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Why
are hybrid emissions different?
There are several
reasons for the reductions. Regenerative braking contributes significantly
to reducing fuel consumption and thereby improving efficiency. Regenerative
braking takes advantage of the energy storage system to capture
the kinetic energy of the vehicle during braking. This is accomplished
by using the drive motors as generators during braking to recapture
the vehicle's kinetic energy and restore a portion of this energy
back to the energy storage device to be used later -- for example,
during acceleration.
Another contributing
factor is the fact that, on a series hybrid, the engine is not directly
coupled to the vehicle drivetrain (i.e., the electric drive motor
alone drives the wheels). This allows the auxiliary power unit (APU)
to operate independently from the vehicle. This would theoretically
allow the engine/generator to operate at peak efficiency and optimized
emission load points. Series hybrid control strategies typically
prevent the engine from operating in zones where its efficiency
may be low and its emissions high.
Detailed information
on the project methodology and on buses
that were tested.
In-depth review
of NOx and NMOC, particulate
matter, carbon monoxide, fuel
economy, CO2 and greenhouse gas emissions.
You
can download a PDF file of the NAVC heavy-duty hybrid report
here.
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