United States
Environmental Protection
Agency
National Risk Management
Research Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SR-97/118
December 1997
&EPA Project Summary
Life Cycle Design of a Fuel Tank
System
Gregory A. Keoleian, Sabrina Spatari, and Robb Beal
This life cycle design (LCD) project
was a collaborative effort between the
National Pollution Prevention Center at
the University of Michigan, General
Motors (GM), and the U.S. Environmen-
tal Protection Agency (EPA). The pri-
mary objective of this project was to
apply life cycle design tools to guide
the improvement of fuel tank systems.
Two alternative fuel tank systems used
in a 1996 GM vehicle line were investi-
gated: a multi-layer high density poly-
ethylene (HOPE) tank system, and a
steel tank system. The design analysis
included a life cycle inventory (LCI)
analysis, performance analysis and pre-
liminary life cycle cost analysis. The
scope of the LCI study encompassed
materials production, the manufactur-
ing processes for each tank system,
the contribution of each tank system to
the use phase burdens of the vehicle,
and the end-of-life management pro-
cesses based on the current vehicle
retirement infrastructure.
The LCI analysis indicated lower en-
ergy burdens for the HOPE tank sys-
tem and comparable solid waste bur-
dens for both systems. Based on the
results of the LCI, streamlined environ-
mental metrics were proposed. While
both systems meet basic performance
requirements, the HOPE system offers
design flexibility in meeting capacity
requirements, and also provided a fuel
cost savings. The life cycle design
framework was useful in evaluating en-
vironmental, performance, and cost
trade-offs among and between both fuel
tank systems.
This Project Summary was developed
by the National Risk Management Re-
search Laboratory's Sustainable Tech-
nology Division, Cincinnati, OH, to an-
nounce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
Integration of environmental consider-
ations into the design process represents
a complex challenge to designers, man-
agers and environmental professionals. A
logical framework including definitions,
objectives, principles and tools is essen-
tial to guide the development of more eco-
logically and economically sustainable
product systems. In 1991, the US Envi-
ronmental Protection Agency (EPA) col-
laborated with the University of Michigan
to develop the life cycle design (LCD)
framework. This framework is documented
in two publications: Life Cycle Design Guid-
ance Manual and the Life Cycle Design
Framework and Demonstration Projects.
Project Description
This pilot project with General Motors
(GM) Corporation applied the LCD frame-
work and tools to the design of fuel han-
dling and storage systems used in the
1996 GMT600 vehicle line. A key compo-
nent of this project was the evaluation of
environmental burdens along with the life
cycle costs and performance of two fuel
tank designs. A cross-functional core team
from GM, Delphi Automotive Systems, a
GM subsidiary, and Walbro Automotive
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Corporation, a GM supplier, participated
with University of Michigan project team
members.
Objectives
The overall purpose of this project was
to apply LCD tools to better integrate en-
vironmental considerations into product
system design and management. The
project focused on material selection analy-
sis and decision-making for the design of
fuel tanks. The project identified specific
tools and developed environmental metrics
to be used in the GM product develop-
ment process. The scope of the study is
to perform a comparative evaluation of
the high density polyethylene (HOPE) and
steel fuel tanks used on the 1996 GMT600
cutaway van and passenger van. Specific
objectives included:
• Compare steel and multi-layer HOPE
fuel tanks and auxiliary components
that were not common between the
two systems using multicriteria matri-
ces, LCI analysis, and life cycle cost
analysis
• Evaluate key criteria and develop en-
vironmental metrics for material se-
lection
• Facilitate cross-functional team inter-
action and networking to effectively
use GM's internal resources
• Demonstrate the value and barriers
associated with the use of LCD as an
engineering design method to man-
agement
Methodology
Product Composition
Figure 1 shows the product composi-
tion by mass for each tank system. The
total weight of the steel and HOPE tank
systems (including shield and straps) are
21.92 kg and 14.07 kg, respectively. Each
fuel tank system consists of three compo-
nents: the tank which contains the fuel,
straps which secure the tank to the frame,
and a shield which has a unique function
for each fuel tank system. The steel tank
is made of plain carbon steel (1008-1010),
with a nickel-zinc coating and an alumi-
num epoxy paint coat. The straps are
made of hot dipped galvanized steel with
a painted finish. The tank shield is made
of HOPE. The HOPE tank is a six-layer
plastic structure which consists primarily
of HOPE. The six layers of the plastic
tank, from outer to inner layer, include :
virgin HOPE mixed with carbon black, a
regrind layer which incorporates flash and
scrapped tanks, an adhesive layer, an ethyl
vinyl alcohol (EVOH) copolymer perme-
ation barrier, an adhesive layer, and fi-
nally a virgin HOPE inner layer. The straps
for this tank system are also hot-dipped
galvanized steel with a PVC coating. The
tank shield is plain carbon steel.
