Meeting Purpose: Review and discuss all work to this point by P11227. Clearly define the problem, show steps taken to understand it, and propose possible solutions to the problem. Main goal of this meeting is to more clearly target and identify the scope of this project.
Materials to Be Reviewed:
· Customer Needs
· Engineering Specs
· Risks Assessment
· Concept Screening Matrices
Meeting Date: Monday, January 17, 2011
Meeting Location: 09-4435
Meeting time: 11AM-12PM
Timeline:
Meeting Timeline /Start time / Topic of Review / Required Attendees /
11:00 / Team Introduction
11:02 / Problem Statement / Dr. Nye, Taylor Hattori, Prof Hanzlik, P11221 Members
11:15 / Sound Physics / Dr. Nye, Taylor Hattori, Prof Hanzlik, P11221 Members
11:25 / Internal Combustion Engine and Noise Generation Sources / Dr. Nye, Taylor Hattori, Prof Hanzlik, P11221 Members
11:30 / Concepts / Dr. Nye, Taylor Hattori, Prof Hanzlik, P11221 Members
11:40 / Propose Test Bench Idea / Dr. Nye, Taylor Hattori, Prof Hanzlik, P11221 Members
11:45 / Questions/Discussion / Dr. Nye, Taylor Hattori, Prof Hanzlik, P11221 Members
Project # / Project Name / Project Track / Project Family
P11227 / Exhaust Acoustic Tuning / N/A / FSAE Autosports
Start Term / Team Guide / Project Sponsor / Doc. Revision
2010-2 / Prof Slack / KGCOE MSD
KGCOE MSD Page 2 of 7 Technical Review Agenda
Project Description
Project Background:
While the RIT FSAE auto sports team has a heritage of being a top competitor at competitions both domestically and internationally, they are consistently penalized at competition for exceeding the maximum allowable exhaust noise. FSAE regulations state that any car that does not pass the sound regulations will not be allowed to participate in the competition until it is modified to pass. To continue being competitive and eliminate the possibility of being excluded from races, the competition vehicle’s exhaust must be re-tuned to reduce engine noise without sacrificing performance.
Problem Statement:
Currently the FSAE team’s vehicle exceeds the exhaust noise limit dictated by FSAE rules. This noise must be reduced through exhaust tuning to maintain vehicle performance while adhering to FSAE rules and guidelines.
Objectives/Scope:
1. Reduce vehicle exhaust noise to under the 110dB limit set by FSAE
2. Maintain or improve the performance of the FSAE vehicle in race conditions
Deliverables:
· Functional device that can be used by FSAE to reduce engine noise and maintain performance
· Instructions and support in installation and maintenance of new system
· Documentation demonstrating project research, development and results for use by the Formula Team.
Expected Project Benefits:
· Project’s Benefits will include bringing the FSAE team within regulation of engine noise restrictions as well as assist the RIT FSAE team in winning races.
Core Team Members:
· Kyle Desrosiers- Team Lead, ME
· Brad Fiedler- EE
· Chris VanWagenen- EE
· Greg Wodzicki- EE
Strategy & Approach
Assumptions & Constraints:
1. Any technology used must maintain or improve performance of FSAE vehicle engine
2. Added weight adversely effects performance and should be minimized.
3. Proposed solutions will be subject to vigorous heat, gas and vibration relative to race environments.
Issues & Risks:
· Lack of execution in industry points to possibility of final product’s results not being within design specs and not practical.
· Test data formulated on Lawnmower engine may not be applicable to Formula team’s vehicle
· Formula Team may not allow final build to be applied to vehicle
· Lawnmower engine failure could result in long delay into taking and testing results
· Filter Design and Closed Loop Process Controls in team is weak and may require outside consultation
· Lack of firmly defined budget leaves design scope in limbo and flexible designs must be used.
· Lack of team understanding of acoustics poses domain knowledge risks that must be overcome.
KGCOE MSD Page 2 of 7 Technical Review Agenda
FSAE Rules for Exhaust System
ARTICLE 10: EXHAUST SYSTEM AND NOISE CONTROL
B10.1 Exhaust System General
B10.1.1 Exhaust Outlet
The exhaust must be routed so that the driver is not subjected to fumes at any speed considering the draft of the car.
B10.1.2
The exhaust outlet(s) must not extend more than 45 cm (17.7 inches) behind the centerline of the rear axle, and shall be no more than 60 cm (23.6 inches) above the ground.
B10.1.3
Any exhaust components (headers, mufflers, etc.) that protrude from the side of the body in front of the main roll hoop must be shielded to prevent contact by persons approaching the car or a driver exiting the car.
B10.2 Noise Measuring Procedure
B10.2.1 The sound level will be measured during a static test. Measurements will be made with a free-field microphone placed free from obstructions at the exhaust outlet level, 0.5 m (19.68 inches) from the end of the exhaust outlet, at an angle of forty-five degrees (45°) with the outlet in the horizontal plane. The test will be run with the gearbox in neutral at the engine speed defined below. Where more than one exhaust outlet is present, the test will be repeated for each exhaust and the highest reading will be used.
