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ChristopherMorehouse

Julie Maier

Ted Zachwieja

Caroline Bills

NOISE REDUCTION

FORINTERNAL COMBUSTION

ENGINE

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Objectives:

Sound attenuation for

performance cars (i.e. Formula

Team)

Minimal performancedegradation

Understand phenomenon of

sound

Engine - l awnmower (Briggs &

Stratton)

PROJECT OVERVIEW

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Engine Firing Frequency

ENGINE NOISE CHARACTERISTICS

Pressure Waves

Sound Sources

Mean Effective Pressure

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ENGINE NOISE CHARACTERISTICS

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DESIGN OPTIONS

ABSORPTION MUFFLER

CONCENTRIC TUBE RESONATOR HELMHOLTZ RESONATOR

ACTIVE NOISE CANCELLATION

Pursued by another Senior

Design Team

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CONCENTRIC TUBE RESONATOR

RESONATOR DEMONSTRATION MODULE

HELMHOLTZ RESONATOR

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RESONATOR TEST SET-UP

HelmholtzTests:

 -1 . Va ry

frequen

cy

Concentric

Tube Tests:

 -1 . Vary

Frequency

 -2. Va ry

Length

SPEAKERS

CONCENTRIC TUBE

RESONATOR

HELMHOLTZ

RESONATOR

TONE GENERATOR

(LAPTOP)SOUND LEVEL

METER

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CONCENTRIC TUBE TEST 1 RESULTS

Fixed Length, Vary

Frequency

Predicted:

½ & ¼ -> max

reduction

Magnitude ~ 10 dB

Result:

Max 4dB

Offset from

Predicted

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CONCENTRIC TUBE TEST 2 RESULTS

Fixed Frequency, Vary Length

Locations offset from

wavelength multiples

Reduction increases with

frequency

Max Attenuation:

550Hz, 10.3 dB (LCT)

550 Hz 8.4 dB (SCT)

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Prediction:

High

reduction

Narrow Band

Result: Reduction

offset

Higher F ->

higher

reduction Errors Sources:

Simple

Equation

HELMHOLTZ RESONATOR TEST RESULTS

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ABSORPTION MUFFLER:

OVERVIEW

Outer steel casing

Perforated inner steel pipe

5 shapes

Steel end caps

Packing material in cavity3 materials

3 densities

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Fiberglass

Mineral Wool

Steel Wool

Fiberglass &

Mineral Wool:

175, 200, and 225 g/L

Steel Wool: Grades 0000, 1, and 4

ABSORPTION MUFFLER:

MATERIAL & DENSIT Y OPTIONS

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OPTIMAL MATERIAL RESULTS

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OPTIMAL SHAPE RESULTS

dB Comparison Average

78.0

80.0

82.0

84.0

86.0

88.0

90.0

92.0

94.0

96.0

98.0

0 5 10 15 20 25

Distance from Muffler (ft)

   d   B

   R  e  a   d   i  n  g  s

Baseline

S tandard

S hort

C avity

Thin

S in

Baseline

Standard

Short

Cavity

Thin

Sine

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POSSIBLE ERROR SOURCES

1. Repeatability

2. Non-uniform engine performance

3. Non-uniform packing

4. Noise contamination from environment

Loaded engine, constant RPM

Anechoic chamber?

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Concentric Tube Resonators

Require further testing

Follow-on

Research Offset

Recordings of Engines

Helmholtz – performed as expected

Absorption

Steel wool better material, but best geometry needs further testing

Follow-on

Higher densities steel wool

Composite packing

Endurance testing

SAE application

Recommend small Helmholtz with Steel Wool packed muffler

CONCLUSIONS

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References:

Bell, Lewis H. Industrial noise control: Fundamentals and

 Applications . New York : M. Dekker, 1982. Print.

http://students.sae.org/competitions/formulaseries/rules/2011fsae

rules.pdf

QUESTIONS??