P11227- Formula Exhaust Acoustic Tuning Design Review – Week 5 Greg Wodzicki Kyle Desrosiers Brad Fiedler Chris VanWagenen
Dec 17, 2015
P11227- Formula Exhaust Acoustic Tuning
Design Review – Week 5
Greg Wodzicki
Kyle Desrosiers
Brad Fiedler
Chris VanWagenen
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.
Engine Exhaust
Noise
>110dB
Glass pack
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
Engine Exhaus
t
Noise
<110dB
Noise Cancelling
System
Introduction / Background
Customer needs
Customer Need #
Importance
Description Comments/Status
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 1Obtain 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)
Engineering specsEngineering Specifications
ES #Importan
ce Specification (Description)Unit of
MeasureMarginal Value
Ideal Value Comments/Status
Person
ES 1 9 Reduce noise level dBA
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 <110SAE Rules
ES 5 3 System Power Draw Watts ES 6 1 System Life hours ES 7 3 Component Costs $ Cheap as possible
ES 8 1 Exhaust Envelope (volume of space) ft3 Discuss with SAE team
ES 9 9 Internal Exhaust Components Survivable Temp
°F Discuss with SAE team
ES 10 9 Internal Exhaust Components Survivable Pressure
psia Discuss with SAE team
ES 11 3 Component Shock Threshold g Discuss with SAE team
ES 12 3 Change in Engine Max Power HP 0Change in power must be justified by significant improvement elsewhere
ES 13 1 Weight limit on exhaust system lbs 8 Approximately equal to current
ES 14 3 Maximum allowed back pressure psi Define from analytical data/literature research
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
NoiseEngin
eExhaust Glass
pack
Inner Pipe
Sound Insulation
Housing
Concepts
Multi-pass Muffler
NoiseEngin
eExhaust
Multi-Pass
Muffler
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
Concepts
Baffle Muffler
NoiseEngin
eExhaust
Baffle Muffler
Reflects Exhaust Throughout Chamber
Reflections Cancel each other
Most Back Pressure created
Greatest Sound Reduction
Concepts
Elimination of Baffle and Multi-PassPros: 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
Noise
Courses of Action
Engine
Exhaust
<110dB
Speaker
Primary Microphone
Feedback Microphon
e
Speaker Signal
Controller
Multiple Speaker with Error Microphone
Noise
Courses of Action
Engine
Exhaust
<110dB
Speakers
Primary Microphone
Feedback Microphon
e
Speaker Signal
Controller
Exhaust in Speaker Chamber
NoiseEngin
eExhaust <110dB
Speaker
Primary Microphone
Speaker Signal
Controller
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 methodIntroduction / Background
Introduction / Background
Risk Assessment
Risk # Description of Risk Possible ConsequencesOverall Risk (81 = high)
Preventative Measures Contingency Plan
1 FSAE Engine is occupied or non-functional
Lack of data from formula car
9Constant communication with RIT Formula team (Taylor Hattori)
Test exclusively on lawn mower engine
2 Microphone not functional Can not record engine waveform
9 Keep in safe place, handle with care, use appropriately
New Microphone
3 Lawn mower engine failureCan not record engine waveform, can not test designs
27Check oil level before each use, otherwise maintain engine properly
Use backup engine
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
27Ensure each aspect of the design is designed as cost effectively as possible
Borrow parts, see what is available from various labs
6None 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.
7Materials/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.
8Lack of scientific knowledge surrounding signal processing
Deliverables missed, sound not attenuated 9
Use simple components and software that we have existing knowledge of or can readily learn
Find expert to assist in signal processing. Simplify design by removing some components.
9Engine noise (non-exhaust) is not negligible for lawnmower engine.
Sound reading not accurate. 9
Make sure measuring sound according to SAE rules.
Insulate engine "chatter" from microphone
10ANC design is improperly calibrated
ANC muffler actually creates more sound rather than attenuates sound.
