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Two-stroke engines offer twice as many power strokes for a given number of rotations and pistons by doing the exhaust and intake simultaneously. This normally happens spanning the end of the power stroke and the beginning of the compression stroke, though ideally it would only steal time from the beginning of the compression stroke. By tradition, nearly all two-stroke engines use a carburetor and are lubricated by oil being mixed into the fuel. The problem is pollution: unburned fuel passes right through the cylinder because the intake and exhaust valves open together, and this is made much worse by having the fuel be about 2% to 3% lubricating oil.
KTM fixes this for their two-stroke motorcycles by adding fuel injection. KTM injects into the transfer port, which isn't as good as injecting directly into the compression chamber but should still be a huge improvement. Honda has also filed a patent for a general purpose two-stroke with fuel injection. If one of them simply adds a normal oil pump, many of the problems of two-stroke pollution and annoyance should be gone. Next up, we need this small enough for chainsaws and weed cutters.
(Score: 3, Interesting) by VLM on Tuesday March 21 2017, @12:50PM (1 child)
In more detail a large part of the problem is stationary and marine (and car) type lube systems usually are designed to assume up is up, and it takes a surprising amount of screwing around to get something like an aircraft engine to run upside down even momentarily.
So a conversion for a weed-whacker is likely simple although converting to lithium battery is probably even simpler, while converting a chainsaw that works in any position sounds almost impossible.
Another interesting engineering problem is handling losses is kind of fixed size but oil sump size is about 1 gallon per 1 liter of engine over a range of less than a liter to like 50 liter marine diesels, so a 35 cc weed whacker would have like a shotglass of lube oil which is going to be problematic to deal with an amount that small.
Sharper chains and smarter lumberjacks would probably save more emissions than screwing around with their engines.
Something interesting to think about with automation and drones and stuff is we're probably not long from replacing lumberjacks with drone operators. You can run the worksite 24x7 if you got the operators using night vision gear. Now you need trained lumberjacks because medical and death claims are expensive and happen too often but if a dumb operator kills a robot you maybe fire him and who cares. That lack of high labor cost means productivity isn't quite as much of a driver and now you can have electric motors somewhat slowly cut a tree.
There are machines right now where a lumberjack drives an arm that grabs the tree and cuts the base off and grinds the stump and haul the tree back for processing... now drone that and add low light cameras or just searchlights to make it a 24x7 operation... the days of a well paid dude doing 12 hours of cutting in a forest with his hand held chain saw are basically over. I'd be surprised if there's anyone using chainsaws in 20 years other than arborists doing specialty pruning or similar.
(Score: 2) by dry on Wednesday March 22 2017, @12:58AM
Friend of mine has a 4 stroke Husky weed whacker with a Honda motor, about 23 CC. It has an oil sump + pressurized pump and seems to work well, very clean smelling. IIRC it takes about 200 ml of 10w30.
I have a Stihl 4 stroke, it actually uses mix gas at 50:1, cleaner then most 2 cycles but still stinks at times. There's also been lots of improvements in 2 cycles, I bought a hedge trimmer last year (23.4 cc), Stihl claims that it is pretty clean and fuel efficient due to the design of the cylinder + ports. Computer modeling is wonderful. Stihl is actually going back to 2 cycle from their 4 cycle as they're now good enough for California.
As for chainsaw operators, you won't find any running dull chains, they're so easy to sharpen and even a slightly dull chain slows things down so much.
Faller bunchers work great on fairly flat ground, hydrolic snipper cuts the tree off, branches get stripped and log loaded on the truck in minutes in ideal conditions. Around here in the mountains where they still do high lead as well as helicopter, they're useless and chainsaws aren't going away soon