Evaporative Emission Control Technologies
`for Gasoline Powered Vehicles
`
`December 2010
`
`Manufacturers of Emission Controls Association
`2020 N. 14th St. * Suite 220 * Arlington, VA 22201
`www.meca.org
`www.dieselretrofit.org
`
`BASF-1020
`U.S. Patent No. RE38,844
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`

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`TABLE OF CONTENTS
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`Executive Summary ........................................................................................................................ 1
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`1.0 Introduction ............................................................................................................................... 3
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`2.0 Current Evaporative Emissions Regulations in the U.S. .......................................................... 5
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`2.1 ARB’s Proposed LEV III Evaporative Emissions Requirements ................................. 7
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`2.2 Test Methods for Measuring Evaporative Emissions ................................................... 9
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`3.0 Technologies to Control Evaporative Emissions .................................................................... 10
` 3.1 Permeation Controls.................................................................................................... 11
` 3.2 Carbon Canisters ......................................................................................................... 12
` 3.3 Activated Carbon ........................................................................................................ 14
` 3.4 Air Intake Systems (AIS) ............................................................................................ 16
` 3.5 On-Board Refueling Vapor Recovery ........................................................................ 17
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`4.0 On-Board Diagnostic Requirements ....................................................................................... 18
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`5.0 Conclusions ............................................................................................................................. 18
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`6.0 References ............................................................................................................................... 18
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`LIST OF FIGURES
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`Figure 1: Emissions Contributions for PZEV and LEV II Vehicles ............................................... 5
`Figure 2. CARB LEV II and PZEV Evaporative Requirements ................................................... 7
`Figure 3. Test set-up for a bleed emissions or mini-rig test .......................................................... 10
`Figure 4. Fuel system with emission control technology ............................................................. 11
`Figure 5. Examples of evaporative carbon canisters .................................................................... 12
`Figure 6. Inside of EVAP canister ................................................................................................ 13
`Figure 7. Canister bleed emissions with and without a scrubber .................................................. 14
`Figure 8. Pore size depiction in activated carbon particle ........................................................... 15
`Figure 9. Examples of extruded carbon honeycombs .................................................................. 16
`Figure 10. Examples of carbon AIS systems ............................................................................... 16
`Figure 11. Examples of carbon AIS systems ............................................................................... 17
`Figure 12. Air Induction System performance on 4 and 8 cyl. engine ........................................ 17
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`LIST OF TABLES
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`Table I: CARB LEV II Evaporative Emission Standards .......................................................... 6
`Table II: U.S. EPA Tier II Evaporative Emission Standards ....................................................... 6
`Table III: Option 1 of ARB’s Proposed LEV III Evaporative Standards ..................................... 8
`Table IV: Option 2 of ARB’s Proposed LEV III Evaporative Standards ...................................... 8
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`Executive Summary
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`Evaporative emission control technology was the first to be used on passenger vehicles as
`a way to control smog forming hydrocarbons in the early 1960’s. Evaporative emissions from
`motor vehicles constitute about half of the reactive organic gas (ROG) inventory in California 1
`and nearly 40% in the Northeastern United States. Ozone is considered to be a respiratory
`irritant harmful to humans and plants and is regulated by the U.S. EPA which sets a National
`Ambient Air Quality Standard (NAAQS) for ozone concentration. Areas that are out of
`attainment or experience concentrations above this ozone concentration, like California, regulate
`evaporative emissions to reduce ground-level ozone. In addition to the negative health effects of
`ground level ozone, it is also a greenhouse gas.
`
`Evaporative emissions are broken down into five primary sources; diurnal, running loss,
`hot soak, permeation and refueling. The magnitude of the relative components depends greatly
`on the engine design, fuel delivery and application. A brief description of the major types of
`evaporative emissions is given below.
`
`Diurnal emissions result from the evaporation of gasoline due to temperature fluctuation
`during the day and night.
`
`Running loss emissions represent gasoline that is vaporized from the engine and fuel
`system while in operation.
