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By: Jason Giacchino
Email: offthepegs @ atvsource.com
September 2009 - Off The Pegs
Honda Looks to the
Future of ATV Fuel Economy
Honda 450ER |
You probably haven’t given it much thought
lately now that the 450cc four-stroke is here to
stay, but a few years ago the industry was
filled with collective uncertainty about the
future. We knew the days of the two-stroke were
numbered (especially since most of the
manufacturers had pulled the plug on theirs
already) but exactly what would replace the
venerable “oil burner” hadn’t yet been
determined.
Early theorists believed the industry would
go the way of the “clean-burning two-stroke,” a
concept that showed potential for retaining the
two-stroke’s desired rapid power delivery while
putting out far less pollution. There were a few
variations of the concept to consider like the
design Ogden which Utah inventor Frank Keoppel
had come up with in the early part of the new
century. Keoppel’s two-stroke engine managed to
burn straight gasoline, meaning premix and oil
injection would have been concepts of the past.
While the details get a little complicated, I’ll
try to summarize as best I can taking limited
column space into consideration.
Keoppel's schematic called for an isolated
holding chamber, which would be kept separate
from the crankcase by a flexible membrane. When
the piston moves upward, the membrane would, of
course flex inward, which would cancel out the
vacuum that would normally be created within the
crankcase. Not only would this draw air and fuel
into that holding chamber, it would draw oil
upward along the cylinder wall.
Once the piston returned down during the
power stroke, the membrane would pull back out,
sucking fuel into the engine. A second ring at
the bottom of the piston would help contain the
oil. In other words, the oil supply in the
onboard tank would continue to be used over and
over again rather than simply burn up during
each piston stroke.
The other, more commonly accepted clean
two-stroke was the result of a direct injection
system (a concept that’s been around since the
early 1900s). A lot like a diesel injection
system, there was a lot of hope in
super-pressurizing inbound fuel (up to 1,200
PSI) where gas would be instantly atomized as it
left the injector nozzle. What all of the
designs had in common were that they intended to
reduce the volume of un-burned hydrocarbons
escaping into the atmosphere.
The entire point is moot, of course, as the
manufacturers (led by consumer demand) have
proven that four-stroke engines, which are
naturally less environmentally-damaging as the
two-stroke, could be made to reap incredible
performance without a substantial increase in
overall weight (which, next to increased
complexity, was the major disadvantage concern).
Some could go as far as to say that the
rejuvenation of the versatile four-stroke high
performance engine spurred the entire ATV
industry’s collective re-interest in racing. So
all is well, right? For the moment, anyway. If
the automotive industry is any indication,
perhaps eventually more fuel-efficient engine
designs may find their way into our
applications.
While it wouldn’t be beneficial to convert
the already-impressive MPG figures of most ATVs
to gas/electric hybrid, Ethanol burners, or
bio-diesel designs, one company is already
showing promise using quite an old-school idea
in its future small-engine designs.
Invented by James Atkinson way back in 1882,
The Atkinson cycle engine is one in which the
intake, compression, power, and exhaust strokes
of the four cycle occur in a single rotation of
the crankshaft. How in the world is this
possible, you ask? Believe it or not, the answer
lies in the idea that the expansion ratio
doesn’t have to be the same as the compression
ratio. In other words, due to the strange shape
of the crankshaft, the power stroke can be
considerably longer than the compression stroke,
which means much better fuel economy when
compared to the same traditional four-stroke
(one with equal ratios).
Until now the Atkinson engine design has been
of little more than historic value, but that
company who has decided it may be beneficial to
start using this ancient concept in future
applications is none other than Honda itself.
They’ve been touting the benefits of this
technology in their single-cylinder engines for
things like portable generators, lawn mowers,
and log-splitters. If significant fuel savings
can be gained without a loss in performance in
these frugal arenas, it’s only a matter of time
before they make their way into ours.
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