Project #
Project Name
Project Track
Project Family
11221
Noise Reduction for Internal
Combustion Engine
Vehicle Systems and
Technologies
N/A
Start Term
Team Guide
Project Sponsor
Doc. Revision
2010-1
Ed Hanzlik
Dr. Alan Nye
A
Project Description
Project Background:
Expected Project Benefits:
The auto industry is currently increasing the focus on
the reduction of noise emitted from a car’s engine. For
consumer vehicles it is largely an issue of comfort and
convenience but for performance competitions with
noise restrictions and requirements, such as the SAE
Formula competition, it can be an issue of meeting
competition requirements while limiting performance
inhabitance. The focus of this project is to develop an
active, passive, or hybrid mechanical and/or electrical
noise attenuating system with minimal engine
performance degradation.


Problem Statement:
Most noise attenuating devices for internal combustion
engines can severely hamper engine performance.
Conventional mufflers and resonators must be tuned to
specific engine conditions that do not efficiently dampen
or inhibit sounds from the full range of engine loads and
conditions. An effective noise reduction system with
low performance impact that is cost effective and can
reduce sound generated from the full spectrum of
engine conditions is desired.
Objectives/Scope:
1.
2.
3.
4.
5.
6.
7.
Investigate the physics of sound generation and
transmission.
Identify and locate the major noise contributors in
an internal combustion engine.
Analyze and model the noise generation of an
internal combustion engine.
Propose design for noise reduction mechanism.
Provide sufficient background to Electrical
Engineering team for potential active noise
cancellation system.
Produce a simple engine test stand for proof of
concept.
Develop Mechanical systems for noise reduction.
Deliverables:





Model engine noise (frequencies & amplitudes vs
RPM) in order to deliver data to the Electrical
Engineering Team.
Develop a list of constraints that the Electrical
Engineering team will need to follow
Develop and build a prototype noise reduction
mechanical systems
Develop and build test stand with running engine
Demonstrate application of noise reduction
systems at Imagine RIT 2011

Demonstrate feasibility of noise reduction methods
Develop correlation between demonstrator and
future application to larger (SAE Formula)
engines.
Better understanding of active noise systems as
they apply to Internal Combustion Engines for
future projects.
Core Team Members:




Christopher Morehouse – Project Leader
Julie Maier – Edge Manager/Mechanical Engineer
Caroline Bills – Lead Engineer
Ted Zachwieja – Mech. Engineer
Strategy & Approach
Assumptions & Constraints:
1.
2.
3.
4.
We shall assume that all other sources of engine
noise are negligible with respect to those emitted
from the exhaust stream.
The project will be focused on application to a 5.5
Hp single cylinder 4-stroke engine.
Any designs will be constrained by their effect on
engine performance, most critically back pressure
in the exhaust stream.
System must be practical and affordable with
respect to component cost, operational life,
manufacturing processes etc.
Issues & Risks:




Experience, accuracy of model

No supporting work from past teams.

Insufficient experience in this field may delay
progress.