`
`Hot Soak emissions occur during the first hour that the vehicle is parked after normal
`operation.
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`Permeation occurs continuously once the polymer components of the fuel system become
`saturated with fuel.
`
`Refueling emissions occur as gasoline is pumped into the tank displacing the gasoline
`rich vapor.
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`
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`The function of the automobile evaporative emission control system is to block or
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`capture the above sources of vaporized hydrocarbons and prevent their release into the
`atmosphere. There are varying levels of complexity and efficacy of these controls with the most
`advanced systems equipped on partial zero emission vehicles being certified to California’s
`PZEV standard under the state’s LEV II emission standards.
`
`
`Companies that manufacture evaporative emission controls have responded to the
`challenge of reducing VOC emissions from gasoline powered vehicles. Through their efforts, a
`wide range of cost-effective technologies have been developed to block HC emissions via the
`above mechanisms. Manufacturers of Emission Controls Association (MECA) member
`companies, together with engine manufacturers, have worked together to meet California’s
`PZEV requirements on over 50 light-duty vehicles and employed evaporative canisters on
`motorcycles and marine engines.
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`Interest in evaporative emissions control has grown considerably in recent years around
`the world. MECA is engaged with California on their LEV III regulation that proposes to extend
`the most advanced evaporative controls across the entire on-road, light and medium-duty vehicle
`fleet. This document has been prepared to supplement information already made available by
`MECA on emission control technologies and provides an overview of the types of technologies
`being developed for new gasoline fueled cars and trucks.
`
`Today’s cleanest gasoline vehicles, certified to California’s PZEV emission limits require
`near zero evaporative emissions and include additional technologies such as canister scrubbers to
`virtually eliminate bleed emissions from the carbon canisters during periods of low purge. Some
`vehicles also incorporate carbon based air-intake HC traps to prevent engine breathing losses
`from escaping through the intake manifold and air induction system (AIS) after the engine is shut
`off.
`
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`Today, viable emission control technologies exist to reduce fuel system based HC
`evaporative emissions from all types of spark-ignited engines including small handheld
`equipment up to large spark-ignited (LSI) vehicles. Applications include marine and recreational
`off-road vehicles. The major technologies that control permeation emissions include:
`
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`• Fuel tanks made of low permeation polymers
`• Multilayer co-extruded hoses
`• Low permeation seals and gaskets
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`Technologies designed to control diurnal, hot soak and refueling HC emissions include:
`
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`• Advanced carbon canisters
`• High working capacity activated carbon
`• Honeycomb carbons scrubbers
`• Air induction system (AIS) HC traps
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`The most stringent evaporative emission control regulations are enforced in the United
`States. Vehicles certified to California’s PZEV low emission vehicle standards must
`demonstrate near zero evaporative emissions from the fuel system at 0.054 g/test using a rig test
`of a vehicle’s fuel system. The California Air Resources Board (CARB) is proposing to extend
`these requirements across the entire light-duty and medium-duty passenger vehicle fleet
`(<14,000 lbs GVWR) by 2022 as part of their LEV III regulations.
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`Demands on vehicle manufacturers to achieve higher fuel efficiency through the use of
`smaller displacement, boosted engines and hybrid electric powertrains will create challenging
`operating conditions for evaporative emission control technologies. The lower purge volumes
`that result from smaller displacement engines or hybrid systems under partial or full electric
`drive will require the development of specialty carbon adsorbents and advanced canister designs
`to achieve the lowest evaporative emissions demanded by future regulations. Gasoline vehicles
`in other parts of the world and SI off-road equipment everywhere can benefit from much of the
`same technologies applied to passenger vehicles in the U.S. This paper will describe the types of
`technologies that are being used to meet the current and future evaporative emission regulations.
