Diesel saws n such

TACOMATODD · February 18, 2019, 06:38:58 AM

Is their such a thing? I would think, that if so, you could do away with the mixing of the fuel. Has anyone had experience with running diesel in a saw, even if it didn't run QUITE as well, maybe 80%, but did run and live?

TACOMATODD · February 18, 2019, 07:27:20 AM

I just wonder, because of all the inherent lube property that it has, and the fact that it will, albeit poorly, light from a spark. These are the things that I think about at odd hours of the morning. Maybe like aircraft jet fuel, JP8 or something. Close relative.

doc henderson · February 18, 2019, 08:07:50 AM

Welcome Todd. I think that diesel will burn slowly and that makes it safer. Gas can vaporize or in a carb. atomize and mix with air and burn quickly. Think explode. Diesel requires extreme compression and therefor requires injectors to put the fuel where it belongs. If you designed a diesel engine for a handheld saw, it would likely be heavy and expensive but they do last longer. Pure diesel in a gas engine I doubt would run at all. gas in a diesel would poss. damage the engine. I know some truckers will add a little gas to diesel in the winter, and I know that diesel is less refined than gas and more like an oil, but my saws are two expensive to want to try that. I will give you credit for thinking outside the box.

I bet some of the engine/chainsaw mechanics will have an opinion and or experience r.e. your question.

Allar · February 18, 2019, 08:53:46 AM

Model Profile: XA

Comet norskprodusert dieseldrevet motorsag fra ca. 1950 (Comet Norwegian Diesel Powered Chainsaw) - YouTube

moodnacreek · February 18, 2019, 09:16:51 AM

Diesel engines where developed to burn cheaper fuel than gasoline. Many gas engines could be ordered to burn kerosene or fuel oil. The heaver fuel required lower compression and as many as 4 different pistons might be available for the same engine. These would be spark fired engines that often started on gasoline to warm up an then switched to the cheaper fuel. The well known Wisconsin air cooled engines where offered in fuel oil burning. probably for export. True diesels are self fired and where more expensive but the real answer to burning cheap fuel. All this has changed as gasoline is now the cheaper fuel and you would not want to be bothered with all the problems spark firing diesel in a chain saw. I would think fuel injection would be next in chainsaws.

mike_belben · February 18, 2019, 11:10:01 AM

Diesels are in the 16 to 21:1 compression ratio for compression ignition to occur. Youd break pull ropes and rotator cuffs left and right. I dont think diesel will ever be the direction saws go. Not to mention the lower lubricity that the ultra low sulphur mandated fuels have to offer.

If youve ever tried to start a diesel genny or plate compact with pull rope and decompressor.. Theyre pretty hard to get going. And need heavy flywheels to dissipate the twisting torsional loads on the crank so youd have to lug that around. In general men are getting wimpier, not tougher.

sawguy21 · February 18, 2019, 11:55:05 AM

The big drawbacks are weight and as mentioned cold weather starting. Diesels are built for torque not speed, a more aggressive chain could be used but the vibration would be unbearable. Run one of the early saws to get a taste of it. ;D

moodnacreek · February 18, 2019, 01:51:24 PM

Anything put on a chainsaw that makes it weigh more that the current model will not sell. Men are getting wimpier and I am old and never pick up a chainsaw any bigger than the job calls for.

Ianab · February 18, 2019, 04:11:33 PM

Quote from: moodnacreek on February 18, 2019, 01:51:24 PMMen are getting wimpier and I am old and never pick up a chainsaw any bigger than the job calls for.

I'd put that down to getting smarter.... :D

joe_indi · February 18, 2019, 10:12:53 PM

In school as an Air force cadet here I had to construct aeromodels powered by miniature compression combustion engines .75cc to 2.5cc
These were called diesel engines, quite different from glow plug engines like Cox /Thimbledrome.
The fuel was 50% Ether (to lower the combustion point) 25% Castor oil and 25% kerosene. These engines had variable compression by way of a cylinder that could be made to move up (low comp) and down (high comp)
Starting was at low compression and then compression was increased to get better combustion.
These were 2 strokes.
Having seen these engines what came to mind was cannot the same technology be repeated in slightly bigger engines. Instead of Ether use gasoline to lower combustion point of regular diesel, have a similar setup for variable compression.
Being two strokes they were relatively light weight
Thinking out of the box. ;)
The video shows a .75cc Mills, a classic
https://youtu.be/-5w1Goa4fok

mike_belben · February 18, 2019, 10:51:19 PM

The diesel cycle makes more torque than gas largely because the injector is post intake valve and can inject for far longer duration than a gas fuel injector spraying into the manifold at a closed valve. This puts diesel bmep peak [cylinder pressure] at much closer to 90* crank angles where it has vastly more leverage to put torque into the crank despite much lower rpm and HP comparatively with gassers of similar size. The kind of torque our puny clutches cant take. And worse, its at much lower RPM than a 2stroke saw. With centrifigul flyweights rpm is everything.