The steel fuel tank has a volume of 31
gallons while the volume of the HOPE
tank is 34.5 gallons. The HOPE tank weight
was normalized to 31 gallons so that the
two tanks delivered equivalent functional-
ity.
Life Cycle Inventory Analysis
A LCI analysis was conducted following
US EPA and SETAC guidelines. The
boundaries and major assumptions for this
study are given in Table 1. A life cycle
cost analysis was conducted following con-
ventional practices. This analysis did not
include external costs that are not reflected
in market prices.
Environmental data evaluated were ma-
terial and energy consumption, solid waste
generation, and air and water pollutant
releases. Environmental data in the mate-
rial production stage were obtained from
published sources. Material production
energy data and emissions factors were
used to evaluate the environmental bur-
dens for the steel and HOPE tank sys-
tems. Environmental data in the manufac-
turing stage were obtained from GM facili-
ties and supplemented with external and
25 T
20 -•
15 --
10 -•
5 --
published sources. In the use phase, fuel
efficiency data was provided by GM and
emissions standards for light duty trucks
were obtained from the US EPA and
supplemented with off-cycle emissions
data from Ross. In the retirement phase,
shredding data was also obtained from
published results.
Emissions and wastes for different life
cycle stages were obtained as the sum of
process and fuel-related emissions and
wastes.
Transport distance data for the linkages
between manufacturing operations were
obtained from the GM project team, while
transport distance estimates for end-of-
life management were obtained from the
American Plastics Council.
Cost data evaluated include material
cost, aftermarket replacement cost, use
cost, and retirement cost. The cost of ma-
terials were evaluated from unit cost data
from published sources. A cost assess-
ment for the manufacturing of each fuel
tank was excluded from the study be-
cause such information is proprietary, and
hence data was not available for publish-
ing. However, aftermarket costs were ob-
tained from a CMC Truck dealership in
Saginaw, Ml. The aftermarket price of each
fuel tank system was used to determine a
rough estimate of manufacturing costs.
Use phase costs were calculated from the
D PVC Coated Steel Straps
L~] Steel Shield
[] Multi-layer HOPE Tank
n Painted Steel Straps
[] HOPE Shield
• Steel Tank
iO.96
1.91
11.2
Steel tank system (31 gal=1171)
Figure 1. Composition of fuel tank systems.
HOPE tank system (31 gal=1171)
normalized
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Table 1. Boundaries and Major Assumptions for Fuel Tank Systems
LC Stage Steel Tank
HOPE Tank
Material Production
The paint applied to the steel straps
was modeled as steel because of the
lack of data on the amount of paint
applied.
HOPE was substituted for the fol-
lowing components of the multi-
layer tank:
Carbon Black
PE-based Adhesive
EVOH
PVC applied to straps wasassumed
to be emulsion PVC.
Manufacturing None of life cycle burdens of process
materials were inventoried due to
data availability.
Scrap rate of 2% was estimated for
HOPE injection molding process
based on generic scrap rate data.
No scrap was considered to be gen-
erated in steel strap fabrication.
Zinc-Nickel coating and soap lubrica-
tion were not included due to data
availability.
Copper is used as a process material
in steel tank fabrication. Copper recy-
cling was not inventoried due to data
availability.
Foam pads used for tank distribution
were excluded based on mass.
None of life cycle burdens of pro-
cessmaterialswere inventoried due
to data availability.
No scrap was considered to be
generated in steel strap fabrication.
The energy consumption for tank
blow molding was based on gener-
ic blow molding/injection molding
energy data.
Use Contribution of tank system weight to use phase energy consumption is cal-
culated by assuming that weight is linearly proportional to fuel consumption.
No secondary weight savings were estimated.
Vehicle use phase emissions are the sum of US EPA in-use emission
standards for light trucks plus off-cycle emissions.
Tank system contribution to vehicle emissions is obtained by assuming that
emissions are proportional to total vehicle fuel consumption allocated to the
fuel tank system; the allocation rule is accurate for CO2 but for other gases
the relationship is non-linear.
End of Life All components are considered to be shredded. Shredding fuel requirements
were considered independent ofthe type of material shredded orshape of the
part.
Steel is assumed to be recovered at 100% within each system.
All HOPE is assumed to be landfilled.
