The
Certification Challenge for Hybrids
Emissions certification
of trucks and buses presently involves testing of the engine only.
The Engine
Compliance Program at the Environmental Protection Agency's (EPA)
Office of Transportation and Air Quality is responsible for certifying
engines for heavy-duty applications. The California Air Resources
Board (CARB) Mobile Sources Control Division performs a similar
function for certification in the state of California. Both EPA
and CARB use the same test procedures for urban bus engine certification.
Engines are certified on the Federal Test Procedure (FTP) transient
cycle. Emissions are measured and reported in units of grams of
emissions per brake horsepower hour (g/bhp-hr) delivered by the
engine under specific load regimes. The emissions are not allowed
to exceed certain standards set by EPA and California. Engine manufacturers
are responsible for complying with exhaust emission standards.
Industry and
regulators have recognized for some time the unique challenge posed
by hybrids in the emissions certification process compared to traditional
transit buses. Current hybrid-electric transit buses often use new
or unconventional engine technology that is smaller and different
in design, control and operation from conventional engines. Although
several of the first-generation hybrid engines in use today did
not meet EPA urban bus standards on the FTP cycle, many demonstrated
superior emissions performance in chassis testing of hybrid-electric
buses. Chassis-based emissions testing in the United States only
occurs on light duty vehicles, except in California where chassis-based
certification of medium-duty vehicles is allowed.
The challenge
is for industry and regulators to find an acceptable engine cycle
on which to test hybrid engines for purposes of emissions certification.
If the FTP transient cycle alone is used, will hybrid engines be
able to meet the urban bus standard and at what cost? Will viable
engine technologies be excluded if the FTP is used? Will the FTP
allow flexibility to improve and optimize hybrid engine controls
for further emission reductions in the future? Is there another
engine cycle that would better represent hybrid engine operation
that could be used for certification purposes? These questions were
being debated in the hybrid industry when the NAVC formed the Hybrid
Transit Bus Certification Workgroup.
More
on the NAVC Certification Workgroup recommendations for engine cycles
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