two strokes
against it
Manila was choking, so they modified a three-wheeler's engine.
By Jeffrey Winters, Associate Editor
Chances
are, you've never seen traffic like the kind they have in Manila. It isn't
just the volume, which is heavy, or the pace, which is slow. The streets
of Manila, Bangkok, and other South Asian cities are choked not simply
with cars and trucks, but with small, three-wheeled vehicles. Called tuk
tuks, auto rickshaws, or simply tricycles, the vehicles are powered by
100- to 150-cubic-centimeter two-stroke engines, similar to the ones found
in large chainsaws.
"One of these two-stroke engines produces the same amount of pollution
as 50 Honda Accords," said Bryan Willson, a professor of mechanical
engineering at Colorado State University in Fort Collins and research
director at the school's Engines and Energy Conversion Laboratory.
And because the vehicles are ubiquitous—there are an estimated 50
million to 100 million two-stroke two- and three-wheelers throughout South
Asia—the pollution from these bikes is equal to as much as 5 billion
midsize automobiles. On streets choked with tricycles, the air above is
choked with smog. The World Bank estimates that air pollution from Philippine
two-stroke engines accounts for as many as 2,000 premature deaths a year.
Willson is an expert in cleaning up two-stroke engines, which were first
patented by the Scottish engineer Dugald Clerk in 1881. Two-stroke engines
are much simpler than their standard four-stroke brethren. They don't
have valves, for instance, a fact that lowers the overall weight. What's
more, the engines have a simpler cycle—they fire once a revolution,
rather than once every other revolution, as with four-stroke engines—which
means that for a given displacement, two-strokes are twice as powerful.
The design gives two-strokes a decided advantage over four-strokes in
torque. "It's not uncommon to see one of these tricycles carrying
12 passengers," Willson said.
Although the engines are powerful, their simple design calls for exhaust
to be flushed from the cylinder by the introduction of the fuel-air mixture
to be combusted in the next cycle. Inevitably, some of the unburned fuel
gets jettisoned as well, leading to clouds of blue smoke.
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| Cheap and dependable—and extremely polluting— custom-built tricycles are common throughout South Asia. But the two-stroke engines that power these vehicles can be cleaned up with a simple $200 fix. |
That pollution quickly adds up. Snowmobiles, many of which possess two-stroke
engines, have been implicated in reducing the air quality in wilderness
areas. This pollution is one of the reasons some environmentalists have
wanted to ban the vehicles from national parklands. But, in 2002, Willson
and his students found a way to clean up snowmobile engines. A simple
change in the cylinder head and the addition of a catalytic converter
reduced hydrocarbon emissions by 99.7 percent and carbon monoxide by an
astounding 99.9 percent.
Last year, Willson was contacted by a non-governmental organization in
Manila about applying the same techniques to Philippine tricycles. Although
there are similarities, Willson said, the differences made the task challenging.
Not only are many of the two-stroke engines maintained by shade-tree mechanics,
which rules out high-tech fixes, but the average owner of a tuk tuk is
poor by Western standards. Whatever the answer, it would have to be cheap.
The price of the modification for two-stroke snowmobiles—about $500
per vehicle—would be beyond the means of the typical owner of a Philippine
tricycle.
The solution Willson's team hit upon required two major changes—altering
the shape of the compression chamber to allow for fuller combustion, and
adding a direct fuel injector. The fuel injector, supplied by the Australian
manufacturer Orbital, delays the introduction of fuel just long enough
for the exhaust to be flushed cleanly from the cylinder through the use
of a blast of compressed air. As a result, Willson's team brought down
hydrocarbon emissions by 90 percent and reduced particulate matter by
more than 70 percent.
"All the components for this can be supplied for an installed cost
of $200," Willson said. That's just a tenth of the cost of a typical
Philippine trike plus a sidecar. But the fuel savings alone (the retrofitted
engines are about one-third more efficient) can reclaim the cost in just
one year. Willson hopes to have test vehicles with the reconfigured engines
on the streets of Manila next year.
With any luck, Willson's solution will be picked up all over South Asia.
Sure, it won't ease the traffic burdens in Bangkok or Calcutta. But it
might make them a whole lot easier to take.