United States Air and Radiation EPA420-P-02-003
Environmental Protection August 2002
Agency NR-013a
vxEPA Refueling Emissions for
Nonroad Engine Modeling
> Printed on Recycled Paper
-------
EPA420-P-02-003
August 2002
for
Report No. NR-013a
Assessment and Standards Division
Office of Transportation and Air Quality
U.S. Environmental Protection Agency
-------
This technical report describes the methods and assumptions used in the draft
NONROAD2002 emissions model to estimate refueling emissions from nonroad equipment.
The discussion primarily focuses on refueling emissions for gasoline fueled equipment.
Refueling emissions for diesel fueled equipment are discussed briefly at the end of this report.
For ease of reference, the previous version of this technical report has been included as an
appendix.
Background
Refueling emissions can be divided into two components: spillage and vapor
displacement. Spillage emissions result when fuel is spilled during the refueling process. Some
or all of the spilled fuel will subsequently vaporize, adding hydrocarbon compounds to the
atmosphere. Vapor displacement emissions result when new liquid fuel being added to a fuel
tank displaces fuel vapors already present in the tank. For example, if one gallon of gasoline is
added to a fuel tank already containing some gasoline, one gallon of gasoline vapor will be
displaced to the atmosphere by one gallon of liquid fuel.
Although spillage and vapor displacement both occur during a single refueling event, the
draft NONROAD2002 model shows them as separate outputs. This is to provide additional
flexibility in using NONROAD output for atmospheric modeling. Spillage emissions and vapor
displacement emissions will typically have different chemical characteristics. Spillage emissions
will be composed of all of the compounds found in gasoline, while vapor displacement emissions
will be primarily composed of the lighter compounds that have vaporized in the gas tank (the
heavier compounds will remain as liquids in the tank). Separating refueling emissions into the
two components in the output allows atmospheric modelers to account for the effects of these
differences on atmospheric chemistry.
For both spillage and vapor displacement, the model initially calculates an emission
factor in terms of grams of emissions per gallon of fuel consumed. Fuel consumption is then
used to calculate total emissions based on the g/gal emissions factors.
Refueling modes - Gasoline Pump vs. Portable Container
Many types of nonroad equipment are commonly refueled from a portable container
rather than from a gasoline pump. Refueling nonroad equipment from a portable container
results in different emissions for both spillage and vapor displacement compared to refueling
from a gasoline pump. These differences are described in detail below. In addition, the use of
portable containers also results in extra refueling events. Both spillage and displacement
emissions will also occur when the container is filled from a gasoline pump. However, due to
lack of data, we have not attempted to quantify this extra set of refueling emissions in the draft
NONROAD2002 model. We welcome comments and data submissions that would help us
quantify these refueling emissions in future versions of NONROAD.
-------
Because the different refueling modes result in different emissions, we must make
assumptions in NONROAD about which equipment will be refueled predominantly using a
gasoline pump and which will be refueled predominantly from a portable container. Table 1
shows refueling mode assumptions that have been used in the past compared to the current
version of NONROAD. The draft NONROAD2002 model allows the refueling mode to be
based on horsepower or tank volume. For some types of gasoline-powered equipment, versions
with larger horsepowers are fueled at the pump while versions with smaller horsepowers are
fueled with a container. All equipment powered by diesel engines are assumed to be fueled at the
pump
Table 1: Alternative Refueling Mode Assumptions.
Source
Portable container
Gasoline pump
NEVES
Lawn and garden (except
chippers/stump grinders),
recreational, light
commercial, all other
equipment with tank volumes
less than 6 gallons.
Chippers/stump grinders, all
other equipment with tank
volumes greater than 6
gallons except lawn and
garden, recreational, and light
commercial equipment.
ARB Small Engine Model
All gasoline 2-stroke engines
and all equipment less than
15 hp.
All gasoline 4-stroke engines
greater than 15 hp
Draft 2002 NONROAD
- All lawn and garden
equipment.
- Smaller horsepower
gasoline recreational,
industrial, commercial,
logging, recreational marine,
and railway maintenance
equipment.
- All gasoline construction
equipment.
- All gasoline agricultural
equipment.
- All gasoline aircraft ground
support equipment.
- Oil Field Equipment.
- Larger horsepower gasoline
recreational, industrial,
commercial, logging,
recreational marine, and
railway maintenance
equipment.