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`1.0 Introduction
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`Evaporative emissions from gasoline powered vehicles consist of volatile organic
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`compounds (VOCs), or hydrocarbons, released from the fuel system, rubber and other plastic
`components of the vehicle, such as tires, plastic interior and exterior trim, carpeting etc. This
`paper will focus on the hydrocarbon vapors emitted from the fuel system as these represent the
`major sources of evaporative emissions from mobile vehicles and equipment. This paper will
`further focus on fuel-related evaporative emissions from light-duty vehicles. Some of the same
`types of technologies that are discussed here for passenger cars have been successfully applied to
`other spark-ignited off-road vehicles and equipment and will not be covered here. A more
`detailed discussion of regulations and evaporative control technologies in these applications can
`be found in MECA’s white papers specific to those applications available at www.meca.org.
`
`Evaporative emissions from motor vehicles constitute about half of the reactive organic
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`gas (ROG) inventory in California 1 and nearly 40% in the Northeastern United States.
`Evaporative emissions depend on ambient temperatures and the vapor pressure of the fuel
`supply. VOCs and other hydrocarbons (HC), such as those emitted from the tailpipe of motor
`vehicles, react with NOx in the presence of sunlight to form photochemical smog which is the
`primary component of ground level ozone. Ozone is considered to be a respiratory irritant
`harmful to humans and plants and is regulated by the U.S. EPA which sets a National Ambient
`Air Quality Standard (NAAQS) for ozone concentration. Areas that are out of attainment or
`experience concentrations above this ozone concentration, like California, regulate evaporative
`emissions to reduce ground-level ozone. In addition to the negative health effects of ground
`level ozone, it is also a greenhouse gas.
`
`
`Evaporative emissions are broken down into five primary sources; diurnal, running loss,
`hot soak, permeation and refueling. The magnitude of the relative components depends greatly
`on the engine design, fuel delivery and application.
`
`Diurnal emissions result from evaporation of gasoline due to temperature fluctuation
`during the day and night. As the fuel tank warms during the day or while parked in the sun,
`expansion of the gasoline vapor above the liquid is vented from the tank. During the night, as
`the tank cools, fresh air is pulled into the tank to mix with the gasoline vapors to start the process
`again the next day.
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`Gasoline vapors coming from the engine and fuel system while in operation are known as
`running losses. The primary source of running loss emissions in earlier passenger cars was from
`the carburetor. Modern vehicles may emit small amounts of emissions from the fuel cap and
`vapor canister. Most of these HCs end up being captured by the evaporative emission control
`system and routed back through the intake of the engine to be consumed during combustion.
`
`Emissions attributed to the hot soak occur during the first hour that the vehicle is parked
`after normal operation. During this time, the engine remains hot and, without convective
`cooling, continues to heat the fuel system. This source is primarily attributed to carbureted
`vehicles and equipment. In modern vehicles equipped with fuel injectors and carbon canisters,
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`the hot soak vapors would be captured and stored until the next time the engine is running. At
`this time they would be purged into the intake air of the engine and combusted.
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`Permeation of gasoline molecules can occur during normal operation or extended periods
`of parking a vehicle. This is caused by the saturation of the plastic and rubber components of the
`fuel system such as plastic fuel tanks and rubber hoses and results in relatively constant
`permeation through these components. Significant advances in polymer chemistry and laminated
`forming techniques have significantly reduced permeation as a source of emissions in modern
`vehicles.
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`Refueling emissions can occur as gasoline is pumped into the tank displacing the gasoline
`rich vapor causing it to be emitted into the atmosphere. In modern passenger vehicles, these
`vapors are stored in the EVAP canister and purged into the intake air of the engine to be
`combusted.
`
`
`The function of the automobile evaporative emission control system is to block or capture
`the above sources of vaporized hydrocarbons and prevent their release into the atmosphere.
`There are varying levels of complexity and efficacy of these controls with the most advanced
`systems equipped on partial zero emission vehicles (PZEV) being certified to California’s
`tightest evaporative standard under the state’s LEV II and future LEV III emission standards.