Preliminary analysis indicated that steel recovered at end of life generated (at
least) the amount of scrap steel needed for steel making. No credit was given
to the system for any steel recovered in excess ofthe amount needed for steel
making.
price of consumed fuel over the useful life
of the vehicle, but this cost was not cor-
rected for potential inflation. Finally, retire-
ment costs were evaluated using tech-
niques from Kar and Keoleian (1996) which
incorporate a retirement spreadsheet
model of the American Plastics Council
(ARC). Transportation and disposal costs
were calculated using data from Franklin
Associates and the National Solid Waste
Management Association (NSWMA)
(1995).
A performance analysis was conducted
which took into consideration the in-use
engineering performance parameters ofthe
two fuel tank designs, and manufacturing
and assembly and end of life manage-
ment performance criteria.
Results and Discussion
The LCI analysis and the life cycle cost
analysis provide comprehensive environ-
mental and cost data for evaluating the
steel and HOPE fuel tank designs. The
results are based on functionally equiva-
lent fuel tank systems. The LCI analysis
also serves to guide the development of
environmental metrics.
Life Cycle Energy
The life cycle energy profile for each
fuel tank based on a vehicle life of 110,000
miles is shown in Figure 2. (The primary
energy consumed for each stage of life
cycle is indicated in units of GJ/tank.) For
both tank systems, the use phase ac-
counts for the majority of the energy con-
sumed. Over the 110,000 miles traveled,
the steel and HOPE tanks (including shield
and straps) are responsible for the con-
sumption of 88.2 and 56.6 liters of gaso-
line, respectively. For comparison, the G
passenger van consumes 25,390 liters
when equipped with a steel fuel tank sys-
tem; whereas when equipped with an
HOPE fuel tank system, it consumes
25,359 liters.
For the steel tank design, the use phase
constitutes 76% of the total life cycle en-
ergy. For the HOPE tank, it is responsible
for 66% ofthe total energy. Although less
HOPE material is used in the fabrication
of one tank relative to steel, the higher
specific energy for HOPE (81 MJ/kg) com-
pared to steel (33.5 MJ/kg) yields compa-
rable total material production energies
for each system. The manufacturing for
the HOPE tank system requires 85% more
energy than for steel which is a conse-
quence of greater energy input for blow
molding of HOPE compared to steel
stamping. End-of-life management energy
is relatively negligible. The current prac-
tice of landfill disposition for the HOPE
tank, however, results in a significant loss
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Material
production
Manufacturing
Use
End of life
System total
Figure 2. Life cycle energy consumption for HOPE and steel tank systems.
of energy in the form of the embodied
energy of the material.
Life Cycle Solid Waste
The solid waste generated across each
stage of the fuel tank life cycle is shown in
Figure 3. The material production and end-
of-life management stages indicate oppo-
site trends for the two systems. The rela-
tively high solid waste from the production
of steel is associated with precombustion
processes (e.g. coal mining) and slag,
whereas the high solid waste from the
plastic system results from end-of-life man-
agement.
A significant fraction of the slag from
steel production is reused in applications
such as road construction, and was not
inventoried as waste. Solid waste from
the end-of-life management stage was
evaluated using a model describing cur-
rent practices. It is recognized that the
infrastructure may change over the next
decade when a majority of these tanks
will be retired. Scenarios involving HOPE
recycling, energy recovery, and tank re-
use could significantly impact the results.
Proposed Environmental
Metrics
A primary objective of this project was
to develop metrics to guide the environ-
mental improvement of automotive parts
and components. These environmental
metrics complement the existing set of
metrics and criteria that support design
analysis and decision making. The LCI of
the fuel tank can be used as a basis to
propose a set of generic metrics for prod-
uct design, although the distribution and
magnitude of environmental burdens and
impacts will vary according to the automo-
tive part/component under development.
Three factors influence the selection of
metrics: reliability and accuracy in repre-
senting environmental burdens and im-
pacts, ease of measurement and evalua-
tion, and their applicability to a wide range
of automotive parts and components.
Based on these preconditions the project
team decided to make recommendations
for the following cases.
Case 1. A comprehensive set of metrics
applicable to all automotive applica-
tions; unrestricted by data availability
(i.e., the ideal case).
Case 2. Metrics that are specific to fuel
tank design.
Case 3. A subset of the metrics defined
in Case 1 but restricted by data avail-
ability.
Specific metrics for each case are pro-
vided in the project report.
Conclusions and
Recommendations
Several differences between environ-
mental profiles appear to be significant.