- All diesels.
Spillage Emissions
EPA has received no significant new information on spillage emissions since the Nonroad
Engine and Vehicle Emission Study (NEVES) was published in 1991. NEVES described two
refueling factors; a value of 17 grams of fuel spilled per refueling event for equipment refueled
-------
from a portable container, and a value of 3.6 grams of fuel spilled per refueling event for
equipment refueled from a gas pump. The first value was derived from an OPEI study and the
second value was derived from MOBILE4 estimates for refueling of on-highway vehicles.
NEVES gives the following reasons for the difference in these two values: (1) fuel containers are
more difficult to use than gas pumps, and (2) fuel containers do not have automatic shutoff
capability. Given the lack of new information, we have kept the NEVES values in draft
NONROAD2002 using the following equations (all gasoline spilled is assumed to evaporate into
the atmosphere):
For refueling from portable containers:
Spillage (g/gal.) = 17.0 + tank volume
For refueling from gasoline pumps:
Spillage (g/gal.) = 3.6 ^ tank volume
By using tank volumes in these equations, we assume that all refueling events are fill-ups
of empty tanks. Given that some portion of refueling events are likely not fill-ups of empty
tanks, this assumption will tend to underestimate spillage emissions. If we knew, on average, the
percentage of the tank volume that was actually being filled, we could develop a better estimate
of spillage emissions. However, we are not aware of any data on which to base an assumption.
We welcome comments or data submissions on this issue.
Tank Volumes
Previous versions of the draft NONROAD Model used the method contained in the
NEVES report [1]. For more information, please see the previous version of this technical report
in the appendix.
For draft NONROAD2002, EPA expanded the regression approach used by NEVES for
larger equipment to include all applications. The regression equation calculates proper tank
volume for each horsepower bin using the appropriate ratio of tank size to horsepower (in gallons
per horsepower) for each application. The resulting tank sizes have been included in the input
data of NONROAD. Since actual tank size values are used in draft NONROAD2002 instead of
the calculated values that could have resulted in unrealistically large fuel tank sizes in previous
versions of the model, the 50 gallon cap on fuel tank size has been removed.
To revise recreational marine fuel tank sizes, EPA used data from an October 1999
database of specifications for new pleasure boats over 25 feet long from Ovation Digital
Productions.1 These data were then analyzed by looking only at the boats with gasoline engines
CD-ROM's containing these data are available on the web at www.boatshow.com. In obtaining these data from Ovation,
the US EPA has agreed that the data contained in the database are provided under license by Ovation digital Productions for
internal use by the US Environmental Protection Agency, Office of Transportation and Air Quality, and that this EPA office
will not resell or redistribute this data, including to other offices of the US government, without the consent of Ovation.
-------
and separating outboards from sterndrive/inboards. Linear regression of these data yielded the
following equations.
Sterndri ve/Inb oard
0-300hp y = 0.3335x r-squared = 0.1996 (forced through 0,0)
over 300 hp y = 1.5871x - 354.1 r-squared = 0.4206
Outboard
0 - 100 hp y = 0.4244x r-squared = 0.2473 (forced through 0,0)
over 100 hp y = 1.2218x - 74.45 r-squared = 0.4246
where: y = fuel tank size (gallons)
x = engine horsepower
Vapor Displacement
For the draft NONROAD2002 model, we revised the methodology using the following
formula from the Onboard Refueling Vapor Recovery Rule to calculate vapor displacement
emissions:
Displacement (g/gal) =
EXP(-1.2798-0.0049 x (Td - Ta) + 0.0203 x Td + 0.1315
where Td = dispensed fuel temperature (degrees F)
Ta = ambient temperature (degrees F)
RVP = Reid Vapor Pressure (psi)
This formula relies on user-supplied input for temperature and RVP. The temperature of
the equipment tank is assumed to be equal to the ambient temperature supplied by the user. The
temperature of the dispensed fuel depends in part on the refueling mode. For equipment refueled
by portable container, we assume that the temperature of the dispensed fuel equals the ambient
temperature. For equipment refueled from a gasoline pump, NONROAD uses the following
equation (derived from the relationship between equipment tank temperature and dispensed fuel
temperature in the NEVES report) to calculate the temperature of dispensed fuel based on the
ambient temperature:
Dispensed Fuel Temperature (°F) = 62 + 0.6 x (ambient temperature - 62)
Effect of Stage II Vapor Recovery Systems
Many ozone nonattainment areas are subject to Clean Air Act requirements for Stage n
vapor recovery systems on gasoline pumps. These systems are designed to capture gasoline
vapors displaced during refueling from a gasoline pump, preventing their release into the
atmosphere. In general, the overall effectiveness of Stage II systems at controlling refueling
-------
emissions depends on a number of factors including the baseline efficiency of the system used,
the amount of refueling done at stations exempt from Stage n requirements, and the frequency
and stringency of enforcement programs. For nonroad equipment, the effectiveness of Stage n
systems will also depend on the refueling mode (refueling from a portable container would not be
affected by Stage n controls), the frequency at which nonroad equipment is refueled at exempt
stations (some categories of nonroad equipment may be more likely to be refueled at private
refueling depots exempt from Stage n requirements), and the efficacy of Stage n systems when
refueling nonroad equipment (fuel tank filler openings on nonroad equipment may not be
compatible with Stage II nozzles designed for refueling highway vehicles).
