A Q‘ E The Engineering Society
`For Advancing Mobility
`Land Sea Air and Space® 400 COMMONWEALTH DRIVE. WARRENDALE, PA 15090-0001 U.S.A.
`
`
`
`901110
`
`The Developmentbf a Real-Time
`Evaporative Emission Test
`
`Harold M. Haskew
`
`William Fl. Cadman
`
`Thomas F. Liberty
`
`Powertrain Control Center
`
`Current Product Engineering
`General Motors Corporation
`
`Governmenfllndustry
`Meeting and Exposition
`Washington, 06
`
`s. A em
`5,. a gfifi f???
`
`/&—J/~fé
` MAHLE-1027
`‘ MAHLE-1027
`U.S. Patent No. RE38,844
`U.S. Patent No. RE38,844
`
`

`

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`ISSN0148-7191
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`

`

`901110
`
`The Development of a Real-Time
`
`Evaporative Emissions Test
`
`Harold M. Haskew, William H. Badman, Thomas F. Liberty
`
`Powertrain Control Center
`Current Product Engineering
`General Motors Corporation
`
`ABSTRACT
`
`In recent years Various parties have proposed
`new evaporative emission test procedures focused
`on controlling "excess" evaporative emissions,
`on hot "ozone prone" days. Studies by General
`Motors established the need for real-time meas-
`urements of daily emissions from parked vehicles
`and of “running losses" from vehicles that are
`driven to quantify and control
`the mobile source
`contribution to VOC inventory.
`“Resting losses"
`are shown to be a previously unidentified major
`source of hydrocarbon emissions. This paper
`describes the theories, data and development of
`GM’s Real-Time Test Procedure.
`
`WRITERS Mow Characterize the 1990's as "The
`Decade of the Environment."
`Public concern for
`the environment
`is at a new high. Many urban
`areas, for example, exceed the National Ambient
`Air Quality Standard (NAAQS) for ozone.
`The
`problem is particularly severe in California.
`Figure 1
`shows the 1988 hourly ozone measure-
`ments for four California locations.
`The hori—
`zontal
`line indicates the 0.12 part per million
`(ppm) standard that should not be exceeded more
`than once a year on average.
`As Figure 1
`indi—
`catgs, Azusa exceeded the standard 125 times in
`198 .
`
`Figure 2, on the other hand, shows the locations
`of the nine most severe ozone areas identified
`by EPA. Figure 3 shows the 1988 ozone monitor
`records for four of these cities, Chicago, New
`York, Houston, and Kenosha.
`These exceedances
`are not as chronic as the California results.
`
`Against that backdrop, additional control meas-
`ures for all organic compounds,
`including the
`
`hydrocarbons from motor vehicles, are being
`considered. The current exhaust and evaporative
`emission test procedures and standards have
`achieved significant reductions in in—use emis-
`sion levels, but they are now more than a decade
`old.
`[1]
`Combinations of higher ambient
`tem-
`peratures, high fuel volatility, extended driv-
`ing, and multiple day park episodes haVe re-
`vealed higher levels of evaporative emissions
`than were previously assumed to exist.
`
`In recent years, and particularly since 1988,
`there have been significant advances in the
`measurement and characterization of
`in-use
`evaporative emissions.
`[2]
`These advances have
`demonstrated that the current procedures and
`standard, as Well as the assumptions about
`in-
`use vehicle performanca upon which they were
`based, are obsolete. This important point
`is
`largely conceded by most participants in the
`current rulemaking process.
`A new focus on high
`temperature, "ozone-prone“ conditions for con-
`trol of evaporative emissions has resulted.
`
`in
`The Environmental Protection Agency (EPA)
`January, 1990 proposed new evaporative emission
`test procedures designed to further reduce the
`mobile source contribution to air pollution.
`Another proposal,
`the subject of this paper, has
`been developed by General Motors.
`[3] Another
`new test procedure from the California Air
`. Resources Board (CARB)
`[4]
`included many fea~
`tures of the GM Real-Time proposal.
`
`EPA’s new evaporative emission control proposal
`[5] differs substantially from the CARB and GM
`proposals.
`The EPA proposal’s most significant
`change from the current test protocol
`is the use
`of multiple diurnal heat builds (two rather than
`one) conducted at higher temperatures (72 to
`96°F instead of 60 to 84°F)
`thought
`to be
`
`1. Numbers in brackets designate references listed at the end of the paper.
`
`

