MC-76-09
Standards Development and Technical Support Report
Motorcycle Tailpipe Dilution CVS Study
October 1976
Notice
Technical support reports for regulatory action do not necessarily
represent the final EPA decision on regulatory issues. They are intended
to present a technical analysis of an issue and conclusions and/or
recommendations resulting from the assumptions and constraints of that
'analysis. Agency policy constraints or data received subsequent to
the date of release of this report may alter the conclusions reached.
Readers are cautioned to seek the latest analysis from EPA before
using the information contained herein.
Standards Development and Support Branch
Emission Control Technology Division
Office of Mobile Source Air Pollution Control
Office of Air and Waste Management
U.S. Environmental Protection Agency
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Abstract
The motorcycle exhaust dilution system has been evaluated for water
condensation and its ability to maintain static pressure variations within
+ 0.25 kPa as measured at the tailpipe of a test vehicle. After multiple
runs over the Urban Dynamometer Driving Schedule with a large displacement
motorcycle, virtually no water condensation was observed in the system
and the static pressure variations ranged from -0.14 to -0.13 kPa.
Prepared by
Project Manager
Motorcycle Regulations
Branch Chief,
Standards Development and
Support Branch
vision Director,
Lssion Control
Technology Division
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Introduction
In the process of diluting motorcycle exhaust prior to entry into the
Constant Volume Sampler (CVS), two requirements must be met as described
in §86.509 (b) and (c) of the motorcycle regulations: 1) static pressure
variations at the tailpipe of a vehicle tested by EPA must be capable of
remaining within +0.25 kPa of the static pressure variations measured
during a dynamometer driving cycle with no connection to the tailpipe,
and 2) the location of the dilution air inlet shall be placed and the
flow capacity of the CVS shall be large enough to virtually eliminate
water condensation in the .system. A new exhaust dilution system has
recently been designed and built for use in motorcycle testing at EPA.
Prior to being put into use, it was necessary to determine if the new
system was capable of meeting the above requirements. The purpose of
this report is to describe the findings of that study.
Summary and Conclusions
—Static pressure variations at the tailpipe of the test vehicle remain
within -0.14 and -0.13 kPa of the static pressure variations at the
tailpipe during the urban driving schedule. This is well within the
closest tolerance specified in the motorcycle regulations.
—Virtually no water condensation was observed in the exhaust dilution
system after multiple testing of a large motorcycle over the Urban
Dynamometer Driving Schedule.
Discussion
The objective of this study was to evaluate the exhaust dilution
system presently used in the motorcycle test cell. This evaluation
stemmed from two requirements as specified in the motorcycle regulations
regarding the dilution system.
A) Sections 86.509(b)(1) and (c)(1) state that the static pressure
variations at the tailpipe of the vehicle tested by EPA must be
capable of remaining within + 0.25 kPa of the static pressure
variations measured during a dynamometer driving cycle with no
connection to the tailpipe.
B) Sections 86.509(b)(4) and C(4) state that the location of the
dilution air inlet shall be placed and the flow capacity of the CVS
shall be large enough to virtually eliminate water condensation in
the system.
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A. j>tatic Pressure Variation
The static pressure variations were evaluated using a 15 cm. long
stainless steel tube connected directly to the test vehicle's tailpipe.
The test vehicle was a two-stroke, three cylinder, Suzuki GT-750 displacing
738cc.
Both the positive displacement pump constant volume sampler (PDP-
CVS) and the critical flow venturi constant volume sampler (CFV-CVS)
were used. The exhaust dilution system is depicted in Figure 1.
MOTORCYCLE
EXHAUST
FILTERS INLETS
PRESSURE
TRANSDUCER
DILUTION
BOX
CVS
Figure 1 - Exhaust Dilution System
The static pressure at the tailpipe of the test vehicle with no
connection (other than the short measurement tube) ranged from 0.00 kPa
at idle to a maximum of +0.02 kPa during high RPM acceleration. Initially
during this evaluation the static pressure at idle was about -0.29 kPa
which is outside of the desired minimum static pressure of -0.25 kPa.
After modifying the flow path in the dilution box, with the tailpipe
connected to the dilution system and the CVS pump turned on, the static
pressure ranged from -0.14 kPa at idle to -0.11 kPa during high RPM
acceleration. Therefore, the difference in static pressure variations
ranged from -0.14 to -0.13 kPa which is well within the + 0.25 kPa
tolerance that EPA must be capable of maintaining. This is summarized
in the following table.
Difference in static pressure (in kPa) between operation
with and without exhaust system connections
PDP-CVS
CFV-CVS
Necessary
capability
of EPA
± 0.25
+ 0.25
At Idle
with re-
stricted
flow path
- 0.29
- 0.29
During Driving
schedule after
modifying flow
path
- 0.14 to - 0.13
- 0.14 to - 0.13
Without motorcycle
connected and
after modifying
flow path
- 0.14
- 0.14
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This table also includes a static pressure reading with the CVS pump
operating and with the motorcycle tailpipe connection point blocked.
This was done because the static pressures in the system were below
atmospheric and by introducing exhaust volume into the system, this
acted to reduce this difference. This procedure was necessary to
simulate a small displacement motorcycle, with a very low exhaust volume
flow rate. Even under such conditions the exhaust dilution system is
within the desired static pressure tolerance.
B. Water Condensation
Using the test vehicle, five sequential urban driving schedules
were performed. Though water condensation was observed in the tailpipe
connectors, virtually no condensation was observed in the exhaust
dilution system or in the cyclonic separator of the CFV-CVS.
Recommendation
When an exhaust dilution system is designed for use in motorcycle
testing, it is recommended that the design consider both the potential
for water to condense in the system and flow restrictions which could
significantly reduce the static pressure as measured at a test vehicle's
tailpipe.
After installation of a new dilution system,pressure tests should
be performed to assure compliance with the requirements specified in
§86.509 of the motorcycle regulations.
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