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| Green
cars don't have to be dull |
Lotus
Engineering has proven with its bi-fuel Elise that environmentally friendly
cars needn’t be boring. It’s strictly a research project that
runs on compressed natural gas (CNG) and petrol, but the Elise’s
compactness shows that virtually any size and style of car can be turned
into an alternative fuel vehicle - even one of Britain’s hottest
sports cars which is tipped to come to India soon.
“There are barriers that have prevented CNG taking off so far,”
says Lotus project engineer and CNG specialist, Elizabeth Durell. “There
will always be a slight reduction in performance using CNG of between
10 and 15 percent unless you convert the engine to run on CNG only.”
Space can be a problem, too. The CNG is stored in a cylinder which has
to be accommodated safely within the crash structure. And because of the
volume it occupies, the range isn’t as high when using natural gas
either - 40 litres of CNG is equivalent to about 10 litres of petrol.
T
| 40-litre
CNG cylinder |
24-litre
petrol tank |
Refueling
point is located in engine bay |
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| CNG
power has slashed CO2 emissions by whopping 30% |
he Elise’s single tank of gas is fitted behind the passenger compartment
with a specially-made 24-litre petrol tank above it. The demonstrator is
powered by a standard 1.8-litre engine, but an aluminium VVC inlet manifold
replaces the standard plastic one, and it’s modified to take an extra
row of injectors especially for the CNG. Petrol is delivered to the cylinders
through the original injectors, but the engine management system has been
swapped for something more suitable.
“The Rover ECU has been repla-ced by one of our own V8 units. That
way we can handle all eight injectors with just one component,” says
Durell. “It’s more simple than some bi-fuel cars which have a
main controller, then another just to handle the gas.”
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| CNG
Elise uses a standard bodyshell |
The
Elise engine starts on petrol then switches to gas automatically like
most bi-fuel cars. But what’s unusual is the way the Lotus also switches
back to petrol at full throttle, giving the driver the same maximum power
as a standard Elise for overtaking. A 10 percent reduction in peak torque
may sound a lot, but switching from petrol to gas manually only reveals
a modest subjective change in feel under acceleration. Yet some emissions
have been slashed by up to 70 percent while CO2 has been reduced by a
whopping 30 percent.
Work goes on and Lotus is currently testing a direct injection version
of the concept using its optical access research engine. Re-searchers
can literally view the inside of the combustion chamber and take measurements
using lasers while the engine is running.
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November 2001 