Methods and apparatus for low back pressure muffling of internal combustion engines

Abstract

Systems and apparatus for muffling sounds produced by an internal combustion engine, and optionally catalytically degrading pollutants within waste exhaust gases. The systems and apparatus utilize a bed of particles within a muffling chamber. The gases are introduced using a diffusion tube with holes therethrough. The muffling particles preferably include silica or alumina, which can also catalytically degrade pollutants. Typically, the muffling / reaction chamber is maintained at a temperature in a range from about 50° C. to about 500° C., which is much lower than temperatures within conventional muffling systems for diesel engines. The muffling systems operate as substantially lower back pressure compared to conventional muffling systems. The systems and apparatus can be adapted to be used in combination with diesel engines or other internal combustion engines and industrial burners.

Description

[0001] This application claims the benefit under 35 U.S.C. .sctn. 119 of earlier filed U.S. provisional application Ser. No. 60 / 183,088, filed Feb. 15, 2000. For purposes of disclosure, the foregoing provisional application is incorporated herein by specific reference.[0002] 1. Field of the Invention[0003] The present invention is in the field of muffling apparatus used to reduce the sound emitted by internal combustion engines. More particularly, the present invention involves methods and systems for muffling the sound emitted by internal combustion engines while maintaining low back pressure for improved power and fuel economy. The methods and systems employ a bed of silica, alumina or other appropriate particulate material for absorbing and / or disrupting sound waves.[0004] 2. Review of the Relevant Technology[0005] Internal combustion engines are ubiquitous in modem life but have the drawback of producing considerable noise, particularly from the exhaust pipe. To effectively muff...

AI Technical Summary

Benefits of technology

[0015] The present invention encompasses improved methods and systems for muffling engine sounds emanating from the exhaust system of internal combustion engines. Such muffling methods and systems employ a muffling chamber filled with an appropriate particulate media capable of absorbing or otherwise disrupting the sound waves found in the exhaust stream corresponding to engine noise. Because moving exhaust gases are able to more freely pass through the spaces between the individual particles comprising the particulate media than through baffling and dampening devices found in conventional mufflers, the muffling systems of the present invention are able to muffle sound while reducing back pressure compared to conventional mufflers. In turn, greatly reducing the back pressure substantially improves the power and fuel efficiency of the engine.

[0016] The inventive muffling systems according to the invention preferably include one or more exhaust muffling chambers, which include muffling particles disposed therein, in gaseous communication with an internal combustion engine. The sound waves generated by the explosions within the cylinders of internal combustion engines are concentrated within and directed through the exhaust pipes or conduits connected to the engine. As the exhaust gases pass through the one or more exhaust muffling chambers the sound waves contained therein and propagated thereby are widely scattered, and thus dissipated and muted, by the surrounding particulate media. More particularly, a diffusion pipe is at least partially sunk beneath a volume of muffling particles so that the exhaust gases are passed from the diffusion pipe into the surrounding muffling particles. It is believed that the particulate muffling particles act to scatter and redistribute the sound waves throughout the muffling chamber in a manner that causes a substantial portion of the sound waves to become substantially out of phase and thus able to cancel each other out. This reduces the amplitude and, hence, the volume of the sound represented by the at least partially cancelled out sound waves.

Problems solved by technology

Internal combustion engines are ubiquitous in modem life but have the drawback of producing considerable noise, particularly from the exhaust pipe.

Because muffling systems typically involve restricting the free flow of exhaust gasses in order to disrupt or otherwise dampen the sound waves generated by the operation of the engine, mufflers can create significant "back pressure", known to reduce fuel economy and power.

The use of catalytic converters in-line with conventional muffling systems further increases back pressure.

Back pressure inherently reduces fuel economy and engine power by increasing the amount of work that the engine must perform just to emit the waste exhaust gases into the air.

It also reduces power by generally requiring an increase in the fuel to air ratio that is fed into the cylinders in order for the engine to run properly.

Unfortunately, headers or other low back pressure muffling systems are costly and generally not approved for conventional vehicles, but are reserved for racing vehicles, because they do not meet present noise reduction standards.

In view of the requirement that vehicles with internal combustion engines must be equipped with muffling systems which meet relevant government noise reduction standards, but in view of other standards relating to the need to reduce pollution and improve fuel economy, there is inherently a tension or conflict with noise reduction goals, on the one hand, and fuel economy and emissions reduction, on the other.

The result of this tradeoff is generally reduced power and vehicular performance.

The problem with this strategy is that there are presently no reasonably priced or sized muffling systems that are capable of significantly reducing back pressure while satisfying present vehicle noise standards.

Although catalytic converters themselves might not create as much back pressure as conventional mufflers, the back pressure imparted by a catalytic converter is cumulative to the back pressure created by the muffler in the same exhaust system, thus further reducing fuel economy and engine power.

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