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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. 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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  1. P11227- Formula Exhaust Acoustic Tuning Brad Fiedler Chris VanWagenen Greg Wodzicki Kyle Desrosiers Design Review – Week 5

  2. Agenda • Introduction / Background • Problem Statement • Customer Needs • Engineering Specs • Understanding the Problem and Current Technology • Concept Review • Test Bench • Closing • Questions

  3. 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

  4. 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

  5. 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

  6. 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

  7. Customer needs

  8. Engineering specs

  9. 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)

  10. 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

  11. 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

  12. Baffle Muffler • Reflects Exhaust Throughout Chamber • Reflections Cancel each other • Most Back Pressure created • Greatest Sound Reduction Noise Engine Baffle Muffler Exhaust Concepts

  13. 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

  14. 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

  15. Parallel ANC with Microphone and Feedback Speaker Noise Engine Exhaust Speaker Signal <110dB Controller Primary Microphone Feedback Microphone Courses of Action

  16. Multiple Speaker with Error Microphone Speakers Noise Engine Exhaust Speaker Signal <110dB Controller Primary Microphone Feedback Microphone Courses of Action

  17. Exhaust in Speaker Chamber Primary Microphone Engine Noise Exhaust <110dB Speaker Speaker Signal Controller

  18. 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

  19. Introduction / Background

  20. Concept Screening

  21. Concept Screening (cont’d)

  22. 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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