More About Leaning During Climb

"John" wrote:
So, what is magic about the 1350 degree sea-level full rich takeoff
temp? Can anyone suggest any good reasons why it is not equally safe
to lean to operate at the 1450 degree conditon during climb?

The EGT isn't what matters; it's the CHT's that are important. As long as
they don't get too high, go ahead and lean as you climb. I have an engine
analyzer that I watch while I climb, using whatever mixture setting I need
to keep the hottest cylinder below 400 deg, F.

If 1450
degrees is good for hours and hours of continuous operation at cruise,
and if cylinder temps are green, why needlessly expend more scarce
fossil fuel operating at 1350 degrees?

No reason at all, IMO.

Won't the engine also develop
more power at 1450 degrees than at 1350, which seems quite worthwhile
for a number of reasons?

Yep.

I'm not trying to be contentious, just
wondering if anyone has ideas about it that I haven't considered.

I think you've got it covered.
--
Dan
C172RG at BFM

wrote in news:beeeb3$13o$1
@solaris.cc.vt.edu:

What do you (or anyone else for that matter) think?

Sounds quite reasonable.

The idea of leaning during climb is to keep the mixture about the same,
and the temps in a good operating range - all of which it seems you are
doing.

Max power is about 100 ROP. That is a point where there is still excess
fuel to vaporize for added cylinder pressure, while at the same time
providing cooling. Lots of power, but it wastes fuel and is not a very
clean burn. Contrary to the original post, higher EGT's does NOT equate
to more power - often the contrary. From Best Power the power actually
declines as you approach peak EGT. This point gives you hotest exhaust
gasses (there are some technicalities here I won't bother with at the
moment), and best economy. LOP, we go further down the power curve
(which we can make up for if we still have more throttle available), and
start cooling with excess air instead of excess fuel. Exhaust is
cleanest.

Critical thing to watch is your CHT's. You are dead on as for keeping
them below 400, and lower would be better but may not be an option in
the climb. Technically EGT's on that Seneca can get to 1650 - but any
EGT measurement is guesswork at best and I prefer not to push it.

Look for CHT's down around 400 in the climb, and 350 in cruise, and you
will be in good shape.


-----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1109-A Shady Lane fax 512-366-4331
Austin, Tx 78721
-----------------------------------------------

Thomas Borchert wrote in
:

That first part of your sentence is something I have NEVER heard of
before. Any source on that?

Anyone here work with water injection internal combustion engines? [Hey,
I round web sites which claim up to 60% more power, with no increase in
fuel flow. But I didn't rush out to give them my credit card number!
G]

And for the latter part: The excess fuel isn't doing any cooling per
se, it is slowing down the burning process, which leads to that
process being cooler.

Quite correct, but there is also a substantial heat of vaporization.

Also, 100 ROP is probably a bad point to be because it is the point of
maximum pressure load during the burning process. A little richer
(like 150) would be better.

True. But "better" is probably open to interpretation however. 100 ROP
gives best power, which also produces the highest peak pressure load -
exactly as you say. Is 150 ROP better? Well, the loads are less, and
so are the temperatures, but so is the power. Less efficient, wastes
more fuel, more pollutants in the exhaust.

A much better solution is to produce the same power but well LOP
(assuming your engine is balanced for it). The pressure wave integrates
to the same effective area under the curve, but the peak is not only
lower but less sharp in form. At the same time the fuel usage is at
maximum efficiency, and the exhaust is cleanest - not only from a
pollution standpoint, but also from the point of reducing any chance of
carbon monoxide risks.

Back to the first two points... anyone who tunes race engines for a
living or some such, want to weight in with more information. Wouldn't
be the first time I'm all wet. G

-----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1109-A Shady Lane fax 512-366-4331
Austin, Tx 78721
-----------------------------------------------

James M. Knox wrote:
: A much better solution is to produce the same power but well LOP
: (assuming your engine is balanced for it). The pressure wave integrates
: to the same effective area under the curve, but the peak is not only
: lower but less sharp in form. At the same time the fuel usage is at
: maximum efficiency, and the exhaust is cleanest - not only from a
: pollution standpoint, but also from the point of reducing any chance of
: carbon monoxide risks.

I feel obligated to throw in a tidbit here. Having worked on
hybrid electric vehicles in a former life, I've run into some interesting
engineering tradeoffs in cars. While it's true that running LOP reduces
CO emissions, it *increases* NOx emissions. With the higher EGTs and
excess O2 running LOP, more of the O2 react with N2 in the mixture to
create NOx's. For cars, the EPA says that's bad too. So, fuel injected,
O2-sensored cars with catalytic converters have a balancing act between
running at peak efficiency, and having to scrub out NOx, or running richer
and burning out excess HC's.

Fortunately, we don't have to put cats on our planes yet, and NOx
is less deadly than CO in flight.

: Back to the first two points... anyone who tunes race engines for a
: living or some such, want to weight in with more information. Wouldn't
: be the first time I'm all wet. G

Usually the racer-performance types are all about the horsepower,
so talking efficiency is generally useless. They run whatever mixture
will maximize HP, nevermind the eye-tearingly rich mixture the exhaust
leaves behind!

-Cory

--
************************************************** ***********************
* The prime directive of Linux: *
* - learn what you don't know, *
* - teach what you do. *
* (Just my 20 USm$) *
************************************************** ***********************

"Mike Rapoport" writes:

Because when cars run ROP they only run slightly rich.

