Outdoor power products like gas-powered chainsaws, weed trimmers, leaf
blowers and water pumps really do run more cleanly and efficiently these
days, and an incidental side-by-side comparison I stumbled upon this past
summer proved it to me.
I first noticed something interesting minutes after firing up a new
gas-powered weed trimmer I'd bought to supplement the 10-year-old model
we've been using at our house. Old faithful still runs as good as new, I
just wanted a second machine now that a couple of my kids are old enough to
help me wrestle our big country lawn into shape. What I wasn't expecting was
any obvious difference in exhaust gas cleanliness and fuel efficiency
between old and new machines. But, as it turned out, the difference was
unmistakable.
Burning the same gas-and-oil mixture from the same gas can, the exhaust from
the new weed trimmer was odourless and invisible while the old model still
puffed out its wisps of pungent blue smoke, just like it always had. And
this difference is especially striking when you understand how dead-simple
'two-stroke' engines are. What could engineers possibly do to make them
better?
The type of power plant in your car is called a four-stroke motor. This
means it uses a complicated series of valves to operate, along with a
reservoir of oil (that you need to change from time to time) to keep
everything lubed. Two-stroke engines, on the other hand, (like those in my
pair of weed trimmers), have none of the same valves. They're also
lubricated by oil that's pre-mixed with gasoline. This makes two-stroke
engines very simple, cheaper to build, lighter in weight and easier to
maintain than four-strokes. On the downside, these two-stroke advantages
have traditionally come with lower fuel economy and much dirtier exhaust
emissions. In fact, when government emissions regulators first took steps to
reduce small engine pollution about a decade ago, pundits predicted that the
two-stroke engine would be forced into extinction because it was impossible
to make them meet new air-quality standards. And while that prediction has
proven true for some kinds of two-stroke motors, it hasn't eliminated all of
them. Some have evolved to deliver remarkably low emissions and fuel
consumption, as I learned first-hand back in August.
When our household water well pump broke this summer, we relied on a
two-stroke gas-powered pump for several days to draw water from Lake Huron
while I gathered hardware for the repair. That little pump used less than
300 ml of gas to fill a 1000 litre tank on the back of my pick-up truck, and
it pumped all this water in less than 15 minutes. Amazing.
To answer the how-they-do-it question, I called Brad Lacroix, technical
manager with ECHO Canada. And to understand his answers, you need a little
technical background.
Almost all internal combustion engines use two parts called a 'piston and
cylinder' to capture the energy released by a burning mixture of gasoline
and air. And where these parts used to be made by factory equipment that
drilled and ground the metal to shape, the ECHO two-stroke cylinders are
actually cut with a kind of laser beam. This creates much smoother internal
surfaces that seal better, last longer and do a better job preventing
unburned gases from escaping into the atmosphere. The microscopic bumps and
valleys on these laser-cut surfaces range from 5 to 10 microns in size. To
put that into perspective, a typical human hair is a whopping 30 microns in
diameter. We're talking very, very smooth and precise parts, here.
Another efficiency-boosting feature of the new two-stroke engines is the use
of a feature called a 'squish band'. This is a raised area of internal
castings that forces the gas-and-air mixture into the middle part of the
piston only. When all combustion occurs here (as opposed to some happening
around the perimeter of the piston) much cleaner and more complete
combustion occurs. Add to this other refinements like variable spark timing,
piston rings that dissipate 60% of all engine heat, and internal intake
ports that prevent unburned gases from leaving the engine prematurely, and
you enjoy some very serious efficiency gains.
If all of these technical details seem too complicated to bother with, don't
worry. The bottom line is simple: today's top two-stroke outdoor power
equipment runs so much more cleanly and efficiently than ever before, and it
does it for reasons that would have seemed impossible just 20 years ago. And
if this doesn't offer some hope for how technical progress can help us live
both comfortably and responsibly at the same time, I don't know what does.
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