Transcript Presentation

NOISE REDUCTION
FOR
INTERNAL COMBUSTION
ENGINE
Christopher
Morehouse
Julie Maier
Ted Zachwieja
Caroline Bills
PROJECT OVERVIEW
 Objectives:
 Sound attenuation for
performance cars (i.e. Formula
Team)
 Minimal performance
degradation
 Understand phenomenon of
sound
 Engine - lawnmower (Briggs &
Stratton)
ENGINE NOISE CHARACTERISTICS
 Sound Sources
Pressure Waves
 Engine Firing Frequency
 Mean Ef fective Pressure
ENGINE NOISE CHARACTERISTICS
DESIGN OPTIONS
 HELMHOLTZ RESONATOR
 CONCENTRIC TUBE RESONATOR
 ABSORPTION MUFFLER
 ACTIVE NOISE CANCELLATION
 Pursued by another Senior
Design Team
RESONATOR DEMONSTRATION MODULE
 CONCENTRIC TUBE RESONATOR  HELMHOLTZ RESONATOR
RESONATOR TEST SET-UP
CONCENTRIC TUBE
RESONATOR
Concentric
Tube Tests:
-1 . Var y
Frequency
-2. Var y
Length
SPEAKERS
Helmholtz
Tests:
-1 . Var y
frequen
cy
TONE GENERATOR
(LAPTOP)
HELMHOLTZ
RESONATOR
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, Var y Length
 Locations of fset from
wavelength multiples
 Reduction increases with
frequency
 Max Attenuation:
 550Hz, 10.3 dB (LCT)
 550 Hz 8.4 dB (SCT)
HELMHOLTZ RESONATOR TEST RESULTS
 Prediction:
 High
reduction
 Narrow Band
 Result:
 Reduction
offset
 Higher F ->
higher
reduction
 Errors Sources:
 Simple
Equation
ABSORPTION MUFFLER:
OVERVIEW
 Outer steel casing
 Perforated inner steel pipe
 5 shapes
 Steel end caps
 Packing material in cavity
 3 materials
 3 densities
ABSORPTION MUFFLER:
MATERIAL & DENSIT Y OPTIONS
Fiberglass
 Fiberglass &
Mineral Wool:
 175, 200, and 225 g/L
Mineral Wool
Steel Wool
 Steel Wool:
 Grades 0000, 1, and 4
ABSORPTION MUFFLER TESTING
 Test 1: Optimal Packing Material & Density
 Standard Shape Option only
 Test 2: Optimal Shape
 Optimal Material & Density only
OPTIMAL MATERIAL RESULTS
OPTIMAL SHAPE RESULTS
dB Comparison Average
98.0
96.0
94.0
dB Readings
92.0
Baseline
Standard
S hort
Short
C avity
Cavity
Thin
Thin
S in
Sine
B as eline
90.0
S tandard
88.0
86.0
84.0
82.0
80.0
78.0
0
5
10
15
Distance from Muffler (ft)
20
25
POSSIBLE ERROR SOURCES
1.
2.
3.
4.
Repeatability
Non-uniform engine performance
Non-uniform packing
Noise contamination from environment


Loaded engine, constant RPM
Anechoic chamber?
CONCLUSIONS
 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
QUESTIONS??
 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