P11227 formula exhaust acoustic tuning
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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

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P11227- Formula Exhaust Acoustic Tuning

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P11227 formula exhaust acoustic tuning

P11227- Formula Exhaust Acoustic Tuning

Brad Fiedler

Chris VanWagenen

Greg Wodzicki

Kyle Desrosiers

Design Review – Week 5


Agenda

Agenda

  • Introduction / Background

    • Problem Statement

  • Customer Needs

  • Engineering Specs

  • Understanding the Problem and Current Technology

  • Concept Review

  • Test Bench

  • Closing

  • Questions


Problem statement

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

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.

Noise

Engine

Glass pack

Exhaust

>110dB

Introduction / Background


Current glass pack design

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

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

Noise

Engine

Noise Cancelling System

Exhaust

<110dB

Introduction / Background


Customer needs

Customer needs


Engineering specs

Engineering specs


Understanding the problem

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

Glass Pack

  • Exhaust Travels through Pipe with Perforated Holes

  • Sound Insulation Absorbs Sound

  • Minimal Back Pressure

  • Least Effective in Reducing Sound

Noise

Engine

Glass pack

Exhaust

Inner Pipe

Housing

Sound Insulation

Concepts


Multi pass muffler

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

Noise

Engine

Multi-Pass Muffler

Exhaust

Concepts


Baffle muffler

Baffle Muffler

  • Reflects Exhaust Throughout Chamber

  • Reflections Cancel each other

  • Most Back Pressure created

  • Greatest Sound Reduction

Noise

Engine

Baffle Muffler

Exhaust

Concepts


Elimination of baffle and multi pass

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

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

Parallel ANC with Microphone and Feedback

Speaker

Noise

Engine

Exhaust

Speaker Signal

<110dB

Controller

Primary Microphone

Feedback Microphone

Courses of Action


Multiple speaker with error microphone

Multiple Speaker with Error Microphone

Speakers

Noise

Engine

Exhaust

Speaker Signal

<110dB

Controller

Primary Microphone

Feedback Microphone

Courses of Action


Exhaust in speaker chamber

Exhaust in Speaker Chamber

Primary Microphone

Engine

Noise

Exhaust

<110dB

Speaker

Speaker Signal

Controller


Performance objective

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


P11227 formula exhaust acoustic tuning

Introduction / Background


Concept screening

Concept Screening


Concept screening cont d

Concept Screening (cont’d)


Proposed design objective

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


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