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By: Jason Giacchino
Email: offthepegs @

September 2009 - Off The Pegs

Honda Looks to the Future of ATV Fuel Economy

Honda 450ER
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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