P11227- Formula Exhaust
Acoustic Tuning
Brad Fiedler
Chris VanWagenen
Greg Wodzicki
Kyle Desrosiers
Design Review – Week 5
Agenda

Introduction / Background








Problem Statement
Customer Needs
Engineering Specs
Understanding the Problem and Current Technology
Concept Review
Test Bench
Closing
Questions
Problem Statement

Formula SAE rules state exhaust noise volume must be
lower than 110 dB before allowing a team’s car to
compete. Any vehicle that does not pass may be modified
and retested until it passes. Current muffler design is glass
pack, which is often repacked at competition to lower the
noise level within spec. The purpose of this project is to
provide the RIT Formula team with means to lower their
exhaust noise consistently and more predictably.
Introduction / Background
Problem Background



FSAE rules dictate engine noise under 110dB.
Current Passive Noise Control device does not involve
extensive design.
Packing material deteriorates over usage time and noise
attenuation decreases throughout season.
Introduction / Background
Current Glass Pack Design





Not currently heavily designed area of car
Packed/repacked onsite at competition to pass
Summer 2010 scored ~102 dB at competition
Life: ½ season before glass melts and attenuation
becomes less affective
Used as reference for concepts explored
Source: P11221
Introduction / Background
Original Design Objectives
Design system to cancel sound output without sacrificing
performance to:
 Bring Engine sound under FSAE limit of 110dB.
 Adhere to all FSAE Rules
 To not add Significant weight to Vehicle
 Maintain/Improve engine performance
Introduction / Background
Customer needs
Customer
Need #
Importance
CN1
9
Reduce the sound level of RIT's Formula SAE engine to meet the legal formula level
CN2
9
Be able to demonstrate RIT's Formula Car will pass FSAE Sound Regulations
CN3
3
Prove concept of sound acoustics (i.e. attenuation, freq shift, etc)
CN4
1
Obtain needed understanding of acoustics and sound waves
CN5
1
Obtain needed understanding of Engine Characteristics (i.e. firing freq, Sound characteristics, torque power)
CN6
1
Analyze data and identify optimal areas of improvement
CN8
9
Maintain Engine Performance (torque, horsepower)
CN9
9
Maintain Vehicle Performance (weight, battery reserve, size, Vibration)
CN10
3
Demonstrate feasibility of active noise cancellation on IC Engine (Test Stand)
CN11
3
Understand the fundamental sources of noise generation from the normal operation of an IC Engine.
(1. Discrete frequency sources, 2. broad band or white noise sources)
CN12
3
Propose noise reduction methods for each source
CN13
9
Easily fixed during competition (if breaks)
CN14
1
Lower center of gravity by location of exhaust system
CN15
3
Resilience of design (lasts at least half a season)
Description
Comments/Status
Engineering specs
Engineering Specifications
Specification (Description)
Unit of Marginal Ideal
Measure
Value Value
dBA
ES #
Importance
ES 1
9
Reduce noise level
ES 2
9
Maximum length extending from rear axle
in
17.6
17.7 SAE Rules
ES 3
9
Maximum distance above the ground
in
23.5
23.6 SAE Rules
ES 4
9
Passes B10.3 of the SAE Formula rules
dBA, fast
weighting
110
<110 SAE Rules
ES 5
ES 6
ES 7
3
1
3
System Power Draw
System Life
Component Costs
Watts
hours
$
Comments/Status
Cheap as possible
3
Discuss with SAE team
ES 8
1
Exhaust Envelope (volume of space)
ft
ES 9
9
Internal Exhaust Components Survivable Temp
°F
Discuss with SAE team
ES 10
9
psia
Discuss with SAE team
ES 11
3
Internal Exhaust Components Survivable
Pressure
Component Shock Threshold
ES 12
3
Change in Engine Max Power
HP
0
ES 13
1
Weight limit on exhaust system
lbs
8
ES 14
3
Maximum allowed back pressure
psi
g
Discuss with SAE team
Change in power must be justified by
significant improvement elsewhere
Approximately equal to current
Define from analytical data/literature
research
Person
Understanding the Problem

Sound Waves (see Figure 1)




Superposition
Human Auditory Range (frequency)
Harmonics
Four-stroke engine (see Figure 2)


