TM
Guide to Generator Set Exhaust Systems
Information Sheet # 16
Your Reliable Guide for Power Solutions
1.0 Introduction
A system designer must consider environmental and performance criteria when sizing and positioning the exhaust system of a generator
set. Correct installation of the exhaust is also crucial to ensuring full performance of the engine.
This info sheet is a guide and discusses the issues to be addressed when installing a generator set’s exhaust system.
2.0 Key purpose of the exhaust system:
All engine systems have exhaust systems to facilitate:
Safe evacuations of gases - Exhaust gases for safety and environmental concerns should be safely vented to atmosphere for both
inside and external locations.
Sound attenuation - Various muffler grades are available to meet different acoustic requirements.
Engine performance - Incorrect exhaust sizing can result in degraded engine performance.
3.0 Safe evacuation of exhaust gases:
When designing a system the following should be noted:
• To prevent re-circulation of gases into other areas outlets should be located upwind and away from any building and equipment
air intakes. Engine exhaust can also be a fire hazard and must never be exhausted adjacent to any combustible material.
• Pipe sleeve or fire proof materials are used when exhaust pipes pass through building material.
• Local codes should be consulted by the designer. (See diagram one for details)
4.0 Sound attenuation:
When designing a system the following should be noted:
• Consult local codes for sound level limitations. Generator set manufacturers offer four types of silencers, industrial, residential,
critical and hospital for very noise sensitive locations.
• Consult the attenuation curves given for a silencer to ensure it is within code. (Continued over)
Air inlet away from exhaust
See inset
5
Flexible sections (Bellows)
6
1
2
3
Inside
generator set
installation
1.
2.
3.
4.
5.
6.
Exhaust thimble (see diagram 1)
Muffler - Available in 4 grades
Water trap with drain
Flexible bellows
Brackets to support weight
of exhaust system
Black iron exhaust pipe
4
Exhaust layout
details
Diagram three - Typical Exhaust System Layout
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Power Systems, Inc. team maintains up-to-date technology and information standards on Power Industry changes, regulations
and trends. As a service, our Information Sheets are circulated on a regular basis, to existing and potential Power Customers
to maintain awareness of changes and developments in engineering standards, electrical codes, and technology impacting the
Power Generation Industry.
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Diagram one - Exhaust Pipe Thimble Installation
Diagram two - Exhaust System Calculations
Drip cap
10000
9000
8000
7000
6000
Rain cap
Corporate Office
P.O. Box 581807
Tulsa, OK 74158-1807
800.324.0066
Tulsa
9310 East 46th Street North
Tulsa, OK 74117
918.836.0068
Flashing
Roof
Little Rock
6800 Intersate 30
Little Rock, AR 72209
501.907.5884
Kansas City
211 E Marley Rd
Kansas City, KS 66115
913.312.2031
St. Louis
53 Millwell Court
Maryland Heights, MO 63043
314.739.8700
Austin
4918 Burleson Road
Austin, TX 78744
512.477.6937
Dallas/Ft. Worth
2916 National Drive
Garland, TX 75041
972.265.0768
101 Industrial Boulevard
Mansfield, TX 76063
817.640.5544
Longview
1913 East US Hwy 80
White Oak, TX 75693
903.291.8305
San Antonio
5803 Rocky Point
San Antonio, TX 78249
210.333.0377
Exhaust thimble is
required when exhaust
pipe passes through
combustible material
Outside or dividing wall
Horizontal vertical wall installation
1.0
4
0.5
5
1.0
0.5
6
0.01
2500
Exhaust Pipe Diameter
plus 12”
9” Minimum
7
0.005
2000
Exhausting through roof installation
Oklahoma City
7300 Melrose Lane
Oklahoma City, OK 73127
405.949.2332
P( in Hg per ft)
5000
5000
4500
4000
3500
3000
Holes in end of
inner sleeve
9” Minimum
3
D (in)
Q (cfm or ft³/min)
8
0.001
1500
0.0005
1000
900
800
0.0001
9
10
P(psi) =
0.00005
L x SL x Q²
13
0.00001
5
5,184 x D
Where:
39.6
S (lb/ft³) =
P = Backpressure in psi
Exhaust Temperature + 460°F
psi = 0.4912 x in Hg
For each 90˚ bend calculate as:
L = Length of pipe in ft
Q = Exhaust gas flow ft³/min
L (ft) = 15 x D
D = Inside diameter of pipe inches
L (in) + 15 x D
S = Specific weight of gas lb/ft³
12
5.0 Engine performance:
The manufacturer can detail the maximum allowable back pressure or restriction with the system. It is specified as
“inches hg”. When the back pressure is exceeded, the air-fuel ratio is reduced which results in a drop in fuel economy
and power output. The following should be undertaken:
• The designer, having the manufacture’s data for gas flow (ft³/min) and maximum back pressure, uses a chart (see
diagram two for details) to determine the inside diameter of the pipe.
• The exhaust system should be designed as short as possible with a minimum of bends. A 90° pipe bend increases
the length of the system and back pressure. (see diagram two)
6.0 Exhaust system criteria:
The designer of the system should also consider the exhaust factors in the design:
Water in the system - Water can be a by-product of exhaust and enter the system as rain. To prevent water from draining
back into the system, slant the horizontal pipe away from the engine and install a water trap at the lowest point. (see
diagram three for details) A rain cap should be fitted on exhaust pipes ending in the vertical position.
Flexible exhaust sections - To prevent damage due to vibration and thermal expansion, flexible bellow type sections
should be installed. Do not use bellows for required bends and alignment adjustment.
Soot deposits - For environmental and aesthetic reasons consider placement of the exhaust outlet to avoid exhaust gas
deposits accumulating on adjacent structures/buildings.
Exhaust structure - The exhaust system weight should be adequately supported and utilize robust material such as
Schedule 40 black iron. The systems can be supported by various means but must remain flexible and the weight should
never be carried by the engine manifold and/or turbo-charger. Galvanized piping should never be used in an exhaust
system. (see diagram three for details)
Wind effect - Consider the prevailing wind at the required locations and position the exhaust outlet to avoid exhaust
gases being returned into the generator set installation or entering other structures.
7.0 CODES:
National Protection Association Code Numbers 99 and 100 are important codes that cover generator exhaust systems.
The designer should also consult all applicable local codes.
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CPS-INFO#16©2011 PLC Enterprises, LLC