Christopher MorehouseJulie MaierTed ZachwiejaCaroline Bills

NOISE REDUCTION FOR

INTERNAL COMBUSTION ENGINE

Objectives: Sound attenuation for

performance cars (i.e. Formula Team)

Minimal performance degradation

Understand phenomenon of sound

Engine - lawnmower (Briggs & Stratton)

PROJECT OVERVIEW

Engine Firing Frequency

ENGINE NOISE CHARACTERISTICS

Pressure Waves

Sound Sources

Mean Effective Pressure

ENGINE NOISE CHARACTERISTICS

DESIGN OPTIONS

ABSORPTION MUFFLER

CONCENTRIC TUBE RESONATOR

HELMHOLTZ RESONATOR

ACTIVE NOISE CANCELLATIONPursued by another

Senior Design Team

CONCENTRIC TUBE RESONATOR

RESONATOR DEMONSTRATION MODULE

HELMHOLTZ RESONATOR

RESONATOR TEST SET-UP

Helmholtz Tests:

-1. Vary frequency

Concentric Tube Tests:

-1. Vary Frequency

-2. Vary Length

SPEAKERS

CONCENTRIC TUBERESONATOR

HELMHOLTZRESONATOR

TONE GENERATOR(LAPTOP) SOUND LEVEL

METER

CONCENTRIC TUBE TEST 1 RESULTS

Fixed Length, Vary Frequency

Predicted: ½ & ¼ -> max

reduction Magnitude ~ 10 dB

Result: Max 4dB Offset from

Predicted

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)

Prediction: High

reduction Narrow Band

Result: Reduction

offset Higher F ->

higher reduction

Errors Sources: Simple

Equation

HELMHOLTZ RESONATOR TEST RESULTS

ABSORPTION MUFFLER:OVERVIEW

Outer steel casing Perforated inner steel pipe

5 shapesSteel end capsPacking material in cavity

3 materials3 densities

Fiberglass

Mineral Wool

Steel Wool

Fiberglass & Mineral Wool:

175, 200, and 225 g/L

Steel Wool: Grades 0000, 1, and 4

ABSORPTION MUFFLER:MATERIAL & DENSITY OPTIONS

ABSORPTION MUFFLER TESTING

Test 1: Optimal Packing Material & DensityStandard Shape Option only

Test 2: Optimal ShapeOptimal Material & Density only

OPTIMAL MATERIAL RESULTS

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)

dB

Rea

din

gs

Bas eline

S tandard

S hort

C avity

Thin

S in

BaselineStandardShortCavityThinSine

POSSIBLE ERROR SOURCES

1. Repeatability2. Non-uniform engine performance3. Non-uniform packing4. Noise contamination from environment

Loaded engine, constant RPM Anechoic chamber?

Concentric Tube Resonators Require further testing Follow-on

Research Offset Recordings of Engines

Helmholtz – performed as expectedAbsorption

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

References: Bell, Lewis H. Industrial noise control: Fundamentals and

Applications. New York : M. Dekker, 1982. Print. http://students.sae.org/competitions/formulaseries/rules/

2011fsaerules.pdf

QUESTIONS??