and exhaust emissions without blocking the flow of exhaust gases from the engine.

Selamet also said that glass fiber can better withstand the high temperatures produced in modern exhaust systems, and potentially even insulate the car from that heat.

"The ultimate silencing device is a potato in the tailpipe," Selamet said with a laugh. "But of course engines need to breathe to work properly, so we have to be more creative."

Owens Corning recently asked Selamet to test and redesign a European muffler system that contained glass fiber stuffing. His task was to reduce the design complexity, reduce the weight of the system, and improve engine performance -- while at the same time maintaining or even improving overall exhaust noise levels.

Fiber-filled mufflers have been used in European and Japanese cars for years, Selamet explained, but not much elsewhere. In North America, most mufflers work by using metal chambers and baffles to slow the flow of air or redirect it.

But chambers and baffles can restrict the flow of the exhaust gases, increasing what is known as back pressure. When that happens, some of an engine's work is wasted pushing the burned gases through the exhaust system, instead of pushing the car forward. With a simpler interior design, a fiber-filled muffler could cause less back pressure and make engines more efficient.

Historically, though, the North American auto industry has been skeptical about using filling in mufflers, and rightly so, Selamet said. Early European designs used basalt wool, which is packed in short fibers. Studies have shown that over time, these short fibers break up and blow out in the exhaust stream.

"Then the car gets louder," Selamet said.

Continuous glass fiber could offer a better alternative to wool, he said, because the fiber strands are too long and intertwined to be blown out of the muffler. According to Owens Corning, a gumball-sized glass marble that is spun into a strand of continuous fiber for exhaust applications can measure 18 miles long, with a diameter one quarter that of a human hair.

Selamet also said that glass fiber can better withstand the high temperatures produced in modern exhaust systems, and potentially even insulate the car from that heat.

Since automakers such as Volvo are using glass fiber in mufflers sold in Europe, Selamet had an opportunity to test the design. Owens Corning supplied him with new and used Volvo mufflers, as well as loose fiber samples. The used mufflers came from cars that had been driven 100,000 miles.

In tests, Selamet and his colleagues found that the fiber reduced engine noise substantially. For example, at the mid-range frequency of 1500 Hertz, the new design reduced the noise by 40 decibels. That's significantly higher than the typical muffler rating of 30 decibels or lower.

The mufflers used for 100,000 miles performed just as well as the new.

The Ohio State engineers developed a computerized tool that manufacturers can use in optimizing the design of a fiber-filled mufflers for different car models.

A major parts maker has also expressed interest in using the fibers in an automotive intake system, where, as Selamet pointed out, automakers have a big opportunity to quiet engine noise.

"One of the most powerful noise-reducers in the intake system of a car is the air cleaner box," he said, referring to the housing that contains filter to clean debris from the outside air before feeding it to the engine.
-end-
Contact: Ahmet Selamet, 614-292-4143; Selamet.1@osu.edu

Written by Pam Frost Gorder, 614-292-9475; Gorder.1@osu.edu

Ohio State University

Related Mechanical Engineering Articles from Brightsurf:

Best practices for mechanical ventilation in patients with ARDS, COVID-19
A team from pulmonary and critical care medicine at Michigan Medicine outlines 20 evidence-based practices shown to reduce time spent on a ventilator and death in patients with acute respiratory failure and acute respiratory distress -- conditions that have many overlaps with severe COVID-19.

How cells use mechanical tension sensors to interact with their environment
In a painstaking experiment, scientists suspended a single protein filament between two microscopic beads.

Mechanical forces of biofilms could play role in infections
Studying bacterial biofilms, EPFL scientists have discovered that mechanical forces within them are sufficient to deform the soft material they grow on, e.g. biological tissues, suggesting a ''mechanical'' mode of bacterial infection.

How mechanical forces nudge tumors toward malignancy
Researchers studying two forms of skin cancer identified a long-overlooked factor determining why some tumors are more likely to metastasize than others: the physical properties of the tissue in which the cancer originates.

Building mechanical memory boards using origami
Origami can be used to create mechanical, binary switches, and in Applied Physics Letters, researchers report the fabrication of such a paper device, using the Kresling pattern, that can act as a mechanical switch.

Not just light: The sensitivity of photoreceptors to mechanical stimuli is unveiled
''We thought we knew almost everything about photoreceptors, but we have proved that is not the case''.

A mechanical way to stimulate neurons
Magnetic nanodiscs can be activated by an external magnetic field, providing a research tool for studying neural responses.

Cell removal as the result of a mechanical instability
Researchers at Kanazawa University report in the Biophysical Journal that the process of cell removal from an epithelial layer follows from an inherent mechanical instability.

Researchers demonstrate transport of mechanical energy, even through damaged pathways
Researchers from the University of Illinois at Urbana-Champaign's Grainger College of Engineering have experimentally demonstrated a new way to transport energy even through wave-guides that are defective, and even if the disorder is a transient phenomenon in time.

Tissues protect their DNA under mechanical stress
Nuclei and genetic material deform.

Read More: Mechanical Engineering News and Mechanical Engineering Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.