`

`Figure 1.
`HOURLY AMBIENT AIR MEASUREMENT — OZONE
`CALIFORNIA LOCATIONS -— CALENDAR YEAR 1933
`
`901110
`
`azusn. CALIFORNIA
`
`
`
`I
`‘
`I:
`ilmlmuygm In
`I
`FEB l-I‘ RAH I
`AFHIL '
`
`L
`QRN "'
`
`J
`
`Mn?
`
`JUNE
`
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`I
`1|
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`LI
`
`MILInylejlulgnanaagmvunwary{mmtumletimguwamm
`
`IBEPT
`DDT m'I NOJ-l
`DE:
`I‘Jfiti
`I‘Ds
`
`PASADENA. CALIFORNIA
`
`
`
`,
`
`..
`
`LIAN
`
`..
`
`MAR
`
`FEB
`
`'
`
`LIN 5.
`[VJ‘
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`APRIL W “LnJLF_
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`AUG
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`TOTEM
`on". Jun»: '
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`
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`3 g
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`.2 .
`4
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`OAN BEHNARDIND. CALIFORNIA
`
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`L L
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`‘
`xi
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`;
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`WW‘WWWWWII“P
`JUNE
`J‘JLV
`APRIL
`"IV
`
`s
`
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`
`
`
`
`
`JAN
`FEB
`MAR.
`APRIL
`MAY
`IJUNE
`JULY
`AUG
`SEPT
`OCT
`NOV
`DEC
`
`Figure 2.
`
`NINE SEVERE OZONE AREAS
`
`Ga: vesgqn .
`
`q
`L
`
`n: AnnArea
`
`San Diana
`
`_.
`4"
`
`‘-
`
`Houston. .
`
`

`

`901110
`
`I.cuD0'-NUh
`
`Figure 3.
`
`HOURLY ANBIENT AIR MEASUREMENT — OZONE
`NON-CALIFORNIA LOCATIONS u CALENDAR YEAR 1953
`
`CHKCABU.
`
`ILLINOIS
`
` -
`
`JAN
`
`res
`
`‘
`
`'uAn
`
`APth
`
`war
`
`NLY
`
`ALIS
`
`1-;
`
`-
`I v‘ -
`SEPT
`
`-A
`OCT
`
`a
`
`.
`
`.
`M1"
`
`-
`
`. .
`
`.
`DEB
`
`
`
`
`
`HOURLYOZONE[ppm]
`
`NEH YORK. NEH YORK
`
`
`
`'
`
`LL
`FEB
`
`'
`
`.
`
`..‘ .
`
`.
`
`.'
`
`IMF!
`
`APRIL
`
`3;!
`
`JAN
`
`JULY
`
`awe
`
`'
`
`‘séPr
`
`act 7
`
`nor
`
`éaé‘
`
`HOUSTON. TEXAS
`
`
`
`'PEB -
`
`nan
`
`APRIL
`
`uAv
`
`
`
`JJNIE
`
`“AUS-
`
`SEPT
`
`OCT
`
`NOV
`
`DEC
`
`JAN
`
`FEB
`
`HIFI
`
`APRIL
`
`KAY
`
`EPA’s new
`representative of high ozone days.
`procedure relies on various design-review re-
`quirements and test procedure changes to influ-
`ence vehicle purge rates in order to regulate
`“running losses".
`It does not directly measure
`vehicle running losses.
`It also leaves the hot
`soak measurement procedure at0 the laboratory
`ambient (i. e. , 76 instead of 96° F} temperatures.
`
`includes direct measure-
`California's proposal
`ments for high-temperature hot soaks and running
`losses.
`It also measures emissions from vehi-
`cles in extended-park situations on a "real-
`time" (24 hour) basis, rather than with the
`traditional
`time-compressed diurnal
`test proce—
`dure.
`It shares many of the same features
`with the GM proposal.
`The major differences are
`the daily high temperature (lOSOF vs. 96°F),
`three diurnals vs.
`two,
`the tank fill level
`(40%
`vs. 60%), and the standard.
`
`The purpose of this paper is to describe the
`theories, data, and
`tests
`that were part of
`the development of the GM "Real-Time" Environ-
`
`mentally Based Evaporative Test Procedure.
`
`There are four parts to this paper:
`
`1.
`2.
`3-
`4.
`
`Test Procedure Goals
`Test Methodologies
`Test Parameters
`the Standard and
`The Procedure,
`Estimated Benefits
`
`TEST PROCEDURE GOALS
`
`the Real-Time test procedure
`As explained below,
`would require manufacturers to optimize vehicle
`evaporative emissions control during a very high
`percentage of hot urban driving episodes and
`during extended-park "diurnal" events.
`It would
`require stringent control of "resting losses",
`which are a large and growing segment of the
`uncontrolled in-use vehicle evaporative emis-
`sions inventory.
`As a result,
`the Real-Time
`test procedure will almost certainly involve
`increased compliance risks in the early years of
`the new program.
`
`