Given these uncertainties, we propose the following approach to account for Stage II
controls in draft NONROAD2002. When the user specifies that Stage II controls are in place,
they would also specify the effectiveness of the controls as a percent reduction in refueling
emissions. That percent reduction would only be applied to vapor displacement emissions for
equipment refueled from a gasoline pump.
Diesel Refueling Emissions
The draft 2002 NONROAD model assumes zero refueling emissions for diesel
equipment. Because diesel fuel has a higher boiling point than gasoline, refueling emissions
from diesel equipment tend to be much less significant than from gasoline equipment. As a
result, very little refueling emissions data exist for diesel equipment. The NEVES report used a
single emission factor of 0.041 g/gal for vapor displacement from diesel equipment under all
conditions. However, this rate was based on a study conducted at fuel tank temperatures of
approximately 80° F. The actual rate at other temperatures was not identified. In addition, EPA
has received no comments or information that supports the use of the NEVES value or suggests
any alternatives.
References
1. "Nonroad Engine and Vehicle Emission Study", Appendix I, U.S. EPA Office of Air and
Radiation, November, 1991.
2. "Offroad Equipment Refueling Emissions", Presentation by California Air Resources staff,
Emissions Inventory Workshop, December 16, 1997.
-------
Appendix
Refueling Emissions for Nonroad Engine Modeling
Report No. NR-013
August 20, 1998
Gary J. Dolce
Nonroad Engine Emissions Modeling Team
Assessment and Modeling Division
US EPA, Office of Mobile Sources
This technical report describes the methods and assumptions used in NONROAD to estimate
refueling emissions from nonroad equipment. The discussion primarily focuses on refueling
emissions for gasoline fueled equipment. Refueling emissions for diesel fueled equipment are
discussed briefly at the end of this report.
Background
Refueling emissions can be divided into two components: spillage and vapor displacement.
Spillage emissions result when fuel is spilled during the refueling process. Some or all of the
spilled fuel will subsequently vaporize, adding hydrocarbon compounds to the atmosphere.
Vapor displacement emissions result when new liquid fuel being added to a fuel tank displaces
fuel vapors already present in the tank. For example, if one gallon of gasoline is added to a fuel
tank already containing some gasoline, one gallon of gasoline vapor will be displaced to the
atmosphere by one gallon of liquid fuel.
Although spillage and vapor displacement both occur during a single refueling event, the final
version of NONROAD will show them as separate output. This is to provide additional
flexibility in using NONROAD output for atmospheric modeling. Spillage emissions and vapor
displacement emissions will typically have different chemical characteristics. Spillage emissions
will be composed of all of the compounds found in gasoline, while vapor displacement emissions
will be primarily composed of the lighter compounds that have vaporized in the gas tank (the
heavier compounds will remain as liquids in the tank). Separating refueling emissions into the
two components in the output allows atmospheric modelers to account for the effects of these
differences on atmospheric chemistry.
For both spillage and vapor displacement, the model initially calculates an emission factor in
terms of grams of emissions per gallon of fuel consumed. Fuel consumption is then used to
calculate total emissions based on the g/gal emissions factors.
