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Review of CO2 Emissions and Technologies in the Road Transportation Sector
Abstract:
The topic of CO₂ and fuel consumption reductions from vehicles
is a very broad and complex issue, encompassing vehicle
regulations, biofuel mandates, and a vast assortment of engine and
vehicle technologies. This paper attempts to provide a high-level
review of all these issues.
Reducing fuel consumption appears not to be driven by the amount
of hydrocarbon reserves, but by energy security and climate change
issues. Regarding the latter, a plan was proposed by the United
Nations for upwards of 80% CO₂ reductions from 1990 levels by 2050.
Regulators are beginning to respond by requiring ~25% reductions in
CO₂ emissions from light-duty vehicles by 2016 in major world
markets, with more to come. The heavy-duty sector is poised to
follow. Similarly, fuel policy is aimed at energy diversity
(security) and climate change impacts. Emerging biofuel mandates
require nominally 5-10% CO₂ life cycle emissions reductions by
2020. Processes that utilize plant cellulose and waste products
show the best intermediate term potential for meeting these goals,
but long-term trends are towards biofeedstocks for refineries.
Vehicle technologies are emerging to meet the regulatory
mandates. Light-duty engine efficiency gains will result in about
30% fuel and CO₂ reductions by 2015. Many of the reductions will
come from the use of direct injection technology in gasoline
engines, and downsizing diesel and gasoline engines for more
specific power. CO₂ savings shows a general linear relationship
with cost. Diesel hybrids offer the greatest CO₂ reduction
potential. Plug-in hybrids can lead to heavy electrification of the
fleet for energy diversity and greenhouse gas reductions, but their
CO₂ reductions are moderate and expensive. Battery performance is
generally acceptable, but cost will be a recurring issue. Most
light-duty efficiency technologies return money to the consumer
over the life of the vehicle, so the CO₂ reductions also come with
an economic gain to the owner.
In the heavy-duty sector vehicle and operational improvements
offer the best gains at 16 to 28% fuel reductions. Engine
technology trends are indicating nominally 15% reductions using
advancements in currently utilized technologies. Research is
shifting to gasoline engines, wherein upwards of 20-25% CO₂
reductions might be realized. Heavy-duty hybridization is emerging
for vocational and urban vehicles, and can offer a 2 to 4 year
payback period.
Black carbon reductions from vehicles can have a profound effect
on GHG impact, accounting for upwards of ~20% of CO₂ reductions
proposed by the Intergovernmental Panel on Climate Change (IPCC) by
2050.