The total life cycle energy consumption
for the steel and HOPE tank systems was
4.9 GJ and 3.6 GJ per tank, respectively.
A majority of this energy was consumed
during the use phase. Conversely, the solid
waste burdens associated with the fuel
tank systems were concentrated in the
material production and end-of-life man-
agement phases. The steel tank system
generated approximately 14 kg of total
solid waste per tank while the HOPE sys-
tem generated approximately 13 kg. These
differences are not significant within the
expected uncertainty of this analysis. The
analysis indicates that most of the solid
waste associated with steel is generated
in the material production phase whereas
the HOPE solid waste is concentrated in
vehicle end-of-life management.
The lighter weight of the HOPE results
in significant savings in use phase energy
relative to the steel for this particular ap-
plication. This contributes to an overall
lower life cycle energy requirement for the
HOPE tank system. The life cycle solid
waste generation for both systems is com-
parable. Currently, the HOPE tank is not
recyclable in the end-of-life management
stage. On the other hand, in the material
production phase, the steel tank system
results in significantly more solid waste
compared to the HOPE system according
to the published data sources available
for this study. Air and water release data
is much less reliable, but in several pollut-
ant categories, the use phase burdens
associated with the full gasoline fuel cycle
dominate. In these instances, the HOPE
tank system has lower burdens.
A performance analysis addressing
manufacturability and use phase perfor-
mance requirements was conducted along
with a life cycle cost analysis of manufac-
turing, gasoline costs, and end-of-life pro-
cessing costs. Both tanks meet basic per-
formance requirements. Evaporative emis-
sions testing showed that the HOPE mul-
tilayer design, with an EVOH layer, served
effectively as a permeation barrier to VOCs
in gasoline. The major performance re-
quirement that distinguished the two tank
designs was design flexibility in meeting
capacity requirements within defined spa-
tial constraints.
The difference in use phase costs be-
tween the two tank systems is significant—
with the HOPE tank system providing a
$10 fuel cost savings to consumers over
110,000 vehicle miles traveled. Although
the savings related to the fuel tank may
appear small, successful application of
LCD to other vehicle components can re-
sult in a much greater total savings to the
consumer. In the waste management
stage, the scrap value associated with the
steel tank system more than offsets the
end-of-life management costs; whereas,
the current scrap value for the plastic fuel
tank system is not significant enough to
cover the end-of-life management costs,
resulting in a net cost for this life cycle
phase.
Environmental metrics for LCD design
were proposed based on the results of
the LCI analysis. LCI metrics were devel-
oped in three categories: life cycle en-
ergy, materials and wastes. A critical need
for implementing LCD is accurate sets of
air emission factors (g of pollutant emis-
sions/kg of product material), waste gen-
eration factors (g of solid waste/kg of prod-
uct material), and energy factors (MJ of
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c
re
0)
V
to
re
;o
"o
W
16000-1
14000-
12000-
10000-
8000 -
6000 -
4000-
2000 -
0 -
D Steel system
• HOPE system
Material
production
Manufacturing
Use
End of life
System total
Figure 3. Life cycle solid waste generation for HOPE and steel tank systems.
energy/kg of product material). These pa-
rameters were compiled for the fuel tank
system from either primary plant data or
previously published data. The inventory
analysis also served to identify metrics
that are associated with a majority of the
environmental burden across the life cycle.
GM recognized the importance of LCD
and management as evidenced by their
corporate environmental principle, which
states: "We are committed to reducing
waste and pollutants, conserving resources
and recycling materials at every stage of
the product life cycle". This demonstration
project represents one initiative to imple-
ment this policy at an operational level
within the company. Further refinement in
the valuation component of life cycle im-
pact assessment is required to guide de-
cision makers in the interpretation of in-
ventory data. Significant trade-offs can ex-
ist within and between inventory catego-
ries. Integration of the full set of perfor-
mance, cost, environmental, and regula-
tory requirements becomes even more
complex. Policies and guidelines are in
place that address vehicle recyclability,
however, issues such as material produc-
tion energy and waste are not specifically
addressed. Design decisions are made in
the context of internal and external poli-
cies. External policies and regulation do
not treat environmental burdens consis-
tently across the life cycle, which makes
design analysis and decision making by
OEMs more difficult. Inventory interpreta-
tion and impact assessment represents a
logical extension of this project and an-
other area for further research.
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Gregory A. Keoleian, Sabrina Spatari, and Robb Beal are with the University of
Michigan, School of Natural Resources & Environment, Ann Arbor, Ml 48109-
1115.
Kenneth R. Stone is the EPA Project Officer (see below).
The complete report, entitled "Life Cycle Design of a Fuel Tank System, "(Order No.
PB98-117856; Cost: $25.00, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Sustainable Technology Division
National Risk Management Research Laboratory
U. S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use $300
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/600/SR-97/118
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