Cycles: intake, compression, power, exhaust
Noise Sources




“Chatter”
Intake
Exhaust- Main source
Firing Frequency (See Fig 3)
Glass Pack




Exhaust Travels through Pipe with Perforated Holes
Sound Insulation Absorbs Sound
Minimal Back Pressure
Least Effective in Reducing Sound
Concepts
Multi-pass Muffler






Concepts
No Baffles
Exhaust Forced to turn
back and forth
Increases Exhaust Length
Increased Back Pressure
with each turn
Sound Insulation Absorbs
Sound
Moderately Effective in
Reducing Sound
Baffle Muffler




Reflects Exhaust
Throughout Chamber
Reflections Cancel each
other
Most Back Pressure created
Greatest Sound Reduction
Concepts
Elimination of Baffle and Multi-Pass
Pros:
 Multi-pass provides better attenuation than glass pack.
 Baffle (chamber style) muffler provides even better
attenuation than multi-pass.
Cons:
 Multi-pass increases exhaust back pressure
 Baffle style will cause the most back pressure of all the
design concepts.
Baffle and multi-pass are quieter, but increase backpressure.
It has already been seen that Glass Pack can achieve FSAE
limit with lower backpressure
Concepts
Variable Length Resonator

Engine
•
•
•
•
Traditional Resonators are tuned to address particular range of frequencies
Generally target the most problematic (loudest) frequencies
As engine speed changes, exhaust frequencies change
Variable length resonator addresses wider range of frequencies
Cons:
• Adds weight
• Waves reflect in accordion (baffles)
• FSAE states system must be tested in all positions. If not at the ideal position for a
given frequency, the resonator will do nothing to attenuate sound
Parallel ANC with Microphone and Feedback
Courses of Action
Multiple Speaker with Error Microphone
Courses of Action
Exhaust in Speaker Chamber
Performance Objective
Possible Performance Effects of Active Noise Cancellation Technology:
 A – No Exhaust Tuning
 B – Traditional Exhaust Length Tuning
 C – Possible Active Noise Cancellation Improvement*
* Dependent on cancellation method
Introduction / Background
Risk Assessment
Risk #
Description of Risk
Possible Consequences
Overall
Risk (81 =
high)
Preventative Measures
Contingency Plan
1
FSAE Engine is occupied or nonfunctional
Lack of data from formula car
9
Constant communication with RIT
Test exclusively on lawn mower engine
Formula team (Taylor Hattori)
2
Microphone not functional
Can not record engine waveform
9
Keep in safe place, handle with
care, use appropriately
3
Lawn mower engine failure
Can not record engine
waveform, can not test designs
27
Check oil level before each use,
Use backup engine
otherwise maintain engine properly
4
Non-ideal testing conditions (rain,
noisy, etc)
Equipment ruined, testing
delayed
27
Keep an eye on weather conditions Reschedule Testing
5
Lack of budget
Design not able to be created
spring quarter
27
Ensure each aspect of the design is
Borrow parts, see what is available from
designed as cost effectively as
various labs
possible
6
None of the muffler designs reduce
sound within the target range
Project fails
9
Use best available, most feasible
design
Explain why designs did not work as
expected.
7
Materials/mufflers are
destroyed/ruined during testing.
Sound absorption of design is
reduced.
27
Purchase excess material,
incorporate factor of safety into
designs
Purchase excess material.
Introduction / Background
New Microphone
8
Lack of scientific knowledge
surrounding signal processing
Deliverables missed, sound not
attenuated
9
Use simple components and
Find expert to assist in signal