`

`
`
`The compliance risks of a new test procedure
`like the Real-Time procedure must be considered
`in light of the alternatives. Other test proce-
`dure proposals that presented the new under'
`gfstanding of "excess“ evaporative emissions have
`"differed from the Real-Time procedure in that
`they did not
`include direct measurement of
`either running losses or resting losses. Direct
`measurement, however, will be critical
`in ensur-
`
`.
`ing that “excess" evaporative control
`systems
`
`' perform effectively in actual use.
`
`
`‘If direct measurement procedures are inevitable,
`it is more effective to spend the resources to
`
`meet new test procedure requirements once,
`rather than to have multiple waves of new re-
`
`-
`quirements for evaporative control over the next
`
`- decade.
`Lower exhaust emission requirements,
`cold tests for CO, higher fuel economy, and the
`censumer's demand for quality and reliability
`
`'5 among other demands all require the designer’s
`'full attention. There is no shortage of chal-
`
`~‘.lenges for the automotive manufacturer
`in the
`1990‘s.
`
`The most effective techniques for the control of
`» “eXcess"‘eVaporative emissions invalves redueing
`;
`the Quantity of vapors generated, as well as
`, containing them.
`“7.
`.1.
`
`I'Thermalgmanagement (less heating) of the fuel
`system is the most effective way to reduce vapor
`generation. Unfortunately,
`the fuel
`tank and
`- assotiated pipes compete for space and function
`with many other underbody components.
`The size
`ofla fuel
`tank is a compromise of many factors,
`'including trunk space,
`room for suspension
`.~c0mponents, and the consumer’s desire for vehi-
`' cle range (i.e.,
`tank capacity) between refuel-
`ings.
`Changes in any one component affect many
`others.
`Even minor changes can cause tooling
`and validation costs to multiply quickly.
`It is
`best
`to fix this once.
`The Real-Time test
`‘procedure provides a framework for achieving the
`- maXimum available reductions in excess evapora-
`tiVe emissions, while maintaining the manufac—
`turer’s ability to use unique,
`innovative and
`costeeffective product designs.
`
`the purpose and goals of the Real-
`'In’summary,
`Time test procedure are driven by the following
`[logic;i~
`
`
`'
`
`the air quality goals of the
`Until
`70’s are met, government will continue
`”to create regulations to force mobile
`source emissions to approach zero.
`
`
`
`
`
`Regulatory agencies may not have the
`best understanding of how to fix the
`”.problem, but they will try.
`
`the level of control de-
`‘w~fCGiven that
`'
`sired is highly stringent, it is in
`the best interest of the vehicle
`manufacturer to participate in the
`
`
`
`901110
`
`rule-making and help create comprehen-
`sive and realistic test procedures
`that provide the maximum reductions in
`real—world Emissions.
`
`therefore is to create a test procedure
`The goal
`that achieves the maximum available reductions
`without unnecessarily limiting the use of inno-
`vative and cost-effective product designs.
`
`TEST HETHODOLOGIES
`
`The Real-Time evaporative emissions test proce-
`dure integrates a series of vehicle precondi—
`tioning and measurement events with the current
`exhaust emission test.
`The purpose of the Real-
`Time evaporative test is to quantify the fuel
`vapor emissions released by the vehicle as it
`experiences a variety of conditions occurring
`during hot weather in an urban area.
`
`EVAPORATIVE EMISSIONS DEFINITIONS - There are
`four broad categories of evaporative emissions
`that occur from well—maintained (non-tampered)
`vehicles.
`These are:
`
`Running losses
`Hot Soak losses
`Diurnal
`losses and,
`Resting Losses
`
`"Running losses" are the fuel vapors that escape
`the system during operation of the vehicle,
`i.e., when the engine is running.
`These losses
`occur when the rate of fuel vapor formation
`exoeeds the capacity of the vapor storage and
`purge systems.
`
`-“Hot soak" emissions are those fuel vapors that
`escape immediately after the vehicle has been
`operated, produced by residual pressure and heat
`input
`into the fuel system. Hot soak emissions
`occur within one hour or
`less from vehicle
`shutdown.
`
`losses" are the fuel vapors that escape
`"Diurnal
`from a parked vehicle as a result of the daily
`ambient
`temperature heating.
`This heating
`produces vaporization of the fuel
`liquid and
`expansion and expulsion of the vapor stored in
`the fuel
`tank.
`
`"Resting losses" are the emissions that escape
`from the fuel system or the evaporative control
`system as a result of permeation throuqh various
`non-metallic fuel system sources, or as a result
`of vapor migration allowed by other system
`design features such as open-bottom canisters.
`Resting lOSses can be affected by ambient
`tem-
`perature changes
`, but
`they are relatively
`constant,
`in comparison with other types of
`vapor loss.
`
`The Real-Time evaporative test procedure has
`three separate evaporative emisSion measure-
`ments. These are:
`
`