`
`Evaporative emission controls were the first type of emission control system on
`automobiles and is often the least expensive approach to controlling VOC and HC emissions
`from gasoline powered engines. In the 1960s positive crankcase ventilation systems were
`introduced to capture crankcase vapors and prevent them from being vented to the atmosphere.
`The technology has advanced to include carbon canisters, low permeation hoses, active purge
`systems and on-board vehicle refueling (ORVR) controls. Eventually on-board diagnostic
`sensors were integrated to insure proper functioning of the entire fuel evaporative control system.
`Hot soak emissions were a problem in carbureted engines releasing gasoline vapors from the fuel
`bowl as the temperature in the engine compartment increased after shut down. Initially air filter
`assemblies were used to capture these emissions and later carbon canisters were connected with a
`hose to the fuel bowl. The introduction of fuel injection greatly reduced evaporative emissions
`due to hot soak and running loss as they isolated the fuel from the atmosphere at all time except
`for refueling. On-board refueling vapor recovery (ORVR) systems have been required on all
`passenger vehicles in the U.S. since 2000 and capture vapors emitted from the tank during
`refueling in the carbon canister and later emit them into the combustion chamber during canister
`purging.
`
`Today’s cleanest gasoline vehicles, certified to California’s PZEV emission limits require
`near zero evaporative emissions and include additional technologies such as canister scrubbers to
`virtually eliminate bleed emissions from the carbon canisters during periods of low purge. Some
`vehicles also incorporate carbon based air-intake HC traps to prevent engine breathing losses
`from escaping through the intake manifold and air induction system (AIS) after the engine is shut
`off. Figure 1 shows the benefit that advanced evaporative controls can have on the relative
`amounts of evaporative emissions contributed from different parts of a vehicle. The bar chart
`quantifies the mass of evaporative emissions that contribute to the SHED test measurement for a
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`typical LEV II and PZEV certified vehicle. The background emissions represent the non-fuel
`related evaporative emissions from carpets, rubber and plastic parts. The emissions that are
`readily impacted by advanced evaporative control technology are those emitted by the air
`induction system (AIS) and fuel system. Carbon AIS traps can reduce emissions by 0.10 to 0.15
`g/test and incorporating canisters with auxiliary scrubbers onto a LEV II vehicle reduces tank
`venting emissions by as much as 0.1 g/test. The advanced emission control technologies used on
`PZEV vehicles are very effective and leave background emissions as the major contributor
`(65%) to the total evaporative emissions.
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`Figure 1: Relative contribution to full vehicle emissions from different sources for PZEV
`and LEVII certified vehicles.
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`After a brief review of the evaporative emission regulations in the United States, this
`paper will describe the specific evaporative control system technologies in greater detail.
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`2.0 Current Evaporative Emission Regulations in the U.S.
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`California has enforced evaporative emissions on light-duty vehicles since 1970. The
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`current requirements under CARB’s low emission vehicle program were fully implemented in
`2006 for the entire fleet. The evaporative emission standards are shown below for the three-day
`diurnal-plus-hot soak test and the two-day diurnal-plus-hot-soak test. The standards are
`expressed in total vehicle HC evaporative emissions and include both fuel and non-fuel vehicle
`emissions. The three-day diurnal test insures that running loss emissions, high temperature hot
`soak and diurnal emissions are controlled whereas the two-day diurnal test verifies that the
`canister is well purged during vehicle operation. For 2001 and newer vehicles, additional testing
`of the ORVR system is required to insure that refueling emissions do not exceed 0.2 g/gal. of
`fuel dispensed. The standards apply to gasoline-fueled, liquefied-petroleum-gas-fueled, and
`alcohol-fueled passenger cars, light-duty trucks, medium-duty vehicles, and heavy-duty vehicles.
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`Included in these requirements are flexible-fuel vehicles, dual-fuel vehicles, hybrid-electric
`vehicles, and zero-emission vehicles with fuel fired heaters. Table I shows the evaporative
`emission limits for the current California LEV II standards.
