Comet Diesel

[jdemaris]

Comet saw is not a diesel engine

A diesel cycle engine has no throttle, speed is controlled only by metering the fuel.

What is usually called a "diesel" engine, is a compression-ignition engine invented by a British guy named Clark. So, if anything, it ought to be called "Clark" fuel, not "Diesel."

A lack of air-shutter throttle is true for many "diesels", but not true for all. Some use air-governors that are controlled by a butterfly valve in the air-intake. So, the throttle is controlled by that valve opening and closing, similar to a gas engine. Many British International Harvester tractors are that way, as well as some Fordsons. They are true compression-ignition engines with air-shutter throttles.

The Coment chainsaw does not have a diesel engine. It only RUNS on diesel, as you already stated. More specifically, it is NOT a compression-ignition engine. It uses a glow plug to create ignition instead of heat from compression. Many European farm tractors use to have the same principal and were called "hot bulb" engines.

Many older US farm tractors that were sold as "all fuel" tractors also burned diesel, alcohol, distillate, etc.

 

[JasonBmac]

Yeah, a hot bulb engine, now I remember! Like some of those crude-oil burning farm tractors the Russians built and such.

Anyway you cut it, I'd damned near kill to own one.

J

 

[roalco]

Yes, it's a "hot bulb" or "semi-diesel" engine, and rather than using an injector (and a lubricating system) it atomises the diesel in a carburettor to lubricate the crankcase. They still use a high compression ratio, normally over 18:1 and are inherently hard to time correctly as you have only original design parameters (and clearances) to time the fuel ignition. Yamaha made a bunch of "Kerosene" semi diesel 30hp outboards in the last 20 years, all seem to have gone to third world countries.
My Toyota Landcruiser diesel (3B) ( 4 stroke) has a butterfly controlled fuel rack for the injector pump.
And don't forget the biggest recipricating engines (marine) in the world are diesel, and 2 stroke (cycle) but with enclose crankcases and forced lubrication, up to 10,000hp per cylinder and up to a 365 ton crankshaft for a 9 cylinder engine ( a bore of about 3 feet and a 5 foot stroke), the injector is larger than a big man....

 

[JasonBmac]

Yeah, I've seen those engines.... Cylinders about 10 men tall IIRC. Sulzer?

Bearing caps you could string a hammock in...

J

 

[roalco]

Yep, you are right on the nose, Sulzer RTA-96 (and the lead up engines)!
But my favorite "over the top" diesel is still the old Napier-Deltic... some serious engineering there!

 

[JasonBmac]

Ah, the triangular abomination! To me, there's an elegance in simplicity.... Napier was not noted for elegance or simplicity :hmm3grin2orange:

 

[jdemaris]

Yes, it's a "hot bulb" or "semi-diesel" engine,

They still use a high compression ratio, normally over 18:1 QUOTE]

That doesn't make any sense, going by anything I know about "semi-diesel" engines. They have to run even lower compression then gasoline engines, and much lower than any true diesel.

The Comet chainsaw could be run on diesel, gasoline, or distillate, just like many old farm tractors. There's no way it could of been 18 to 1 compression and suitable for gasoline running. Semi-diesels are usually around 3 to 1, to 4 to 1. That goes along with reports of how easy the Comet was to turn over.

I've worked on many European two-stroke-cycle semi-diesels and they all have very low compression-ratios.



I've converted many old "all fuel" farm tractors to "gasoline only." That entails bumping up the compression ratio to 7 or 8 to 1 ratio. They make more power, are more efficient, but can no longer be run on diesel or kerosene.

 

[eyolf]

I don't know what the static comp ratio of semi-diesels, or hot bulb diesels were, and I suspect some really were as low as 3:1, especially the really old ones designed to run on crude oil. Some of those had injectors that squirted the crude against the hot piston head to vaporize (some of) it and still relied on the hot bulb for ignition.

In a sense, we really shouldn't call them semi-diesels, because most of us understand "Diesel" to mean compression ignition, as so well explained above. The Hot bulb starts the fire about the same as a spark plug or igniter, burning as a controlled bang.

Its pretty telling that Jonsered abandoned the semi-diesel concept pretty quickly; while there was an advantage in not being finisky about fuel, there was definite advantages to the spark ignition engines and by the 1950's flywheel magnetoes worked very well. Those old comets and Jonsereds might be a lot of fun to fondle and enjoy today, but if that's what you had to earn your bacon with and somebody offerred you something more modern you'd certainly be listening!

 

[Rudolf73]

What is usually called a "diesel" engine, is a compression-ignition engine invented by a British guy named Clark. So, if anything, it ought to be called "Clark" fuel, not "Diesel."
[snip]

As far as I know the "diesel" compression-ignition engine was invented by Rudolf Diesel - hence the name.

