LOP operation

On Thu, 15 Apr 2004 20:53:48 -0700, "kage"
wrote:

*****Once again, not necessarily. Once the GAMI injectors are installed,
Deakin has been able to lean right to the point of having the engine
quit due to a mixture too lean to fire, without any roughness at all.
If there's roughness then the injectors are not matched properly.*****

That is just simply incorrect. There is roughness that anyone, including
Deakin and Braly notice. It has nothing to do with the injectors being
mismatched. It has everything to do with the need for the engine's timing to
be adjustable. LOP REQUIRES the timing to be further advanced. GAMI knows
this, and is the reason they are developing their Prism system of engine
management.

Best,

According to Deakin's article "Mixture Magic", the speed at which the
fuel air mixture burns varies depending on the stochiometric ratio.
At the ideal mixture ratio of about 15 to 1 by volume, the mixture
burns fastest. On either side of that ratio, the burning slows down.

Because the timing is fixed, adjusting the mixture is the only way to
vary where the Peak Pressure Point (the point at which the combustion
process produces the highest pressure within the cylinder. It's
important that this occur when the crankshaft throw is about 16
degrees past TDC so that maximum leverage is applied to the piston.
If PPP occurs when the piston is closer to TDC, there is little
mechanical advantage and the pressure of the combustion pushes against
a piston that just pushes back instead of accelerating away and adding
thrust to the rotation of the crankshaft). The timing of the engines
and the mixture setup (full rich) is specifically adjusted such that
during full power operation, the PPP occurs at about 16 degrees past
top dead center. This is the source of the common knowledge that a
rich mixture cools the engine. The rich mixture doesn't hose down the
inside of the combustion chamber, it merely slows down the rate of
burning such that PPP occurs at 16 degrees past top dead center. When
the mixture is leaned out so that it approaches the ideal burning
ratio, the mixture burns faster and the PPP begins to occur while the
piston is much closer to TDC. This increases the pressure inside the
combustion chamber and heat goes up. This is the "peak" part of the
LOP or ROP operation. Either side of "peak" the mixture burns slower
which allows the engine to run cooler.

But lean the mixture further, beyond the ideal, and the rate of burn,
as mentioned above, slows down. This allows the piston to be at 16
degrees past TDC again which greatly reduces heat. It also reduces
the amount of gas you use.

As Deakin points out, at about 8,000 feet and full throttle, the
engine is only producing about 60% power and at that power setting you
cannot hurt the engine no matter where you put the mixture, so you
might as well lean to best power setting (which is rich of peak) and
leave it there, if you want to fly at your fastest cruise speed and
range is not an issue.

If the timing ***COULD*** be varied, there would be no need for a
mixture control knob, it could be set for best ratio by the mechanic
and the variable timing would take care of keeping the PPP at the
proper location. Variable timing would also simplify starting.
Engines start much easier when the timing can be retarded to fire the
plugs when the piston is at about TDC, or perhaps even a little after
TDC.

So in answer to your last statement above, LOP operation does not
require that the timing be further advanced. LOP operation actually
has the affect of retarding the timing because it slows down the
combustion process just as an over-rich mixture likewise slows down
the combustion process, allowing the PPP to occur in the desired
place.

Corky Scott