Honda’s FI-Two stroke engine

Two-strokes are far simpler machines than four-stroke engines. They’re also lighter, easier to work on, and downright angrier, pumping out a lot more power per cubic centimeter of displacement, which has won them a lot of fans. But they’ve had a reputation for belching out a fair bit of smoke and unburned fuel, a situation that just couldn’t fly alongside tightening emissions regulations around the world, so they’ve fallen out of favour. But now there’s a glimmer of hope. Earlier this month, Honda submitted a patent application for a brand new two stroke motor that uses direct fuel injection for a cleaner burn and better piston cooling. We may yet see a resurrection of the ring-dingers.

Uncovered by eagle-eyed patent hawks at More bikes, the new patent describes a new two-stroke engine with a fuel injection system mounted on the back of the cylinder, pointing upwards toward the back wall of the cylinder bore. The injector is set to spray the fuel when the piston is near top dead center, so that unburned fuel won’t get swept out with the exhaust gases, and the fuel is aimed such that the cylinder and piston can both be partially cooled as the fuel evaporates against them.


Honda believes this design can help eliminate some of the complexity of other injected two-stroke designs, helping bring the production and maintenance costs down and potentially making them relevant for manufacture again.

It’s widely believed that Husqvarna and KTM, among others, are sitting on injected two-stroke motor designs and waiting on the right time to debut something. But word is, KTM expects its injected two-strokes to be so complex that they’ll end up being expencive four stroke engines, which could well kill demand. Perhaps with this design, Honda has managed to break down some of that complexity and find a package that can welcome the braappers back into the modern motorcycle landscape.


But language in this Honda patent, as well as the design drawings, suggest that this might not be conceived as a motorcycle engine at all – at least, not in its current form. In the first background paragraph of the application, Honda states that “the two-stroke engine is often preferred over the four-stroke engine in the field of general purpose engines because of the simplicity in the structure.”

Furthermore, that diagram would seem to show a long-stroke engine with a pushrod valve system and a thick mounting flange at the bottom. In addition, the patent wording states that “the liquid fuel may consist of diesel oil or any other fuel that is provided with a lubricating property.” All of which points toward an industrial generator-type machine rather than a high-performance motorcycle engine.



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