software that we have existing processing. Simplify design by
knowledge of or can readily learn removing some components.
9
Engine noise (non-exhaust) is not
negligible for lawnmower engine.
Sound reading not accurate.
9
Make sure measuring sound
according to SAE rules.
10
ANC muffler actually creates
ANC design is improperly calibrated more sound rather than
attenuates sound.
81
Have a system that is able to be
Re-calibrate and try again.
modified and recalibrated.
11
Deviation from project timeline.
9
Allot appropriate time for each
task
12
Exhaust system design might
Oversimplified or bad assumptions
be incorrect and need to be
lead to incorrect data.
modified
9
Double-check all assumptions
Exhaust design would have to be
with subject matter expert, test modified to accommodate
assumption with data collection. misconceptions.
13
Equipment doesn’t exist that can
Design not able to be built in
survive in the conditions around the
SD2
engine
81
Go through each aspect of the
design, keeping in mind
survivability conditions.
Change materials or geometry.
14
Customer needs change
3
Constant communication with
RIT Formula team (Taylor
Hattori)
Change the project plan to
accommodate changes and discuss
feasibility of changes with customer
Fall behind on project
objectives
Project plan no longer
completes customer needs by
the end of senior design.
Insulate engine "chatter" from
microphone
Simplify and re-prioritize tasks.
Concept Screening
A
B
C
D
E
F
ANC1
G
ANC2
H
ANC3
Selection Criteria
Glass pack
Modified Glass pack
Multlipass
Baffle muffler
Variable length
resonator
Speaker parallel to
exhaust
Multiple speakers
Exhaust in speaker
chamber
Ease of manufacture
Noise reduction
Weight
Ease of field repair
Costs
Effect on back pressure
Center of gravity
Size
Power usage
Survivability
Sum + 's
Sum 0's
Sum -'s
Net Score
0
0
0
0
0
0
0
0
0
0
0
10
0
0
0
+
+
0
0
0
0
0
0
2
7
1
1
+
0
0
0
0
1
4
5
-4
+
0
0
0
0
1
4
5
-4
+
0
0
0
0
1
4
5
-4
0
0
+
+
+
3
2
5
-2
0
+
+
+
3
1
6
-3
+
0
+
0
0
0
2
4
4
-2
Rank
2
1
6
6
6
3
5
3
Y
N
N
N
Y
N
Y
Continue?
Concept Screening (cont’d)
A
Glass pack
Selection Criteria
Rating Wtd
Ease of manufacture
Noise reduction
Weight
Ease of field repair
Costs
Effect on back pressure
Center of gravity
Size
Power usage
Survivability
Rank
Rating
Wtd
C
Multipass
Rating Wtd
D
Baffle Muffler
E
Variable length resonator
F
Speaker Parallel to exhaust
G
Multiple Speakers
H
Exhaust in speaker chamber
Rating
Wtd
Rating
Wtd
Rating
Wtd
Rating
Wtd
Rating
Wtd
0
0.00
0
0.00
-1
-0.07
-1
-0.07
-1
-0.07
-3
-0.20
-3
-0.20
-9
-0.61
0
0.00
1
0.20
3
0.61
9
1.84
3
0.61
1
0.20
3
0.61
3
0.61
0
0.00
1
0.20
-1
-0.20
0
0.00
-1
-0.20
0
0.00
-3
-0.61
0
0.00
0
0.00
0
0.00
-1
-0.07
-1
-0.07
-3
-0.20
-3
-0.20
-3
-0.20
-3
-0.20
0
0.00
-1
-0.07
-1
-0.07
-3
-0.20
-3
-0.20
-3
-0.20
-9
-0.61
-3
-0.20
0
0.00
1
0.20
-3
-0.61
-9
-1.84
0
0.00
3
0.61
3
0.61
3
0.61
0
0.00
0
0.00
0
0.00
0
0.00
0
0.00
3
0.07
3
0.07
3
0.07
0
0.00
-1
-0.02
-1
-0.02
-3
-0.07
-1
-0.02
3
0.07
9
0.20
0
0.00
0
0.00
0
0
0.00
0
-3
-0.20
-9
-0.61
-3
-0.20
0.00
0
0.00
-1
-3
-0.20
-3
-0.20
-1
0
Total Score
B
Modified Glass Pack
0
0.00
0
0.00
0
-0.07
-0.07
0.00
0.52
-0.43
-0.41
-0.16
-0.07
-0.95
0.00
2
1
7
6
5
4
8
2
Proposed Design Objective

Test Bench that can be used as a tool by the formula team to
facilitate muffler design and evaluate possible solutions prior to
competition

Characteristics to be analyzed may include:




Pressure drop across muffler
Flow rate (volumetric, mass flow rate)
Sound level output
Waveform data
Test Bench