United States National Risk Management

Environmental Protection Research Laboratory

Agency Cincinnati, OH 45268

Project Summary

Research and Development EPA/600/SR-97/118 December 1997

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. Environmental Protection Agency (EPA). The primary 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 investigated: a multi-layer high density polyethylene (HDPE) tank system, and a

steel tank system. The design analysis

included a life cycle inventory (LCI)

analysis, performance analysis and preliminary life cycle cost analysis. The

scope of the LCI study encompassed

materials production, the manufacturing 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 processes based on the current vehicle

retirement infrastructure.

The LCI analysis indicated lower energy burdens for the HDPE tank system and comparable solid waste burdens for both systems. Based on the

results of the LCI, streamlined environmental metrics were proposed. While

both systems meet basic performance

requirements, the HDPE system offers

design flexibility in meeting capacity

requirements, and also provided a fuel

cost savings. The life cycle design

framework was useful in evaluating environmental, performance, and cost

trade-offs among and between both fuel

tank systems.

Life Cycle Design of a Fuel Tank

System

Gregory A. Keoleian, Sabrina Spatari, and Robb Beal

This Project Summary was developed

by the National Risk Management Research Laboratory’s Sustainable Technology Division, Cincinnati, OH, to announce 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 considerations into the design process represents

a complex challenge to designers, managers and environmental professionals. A

logical framework including definitions,

objectives, principles and tools is essential to guide the development of more ecologically and economically sustainable

product systems. In 1991, the US Environmental Protection Agency (EPA) collaborated with the University of Michigan

to develop the life cycle design (LCD)

framework. This framework is documented

in two publications: Life Cycle Design Guidance Manual and the Life Cycle Design

Framework and Demonstration Projects.

Project Description

This pilot project with General Motors

(GM) Corporation applied the LCD framework and tools to the design of fuel handling and storage systems used in the

1996 GMT600 vehicle line. A key component 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
2

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 environmental considerations into product

system design and management. The

project focused on material selection analysis 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 development process. The scope of the study is

to perform a comparative evaluation of

the high density polyethylene (HDPE) and

steel fuel tanks used on the 1996 GMT600

cutaway van and passenger van. Specific

objectives included:

• Compare steel and multi-layer HDPE

fuel tanks and auxiliary components

that were not common between the

two systems using multicriteria matrices, LCI analysis, and life cycle cost

analysis

• Evaluate key criteria and develop environmental metrics for material selection

• Facilitate cross-functional team interaction 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 management

Methodology

Product Composition

Figure 1 shows the product composition by mass for each tank system. The

total weight of the steel and HDPE tank

systems (including shield and straps) are

21.92 kg and 14.07 kg, respectively. Each

fuel tank system consists of three components: 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 aluminum epoxy paint coat. The straps are

made of hot dipped galvanized steel with

a painted finish. The tank shield is made

of HDPE. The HDPE tank is a six-layer

plastic structure which consists primarily

of HDPE. The six layers of the plastic

tank, from outer to inner layer, include :

virgin HDPE mixed with carbon black, a

regrind layer which incorporates flash and

scrapped tanks, an adhesive layer, an ethyl

vinyl alcohol (EVOH) copolymer permeation barrier, an adhesive layer, and finally a virgin HDPE 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 HDPE

tank is 34.5 gallons. The HDPE tank weight

was normalized to 31 gallons so that the

two tanks delivered equivalent functionality.

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 conventional practices. This analysis did not

include external costs that are not reflected

in market prices.

Environmental data evaluated were material and energy consumption, solid waste

generation, and air and water pollutant

releases. Environmental data in the material production stage were obtained from

published sources. Material production

energy data and emissions factors were

used to evaluate the environmental burdens for the steel and HDPE tank systems. Environmental data in the manufacturing stage were obtained from GM facilities and supplemented with external and

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-oflife 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 materials were evaluated from unit cost data

from published sources. A cost assessment for the manufacturing of each fuel

tank was excluded from the study because such information is proprietary, and

hence data was not available for publishing. However, aftermarket costs were obtained from a GMC Truck dealership in

Saginaw, MI. 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

Figure 1. Composition of fuel tank systems.

17.88

3.34

11.2

1.91

0.7

0.96

5

10

15

20

25

Steel tank system (31 gal=1171)

Weight (kg)

PVC Coated Steel Straps

Steel Shield

Multi-layer HDPE Tank

Painted Steel Straps

HDPE Shield

Steel Tank

HDPE tank system (31 gal=1171)

normalized
3

price of consumed fuel over the useful life

of the vehicle, but this cost was not corrected for potential inflation. Finally, retirement costs were evaluated using techniques from Kar and Keoleian (1996) which

incorporate a retirement spreadsheet

model of the American Plastics Council

(APC). 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 of the

two fuel tank designs, and manufacturing

and assembly and end of life management performance criteria.

Results and Discussion

The LCI analysis and the life cycle cost

analysis provide comprehensive environmental and cost data for evaluating the

steel and HDPE fuel tank designs. The

results are based on functionally equivalent 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 accounts for the majority of the energy consumed. Over the 110,000 miles traveled,

the steel and HDPE tanks (including shield

and straps) are responsible for the consumption of 88.2 and 56.6 liters of gasoline, respectively. For comparison, the G

passenger van consumes 25,390 liters

when equipped with a steel fuel tank system; whereas when equipped with an

HDPE fuel tank system, it consumes

25,359 liters.