`

`901110
`
`5
`
`An example of the temperature and pressure
`measurements for a late model GM Passenger car
`is shown in Figure 4.
`
`Running Loss Measurement Techhigues - Two meth-
`ods can be used to collect the running loss
`emissions,
`the enclosed dynamometer and the
`point source collectors.
`
`The enclosed dynamometer method involves sur-
`rounding the test cell with an air-tight enclo-
`sure, and measuring the increase in hydrocarbon
`(HC) concentration in the enclosure as the
`vehicle is driven.
`The basic measurement
`tech-
`niques were first outlined by EPA’s test engi-
`neering group over 15 years ago.
`[6]
`The calcu-
`lations to convert internal HC concentrations to
`grams are similar to the current Part 86 method-
`ology for evaporative emissions as measured in
`an enclosure.
`
`Figure 5.
`
`Eunoseo Dnuuunsnsn CELL
`
`1’31 Cm. first human:
`
`A
`
`Figure 5 shows the general arrangement for the
`enclosed dynamometer method.
`Intake air for the
`engine is supplied through a duct from outside
`the cell, and the vehicle’s exhaust
`is also
`routed to the outside.
`Care must be taken to
`insure that there are no leaks or mixing of the
`exhaust with the trapped air in the enclosure.
`Heat exchangers with active controllers are
`required to maintain the ambient
`temperature at
`the desired set-point. % large internal volume,
`on the order of 6000 ft , can help to provide
`the internal
`thermal control necessary.
`The
`approximate internal dimensions of such an
`enclosed cell might be 18 feet wide by 34 feet
`‘ long by 10 feet high.
`
`A second method for measuring running losses is
`the point source collection method.
`The point
`source collection method involves placing vapor
`collectors at each of the vehicle system’s
`designed vapor vents,and at any other suspected
`sources of measurable vapor losses during vehi-
`cle operation. Vapor collected by the equipment
`is transported to a critical
`flow venturi
`(CFV)
`or positive displacement pump (PUP) based dilu-
`tion and measurement system, as is currently
`Jsed to measure exhaust emissions.
`
`1).
`
`A direct measurement procedure for
`running losses
`
`2).
`
`A hot soak measurement period, and
`
`3).
`
`An extended vehicle park episode to
`measure diurnal and resting losses.
`
`THE RUNNING LOSS MEASUREMENT - Vehicle running
`loss measurements are made using a chassis
`dynamometer in a test cell which is maintained
`at an ambient temperature of 96°F.
`
`Airflow in the test cell, and particularly under
`the vehicle in the area of the fuel
`tank,
`is
`managed in order to match tank temperature and
`headspace pressure measurements
`taken from
`similar vehicles that had been operated on a
`road.
`The road test vehicle is driven for three
`LA—4s at an ambient temperature in the 87 to
`100°F.
`range and corrected to an equivalent
`96°F.
`temperature profile.
`
`Road Temperature Measurements - As part of the
`Real-Time evaporative emission test procedure.
`the tank temperature profile is established by
`the vehicle manufacturer as part of the vehicle
`certification process. Representative combina-
`tions of powertrains and vehicle body styles are
`instrumented and tank temperatures measured
`during on-road operation. Additional details
`concerning road temperature measurements is
`contained in Appendix A.
`
`Figure 4.
`
`FUEL TEMPERATURE and PRESSURE MEASUREMENTS
`DURING DN-RDAD OPERATION
`LATE MODEL 5H PASSENGER CAR
`3 Liv-4'. “T“ I!“ ”alums: an
`E Di: l’ ”HIM TWINE
`
`140
`
`,...
`5-.
`Lu sea
`[I
`
`3 Ea
`
`: :10
`E
`“2"
`'— aoo
`
`13D
`
`
`a
`in s
`5
`5 ‘6.”
`amIn
`a 5
`
`:0
`
`so
`
`no
`
`0
`
`ram: Paessune —-—>
`
`so
`
`an
`
`so
`
`an
`
`so
`
`so
`
`imDhl
`SPEED
`
`TIME IN MINUTES
`
`

