|
Tractor Talk Discussion Board |
Re: Re: a little tune-up idea
[ View Follow Ups ] [ Post Followup ] [ Return to Tractor Talk Discussion Board ]
Posted by RKS on May 22, 1999 at 07:53:20 from (171.213.145.85):
In Reply to: Re: a little tune-up idea posted by Butch on May 22, 1999 at 06:36:06:
also - - pre-ignition "dieseling" can often be prevented by using high octane rather than low octane fuel, but not because it is less volatile, but because it is "more" volatile. Again, you are right but for the wrong reason. Actually, the pre-ignition occurs because the fuel detonation is slow and there are still hot combustion gases in the cylinder "dome" as the intake valve opens bringing in new mixture in preparation for the compression stroke. As the crankshaft rotates, momentum will carry the piston mass around the crank bringing in a new fuel "charge" and even before the compression stroke the mixture is already "ignited" from the left-over burning exhaust mixture. This can acually cause the intake stroke to become a "power" stroke, which will rattle the intake valve, and backfire through the carburetor. (you'd hear muffled "pops" back through the air intake) The engine will stumble, the valves will rattle, but it may continue running, often until some load is put on the engine to prevent the momentum of the crank from continuing to close the exhaust valve before the detonation is finished. The high octane fuel will complete the combustion detonation sooner and be fully exhausted past the exhaust valve before it closes completely, and will not pre-ignite the intake mixture. With the switch off, there is no longer a source of ignition and dieseling won't occur. RKS
Follow Ups:
Post a Followup
|