Then their EGTs would be higher, wouldn't they (assuming that the "P"
still stands for peak EGT)?


All the best,


David

--
David Megginson, , http://www.megginson.com/

wrote in message
...

While it's true that running LOP reduces
CO emissions, it *increases* NOx emissions. With the higher EGTs and
excess O2 running LOP, more of the O2 react with N2 in the mixture to
create NOx's.

Higher EGTs? 50 deg LOP is same EGT as 50 deg ROP.

Stan

Stan Prevost wrote:

: wrote in message
: ...

: While it's true that running LOP reduces
: CO emissions, it *increases* NOx emissions. With the higher EGTs and
: excess O2 running LOP, more of the O2 react with N2 in the mixture to
: create NOx's.

: Higher EGTs? 50 deg LOP is same EGT as 50 deg ROP.

Higher EGT's than running rich. Yes, 50 ROP is the same as 50 LOP
by definition, but when rich, there's no more O2 to react and make NOx. I
was actually referring to peak vs. ROP with regards to EGT, but it doesn't
matter all that much. 1450 or 1500 isn't much difference, as they're both
hot as hell. It'll make the exhaust stack glow a nice orange, unless it
gets enough air cooling.

In any event, it's the excess of O2 with high EGT's (close to
stoichiometric burn) that'll make lots of NOx. With all that O2, most of
the CO will be CO2 instead.

-Cory



--
************************************************** ***********************
* The prime directive of Linux: *
* - learn what you don't know, *
* - teach what you do. *
* (Just my 20 USm$) *
************************************************** ***********************

David Megginson wrote in
:

That's interesting information -- I've often wondered why car engines
don't run LOP to cut down CO emissions. Why would the EGTs be higher
LOP than ROP, though?

Actually, I believe most modern automobiles with electronic ignitions run
substantially LOP in cruise. And the EGT's may well be cooler than when
ROP - that's just a question of *how* LOP they are running.

Slightly different issue: Catalytic converters and exhaust gas sensors
potentially could have their place in piston aircraft (I am *not* making a
pitch for the converters, but the exhaust gas sensor would provide very
useful information). Unfortunately, the life of either, in the presence of
unleaded gas being used, is essentially zero. {:(

-----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1109-A Shady Lane fax 512-366-4331
Austin, Tx 78721
-----------------------------------------------

"Mike Rapoport" wrote in news:behdld$nn0$1
@slb6.atl.mindspring.net:

Vaporizing excess fuel (or water) lowers cylinder preasure, it does not
raise it.

Okay... why?

Agreed that each GMW vaporized will absorb some heat, and lower
temperatures (for a given trapped gas) reduces pressure, but each GMW that
is vaporized also represents a substantial increase in either pressure or
volume.

So again, why? [I'm perfectly happy to be wrong, but what you say would
seem to go against every chemistry and physics class I've had over half a
century. [Okay, some of the teachers probably weren't very good, but I
think the basic physical laws are still true. G]

-----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1109-A Shady Lane fax 512-366-4331
Austin, Tx 78721
-----------------------------------------------

Mike Rapoport wrote:
: If you inject water into an engine with no other changes, power will go down
: a lot. I have used water injection to get a high compression engine to run
: on 92 octane fuel and the H2O decreases performance. Now if it were a
: turbocharged engine, I could increase the MP without detonation and produce
: more power, but that power would be the result of burning more air and fuel
: (not the water).

This could also be due to the poor ignition timing after this is
done. The timing (24 BTDC typical) will put the peak pressure pulse after
TDC. If you effectively retard this by slowing the burn with water
injection, the power will go down appropriately.

: Like you said, you are consuming energy to heat and vaporize the excess
: liquid. The energy used to heat the liquid to the boiling point and then
: effect a phase change is lost. You are puting liquid into an engine and
: having it come out the exhaust at a higher energy level (hotter and
: vaporized). That energy came from somewhere. It came from the power output
: of the engine.

Perhaps somewhat, but remember that typically almost 70% of the
energy in the fuel for a gasoline engine is *not* used to turn the crank,
but rather just makes your muffler glow a nice cherry red. It's the
integral of pressure, area, and crank throw that produces rotational
energy in the form of torque and RPM. I believe that water injection is
pretty much like high octane fuel. Some people (idiots, mostly) believe
that by putting fuel in their car that's higher octane than the car's
manual stipulates results in increased performance. All higher octane
does is let *OTHER* changes that can then be done (advanced timing,
increased CR, etc) to increase the power be performed and not damage the
engine. Water injection should amount to the same... all other things
equal, it will reduce the power somewhat. BUT if you do it, you can then
increase the CR, advance the timing, etc... and get more back out of it.


Imagine this: inject water into a high compression
: cylender and rotate the crank. The water will vaporize into steam. If what
: you are suggesting (that the steam is higher in volume and will drive the
: piston) where true, you could make an engine that would produce power and
: steam from water alone.

Man... if only I could get my carb set right for that....


: Try this: Lean to best power mixture in your airplane, note your speed or
: climb rate then go full rich and watch the performance decline.

Oh yeah... here in SW VA at 2100' field elevation, it about
vibrates off its mounts if you takeoff full rich on a 4200' DA day.
Doesn't climb too well either. Too rich is bad for everything except
CHT's.

-Cory


--
************************************************** ***********************
* The prime directive of Linux: *
* - learn what you don't know, *
* - teach what you do. *
* (Just my 20 USm$) *
************************************************** ***********************