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Review of CO2 Emissions and Technologies in the Road Transportation Sector

Journal Article
ISSN: 1946-3936, e-ISSN: 1946-3944
Published April 12, 2010 by SAE International in United States
Review of CO2 Emissions and Technologies in the Road Transportation Sector
Citation: Johnson, T., "Review of CO2 Emissions and Technologies in the Road Transportation Sector," SAE Int. J. Engines 3(1):1079-1098, 2010,
Language: English


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.