PRENSENTATION TO THE
CLEAN CITIES CONFERENCE
SPORTRAN’S EXPERIENCE WITH HYBRID BUSES AND CONVERSION
TO BIODIESEL FUEL
Hybrid Diesel-Electric Transit Bus
Below is information from our press conference when SporTran introduced the Clean Air Bus:
Information for Clean
Air Bus Press Conference
SporTran, the City of
Shreveport’s Mass Transit System, is proud to announce the receipt of 6 new
diesel buses that are currently in service, and a Hybrid Clean Air Bus that
will be put into service next week.
What is the Clean Air
Bus? A hybrid diesel-electric bus,
manufactured by Gillig Bus Corporation in
How much did it
cost? $517,000
How was it paid
for? $ 429,000 paid for from Federal
Transportation Administration; $64,000 was paid for from a Supplemental
Environmental Project funded by Pennzoil –
How does it work? Like all hybrid vehicles, the Clean Air Bus
is powered by an internal combustion engine (in our case a small diesel engine)
and a battery-powered electric motor. It uses a parallel drive system, where
the engine and electric motor provides power to the transmission at the same
time, in order to turn the wheels. Along
with propelling the bus, the diesel engine also recharges the battery system
(Other hybrid vehicles use a series system where the engine is connected to an
electric generator which feeds an electric motor, which in turn powers the bus
wheels.)
The electric motor
does most of the work at start-up, with the diesel engine assisting as speed
builds, then taking over more at higher speeds.
The process makes for a cleaner burning and more fuel efficient
engine. This cuts the amount of time the
diesel engine operates at a high strain level, when you hear the “diesel roar”
and see the dark smoke. The hybrid
system is especially effective on a transit bus whose entire duty cycle is made
up of stopping and going.
The entire engine
system is computer controlled, although the driver operates it just as he or
she would any other bus. All controls and gauges are the same, with a few
exceptions. The driver has to wait for
the computer to boot up each day when he starts the bus. Diagnostics have to be done by computer, and
mechanics will have to be more familiar with digital systems.
The Clean Air Bus also
features a system that recaptures normally lost braking energy, converts it to
electricity, and store it in the a nickel–metal-hydride battery.
The Bus has a continuously
variable transmission controlled by computer that eliminates the shift points
and surges you normally feel as the bus speeds up and slows down.
Engine noise is a lot
lower, in some cases hardly noticeable by the passengers. People outside the bus are surprised at how
much quieter the bus.
How does it compare to
our buses? It is runs cleaner, uses less
fuel, accelerates better, is quieter, and rides more smoothly than a regular
diesel bus.
Emissions – NOX, CO,
CO2 and Particulate emissions are much lower than on a regular bus. Field measurements from other systems show
improvements in the 50 percent range.
Fuel Consumption –we
are expecting 20% better fuel mileage, based on other systems experience.
Acceleration- Drivers
will be able to accelerate from a stop better, letting us keep up with traffic
flow better.
Noise – Much lower
than regular buses. In fact, during
summer months, the air conditioning blower fan is the loudest noise inside the
bus. Outside, the diesel engine noise is
reduced, since noiseless electric motors do most of the work at start –up
Ride – the
continuously variable transmission eliminates the surges normally felt during
upshift and downshift.
How has the bus performed in the 18 months that we’ve had
it?
The Clean Air Bus got a lot of favorable attention from the
media and from our non-riders. It is
popular with drivers and passengers.
Maintenance experienced initial problems with some computer
components. It was frustrating, but we
got good cooperation from the components supplier and the factory, and problem
has not recurred.
We encountered a problem that we did not expect. Height clearance needed because of 24 inch
high the battery pack on the top of the bus turned out to be more of a problem
than we thought it would be. We knew two
of our routes would be restricted because of older railroad overpasses. But we found that all but four of our 16
routes are restricted because of overhanging branches, especially live oaks
that require major pruning – some limbs as much as 7-8 inches in diameter. We are getting Public Works to clear the
branches as they can get to it.
Fuel mileage is as expected –we get between 20 and 25
percent better mileage than our other buses.
Given our average annual miles per bus at 36,000, with average MPG at
4.1, and fuel at about $2.50 a gallon, we spend about $22,000 per bus annually
for fuel. For us, this means we save between $4,000 and $5,000 per year on
diesel fuel with our hybrid bus. Using
these rates, over the expected 12 year life, we can save $50,000 to $60,000 in
fuel costs.
The battery pack that drives the electric motors will have
to eventually be replaced. We are hearing
that five years is an average replacement interval, but we don’t know if our
warmer than average environment will affect the interval. Heat is supposed to affect the battery life –
the battery pack has its own refrigeration system. The latest quoted cost of replacement is
approximately $35,000.
The regenerative braking system should double brake life,
which would keep brake costs down.
We don’t have any estimates on diesel engine and
transmission life, although the diesel engine (a much smaller engine than is
used in all-diesel buses) operates under lighter loads and should operate with
longer intervals between rebuilds.
Hybrids such as ours have been running in other systems for
as much as seven years. Other systems tell us their hybrids don’t appear to
have any more problems than regular buses.
Will we buy more hybrids?
We are not ready to commit to all hybrid buses. The initial price is still too high. We have enough local match funds to replace
eleven older model buses. If we bought
all hybrids, we could only buy six, and would have to run five older buses
longer.
We recently got a special waiver on local share for capital
equipment purchased in order to provide more service as a result of Katrina
evacuees relocating in
Stay tuned.
Bio-Diesel
SporTran started taking the idea
of biodiesel seriously when we found out three important things.
1 It was available locally.
When we first looked into it over a year ago, it was not available
except by hauling over long distances, which drove the price up, and would
require two dealers.
2 It cost no more than ultra-low sulfur diesel, and one dealer
could provide both fuels.
3 Other systems were using it without apparent problems.
In November last year we decided to go to a 20% mix – other
systems were using lower ratios – in the 5% range. We took our dealer’s word
for it that we could go to a 20% mix without problems, and it appears he was
right.
We arranged deliveries so that we gradually ramped up to a
20% mix over a six week period, so that the solvents in the biodiesel did enter
the system in a diluted form. There were
reports that the sludge in older engines and pump systems was being dislodged
by the solvents in the new biodiesel, lodging in fuel lines – the diesel engine
version of a stroke.
We had no problems with fuel filters in our buses, and
replaced the filter in our dispensing pumps twice during the ramp – up, but no
major problems.
A month ago we dropped to a 90-10 mix with the colder
weather, after finding that there was some gelling in the dispensing pump
filters on our coldest days.
This seems to have worked fine.
So far we have not noticed any difference in performance or
engine wear, but did not expect any.
Hopefully biodiesel production costs will not be subject to
the price spikes we have seen in petro-diesel, and that there continue to be
price supports for biodiesel.
At this point we are happy with the conversion.
Gene Eddy
Manager, SporTran
City of
318-673-7400
gene.eddy@ci.shreveport.la.us