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

Transportations Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
compression ratio technology is not expected to enter the market in a substantial way for
at least five years, and will likely have lower penetration due to its greater complexity. As
a group, these technologies hold promise primarily for gasoline engine improvements, but
could benefit diesel engines as well.
Other potential improvements in engine operation include changes to gasoline
combustion systems. Gasoline direct injection (GDI) allows more precise control over incylinder
combustion by injecting finer droplets of gasoline into the cylinder instead of the
intake, as is the case with conventional fuel injection. This technology also allows for
higher compression ratios to be used, which result in greater engine efficiency. GDI has
the additional benefit of increased torque output. A long-term goal of GDI research is the
development of lean (or stratified)
burning gasoline engines which would
provide further increases in efficiency,
although increased NO x emissions
would need to be offset by further
improvements in exhaust treatment
technologies.
Another combustion improvement
option is Homogeneous Charge
Compression Ignition (HCCI). Instead
of a spark plug causing fuel ignition as
in a standard gasoline engine, the
HCCI combustion method uses the
heat of compression to cause ignition
in a fashion similar to a diesel engine.
HCCI requires high rates of Exhaust
Gas Recirculation (EGR), a technology
Advanced Conventional Gasoline Vehicles
Per-Vehicle GHG Reductions: 8-30% e
Net Included Costs: Net Savings: -$180 to -$30 per
tonne
Confidence in Estimates: Moderate
• Primary benefits uncertainty is market penetration
• Cost-effectiveness will depend on fuel prices
Key Cobenefits and Impacts: Insignificant
Feasibility: High
• Many technologies proven
Key Policy Options:
• Financial and/or regulatory incentives for
improved fuel efficiency
currently employed in both gasoline and diesel engines. A high rate of EGR allows for
higher engine efficiency by eliminating the throttling losses experienced in a gasoline
engine at low engine loads. This technology can achieve efficiency gains similar to those
of lean-burn GDI engines, without the increased exhaust pollutant formation. One
drawback is that HCCI combustion can only take place over a limited range of operating
conditions and an enhanced electronic control system must manage the engine across
different combustion modes.
Two transmission technologies are being developed to increase powertrain efficiencies.
One new technology that is commercially available is the continuously variable
transmission (CVT). Instead of discrete gears, this type of transmission changes its gear
ratio in a seamless fashion to eliminate shifting and allow the engine to stay in the most
efficient operating condition possible. Internal power losses in this type of system
partially negate its benefits, however. Another transmission technology currently
entering the market is the dual-clutch transmission (DCT). This type of transmission
offers automated control of discrete gears as in an automatic transmission, but eliminates
much of the hydraulic loss associated with an automatic. It operates by having two
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