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`Table I: CARB LEV II Evaporative Emission Standards
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`The standards were also adopted by U.S. EPA as part of their Tier II light-duty vehicle
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`standards with a different phase-in period. Both agencies introduced the standards in 2004 with
`requirements for 40% of the fleet in California and 25% federally. California completed the
`phase in by 2006 with full harmonization by both agencies in 2009 for evaporative emissions.
`The fleet average evaporative limits for EPA’s Tier II standards are shown in Table II. The
`evaporative emission control system standards include a useful-life requirement of 15 years or
`150,000 miles, whichever comes first.
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`Table II: Evaporative Emission Limits under EPA’s Tier II Standards
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`Federal
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`Vehicle Type Model Year
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`LDV/LLDTs
`HLDTs
`MDPVs
`LDV
`LLDT
`HLDT
`MDPV
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`2004
`2004
`2004
`2009
`2009
`2010
`2010
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`3 day Diurnal + Hot
`Soak
`(g/test)
`0.95
`1.20
`1.40
`0.50
`0.65
`0.90
`1.00
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`Supplemental
`2 day Diurnal + Hot
`Soak
`(g/test)
`1.20
`1.50
`1.75
`0.65
`0.85
`1.15
`1.25
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`Running
`Loss
`(g/mi)
`0.05
`0.05
`0.05
`0.05
`0.05
`0.05
`0.05
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`California allows manufacturers to certify to their zero-fuel evaporative standards as a
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`way to generate credits toward meeting the states zero-emission vehicle (ZEV) requirements.
`The PZEV requirements are compared to the LEV II limits for passenger cars and light-duty
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`trucks in Figure 2. In addition to tighter limits for the diurnal tests, manufacturers must also
`meet a near zero (0.054 g/test) limit for the fuel system using a rig test. The EVAP test
`procedures will be described in greater detail in Section 2.1.
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`Figure 2: CARB LEVII and PZEV Evaporative Requirements
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`Meeting the PZEV limits requires the use of advanced fuel and evaporative control
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`systems that are capable of essentially eliminating fuel-related evaporative emissions. These
`advanced technologies include a pressurized and sealed fuel system such as an insulated, bladder
`fuel tank, larger chambered carbon canister equipped with a bleed emissions scrubber and an
`AIS carbon filter. A more detailed description of LEVII and PZEV technologies will be
`provided in Section 3.0.
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`2.1 ARB’s Proposed Evaporative Emission Requirements for LEV III
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`ARB is in the final stages of finalizing their evaporative emission requirements as part of
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`their LEV III proposal that will be presented to the Board in April of 2011. ARB is proposing to
`extend “zero” evaporative emission technology to all light-duty and medium-duty vehicles.
`Phase-in of these proposed vehicle evaporative emission requirements would begin
`with model year 2018 and be complete by model year 2022. The phase-in would require that
`60% of the fleet is in compliance in the 2018-19 time frame ramping up to 80% compliance by
`2020 to 2021 and full coverage of the fleet by 2022. To certify to the new standards ARB is also
`proposing to require the use of an E10 certification fuel starting with the 2014 model
`year for new vehicles. Because all gasoline fuel in California contains 10% ethanol, this will
`bring certification data more in-line with real world emissions. All certifications would need to
`use the E10 fuel starting in model year 2018.
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`Vehicle manufacturers would have two options for evaporative emissions compliance.
`The first option is to comply with the current “zero” evaporative, whole vehicle standard that
`varies with vehicle weight and use the current complete fuel system rig test to confirm that the
`fuel system has no more than 0.054 g/test of evaporative emissions.
