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