Comet Diesel
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I have never seen one up close.
But all diesels have to have the fuel injected
under pressure so it will fire.
My guess is the saw has somekind of a small
injection pump and a fuel line to an injector
in the cylinder head somewhere.
Lee
But all diesels have to have the fuel injected
under pressure so it will fire.
My guess is the saw has somekind of a small
injection pump and a fuel line to an injector
in the cylinder head somewhere.
Lee
well http://3.bp.blogspot.com/_4pPwn3qLQV8/SxjptldmqdI/AAAAAAAACyk/kkiUa7tb0TQ/s1600-h/como-3.jpg
i dont know, looks like a regular carb with extra fuel lines.
i dont know, looks like a regular carb with extra fuel lines.
Lee is right - Diesel engines operate on the principle of compression ignition whereby the fuel is injected (so it is atomised - and in turn enabled to burn) into the hot air mixture caused by the compression stroke of the engine. Various designs may incorporate a pre combustion chamber, however modern engines almost always follow the direct injection principle - the most efficient method being common rail, where a high pressure pump and 'manifold' is used as opposed to mechanical unit injectors (MUI's), and jerk pump systems (CAV etc) which are less efficient.
Definitely an interesting saw though - would be good to see one stripped down or a drawing of the fuel system.
Regards,
Chris.
fatboymoe
ArboristSite Operative
It may be a 2 stroke diesel. I just watched a TV program last night that showed how small model airplane diesels worked. They used a carb. set up on the crankcase that went directly to the transfer ports.
JasonBmac
ArboristSite Operative
I can't speak directly for the Comet or other diesel saws, but many very small 2 cycle diesel engines (most often on the nose of an RC plane) are not true diesel cycle engines.... They are compression ignited otto cycle engines, and are carbureted.
The difference is in how the fuel is actually burned.
A diesel cycle engine has no throttle, speed is controlled only by metering the fuel. The mixture is always very lean, in fact it's not a mixture, but a flame burning within the cylinder. Fuel begins to be injected into the compressed air just before the piston reaches TDC, and is ignited by the heat of compression. Fuel continues to be injected as the piston is in the power stroke, and ideally, the burn phase is under constant pressure, as the cylinder volume increases at pace with the fuel burn....
An Otto cycle engine, on the other hand, uses a throttle to control the volume of air introduced to the engine.... And the mixture should always be near the ideal ratio of 14:1 (usually closer to 12:1 in 2 cycle practice). The fuel and air are mixed before compression, and are ignited all at once just before TDC. All the combustion is over by a few degrees after TDC (called "constant volume combustion"), and the power stroke is simply extracting power from the pressure spike that resulted.
If the Comet has a throttle, it is NOT a diesel... But a diesel fuelled Otto engine.... And I suspect that's what it is, as it's easier to implement, especially in a fuel mix lubricated 2 cycle engine.
J
The difference is in how the fuel is actually burned.
A diesel cycle engine has no throttle, speed is controlled only by metering the fuel. The mixture is always very lean, in fact it's not a mixture, but a flame burning within the cylinder. Fuel begins to be injected into the compressed air just before the piston reaches TDC, and is ignited by the heat of compression. Fuel continues to be injected as the piston is in the power stroke, and ideally, the burn phase is under constant pressure, as the cylinder volume increases at pace with the fuel burn....
An Otto cycle engine, on the other hand, uses a throttle to control the volume of air introduced to the engine.... And the mixture should always be near the ideal ratio of 14:1 (usually closer to 12:1 in 2 cycle practice). The fuel and air are mixed before compression, and are ignited all at once just before TDC. All the combustion is over by a few degrees after TDC (called "constant volume combustion"), and the power stroke is simply extracting power from the pressure spike that resulted.
If the Comet has a throttle, it is NOT a diesel... But a diesel fuelled Otto engine.... And I suspect that's what it is, as it's easier to implement, especially in a fuel mix lubricated 2 cycle engine.
J
JasonBmac
ArboristSite Operative
That would probably be a viable approach.... Also, very beefy conrod and mains, stronger (heavier) than normal cylinder, perhaps bored for a counter piston (adjustable compression would be nice, no?)....
If I were to try to build one, I'd borrow as much as possible from model engine construction.... THey've been making diesels for a LONG time.
J
If I were to try to build one, I'd borrow as much as possible from model engine construction.... THey've been making diesels for a LONG time.
J
JasonBmac
ArboristSite Operative
No gasoline 2 cycle engine will be beefy enough. You need to take the compression ratio WAY higher, and you'll break the crank or bend the rod or pound the bearings to bits. I've seen cylinders shear off at the ports, launching the head....
The effective compression ratio of the average gasoline 2 cycle is like 7:1-9:1... You need 15:1 - 20:1 effective compression...
J
The effective compression ratio of the average gasoline 2 cycle is like 7:1-9:1... You need 15:1 - 20:1 effective compression...
J
Mange
Addicted to ArboristSite
These engines have low pressure fuel injector system.
Not directly in cylinder, but in to crankcase.
Then flushed up above piston were it is compressed.
It ignites as there is a preheated chamber above piston that after start is maintaining heat from engine.
Problem is when running without load and engine cool of, it will need some additional heat from propane stored in the handles.
It can start and run on Diesel, gas and many other types of fuel.
All parts of these engines are made in Jonsered, even the Comets.
Not directly in cylinder, but in to crankcase.
Then flushed up above piston were it is compressed.
It ignites as there is a preheated chamber above piston that after start is maintaining heat from engine.
Problem is when running without load and engine cool of, it will need some additional heat from propane stored in the handles.
It can start and run on Diesel, gas and many other types of fuel.
All parts of these engines are made in Jonsered, even the Comets.
look what I found http://www.youtube.com/watch?v=hXR3ZOPlRys
I kept waiting for the smoke to clear
I think he mixed it like the directions said and used the new oil. way over oiled
I think he mixed it like the directions said and used the new oil. way over oiled