 

[roalco]

Well, I'm only going on my personal diesel operational training and experience, but I will refer to "Southerns Marine Diesel Oil Engines", 10th edition, pp C34-35 where they discuss Hot Bulb engines. They state that for the action of a "2-cycle Explosive Engine (Hot bulb semi-diesel)" on the upstroke you have "compression of scavenge air to about 200 psi..." and "firing is obtained by the combined effects of moderate compression and the hot bulb, or uncooled part of the cylinder head against which the liquid fuel is injected by the pump".
Now, I'm not sure how you would achieve that pressure with a 3:1 CR, and given a normal gasoline engine with a CR of 10.5:1 (not at all near the peak thermal efficiency range of gas engines at 16-18:1 with the appropriate octane rating fuel) will give you about 165psi, I will grant you I may have been a bit high (although I do recall Bolinder SD engines having a CR close to that) so maybe 14:1 or 15:1 is a more suitable number. I stand corrected.
Still, it's all moot until we have a spare Comet to tear down, inspect and measure, and unfortunately, with scarcity, that will probably not happen!

 

[ironman_gq]

The engine in my jeep is only an 8:1 motor and it develops well over 150-160psi. My race friends with engines in the 11-12:1 and up have over 250psi and run on alcohol.

 

[jdemaris]

As far as I know the "diesel" compression-ignition engine was invented by Rudolf Diesel - hence the name.

Nope, Rudolph Diesel was not even close. At best, he was the third.

Dugald Clark invented and marketed the first working "diesel engine" in 1878. That's 18 years before Rudolph Diesel. The design much later got bought by General Motors and became the famous "Detroit Diesel", a supercharged two-stroke-cycle compression-ignition engine.

Herbert Stuart perfected a fuel injection system along with an 18 to 1 compression ratio of a "diesel" and got it patented in 1890.

Rudolph Diesel's first attempt to build a "diesel" was in 1893, and it blew to pieces the first time he tried to demonstrate it. His first successful "diesel" was in 1896.

 

[jdemaris]

Now, I'm not sure how you would achieve that pressure with a 3:1 CR,

The working high limit for any hot-bulb engine is around 7 to 1 mechanical compression ratio. Anything above that causes problems with premature combustion with the use of a vaporizing carburetor. In a nut-shell, that's how the first compression-ignition engine got invented. It happened with experiments and efforts to make the hot-bulb engine more efficient by raising compression. Since 7-1 is the high-limit with a carburetor, fuel injection was tried instead. Once this was done, with the time-of-injection creating the beginning of the internal explosion, the engine became, by definition, a compression-ignition engine.

With the Comet? It could not be anywhere near 18 to 1, because it is also capable of running on gasoline. The use of gasoline would give it a high limit somewhere around 6 to 1.

 

[eyolf]

Couldn't help it, I went looking for a few facts surrounding diesel engines and relatives.

Astounding, what you can learn in a short time with nothing more than a computer and a telephone line. In the end, a large number of engine designs seem to fall under the heading "Diesel" today, even though Diesel's ideas refer to just one type, and that was really all about improving efficiency and use of cheap fuels like coal dust and unprocessed veggie oils, not about the basic design of the engine.

Isn't it usually true that any new idea is more like a series of improvements on what came before? How do we pick who gets to put their name on it?

The Comet and Jonsered "Diesels" weren't top sellers, for obvious reasons. I am not sure what happened to the Comet people, but Jonsered folks still put their name on stuff today, and not just chainsaws. Im a Jonsered man, myself, and believe they had the best saws, period, for a short time in the 1960's and 1970's, so they must have learned fast.

I will say I wholeheatedly disagree with Jonsered's saying they had the first lightweight, one-man chainsaw in 1954. Maybe the first lightweight, one-man saw that started with a match, and could burn kerosene, paint thinner, etc.

****

 

[jdemaris]

a large number of engine designs seem to fall under the heading "Diesel" today, even though Diesel's ideas refer to just one type, and that was really all about improving efficiency and use of cheap fuels

Isn't it usually true that any new idea is more like a series of improvements on what came before? How do we pick who gets to put their name on it?

About inventions, many of the most famous inventions were first created by people who never got any credit. Often someone higher up on food-chain would pick-up on a idea done by someone else (sometimes an employee). That's true with inventions, medical cures, land discoveries, etc.

Scurvy used to be the #1 disease problem associated with long sea travel. French explorers in the "New World" (Cartier and Champlain) were given cures twice by local Indians (Sassafrass) starting in the 1500s. And who took credit years later? A British doctor using lime fruit to give the same vitamin C for prevention and cure.

A way to prvent Variolas (small pox) was discovered by observing captured black slaves from Africa. Who took credit for it? Many white doctors including Cotton Mather in Boston, Massachusetts in the early 1700s.

Who invented the automobile? I often hear Mercedes Benz taking credit for "inventing the auto in their commercials. Hmm. What exactly is an "automobile?"