No experience in gathering or analyzing this
type of data
System Survivability

Survive high temperatures

Survive corrosive gases
Engine performance inhibited

System may cause higher than expected
back pressure

System may have as yet unconsidered
performance effect
System Doesn’t Work

For unanticipated reasons we do not inhibit
the noise of the engine
Senior Design Project 11221 Week 9 Design Review
Friday November 5th, 2010
Room 78-2150
12:30-2:30 pm
Presentation Agenda:
Team Introduction
Presentation Overview
Project Scope Overview
-Engine Focus Changes
-System Constraints Changes
-Project Goals & Deliverables
Customers & Users
-Customer Needs
-Engineering Specs
Project Flow Chart
Project Plan
-Gantt Chart
-Time line by week
-Major Goals/Dates
Engine Test Data
Design Concepts
Engine Test Setup
Metal Foam Absorption Muffler
Variable Geometry Resonators
Fixed Geometry Resonator
Active Noise Cancelation System
Imagine RIT Demo Setup
Expected Outcomes – Near Future Plans
Questions and Discussion
Engine Test Stand
Briggs & Stratton 5.5Hp 1-Cylinder 4-Stroke Engine
Stock Muffler is a simple Absorption type muffler.
Mount
Engine
Cart
Exhaust
Engine Load
The Engine is mounted on a steel frame rolling cart with the crank shaft pointing down.
A 1” ID exhaust pipe will be mounted to the engine with a simple flange to facilitate easy
installation and removal of the different muffler systems. A load mechanism will be
applied to the crank shaft to facilitate predictable engine operation.
Metal Foam Absorption Muffler
The principles behind an Absorption Muffler are simple. As sound waves pass through the
absorption muffler they come into contact with the absorption material. While passing through
the absorption material the noise is damped as the material, typically fiberglass, absorbs some of
the acoustical energy and transfers it to heat.
http://static.howstuffworks.com/gif/muffler-glasspack.jpg
For maximum noise abatement the sound waves must be kept in the absorption material for as
long as possible. This is achieved in several ways, the most prominent being the thickness of the
material and geometry of the muffler. The contact area between the exhaust stream and
absorption material should be maximized, but its effects on exhaust flow must be considered.
Figure 1-3: Metal Foam Insert concepts
The design concepts we considered are represented in the above figures.
Resonators Basic Overview:
The main concept is to cancel sound waves through reflection. The sound travels into the
chamber and is reflected back onto itself, thus cancelling or reducing the sound level.
There are two main types of resonators: single pass and multi-pass, which are depicted
below. Absorption material can be added around the pipe to increase the sound reduced.
The geometry of the resonator is optimized to cancel out specific wavelengths and thus a
passive resonating muffler must be designed with specific frequencies in mind. The
concept of a variable geometry resonator to cover a spectrum of wavelengths will be
discussed at our design review.
Absorption Material
would be in this area
Figure
Figure
1:4:
Single-pass
Single-pass
Resonator
Resonator
(with
(with
optional
optional
absorption
absorption
material)
material)
Exhaust Gas
Flow
Inner Pipe
Holes in pipe
Resonating
Chamber
Figure 5: Mutli-pass Resonator
(with optional absorption material)
Source: Fundamentals of Motor Vehicle Technology
By: Victor Hillier & Peter Coombes
Unfortunately for reflective resonators such as these the ideal length of the resonating
chamber is ½ or ¼ wavelength. This present a problem when applying to our new
Engine Focus, as a 1 cylinder engine produces lower frequencies than a 4 cylinder engine
which results in longer wavelengths. For these types of resonators to be effective the
resonating chamber would need to vary from approximately 2.5-5 meters.
A volume based or Helmholtz resonator is more practical at lower frequencies. A
Helmholtz resonator uses an off branch expansion chamber to create tones. It is driven
by the pressure wave which passes the branch off, or neck, of the resonator and acts on
the volume of gas in the chamber which responds similar to a classic mass-spring-damper
system. The tone generated by the Helmholtz resonator is dependent on the frequency of
the pressure wave and the geometry of the resonator.
Figure 6: Helmholtz Resonator
𝑐
𝐴
𝐹 = 2𝜋 ∗ √(𝐿+.8∗√𝐴)∗𝑉 - Helmholtz resonator frequency with
c=Wave Speed
A=Neck Area
L=Neck Length
V=Chamber Volume
Active Noise Control Basic Overview:
Active noise cancellation is the generation of a sound wave that is exactly 180
degrees out of phase of the noise that is being cancelled. The fact that active noise
cancellation occurs in real time makes it desirable as well as difficult. Methods of real
time noise cancellation have are a fairly technology mainly due to the increase of
processing powers that digital signal processors are now capable of. This method of
sound reduction is demonstrated below:
Simply sinusoidal sound wave
Sum of two waves slightly out of phase
out of phase
Sum of 2 waves that are 180 degrees
ANC has two basic types of control that can be drive the system. One way is the
Feed Forward control system and the other is the Feedback system.
Feed Forward requires measuring the incoming disturbance. This method is ideal
for periodic noise and is generally utilized with a digital filter to a control source. A
basic diagram is shown below in Figure 3.
Feedback control system requires no knowledge of the incoming disturbance
noise. When applying this method feedback control requires changing the systems
resonance, frequency, and dampening. Feedback systems require high gains in the
feedback loop, this can cause instability. Feedback systems are primarily used when
incoming noise cannot be collected using sensors. A diagram of a basic feedback control
system is shown in figure 4.
There are two methods of applying ANC to the muffler of the SAE formula car. One
method would be placing speakers inside the muffler to actively cancel the sound before
it leaves the pipe. Another method would be to place speakers that are parallel to the
muffler and direct the sound generation in the same direction as the muffler to actively
cancel sound in a 3D motion.
Figure 3: Feed Forward Control
Figure 4: Feedback Control
Active Noise Control Layout
Figure 5: Proposed ANC Layout
This is the proposed design for the Active Noise Control system. As you can see
the large cube represents the engine with an exhaust extension added. The exhaust
extension and speaker pipe are both routed into a steel box and are parallel to each other.
The speaker pipe is shown in the figure above. The proposed layout is a setup for a
Feedback control system where the sensor would be located inside the steel box with both
the exhaust and speaker pipe outlets. The speaker box itself is not shown in Figure 5 but
will be placed next to the engine system and has no loose restraints on size since the
transformation of our project scope.