ORIGINAL: Flyboy Dave
Someone once said...."don't confuse me with the facts, I already have my mind
made up."
Fact: there is no circumstance where-in and engine will detonate due to a rich
condition. Nor will an engine detonate and backfire due to an accumulation of fuel
(resulting in a rich condition) suddenly "rushing" from the crankcase to the
combustion chamber.
2. Although "octane" (gasoline) does not apply directly to our alcohol/glow engines,
the fuel in our case is still the second leading cause of detonation in our engine. A
high compression (even a European two stroke) will detonate like heck if too much
nitro is used in the fuel.
Fact: there is no adjustment that can be made to the carb needles that will eliminate
the detonation. You can mask it, and you can extend the burn time to get it further
over the TDC point....but you cannot eliminate it without either lowering the amount
of nitro, or lowering the compression ratio by adding shims to the head.
Fact: (again) the compression determines the timing (firing) of the charge, not the
needle settings. The nitro makes it worse because the fuel burns faster, and hotter
Heat=Power.
Dave,
How can the first small paragraph in your post, agree with the second paragraph?
The second paragraph, or rather the exact opposite of it is FACT, yet you are not willing to accept it.
The detonation that causes this type of kick-back, results
not from a rich mixture, but from the sheer volume of the accumulated fuel, from the crankcase, which is suddenly transferred into the combustion chamber and causes an artificially high compression ratio.
When there is a lot of liquid fuel in the chamber, there is less room for the compressed mixture, hence the reason for detonation.
Another fact; a cool, rich mixture is less volatile than than a lean, lukewarm air+fuel mixture.
In other words, a rich mixture will ignite later than a lean mixture, which means a lean mixture will result in more ignition advance...
Isn't this exactly what you are trying to disprove??
Also; the amount of energy that an engine releases in one cycle is a function of the amount of air... Yes, if there is enough fuel, or more than enough fuel,
the amount of air determines how much of this fuel will burn.
And in a mass-to-mass stoichiometric ratio, the amount of air changes very little, but the amount of fuel can be halfed, or doubled, or tripled.
If you decrease the amount of fuel to about 80% of stoichiometric, the engine will not fire (no stratified charge in our glow engines...)
But you can double, or even triple the amount of fuel.
But will you get significantly more power??? NO!
Not beyond about 1.2 stoichiometric, which we normally run and even then it is only about 5% more than 1.0 stoichiometric.
So, I would not want to burden you with facts, Dave, but why does the torque actually increase by about 30-40%, while leaning from a rich two-cycle setting, to peaked, at the same RPM? We are, after all, using the same amount of air, aren't we?
An engine will spin a much large prop at a given RPM, when leaned out, than when running rich.
Could we just be getting closer to the ideal ignition advance, by leaning the mixture? Nah, that can't be... You say.
But the fact is this is exactly what we are doing.
And as far as octane rating goes, methanol is around 120 (please correct me, Brian, if I am in error), even though it contains absolutely no octane (C8H18 hydrocarbon).