Fuel Injection and Variable Timing

I was curious how much fuel injection and variable spark timing reduces fuel
consumption and increase power in an airplane engine. Auto engine data does
not help because auto engines are run over a wide range of conditions,
wereas an aviation engine typically runs at cruise power and can be
optimized for that.

So ... how much does the more modern fuel injection and electronic timing
help?

Are there any engines that come in both versions such that easy comparisions
can be made?

-Much Thanks

GAMI has done quite a bit of research into that, since their PRISM
system continually varies ignition timing with conditions (including
the fuel octane). Frankly, I paid more attention to the increased
cruise power at altitude than I did the fuel economy potential savings.

Check their web site and see if they have released any of their
numbers. [Since the existing magneto timing on a typical spamcan is
fixed, it's a compromise. The other side of the coin is that with
variable timing you also get a MUCH easier engine start.]

"jmk" wrote in message
ups.com...
GAMI has done quite a bit of research into that, since their PRISM
system continually varies ignition timing with conditions (including
the fuel octane). Frankly, I paid more attention to the increased
cruise power at altitude than I did the fuel economy potential savings.

PRISM hasn't been certified and they've been working on it for six years.

Cars also use port fuel injection. I"m not aware of any airplane engine
that has port fuel injection. I'm sure that must add to the efficiency
of cars a lot. In the 80's some car manufactors used the intake
injection system airplanes use today (as well as throttle body
injection). Apparently they were very difficult to smog, that may tell
you something.

-Robert

Variable timing is also why cars idle nicely and airplanes sound like
they are stumbling when idling.

Most aircraft engines ARE port fuel injection. The other style is the
pressure carb found on earlier models. Of course it is not the
electronic timed port injection most new cars run today that have the
ability to change injector pulse width.

Ben
www.haaspowerair.com

"Robert M. Gary" wrote in message
oups.com...
Cars also use port fuel injection. I"m not aware of any airplane engine
that has port fuel injection. I'm sure that must add to the efficiency
of cars a lot. In the 80's some car manufactors used the intake
injection system airplanes use today (as well as throttle body
injection). Apparently they were very difficult to smog, that may tell
you something.

-Robert


The big advantage to port injection (v.s. throttle body injection) is that
you don't have the whole surface of the intake manifold covered with fuel.
With port injection the puddles are limited to the port area (including the
back of the intake valve). With less liquid fuel mass (and surface area) in
the intake, it is WAY easier to compensate for transient conditions when the
puddle mass is changing. The other advantage, is that it is difficult to get
good cylinder to cylinder fuel distribution with throttle body injection (or
carburetors for that matter).

Aircraft engines don't have the problem with transient conditions since they
pretty much run steady state. The cylinder to cylinder distribution
advantage still stands.

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

The big advantage to port injection (v.s. throttle body injection) is that
you don't have the whole surface of the intake manifold covered with fuel.
With port injection the puddles are limited to the port area (including the
back of the intake valve).

I would say that the advantage of direct port injection is that the
computer puts exactly the right amount of fuel in that cylinder at the
exact right time. The injectors on my Mooney are running all the time,
the injectors on my Saturn only run (actually pulse) when on the intake
stroke. I've never seen aircraft injectors that had computer wires
going to them.

-Robert

Neither your Saturn or your Mooney's injectors squirt fuel directly into the
cylinder. Both squirt outside the intake valve and are basically the same
design except the Saturn has a pulse computer and the Mooney's squirt
continuously.

For the most part, only diesel engines have direct injection.

Karl
ATP, CFI, Etc.
"Curator" N185KG

"Robert M. Gary" wrote in message
ups.com...
The big advantage to port injection (v.s. throttle body injection) is
that
you don't have the whole surface of the intake manifold covered with
fuel.
With port injection the puddles are limited to the port area (including
the
back of the intake valve).

I would say that the advantage of direct port injection is that the
computer puts exactly the right amount of fuel in that cylinder at the
exact right time. The injectors on my Mooney are running all the time,
the injectors on my Saturn only run (actually pulse) when on the intake
stroke. I've never seen aircraft injectors that had computer wires
going to them.

-Robert

"Robert M. Gary" wrote in message
ups.com...
I would say that the advantage of direct port injection is that the
computer puts exactly the right amount of fuel in that cylinder at the
exact right time. The injectors on my Mooney are running all the time,
the injectors on my Saturn only run (actually pulse) when on the intake
stroke. I've never seen aircraft injectors that had computer wires
going to them.

-Robert

Robert,

Check out the Liberty with the TCM IOF-240. It has pulsed injectors just
like (well, similar to) your Saturn.

Allen