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`Table III: Option 1 of ARB’s Proposed LEV III Evaporative Standards
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`The second option allows manufacturers to comply with a lower whole vehicle emissions
`standard and use a new bleed emissions test protocol to confirm that the carbon canister bleed
`emissions are less than or equal to 0.02 g/test for all light-duty vehicle classes and less than or
`equal to 0.03 g/test for medium-duty and heavy-duty vehicle classes (Table 4). Within this
`second option, manufacturers would be allowed to comply with a fleet average whole vehicle
`standard within each weight class. Manufacturers will be required to report the highest value of
`the 3-Day Diurnal and 2-Day Diurnal plus hot soak for a given certification test vehicle. The
`test procedures for the fuel system rig test and bleed emissions test will be described in Section
`2.2. Evaporative emission system certification for hybrid electric vehicles will have specific test
`procedures as these vehicles can have low canister purge rates relative to non-hybrid vehicles.
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`Table IV: Option 2 of ARB’s Proposed LEV III Evaporative Standards
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`Europe and other countries around the world have implemented evaporative emission
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`standards on automobiles and other gasoline powered vehicles since 1983. Most of these have
`followed the European standards for fuels and emission limits and will not be discussed here.
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`These EURO based regulations for evaporative emissions are generally less stringent than U.S.
`or California regulations. Evaporative limits have also been established for non-automotive
`applications including motorcycles, small and large off-road spark-ignited engines as well as
`marine engines. Although these will not be covered here, some information on evaporative
`emission standards and technologies for non-automotive applications can be found in MECA’s
`small engine2 and motorcycle3 white papers.
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`2.2 Test Methods for Measuring Evaporative Emissions
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`The apparatus used to evaluate the diurnal and hot soak emissions from automobiles is
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`known as a SHED or Sealed Housing for Evaporative Determination. To conduct the
`measurements, the vehicle is driven into the chamber and the doors are sealed. The SHED is
`equipped with analyzers to measure HC emissions inside the chamber at various intervals. A
`flame ionization detector (FID) measures the total hydrocarbons at the beginning and end of each
`test to determine emissions from the hot soak and each diurnal day. An infrared detector is used
`to distinguish between fuel based HC’s and non-fuel based HCs such as those from polymers,
`rubber and plastics. The two-day plus hot soak test consists of running the vehicle on a Federal
`Test Procedure (FTP) drive cycle with a loaded carbon canister followed by a one-hour hot soak
`at elevated temperature and monitoring over two-diurnal days. The result that is reported is the
`total of the hot soak and the highest value from one of the diurnal days. The canister is pre-
`loaded with a mixture of butane and nitrogen to simulate the state of the canister if the vehicle is
`not driven for several days or recently refueled. The hot soak simulates parking the vehicle at
`72 οF after driving. The temperature range for the diurnal day to represent a California ambient
`environment consists of a soak at 65 οF followed by a 12 hour ramp up to 105 οF and a
`subsequent 12 hour cool down to 65 οF. The U.S. EPA diurnal cycle consists of a temperature
`cycle from 72 οF to 95 οF.
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`The three-day diurnal test for CARB includes an additional running loss test which
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`involves an FTP drive cycle performed at an ambient temperature of 105 οF. Additional
`emissions measurements are taken at the filler cap and canister to make sure that the purge
`system is functioning properly and emissions are contained during operation. Following the
`running loss test, the vehicle emissions are measured after a one-hour hot soak at 105 οF
`followed by three days of diurnal cycles as in the two-day test. The results that are reported for
`the three-day diurnal test combine the emissions measured during the hot soak and the highest of
`the three diurnal days.
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`In order to meet the PZEV emission requirements, manufacturers must demonstrate
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`elimination of fuel system related evaporative emissions. The zero-evaporative standard has
`two components that must be tested separately. First, the whole vehicle must be tested in a
`SHED for the two and three-day diurnal to show that emissions from all HC sources do not
`exceed 0.35 g/test for passenger cars under LEV II and Tier 2. Larger vehicles are allowed
`higher whole vehicle limits as shown in Figure 1. Second, to test only the emissions from the
`fuel system components, a rig test is used. For this test, the fuel system of the vehicle is
`reassembled inside the SHED and subjected to diurnal testing. The emissions from this test must
`not exceed 0.054 g/test.
