Transportation's Role in Reducing U.S. Greenhouse Gas Emissions ...

Transportations Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
addition of the turbocharger and other components, while the findings of the CAFE
analysis did not show that to be the case.
Cobenefits
In many cases advanced gasoline LDVs may have lower criteria and toxic emissions than
comparable conventional gasoline LDVs, resulting from lower fuel consumption and
better engine load management, potentially smaller engines, and other factors. However,
variation across the different available models makes it difficult to quantify criteria
pollutant reductions for advanced gasoline LDVs as a whole, and engines will generally
be designed to meet pollution control standards.
Some of the technologies in question offer cobenefits to vehicle owners/operators.
Transmission technologies such as DCT and CVT offer the added advantage of reduced
shift time or the elimination of shifting all together. Possible cobenefits of higher voltage
DC systems and thermoelectric generation technologies include faster engine warm-up
from increased control of the water pump, and increased power output at high RPM from
not overpowering vehicle accessories.
Most of the improvements discussed here will not impact vehicle safety, with the possible
exception of weight reduction strategies, which may require expenditures for additional
safety features.
Feasibility
The level of market penetration attainable by these technologies will depend largely on
regulatory drivers such as CAFE and possibly other GHG reduction mandates, as well as
fuel prices and consumer preferences. Regulatory and other policy issues regarding LDV
fleet efficiency improvements are discussed in Section 3.1, while fuel price impacts are
evaluated under cost-effectiveness above. The following discussion focuses on technical
barriers, cost, and other constraints associated with advanced technology deployment.
In order to realize the full benefit from GDI technology, the engine can be calibrated to run
lean (i.e., with an excess of oxygen in the cylinder). Under such conditions, NOx
formation is increased, which would require an enhanced and more costly form of aftertreatment.
Costs of GDI technology also prevent widespread implementation in the near
term. HCCI technology, meanwhile, is not yet mature enough to operate seamlessly over
the wide range of conditions encountered while in use. In addition, the benefits of HCCI
cannot be realized with a cold engine, with the associated efficiency improvements limited
to hot operating modes.
In addition to cost, a significant barrier to the further market penetration of CVT
technology is that its transmission efficiencies are typically lower than conventional
automatic or manual transmissions, due to the lower efficiency of the ratio adjustment
mechanism. While this inefficiency is offset by the increased engine efficiency, the
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