In 1769, Joseph Cugnot in France built a working auto that could be driven on the road with steam power.

In 1858, Jean Lenoir built an auto that ran on coal gas and drove it 50 miles to demonstrate.

In 1864, Siegfried Marcus built and demonstrated the world's first know automobile to run on gasoline.

In 1886, Gottleib Daimler built his first gasoline powere four-wheel auto. NOT exactly first and never offered for sale to the public.

In 1889, the first automobile in the world that was built and offered for sale to the public was in France, by Panhard and Lavassor.

 

[jdemaris]

. . . they discuss Hot Bulb engines. They state that for the action of a "2-cycle Explosive Engine (Hot bulb semi-diesel)" on the upstroke you have "compression of scavenge air to about 200 psi..." and "firing is obtained by the combined effects of moderate compression and the hot bulb, or uncooled part of the cylinder head against which the liquid fuel is injected by the pump".
Now, I'm not sure how you would achieve that pressure with a 3:1 CR, and given a normal gasoline engine with a CR of 10.5:1 measure

Some of the most famous hot-bulb "semi-diesels" in Europe are the Landini, Field Marshall, and Lanz Bulldog that were used in many farm tractors up to the late 1950s. They started out with compressioin ratios of 3 to 1, and reached a high of around 6.5 to 1.

In the USA, many farm tractors used "all-fuel" engines that used controlled spark ignition instead of a glow-plug. One example is the John Deere B farm tractor. The "all fuel" version that ran on kerosene, diesel fuel or gasoline had a compression ratio of 4.7 to 1 (and cranked at 70 PSI). The gasoline-only version was upped to a compression ratio of 5.8 to 1 (cranked at 110 PSI).

 

[eyolf]

I've also heard of the indians giving the white man juniper (cedar) berries and boiling the twigs and scaly needles to make a nasty tea for vitamin C. To be really fair, the whole scurvy cure thing was "discovered" several times in Asia and S. America as well. Are we whiteys dense, or maybe not to quick to share what we've learned?

AS regards the automobile, not many people thought of it as a great invention at first. In fact, they were widely hated, as they were noisy, smelly, expensive to own and operate, and there were few places they could legally be used. Maybe we thought of "inventions" as useful things like mousetraps, not contraptions like the horseless carriage.

 

[JJuday]

There are many engines and specific designs that end up being lumped under the diesel banner. Rumley-Oilpull and many other manufactureres built farm equipment that ran on tractor gas/kerosene. These engines still needed a spark ignition source, but the ignitor more resembled a modern glow plug in operation than a spark plug. Many of these engines either had to have a pony motor to start or had to be a true multi-fuel and start on gasoline.

Diesel engines are true compression ignition engines, while many others given credit for being the first or before Rudolph Diesel's design were not exactly true compression ignition engines. Diesel's CIE was the first truly successful and viable design.

Many OEM's realized that Kerosene burners were a lost cause before the end of WWII. From then on it was a race between gasoline and diesel. Early diesel engines use a pre-combustion chamber know as Lanova Energy Cell combustion. By the dawn of the 60's Direct injection was replacing the indirect Lanova system and turbocharging was becoming common.

Some of you may have seen, used or worked on the older Contenential or Hercules multi-fuel engines in the old duces of Vietnam vintage. They were not particularly good at anything but holding the front of those truck down! The last attempt of the multi-fuel engine.

JJuday

 

[jdemaris]

I've also heard of the indians giving the white man juniper (cedar) berries and boiling the twigs and scaly needles to make a nasty tea for vitamin C. .

As far as can be told from written history, the sassafrass tree was misidentified as the red cedar. It was first given to Jacques Cartier by some Algonquian speaking Indians near what is now Québec. That's why the Red Cedar was wrongly named "Tree of Life" or Arbor Vitae. The actual credit should of been given to sassafrass.

Sir Walter Raleigh, of tobacco fame, got rich harvesting sassafrass from the "New World" and selling it all over Europe. It was considered a cure-all for just about anything, at the time.

 

[Freehand]

Yes, it's a "hot bulb" or "semi-diesel" engine, and rather than using an injector (and a lubricating system) it atomises the diesel in a carburettor to lubricate the crankcase. They still use a high compression ratio, normally over 18:1 and are inherently hard to time correctly as you have only original design parameters (and clearances) to time the fuel ignition. Yamaha made a bunch of "Kerosene" semi diesel 30hp outboards in the last 20 years, all seem to have gone to third world countries.
My Toyota Landcruiser diesel (3B) ( 4 stroke) has a butterfly controlled fuel rack for the injector pump.
And don't forget the biggest recipricating engines (marine) in the world are diesel, and 2 stroke (cycle) but with enclose crankcases and forced lubrication, up to 10,000hp per cylinder and up to a 365 ton crankshaft for a 9 cylinder engine ( a bore of about 3 feet and a 5 foot stroke), the injector is larger than a big man....

Yup.