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`The rig test requires that a support frame and the entire fuel system be assembled inside a
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`SHED apparatus. The assembly includes the fuel tank, fuel metering system, including injectors
`and fuel vapor control system such as the canister. The testing takes over 160 days to complete
`including time to age the components and a 140 day stabilization period. The actual SHED
`diurnal testing takes about 1-2 weeks. The bleed emissions test or mini-rig test that ARB has
`included under compliance option 2 of the LEV III proposal was suggested by MECA as a way
`to insure against backsliding by de-contenting advanced canister technologies from PZEV
`vehicles that might occur if only a whole vehicle test was required. Because a whole vehicle test
`combines evaporative emissions from the fuel system with non-fuel related VOCs, without a
`separate fuel system test, manufacturers could trade-off higher fuel related emissions for lower
`non-fuel emissions to pass a higher vehicle limit. This may result in the removal of the best
`available canister technologies and lead to higher overall evaporative emissions during real
`world operation.
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`The bleed emissions test is much simpler because it only tests the critical fuel vapor
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`control components in a SHED apparatus.5 The components involved in the test include the fuel
`tank, tank vent lines and carbon canister (Figure 3). Under this test, the canister can be aged and
`prepared in under 2 weeks resulting in a total test time of only two and a half weeks. Only the
`canister venting emissions are measured and included to meet the 0.02 g/test limit as proposed
`for LEV III.
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`Figure 3: Test set-up for a bleed emissions or mini-rig test
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`3.0 Technologies to Control Evaporative Emissions
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`Evaporative emissions from vehicles can be significantly reduced by addressing the
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`primary sources of HC leakage from the fuel system such as permeation, diurnal, and refueling.
`The technologies employed in modern fuel systems to address these mechanisms will be the
`topic of this section. The sources of these emissions are better illustrated in Figure 4 which
`depicts a typical fuel system.
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`Figure 4: Fuel system with emission control technology. Circles identify common joints
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`and connectors as sources of liquid and vapor leakage.
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`3.1 Permeation Controls
`
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`Permeation emissions can be addressed by reducing the permeability of plastics and
`polymers to gasoline in either the liquid or vapor phase. This can be accomplished through both
`design and selection of materials. Reducing the number of joints and connectors in a fuel system
`and the design of the fuel tank are some of the ways to reduce fuel leakage and permeation. Fuel
`system design is not within the scope of this paper but we will touch briefly on materials of
`construction as a way to control permeation. This is important in tanks, hoses, seals and
`connectors. Although metal tanks offer the highest barrier to permeation, they add weight and
`limit the shape necessary to meet stringent packaging requirements. Advanced tanks consist of
`coextruded, multilayer construction with a barrier layer of ethylene vinyl alcohol and
`fluoropolymers to reduce permeation. Furthermore, polymers can be treated via sulfonation or
`fluorination to further reduce permeability.
`
`Similar approaches of material selection can be applied to fuel hoses, seals, fuel caps and
`gaskets used within the fuel system. The use of coextruded, low permeation polymers such as
`nylon, fluoropolymers, and fluoroelastomers can be employed in fuel lines to significantly
`reduce permeation emissions. Special challenges in permeation emissions and materials
`compatibility have resulted since the introduction of ethanol blends in gasoline. The newest
`vehicles and, in particular, Flexible Fuel Vehicles (FFV) are equipped with the lowest
`permeation materials in the fuel tanks, hoses, seals and gaskets. Older vehicles and, in particular,
`spark-ignited off road engines like those used in lawn equipment, marine engines, recreational
`motorcycles and ATVs still use conventional fuel system materials which are not compatible
`with ethanol levels above 10%. There is a concern that if this equipment and vehicles are fueled
`with ethanol-gasoline blends greater than E10 they will result in significant emissions of
`hydrocarbons into the atmosphere contributing to ozone formation. Furthermore these engines
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`are not calibrated to operate on higher ethanol blends. The low permeation