`

`.
`CAN'ISTER
`
`VAPDR
`rune
`
`COLLECTOR
`
`EVAPORATIVE
`
`CANISTER
`
`
`
`HEATED
`
`
`
`PUMP
`
`
`
`
`
`fig—HEATED
`
`/
`PUMP
`FRDH omen
`VENTS (IF ANY)
`
`sxucnne
`
`moi
`
`
`
`man-m1 AIR
`INLET
`
`,
`
`/-
`
`
`arrangement for the
`Figure: 6=1shows the generai
`
`point source collection technique.
`The coiiec-
`tion system consists of a coliector at each
`
`vehic'le vapor vent, 1engths 01° heated sampie
`
`line (175-2000F.) connecting each coiiector to
`
`the him of a heated samp‘le pump (40 scfh), and
`
`1engths of heated sampie 1ines connecting the
`
`outiet of the samp'le pump(s)
`to the bulk stream
`
`'Of'thfi‘ CFV 0‘" PUP vapor measuring system.
`
`
`
`901110
`
`The sampie pump(s) draw a flow of ambient air
`through the coiiector(s).
`The inlet to the
`co'liector(s) are placed in proximity to the
`vehicie’s fuei
`system vapor vent and configured
`to capture any fuel vapor emissions without
`imposing any significant flow or pressure impact
`on the normal action of the vent.
`
`For vapor vents that terminate in a tube or hose
`
`
`
`
`BILUTIDN AIR
`
`Tu
`omen» FILTER
`
`AMBIENT MG FILL
`30K
`
`Figure 6.
`
`IJILUTIUN AIR
`
`
`
`fEATED LINE
`
`
`LEAK TIGHT _/
`\ FUEL w ENCLUSURE
`
`' SEAL /
`
`
`
`
`
`
`
`
`
`
`
`FUEL TANK FILL PIPE
`
`MIXING DEVICE
`
`CLAMP
`
`TD FUEL TANK
`
`FUEL CkP
`
`
`
`POINT SOURCE COLLECTION
`
`SCHEMATIC:
`
`
`
`