-------
Refueling modes - Gasoline Pump vs. Portable Container
Many types of nonroad equipment are commonly refueled from a portable container rather than
from a gasoline pump. Refueling nonroad equipment from a portable container results in
different emissions for both spillage and vapor displacement compared to refueling from a
gasoline pump. These differences are described in detail below. In addition, the use of portable
containers also results in extra refueling events. Both spillage and displacement emissions will
also occur when the container is filled from a gasoline pump. However, due to lack of data, we
have not attempted to quantify this extra set of refueling emissions in this version of
NONROAD. We welcome comments and data submissions that would help us quantify these
refueling emissions in future versions of NONROAD.
Because the different refueling modes result in different emissions, we must make assumptions
in NONROAD about which equipment will be refueled predominantly using a gasoline pump
and which will be refueled predominantly from a portable container. Table 1 shows refueling
mode assumptions that have been used in the past. Please note that the simplified method used
in the draft version of NONROAD was in part necessitated by the fact that draft version of
NONROAD was not designed to easily handle differences in refueling mode based on
horsepower or tank volume cutoffs. The final version of NONROAD will allow the refueling
mode to be based on more complicated criteria such as horsepower or tank volume. We could
use the Nonroad Engine and Vehicle Emission Study (NEVES)1 approach, the California Air
Resources Board (ARE) small engine2 approach, or some other approach. We invite comment
on what to assume in the final version of NONROAD. We are also interested in any data
submissions, such as survey results, that would be useful in separating equipment by refueling
mode in future versions of NONROAD.
Table 1. Alternative refueling mode assumptions.
Source
Portable container
Gasoline pump
NEVES
Lawn and garden (except
chippers/stump grinders),
recreational, light
commercial, all other
equipment with tank volumes
less than 6 gallons.
Chippers/stump grinders, all
other equipment with tank
volumes greater than 6
gallons except lawn and
garden, recreational, and light
commercial equipment.
ARE Small Engine Model
All gasoline 2-stroke engines
and all equipment less than
15 hp
All gasoline 4-stroke engines
greater than 15 hp
Draft NONROAD
All lawn and garden,
recreational equipment,
outboards and personal
watercraft.
All others.
-------
Spillage emissions
We have received no significant new information on spillage emissions since the Nonroad
Engine and Vehicle Emission Study (NEVES) was published in 1991. NEVES described two
refueling factors; a value of 17 grams of fuel spilled per refueling event for equipment refueled
from a portable container, and a value of 3.6 grams of fuel spilled per refueling event for
equipment refueled from a gas pump. The first value was derived from an OPEI study and the
second value was derived from MOBILE4 estimates for refueling of on-highway vehicles.
NEVES gives the following reasons for the difference in these two values: (1) fuel containers are
more difficult to use than gas pumps, and (2) fuel containers do not have automatic shutoff
capability. Given the lack of new information, we have incorporated the NEVES values into the
draft version of NONROAD using the following equations (all gasoline spilled is assumed to
evaporate into the atmosphere):
For refueling from portable containers:
Spillage (g/gal.) = 17.0 + tank volume
For refueling from gasoline pumps:
Spillage (g/gal.) = 3.6 ^ tank volume
By using tank volumes in these equations, we assume that all refueling events are fill-ups of
empty tanks. Given that some portion of refueling events are likely not fill-ups of empty tanks,
this assumption will tend to underestimate spillage emissions. If we knew, on average, the
percentage of the tank volume that was actually being filled, we could develop a better estimate
of spillage emissions. However, we are not aware of any data on which to base an assumption.
We welcome comments or data submissions on this issue.
Tank Volumes
The NEVES report includes a lengthy discussion of gasoline fuel tank volumes. Fuel tank
volumes in NEVES were primarily derived from manufacturer supplied information with
adjustments made to deal with mismatches between the way manufacturers and EPA describe
equipment categories. For a few equipment categories where manufacturer information was not
available, tank volumes in NEVES were based on EPA judgement. For larger farm and
construction engines, NEVES estimated tank volumes using a regression equation that related
engine horsepower to tank volume. Based on this equation, NEVES used the average
horsepower of each application to estimate an average tank volume.