B10.2.2 The car must be compliant at all engine speeds up to the test speed defined below.
B10.2.3 If the exhaust has any form of movable tuning or throttling device or system, it must be compliant with the device or system in all positions. The position of the device must be visible to the officials for the noise test and must be manually operable by the officials during the noise test.
B10.2.4 Test Speeds
The test speed for a given engine will be the engine speed that corresponds to an average piston speed of 914.4 m/min (3,000 ft/min) for automotive or motorcycle engines, and 731.5 m/min (2,400 ft/min) for “industrial engines”. The calculated speed will be rounded to the nearest 500 rpm. The test speeds for typical engines will be published by the organizers. An “industrial engine” is defined as an engine which, according to the manufacturers’ specifications and without the required restrictor, is not capable of producing more than 5 hp per 100cc. To have an engine classified as “an industrial engine”, approval must be obtained from organizers prior to the Competition.
B10.3 Maximum Sound Level
The maximum permitted sound level is 110 dBA, fast weighting.
B10.4 Noise Level Re-testing
At the option of the officials, noise can be measured at any time during the competition. If a car fails the noise test, it will be withheld from the competition until it has been modified and re-passes the noise test.
Figure 1: Sound Physics
Figure 1a: Longitudinal Waves in Air (Sound Waves)
Source: passmyexams.co.uk
Sound, as perceived by the human ear, consists of pressure waves traveling through air. As the wave travels, it compresses and then expands the air around it, creating a vibration. Normal human hearing is in the range of 20-20,000Hz.
Figure 1b: Illustration of Different Frequencies
Source: Wikipedia
A shorter wavelength equates to a higher frequency. Sound waves, while easy to understand in a one-dimensional sense as above, travel in three dimensions as a plane wave. This makes the wave more complicated to model, especially when confined to a finite space such as an exhaust pipe or muffler. Higher frequency waves also tend to be even more complicated, as they often reflect and amplify or cancel each other much more than low frequency waves.
The amplitude of the wave, in this case, is measured with a pressure meter. This device measures in dBA, or A-weighted decibels. A decibel (dB) is the common unit of measurement for sound pressure levels; a 3dB increase/decrease is barely noticeable to human hearing, while a 10dB increase/decrease is heard to be twice/half the intensity respectively. The A-weighting is a compensation used to make up for the fact that humans do not hear all frequencies at equal loudness; this curve favors higher frequencies, which humans tend to hear at a lower loudness than low frequencies.
To cancel out a sound wave or lower its intensity, an identical wave with opposite phase must be created. This can be done by reflecting the original sound wave in such a way as to cause a 180 degree phase shift, or by generating a new wave using a speaker or similar apparatus with a 180 degree phase shift from the original.
Figure 2: Four Cycle IC Engine
The four stages of a Four Cycle Engine
Figure 1: Intake Stroke Figure 2: Compression Stroke Figure 3: Power Stroke Figure 4: Exhaust Stroke
Intake Stroke: Intake Valve opens just prior to Top Dead Center (TDC). As the piston goes down into the cylinder, it draws in the air/fuel mixture into the cylinder.
Compression Stroke: Intake Valve closes and piston travels back up, compressing the air/fuel mixture (high pressure, temperature).
Power Stroke: Spark ignites the air/fuel mixture. Increased pressure forces the piston down, turning the crank shaft.
Exhaust Stroke: As the piston approaches Bottom Dead Center Exhaust valve opens and piston begins back up the cylinder forcing exhaust gases from combustion out.
Sound Sources from IC Engines
Engine “chatter”:
This source accounts for all of the moving parts of the engine. Valves opening and closing, crank shafts rotating, cam lobes hitting valve stems, etc all generate sound.
Intake:
As the intake valve opens, air (and fuel) from the intake manifold passes through to the relatively low pressure in the cylinder. This pressure difference causes pressure waves, making sound.
Exhaust:
As with the intake, when the exhaust valve opens there is a pressure differential between the conditions inside the cylinder and the other side of the exhaust valve (the exhaust manifold or headers). High pressure in the cylinder travels to the low pressure outside of the cylinder and sound waves propagate.
Main Sound Source:
Since the pressure differential is significantly higher in the case of the exhaust, it generates significantly more sound than the intake valve occurrence. Also, compared to the exhaust sound, general engine chatter is negligible. This can be verified by observing the sound wave recorded and comparing to the firing frequency of the engine. Each peak of the sound wave is directly correlated to the firing frequency and its harmonics (multiples of the main frequency).
Firing Frequency of an ICE:
For every two engine revolutions, each cylinder of the engine fires one time (completes a power stroke). As such, the firing frequency can be defined as:
Figure 3: Spectrum Analysis of Lawnmower Engine
KGCOE MSD Page 2 of 7 Technical Review Agenda