christopher morehouse julie maier ted zachwieja caroline bills noise reduction for internal...
Post on 20-Dec-2015
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TRANSCRIPT
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
DESIGN OPTIONS
ABSORPTION MUFFLER
CONCENTRIC TUBE RESONATOR
HELMHOLTZ RESONATOR
ACTIVE NOISE CANCELLATIONPursued by another
Senior Design Team
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 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