29-12-2012, 06:15 PM
Estimated Cost of Emission Reduction Technologies for Light-Duty Vehicles
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Executive Summary
There are great opportunities around the globe to reduce conventional
pollutant emissions from light-duty vehicles (LDVs), with positive effects
on air quality and public health. Even though the benefits of more stringent
standards have been demonstrated and the technologies to achieve
those benefits are readily available, there are still large differences in the
implementation schedules for increasing emission stringency (Figure ES-1).
Among the reasons for delaying the implementation of stricter emission
levels is the extra cost added to the vehicle by the emission control system.
This report directly addresses the cost to LDV manufacturers of deploying
technology in order to meet more stringent emission regulations. Costs
were assessed by government agencies during the rulemaking process
establishing each new standard in the US and Europe. However, some
of these standards were established many years ago. There have been
substantial improvements in emission control technology since then, which
are not reflected in the original cost estimates. This report updates the
cost of meeting each emission standard level so that countries considering
adoption of more stringent standards can make a more informed decision.
The objective of this study is to assess the technology requirements’ costs,
in current terms, derived from advancing to more stringent regulatory
standards on LDVs.
Emiss ion Reduction Technologies
Technologies required for control of regulated pollutants are presented
below for gasoline and diesel vehicles. Emissions control technologies can
be divided into two groups: in-cylinder control and aftertreatment control. A
brief description of each technology, including operational principle, applicability,
reduction capabilities and special conditions, is provided.
ES-1.1 Gasoline vehicles
Almost all gasoline, spark-ignited (SI) engines run at stoichiometric conditions,
which is the point where available oxygen from the air is completely consumed,
oxidizing the fuel delivered to the engine. Stoichiometric SI engines use a
homogenous air-fuel mixture with early fuel introduction for good fuel vaporization.
Gasoline fuel delivery systems have evolved from carbureted systems
to throttle body injection (TBI), multipoint fuel injection (MPFI), and sequential
MPFI. The latest evolutionary step, stoichiometric direct injection, represents
a significant improvement for spark-ignited engines and when combined with
turbocharging and engine downsizing makes them competitive with diesel
engines in terms of fuel economy and performance.
Air-fuel control has a major impact on the formation of hydrocarbons (HC),
or unburned fuel, and carbon monoxide (CO), which is partially oxidized
fuel. In contrast, NOX is a byproduct of combustion, created when nitrogen
and oxygen in the air combine during the combustion process. The higher
the cylinder temperature, the more NOX is formed. Thus, the primary
strategy to reduce the formation of NOX in the engine is to reduce combustion
temperatures, using faster burn combustion chamber design and
exhaust gas recirculation (EGR).
Diesel Vehicles
Unlike gasoline SI engines, which always control both the amount of air
and the amount of fuel close to complete combustion conditions, the
diesel engine runs unthrottled with an excess of air (lean operation). HC
and CO emissions are not usually a concern with diesel engines, as the
lean operation reduces engine-out HC and CO emissions and enables high
oxidation efficiency in simple oxidation catalysts. PM and NOX emissions
are more challenging to control and are the main focus of diesel emissions
control research, as well as the main source of technology costs.
Engine-out PM emissions are also much higher than on SI engines due to
direct in-cylinder fuel injection. The timing of fuel combustion is controlled
when fuel is injected and the fuel ignites almost immediately after injection.
This allows little time for the fuel to vaporize and mix with air, creating flame
plumes. During this combustion process, carbonaceous particulates grow
by aggregating with other organic and inorganic particles. Thus, particulate
matter (both mass and number) is also much more challenging to control in
a CI diesel engine.
Diesel technologies
Light-duty diesel vehicles have steadily gained market share in Europe,
from about 23% in 1994 (Euro 1) to more than 50% in 2006 (ACEA, 2010). A
similar trend is seen in India. The shift in emission control technology is more
complex than the gasoline case, including improvements and adoption of
new technologies for in-cylinder control and aftertreatment systems.
Euro 1 and 2: Technologies required for compliance with Euro 1 emission
levels are based on mechanical fuel injection systems, mostly indirect
fuel injection. Air management is naturally aspirated (not turbocharged).
Mechanically activated EGR circuits are introduced in vehicles that meet
these standards. Euro 2 regulations started the shift from mechanical
injection to electromechanical that eventually led to the phasing out of
mechanical injectors altogether to meet Euro 3 requirements. Electronic
fuel timing and metering becomes the dominant technology. Turbocharging
start spreading among the larger size light-duty diesel engines.
Historically, aftertreatment through oxidation catalyst was introduced as
a commercial tool for odor (hydrocarbons) control in Euro 1 and 2 diesel
vehicles, which were mainly IDI engines (Koltsakis and Stamatelos, 1997).
For current Euro 2 vehicles, advances in direct fuel injection technology are
expected to provide PM engine-out emission levels compliant with Euro 2
standards without the need for aftertreatment. Thus, for the purposes of
this report, fuel injection technology for current Euro 2 vehicles is based on
a rotary pump with electronic assistance for fuel metering. NOx emission is
controlled with cooled EGR.