81Have a system that is able to be modified and recalibrated.
Re-calibrate and try again.
11Deviation from project timeline.
Fall behind on project objectives 9
Allot appropriate time for each task Simplify and re-prioritize tasks.
12Oversimplified or bad assumptions lead to incorrect data.
Exhaust system design might be incorrect and need to be modified
9
Double-check all assumptions with subject matter expert, test assumption with data collection.
Exhaust design would have to be modified to accommodate misconceptions.
13Equipment doesn’t exist that can survive in the conditions around the engine
Design not able to be built in SD2 81
Go through each aspect of the design, keeping in mind survivability conditions.
Change materials or geometry.
14 Customer needs change
Project plan no longer completes customer needs by the end of senior design.
3Constant communication with RIT Formula team (Taylor Hattori)
Change the project plan to accommodate changes and discuss feasibility of changes with customer
Concept Screening A B C D E F G H ANC1 ANC2 ANC3
Selection CriteriaGlass pack
Modified Glass pack
MultlipassBaffle
muffler
Variable length
resonator
Speaker parallel to exhaust
Multiple speakers
Exhaust in speaker chamber
Ease of manufacture
0 0 - - - - - -
Noise reduction 0 + + + + 0 0 +Weight 0 + 0 0 - 0 - 0
Ease of field repair 0 0 - - - - - -Costs 0 0 - - - - - -
Effect on back pressure
0 0 - - 0 + + +
Center of gravity 0 0 0 0 0 + + 0Size 0 - - - - + + 0
Power usage 0 0 0 0 0 - - -Survivability 0 0 0 0 0 - - 0
Sum + 's 0 2 1 1 1 3 3 2Sum 0's 10 7 4 4 4 2 1 4Sum -'s 0 1 5 5 5 5 6 4
Net Score 0 1 -4 -4 -4 -2 -3 -2Rank 2 1 6 6 6 3 5 3
Continue? Y N N N Y N Y
Concept Screening (cont’d)A B C D E F G H
Glass pack Modified Glass Pack Multipass Baffle Muffler Variable length resonator Speaker Parallel to exhaust Multiple Speakers Exhaust in speaker chamber
Selection Criteria Rating Wtd Rating Wtd Rating Wtd Rating Wtd Rating Wtd Rating Wtd Rating Wtd Rating Wtd
Ease of manufacture0 0.00 0 0.00 -1 -0.07 -1 -0.07 -1 -0.07 -3 -0.20 -3 -0.20 -9 -0.61
Noise reduction0 0.00 1 0.20 3 0.61 9 1.84 3 0.61 1 0.20 3 0.61 3 0.61
Weight0 0.00 1 0.20 -1 -0.20 0 0.00 -1 -0.20 0 0.00 -3 -0.61 0 0.00
Ease of field repair0 0.00 0 0.00 -1 -0.07 -1 -0.07 -3 -0.20 -3 -0.20 -3 -0.20 -3 -0.20
Costs0 0.00 -1 -0.07 -1 -0.07 -3 -0.20 -3 -0.20 -3 -0.20 -9 -0.61 -3 -0.20
Effect on back pressure0 0.00 1 0.20 -3 -0.61 -9 -1.84 0 0.00 3 0.61 3 0.61 3 0.61
Center of gravity0 0.00 0 0.00 0 0.00 0 0.00 0 0.00 3 0.07 3 0.07 3 0.07
Size0 0.00 -1 -0.02 -1 -0.02 -3 -0.07 -1 -0.02 3 0.07 9 0.20 0 0.00
Power usage0 0.00 0 0 0 0.00 0 -3 -0.20 -9 -0.61 -3 -0.20
Survivability0 0.00 0 0.00 0 0.00 0 0.00 -1 -0.07 -3 -0.20 -3 -0.20 -1 -0.07
Total Score 0.00 0.52 -0.43 -0.41 -0.16 -0.07 -0.95 0.00
Rank 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