`

`Figure 7.
`
`ONE HOUR HUT SDAK AFTER EXTENDED DRIVING
`22.5 III—ES AT 95 It: F
`
`("—‘ SHED TEMPERATURE
`
`10
`
`SHED CONCENTRATION --~—>
`
`ED
`
`5SHEDflDM
`
`901110
`
`such as the evaporative control canister,
`barb,
`a short length of tubing is used to extend the
`vent
`into the mouth of the collector (basically
`a "funnel").
`The dimensions of the collector
`are chosen to ensure that any vapors that might
`appear are directed into the collection system,
`but that no significant depression is imposed
`upon the vent.
`
`The fuel cap vapor vent collector consists of a
`boot that surrounds the cap and allows ambient
`air to be drawn through the boot volume.
`Fuel
`cap safety pressure relief is typically set at
`the 55 in. H20 (2.0 psi) level. Vehicle systems
`calibrated to comply with the new regulations
`should never vent
`the cap during these tests.
`Other vapor vents,
`if any, are fitted with
`similar and appropriate collectors.
`
`TEMPERflTUHE-F
`
`HOT SDAK - Within five minutes after the comple-
`tion of the running loss test (more than an hour
`of vehicle aperation),
`the Vehicle is placed
`into a SHED
`for a one hour hot soak.
`To be
`consistent with the high temperature ozone
`focused conditions,
`the SHED ambient temperature
`is maintained between 90‘1000F. after the vehi-
`cles is initially put
`in the SHED. This meas-
`urement is more stringent than the current FTP,
`insofar as it follows extended driving (22.5
`instead of 11.1 miles) and occurs at higher
`ambient temperatures (SO-IUDOF).
`
`Figure 7 shows the test results from a vehicle
`placed in a conventional SHED for one hour
`following the running loss test.
`The SHED,
`which is located in a laboratory with an ambient
`temperature of 76°F., was operated with the
`cooling system turned off. Putting the hot
`vehicle into the SHED rapidly increases the
`enclosure temperature within five minutes,
`to
`levels that are appropriate (90 to 100°F.) for
`the hot soak measurement.
`
`Figure 7 also indicates that a one hour period
`is an appropriate measurement
`interval for a hot
`soak.
`The rapid increase in the SHED concentra-
`tion occurs within 20 minutes from the start of
`the test. After this initial
`increase,
`the SHED
`concentration continues to increase at a steady
`but much slower rate. This constant rate of
`evaporative emissions is characteristic of
`“resting losses“, which will be discussed in
`more detail
`in the following section.
`
`MULTIPLE DAY PARK — The final step in the Real-
`Time procedure is a multiple day park.
`The
`vehicle is placed into a Variable Temperature
`SHED (VT-SHED) for two days.
`The ambient
`tem-
`perature inside of the VT-SHED is cycled from a
`
`o
`
`an
`
`so
`20
`TIME IN MI NUTES
`
`so
`
`so
`
`so
`
`low of 72 0F. to a high of 96 or. over a 9 hour
`period, and from 96 0F. back to 72 0F. over a 15
`hour period.
`The temperature profile is based
`on real hourly temperature data, as will be
`discussed in-a later section.
`
`temperature cycling inside of the
`The ambient
`VT-SHED results in large volume changes that the
`conventional SHED is not capable of handling.
`A
`perfect gas law calculation shows that a 72 to
`96°F.
`temperature change results in a 4.5%
`volume change at constant pressure.
`For a
`normal 1600 cubic foot SHED that represents a
`change of 72 cubic feet. Daily changes in the
`barometric pressure would also compound the
`volume changes due to the temperature cycling.
`There are various solutions that can be imple—
`mented to handle the volume changes,
`three of
`which will be briefly discussed.
`
`shown in Figure 8, has a
`One type of a VT—SHED,
`movable roof allowing for large changes in SHED
`volume. The VT-SHED roof is adjusted up or down
`such that a delta pressure of zero is maintained
`between the inside and outside of the SHED.
`The
`SHED is also well
`insulated to reduce heat
`‘ losses during high temperature operation.
`This
`type of facility was used in the work previously
`published by GM.
`[2]
`
`A second technique is a retrofit package that
`could be applied to existing SHEDs.
`The package
`
`2. The current §ealed Housing for Evaporative Determination (SHED) test
`methodology was derived from a SAE procedure, Jllla, "Measurement of
`Fuel Evaporative Emissions from Gasoline Powered Cars and Light Trucks
`Using the Enclosure Technique", and replaced the previous carbon trap
`measurement method.
`
`

`

`
`
`
`
`"§§"‘ VARIABLE TEMPERATURE SHED
`
`GMR/PROVING GROUND
`‘
`
`u
`nufiig
`
`Figure 8.
`
`901110
`
`
`
`
`
`
`
`
`
`-”mm,...
`wan—mama“,,1. a;
`
`
`
`
`
`
`
`
`its
`
`s
`a
`w
`,3,
`
`
`The Variabie Temoerature SHED is unique in that it aiiows “reei-time" measurements of
`evaporative emissions over a broad range of temperatures and time and 18 fully
`automated. Constructed under the guidance of C. Gus Mitsopouios, R951dent Manager and
`Norman u. Laursen, Staff Research Engineer.
`
`
`
`
`