So now we need a stouter piston and rod, a tougher jug and block with bigger bolts to hold the pressure in. a steel injection pump and injector, a decompressor, a heavy flywheel and heavy clutch, a stout starter and pull rope. Problem is above maybe 6000 rpm or so there just isnt gonna be enough time for a stratified direct injected diesel charge to find air, so the result is smoke which epa is not gonna allow, nor will the consumer want to stand in a coal plume cutting a tree. And how much extra patience has anyone got to go back to 1950s chain speed? A crosscut bucksaw might be faster.

Basically theres nothing wrong enough with gas saws that warrants the switch. The consumer today is thinking lithium ion or gas, not gas or diesel. This is all in my opinion and i could be mistaken, nor do i intend any offense. Its a good discussion to kick around.

TACOMATODD · February 19, 2019, 03:11:13 AM

No offense has been taken and I have only taken good educational experience and opinions from this thread. After all, that is why I asked. As always, when I ask a well formulated question, I get very good responses. It's like I have told people and learned SEVERAL decades ago, "you don't know if you don't ask". Treat people like you want to be treated, and say please n thank you. To me, those VERY simple things will take you a long way in life. THX!

Air Lad · February 19, 2019, 04:46:25 AM

Saw a 4 stroke also
Too heavy
When two stroke is dead batterys will probably prevail
And I will cryingsmiley_cry

mike_belben · February 19, 2019, 06:57:57 AM

I agree with you there todd.

HolmenTree · February 19, 2019, 11:37:31 AM

Diesel saws can be lightweight, in 1949 a Norwegian invented one that weighed only 18 lbs.

sawguy21 · February 19, 2019, 11:41:21 AM

Quote from: Air Lad on February 19, 2019, 04:46:25 AM
Saw a 4 stroke also
Too heavy
When two stroke is dead batterys will probably prevail
And I will cryingsmiley_cry

Shindaiwa had an 80cc 4 stroke prototype, a rep said the torque was unbelievable but they are not yet ready to market it.

HolmenTree · February 19, 2019, 11:50:48 AM

There's a few Chinese 4 strokes on the market already that are surprisingly lightweight.

Somewhat Handy · February 19, 2019, 02:03:51 PM

So, do these diesel saw prototypes use special alloys and/or forged parts to keep crank, piston and cylinder lighter? Also could a diesel saw sacrifice some of its prodigious torque with added gearing to keep rpms up? This just begs more questions...

Somewhat Handy · February 19, 2019, 02:10:30 PM

Here is a neat read about an 18cc diesel that powered bicycles back in the 50's:

1951 LOHMANN 18cc DIESEL ENGINE (New-old-Stock, Unused) | The Online Bicycle Museum

I guess these things can get pretty small

doc henderson · February 19, 2019, 04:43:29 PM

that is cool, I would get one just to have. I assume that is an old comment or are they still available, "new old stock".

Ianab · February 19, 2019, 05:12:30 PM

Quote from: Somewhat Handy on February 19, 2019, 02:10:30 PM
Here is a neat read about an 18cc diesel that powered bicycles back in the 50's:

1951 LOHMANN 18cc DIESEL ENGINE (New-old-Stock, Unused) | The Online Bicycle Museum

I guess these things can get pretty small

Did you read the "cold start" instructions. Basically put the thing in gear, then pedal for about a block with the engine turning over. I guess that warms the cylinder up enough for it to then fire...
I don't think that would go down well with a chainsaw. "Pull rope briskly 100 times, then open throttle and pray"
As for small diesels, here's a 0.8 cc compression ignition engine. ;D
Cox .049 Diesel Bee Engine
Fuel mix is a bit exotic though.

Somewhat Handy · February 19, 2019, 05:15:35 PM

Yeah, I thought about the difference between leg and arm strength, then I briefly pictured a kick start chainsaw. :D

mike_belben · February 19, 2019, 06:37:13 PM

Maybe on hotsaw night at the county fair. Bring your overalls, leave your tshirt at home.

;D

samm · February 23, 2019, 12:43:54 AM

Not 4 stroke, but Stihl 500i, new fuel injected chainsaw. Seems to be pretty legit:
https://www.stihl.com/STIHL-power-tools-A-great-range/Chainsaws/Petrol-chainsaws-for-forestry/287735-131/MS-500i.aspx

Woodcutter_Mo · March 01, 2019, 09:49:23 AM

I think it would be neat to own a diesel powered chainsaw, but I can't imaging it being light enough or fast enough to be practical for regular use.

To combat tricky cold starts, I would think having a small glow plug like the nitro RC engines with a hand held glow plug heater would help?