For the steel tank design, the use phase

constitutes 76% of the total life cycle energy. For the HDPE tank, it is responsible

for 66% of the total energy. Although less

HDPE material is used in the fabrication

of one tank relative to steel, the higher

specific energy for HDPE (81 MJ/kg) compared to steel (33.5 MJ/kg) yields comparable total material production energies

for each system. The manufacturing for

the HDPE tank system requires 85% more

energy than for steel which is a consequence of greater energy input for blow

molding of HDPE compared to steel

stamping. End-of-life management energy

is relatively negligible. The current practice of landfill disposition for the HDPE

tank, however, results in a significant loss

Table 1. Boundaries and Major Assumptions for Fuel Tank Systems

LC Stage Steel Tank HDPE Tank

Material Production The paint applied to the steel straps HDPE was substituted for the folwas modeled as steel because of the lowing components of the multilack of data on the amount of paint layer tank:

applied.

Carbon Black

PE-based Adhesive

EVOH

PVC applied to straps was assumed

to be emulsion PVC.

Manufacturing None of life cycle burdens of process None of life cycle burdens of promaterials were inventoried due to cess materials were inventoried due

data availability. to data availability.

Scrap rate of 2% was estimated for No scrap was considered to be

HDPE injection molding process generated in steel strap fabrication.

based on generic scrap rate data.

The energy consumption for tank

No scrap was considered to be gen- blow molding was based on genererated in steel strap fabrication. ic blow molding/injection molding

energy data.

Zinc-Nickel coating and soap lubrication were not included due to data

availability.

Copper is used as a process material

in steel tank fabrication. Copper recycling was not inventoried due to data

availability.

Foam pads used for tank distribution

were excluded based on mass.

Use Contribution of tank system weight to use phase energy consumption is calculated 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 of the type of material shredded or shape of the

part.

Steel is assumed to be recovered at 100% within each system.

All HDPE 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 of the amount needed for steel

making.
4

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 endof-life management stages indicate opposite trends for the two systems. The relatively 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 management.

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 current practices. It is recognized that the

infrastructure may change over the next

decade when a majority of these tanks

will be retired. Scenarios involving HDPE

recycling, energy recovery, and tank reuse could significantly impact the results.

Proposed Environmental

Metrics

A primary objective of this project was

to develop metrics to guide the environmental 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 product design, although the distribution and

magnitude of environmental burdens and

impacts will vary according to the automotive part/component under development.

Three factors influence the selection of

metrics: reliability and accuracy in representing environmental burdens and impacts, ease of measurement and evaluation, 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 applications; 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 availability.

Specific metrics for each case are provided in the project report.

Conclusions and

Recommendations

Several differences between environmental profiles appear to be significant.

The total life cycle energy consumption

for the steel and HDPE 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 management phases. The steel tank system

generated approximately 14 kg of total

solid waste per tank while the HDPE system 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 HDPE solid waste is concentrated in

vehicle end-of-life management.

The lighter weight of the HDPE results

in significant savings in use phase energy

relative to the steel for this particular application. This contributes to an overall

lower life cycle energy requirement for the

HDPE tank system. The life cycle solid

waste generation for both systems is comparable. Currently, the HDPE 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 HDPE system according

to the published data sources available

for this study. Air and water release data

is much less reliable, but in several pollutant categories, the use phase burdens

associated with the full gasoline fuel cycle

dominate. In these instances, the HDPE

tank system has lower burdens.

A performance analysis addressing

manufacturability and use phase performance requirements was conducted along

with a life cycle cost analysis of manufacturing, gasoline costs, and end-of-life processing costs. Both tanks meet basic performance requirements. Evaporative emissions testing showed that the HDPE multilayer design, with an EVOH layer, served

effectively as a permeation barrier to VOCs

in gasoline. The major performance requirement that distinguished the two tank

designs was design flexibility in meeting

capacity requirements within defined spatial constraints.

The difference in use phase costs between the two tank systems is significant—

with the HDPE 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 result 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 developed in three categories: life cycle energy, materials and wastes. A critical need

for implementing LCD is accurate sets of

air emission factors (g of pollutant emissions/kg of product material), waste generation factors (g of solid waste/kg of product material), and energy factors (MJ of

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Material

production

Manufacturing Use End of life System total

Energy consumption (GJ/tank)

Steel System

HDPE System

Figure 2. Life cycle energy consumption for HDPE and steel tank systems.
5

energy/kg of product material). These parameters 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

0

2000

4000

6000

8000

10000

12000

14000

16000

Material

production

Manufacturing Use End of life System total

Solid waste (g/tank)

Steel system

HDPE system

Figure 3. Life cycle solid waste generation for HDPE and steel tank systems.

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 implement this policy at an operational level

within the company. Further refinement in

the valuation component of life cycle impact assessment is required to guide decision makers in the interpretation of inventory data. Significant trade-offs can exist within and between inventory categories. Integration of the full set of performance, cost, environmental, and regulatory requirements becomes even more

complex. Policies and guidelines are in

place that address vehicle recyclability,

however, issues such as material production energy and waste are not specifically

addressed. Design decisions are made in

the context of internal and external policies. External policies and regulation do

not treat environmental burdens consistently across the life cycle, which makes

design analysis and decision making by

OEMs more difficult. Inventory interpretation and impact assessment represents a

logical extension of this project and another area for further research.
6

Gregory A. Keoleian, Sabrina Spatari, and Robb Beal are with the University of

Michigan, School of Natural Resources & Environment, Ann Arbor, MI 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

EPA/600/SR-97/118

Official Business

Penalty for Private Use $300

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