`

`901110
`
`would include two large low—permeation plastic
`bags mounted to the existing enclosure, one on
`the inside and the other on the outside.
`The
`inside bag would account for decreasing volumes
`and the outside bag for increasing volumes. At
`the start of the test the two bags would be
`pOSitioned to a known reference volume.
`The two
`day test ends at the same ambient temperature at
`which it started, so that the only change in
`SHED volume would be due to barometric pressure.
`The ideal gas law could be used to calculate the
`volume change due to the change in the baromet-
`ric pressure.
`The retrofit package would also
`include a heating and cooling package plus
`insulation for the outside of the SHED walls.
`
`A third technique is described as a Hybrid SHED.
`The Hybrid SHED is a fixed volume enclosure that
`is maintained at a slightly negative pressure.
`
`The SHED is maintained at a negative pressure
`using a CVS pump that fills a sample bag.
`Fresh
`air enters the SHED through a controlled pres-
`sure regulator.
`The final mass
`includes the
`enclosure grams and also the amount removed into
`the sample bags.
`
`The Two—Day Test - The vehicle is placed into
`the VT-SHED during the cooling portion of the
`ambient temperature cycle. This allows the fuel
`temperature to assume its natural relationship
`with the ambient temperature prior to the start
`of the heating cycle.
`An example of a two day
`park in a VT-SHED is shown in Figure 9.
`The
`ambient SHED temperature at
`to corresponds to
`midnight on the hourly temperature profile.
`This allows approximately 5—6 hours of cooling
`prior to the start of the ambient
`temperature
`heating period.
`
`The emission measurement period is the second 24
`hours of the test (t43 — t2 ).
`Included is this
`measurement are 24 hours oi resting losses and
`the 2nd days diurnal.
`An indication of the
`magnitude of resting losses is the increase in
`the SHED concentration during the portion of the
`test when the fuel
`temperature is decreasing.
`During this portion of the test there should be
`no out-gassing of vapor from the fuel
`tank.
`Losses measured during this period should con—
`sist only of permeation losses and vapor migra-
`tion, plus non-fuel background emissions.
`
`Over long periods of time, such as 48 hours,
`SHED retention is a concern.
`Loss of gases from
`the VT—SHED must be minimized, and if necessary,
`accounted for in the emission measurement calcu-
`_lation.
`The previous figure'(Figure 9),
`showed
`‘the SHED grams in terms of "corrected" SHED
`grams.
`The correction factor applied to the
`data was D.4%/hour, based on actual
`retention
`tests.
`An appropriate correction factor for
`individual VT-SHEDs can be established using
`propane injection techniques similar to the
`current SHED retention test).
`
`Figure 9.
`A THO DAY PARKED CAR EXPERIENCE
`
`£20
`
`SOD
`
`mD
`
`TEMPERATURE-F OIa
`
`40
`
`D
`
`2‘
`12
`TIME IN HOURS
`
`m CORRECTED
`
`SHEDGRAN
`
`35
`
`45
`
`TEST PARAMETERS
`
`The Real-Time evaporative emission test proce—
`dure outlined above requires direct measurement
`of running losses, hot soaks and extended park
`episodes.
`In addition to requiring new test
`methodologies,
`the Real-Time test procedure
`involves new test parameters.
`Six parameters
`.are discussed in this part of the paper:
`
`1. The length of the extended park episode
`2. Daily high temperature
`3. Daily temperature profile
`4. Representative tank fill level
`5.
`Fuel RVP, and
`6. Trip length
`
`- The
`The 24—Hour Extended Park Measurement
`intent of the Real-Time test is to simulate the
`€in-use
`conditions of public concern and thereby
`require control of the emissions that contribute
`to the real—world inventory.
`The Real—Time
`measurement procedure accordingly requires
`measurement of emissions during the last 24
`hours of a 48 hour park. During both time peri-
`ods,
`the ambient
`temperature is cycled over the
`high-temperature profile described in later
`sections. First, however it is important
`to
`discuss the need for a 24 hour measurement
`interval. Shorter compressed-time measurement
`periods have a number of shortcomings compared
`to a Real-Time test.
`A few of those shortcom-
`ings are discussed below.
`
`