While developing the draft version of NONROAD, we considered modifying and expanding the
regression approach used by NEVES for larger equipment to include all applications and to have
the model calculate the proper tank volume for each horsepower bin using the appropriate ratio
of tank size to horsepower (in gallons per horsepower) for each application. We did a
-------
preliminary analysis of a small amount of available data and incorporated the resulting ratios in
the draft version of NONROAD.
After further review of the data and methodology used in the draft NONROAD, we have
concluded that this new approach needs a considerable amount of additional work before we can
be certain that it improves on the NEVES methodology. Therefore, for the final version of
NONROAD, we propose to go back to using the original NEVES methodology and data. We
invite comment or data submissions that would help us to develop a better tank volume
methodology.
Vapor Displacement
For the final version of NONROAD, we propose to adopt the methodology described in the
NEVES report with some minor modifications. NEVES used the following formula to calculate
vapor displacement emissions:
Displacement (g/ gal) = -5.909 - 0.0949 x dt + 0.0884 x T + 0.485 x RVP
where:dt= Temperature of Equipment Tank - Temperature of Dispensed Fuel (°F)
T = Temperature of Dispensed Fuel (°F)
RVP= Reid Vapor Pressure
NEVES used this formula to create a simple lookup table of average summer and winter season
emissions based on average temperatures and RVP values. The final version of NONROAD will
incorporate this formula and rely on user supplied input for temperature and RVP. The
temperature of the equipment tank is assumed to be equal to the ambient temperature supplied by
the user. The temperature of the dispensed fuel depends in part on the refueling mode. For
equipment refueled by portable container, we assume that the temperature of the dispensed fuel
equals the ambient temperature. For equipment refueled from a gasoline pump, we will
incorporate the following equation (derived from the relationship between equipment tank
temperature and dispensed fuel temperature in the NEVES report) to calculate the temperature of
dispensed fuel based on the ambient temperature:
Dispensed Fuel Temperature (°F) = 62 + 0.6 x (ambient temperature - 62)
Effect of Stage II Vapor Recovery Systems
Many ozone nonattainment areas are subject to Clean Air Act requirements for Stage II vapor
recovery systems on gasoline pumps. These systems are designed to capture gasoline vapors
displaced during refueling from a gasoline pump, preventing their release into the atmosphere. In
general, the overall effectiveness of Stage n systems at controlling refueling emissions depends
on a number of factors including the baseline efficiency of the system used, the amount of
refueling done at stations exempt from Stage n requirements, and the frequency and stringency of
enforcement programs. For nonroad equipment, the effectiveness of Stage n systems will also
-------
depend on the refueling mode (refueling from a portable container would not be affected by
Stage II controls), the frequency at which nonroad equipment is refueled at exempt stations
(some categories of nonroad equipment may be more likely to be refueled at private refueling
depots exempt from State n requirements), and the efficacy of Stage n systems when refueling
nonroad equipment (fuel tank filler openings on nonroad equipment may not be compatible with
Stage II nozzles designed for refueling highway vehicles).
Given these uncertainties, we propose the following approach to account for Stage n controls in
the final version of NONROAD. When the user specifies that Stage n controls are in place, they
would also specify the effectiveness of the controls as a percent reduction in refueling emissions.
That percent reduction would only be applied to vapor displacement emissions for equipment
refueled from a gasoline pump. EPA will develop guidance as to the appropriate effectiveness
levels for Stage II controls for nonroad equipment.
Diesel Refueling Emissions
Because diesel fuel has a higher boiling point than gasoline, refueling emissions from diesel
equipment tend to be much less significant than from gasoline equipment. As a result, very little
effort has been spent studying diesel refueling emissions. NEVES did not include any spillage
emissions for diesel equipment. NEVES used a single emission factor of 0.041 g/gal for vapor
displacement from diesel equipment under all conditions. However, this rate was based on a
study conducted at fuel tank temperatures of approximately 80 °F. The actual rate at other
temperatures was not identified. We invite comment on whether to use the single emission rate
used in NEVES for all diesel refueling emissions due to vapor displacement, or to assume no
diesel refueling emissions until further information is available.
References
1. "Nonroad Engine and Vehicle Emission Study", Appendix I, U.S. EPA Office of Air and
Radiation, November, 1991.
2. "Offroad Equipment Refueling Emissions", Presentation by California Air Resources staff,
Emissions Inventory Workshop, December 16, 1997.
10
------- |