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3.0  Definition of Fuel Cycles

This study considers fuel-cycle emissions from vehicle fuels.  The analysis considers the marginal, or incremental gallon (or equivalent fuel unit), consumed in the SoCAB.

Three example scenarios were developed to cover the range in emissions due to fuel-cycle assumptions.  Many of these fuels can be produced from several feedstocks.  Table 3-1 shows the fuel/feedstock combinations considered in this study.  The codes that correspond to the fuels and feedstocks are used later to identify emission rates in a database.  The combination of feedstocks and fuels represents a specific combination of production technologies and feedstocks.  For example, methanol from natural gas is considered separately from methanol from biomass, while a combination of feedstocks is considered for electricity production.

Table 3-1:  Feedstock/Fuel Combinations Considered in This Study

Feedstock

Codea

Fuel

Code

Vehicleb

Crude Oil

o

Diesel

D

CI IC

Crude Oil

o

RFD

RD

CI IC

Crude Oil

o

LPG

P

SI IC

Natural Gas

n

Synthetic Diesel

F

CI IC

Natural Gas

n

LPG

P

SI IC

Natural Gas

n

Methanol

M

Steam reformer PEMFC

Landfill Gas

l

Methanol

M

Steam reformer PEMFC

Biomass

b

Methanol

M

Steam reformer PEMFC

Various

x

Electricity

J

Battery only EV

aCodes refer to feedstock and fuel designations used in database.

bCI IC = compression ignition internal combustion engine, SI CI = spark ignited internal combustion engine, PEMFC = proton exchange membrane fuel cell, EV = electric vehicle.

The fuel-cycle emissions in this study are represented as the weighted average of different production and distribution technologies described in this section.  Some fuel/feedstock combinations, such as methanol from natural gas, were represented separately while others were combined to simplify the comparison of fuels in Section 7.  The basis for scenarios, mix of feedstocks, as well as production and distribution technologies is described below.

3.1  Scenarios

The scenarios in this study, identified as Scenarios 1 through 3, represent emissions for the years 1996 and 2010.  Scenario 1 considers emissions for the base year, 1996.  The two scenarios for the year 2010 consider a high and low estimate based on certain

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