`

`
`
`in-
`:EmisSiOns’that are measured during a test
`tended to simulate the multiple day park must
`include both diurnal emiSSions —
`those that
`
`occur during the portion of the day when the
`.
`
`‘Tfuelntemperature is increasing, and resting
`
`losses (which occur 24 hours a day).
`The magni—
`tude of the resting losses can be quantified
`
`during the fourteen hour fuel cooling periods of
`
`” the Realnlime test.
`
`_Resting losses can be a large contributor to
`
`inventory, but are difficult to detect
`in short
`jincrements of time.
`The point is illustrated in
`.;_
`
`:~ yFigure 10.
`Two vehicles, one with an open
`
`4*
`bottom canister,
`the other with a closed bottom
`
`canister, were subjected to a traditional one
`hour forced blanket diurnal
`fuel heating from 70
`
`gto 91 0F and then sat in the SHED for an addi-
`
`tional 9 hours. These tests were d0ne in a
`
`contentional SHED at a constant ambient
`tempera-
`
`ture'of 76 oF.
`The two vehicles had similar
`
`“-emiSSions at the end of 1 hour, as shown in
`
`Figure‘lO.‘ As Figure 10 also shows, however, at
`the end of the 10 hour period,
`the vehicle with
`
`the open bottom canister had 4.5 times higher
`emissions than the vehicle with a closed bottom
`'canister.
`
`
`
`Figure 10.
`
`iifiiURNAL AND RESTING LDSS MEASUREMENTS
`CONVENTIONAL SHED AT CONSTANT'AHBIENT TEHPEHATUHE
`1 HOUR DIUHNAL 70-95 F - FflLLflHED BY A 9 HOUR SOAK
`
`.35 o/nr ---—>
`
`ASHEDGRAMS
`
`DFEN BOTTOM CANISTER
`
`“o
`k
`
`s
`
`2
`
`a
`
`e
`5
`4
`TIME IN HOURS
`
`7
`
`a
`
`a
`
`in
`
`The same open bottom canister vehicle was sub-
`jected to a real-time three day test and the
`results are shown in Figure 11.
`(In this par-
`ticular test the VT-SHED ambient temperature was
`cycled from 66 to 95 0F.)
`The open—bottom
`
`‘-canister’s inherent ability to purge itself is
`
`, evidenced by the traces on Figure 11 showing
`
`canister weight and SHED grams.
`The SHED grams
`
`
`
`901110
`
`Figure 11.
`A THREE DAY PARKED CAR EXPERIENCE
`DPEN BOTTOM CANISTEH - 9 RVP FUEL
`1953 DLDEHDBILE REGENCY 95
`
`AMBIENT TEIP
`
`<_____
`
`EANIH'ER HEIEHT HERE‘S!
`
`SHED Ennis
`----r
`
`
`
`
`
`CORRECTEDSHEETGRAHS
`
`120
`
`TEMPERATURE-F m0
`
`p.O
`
`ED
`
`0
`
`12
`
`<—-—- on 1
`
`E¢
`
`35
`TIME IN! HOURS
`---><---- on e
`----><--- on a
`
`AB
`
`50
`
`72
`
`---->
`
`continue to increase at a substantial rate even
`during the non-fuel heating periods.
`Figure 11
`indicates that
`the canister begins losing
`weight, clearly shown at
`the 36th hour of the
`test, when it is not only failing to contain the
`incoming vapors, but
`is also loosing some of the
`vapors previously adsorbed.
`
`Open bottom canisters are not the only source of
`resting losses. Rubber hoses, non-metallic fuel
`lines, and non-metallic fuel
`tanks, all have the
`potential of releasing significant resting
`losses.
`The real-time diurnal would identify
`these sources and prevent
`them from being a
`major source to inventory.
`In addition, materi-
`als or components whose resting losses are a
`function of temperature would also be accounted
`for by using a real-time temperature cycle.
`
`Another very important phenomenon that occurs
`naturally in real-time in the real world is
`backpurge.
`Backpurge,
`its occurrence and the
`effect on canister capacity, has been discussed
`in detail.
`[2] The-occurrence of backpurge and
`its effect on canister capacity are clearly
`demonstrated in Figure 12.
`A vehicle was parked
`in a VT SHED for eight days with the ambient
`temperature cycled from 72 to 96 0F.
`As
`the
`canister became more loaded,
`the backpurge
`effect was much more pronounced.
`The backpurge
`effort was evidenced by the decreasing canister
`weight and only a slight increase in the SHED
`grams, during the period of time when the fuel
`is cooling.
`
`The eight day park data is also summarized in
`
`

`

`901110
`
`11
`
`Figure 12.
`
`AN EIGHT DAY PARKED CAR EXPERIENCE
`9 Fill? FUEL - do! TANK FILL
`1985 DLDSHDBILE REGENCY QB
`
`METER HEIGHT INCREASE
`
`HEIGHT'aroma
`CDHREGTEDSHEDandDELTACANISTEH
`
`
`
`A final point to be made favoring real-time
`measurements concerns the time-rate of hydrocar-
`bons delivered to the canister during diurnal
`heating.
`If duplicating the quantity of vapor
`generated from a real-time diurnal was the only
`concern,
`then a time compressed diurnal could
`accomplish that. However,
`the real-world mecha-
`nisms are much more complex.
`
`Compressed diurnal heating periods increase the
`amounts of vapors per unit time that the canis-
`ter must contain. Directionally,
`this leads to
`reduced canister capacities due to the increased
`canister bed temperatures.
`
`Vapor migration within the canister happens in
`real-time, another factor not comprehended in a
`compressed time test. Both of these factors may
`be important is terms of future canister designs
`that are more efficient for controlling real-
`world emissions.
`
`the advantages of a real-time
`To summarize,
`diurnal outweigh the shorter time compressed
`tests when the real goal
`is to simulate and
`control real-world emissions. Use of time-
`
`TEMPER‘TURE-F
`
`O
`
`24
`
`4B
`
`72
`
`120
`95
`TIME IN HOURS
`
`144
`
`155
`
`192
`
`The lower
`shoWn in Figure 13.
`the bar chart
`portion of Figure 13 shows the resting-loss data
`for the Vehicle, which ranged from .06 to .09
`grams per hour.
`The upper portion of the graph
`shows incremental SHED grams measured during the
`fuel