Fuel Injection and Variable Timing

[Charles Talleyrand]

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

[jmk]

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.]

[Matt Barrow]

"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.

[Robert M. Gary]

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

[Robert M. Gary]

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

[[email protected]]

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

[Capt. Geoffrey Thorpe]

"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.

[Robert M. Gary]

> 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

[karl gruber]

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
>

[Allen]

"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

[Allen]

"Allen" > wrote in message
. net...
>
> "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
And I forgot to add: computer controlled variable ignition timing. No
magnetos.

http://www.libertyaircraft.com/libertyxl2/engine.php

Allen

[J. Severyn]

"karl gruber" > wrote in message
...
>
> For the most part, only diesel engines have direct injection.
>
> Karl
> ATP, CFI, Etc.
> "Curator" N185KG
>

But there are a few new gasoline engines that do use direct injection. The
Mitsu/Volvo engine is one.
http://www3.bc.sympatico.ca/Volvo_Books/engine6.html

GM has several DI engines also:
http://www.greencarcongress.com/2006/05/gm_powertrain_u.html
I believe one of these engines is used in the Saturn Sky roadster.

It would be nice to see this technology transferred to aero engines as it
looks like it improves fuel economy and gets more power for the same size
engine. Well, don't hold your breath....unless you jump over to
rec.aviation.homebuilt

Regards,
John Severyn @KLVK

[Capt. Geoffrey Thorpe]

"J. Severyn" > wrote in message
...
>
> "karl gruber" > wrote in message
> ...
>>
>> For the most part, only diesel engines have direct injection.

<...>
> But there are a few new gasoline engines that do use direct injection. The
<...>
> It would be nice to see this technology transferred to aero engines as it
> looks like it improves fuel economy and gets more power for the same size
> engine. Well, don't hold your breath....unless you jump over to
> rec.aviation.homebuilt

The fuel economy improvements are seen at lighter loads. At aircraft type
loads (60+%) and at altitude you can't run lean and/or stratified so you
don't gain much economy.

The improvment in power from the increased volumetric effciency and charge
cooling would still apply.


Geoff.

[[email protected]]

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


>Allen
...

Thanks for the info. It is about time the major aircraft engine makers
got out of the stone age.

Ben
www.haaspowerair.com

[[email protected]]

: The fuel economy improvements are seen at lighter loads. At aircraft type
: loads (60+%) and at altitude you can't run lean and/or stratified so you
: don't gain much economy.

: The improvment in power from the increased volumetric effciency and charge
: cooling would still apply.


The "stone-age" of aviation engines which many people gripe about do not appreciably affect the
steady-state operational efficiency save one: air-cooling and octane requirements. Magnetos, fixed timing,
carbs, etc all work rather well in the fixed operating regime of cruise power. A few percent might be
obtainable with variable timing or direct injection, but a BSFC of 0.42 lb/hp*hr (typical for LyContosaurus)
is pretty good for a spark-ignition gasoline engine. If the same engine were to be liquid-cooled and run 12:1
on the 100LL like the automotive counterparts (or 87 AKI "crapgas" on 8.5:1 like their automotive
counterparts), that's more to the tune of 10% efficiency gain. Point-maintainence and ham-fisted-leaning
aside, the old-school works well for efficiency if properly used... just takes more care and feeding to keep
it there.

-Cory


--

************************************************** ***********************
* Cory Papenfuss, Ph.D., PPSEL-IA *
* Electrical Engineering *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

[Matt Barrow]

> wrote in message
oups.com...
> >Check out the Liberty with the TCM IOF-240. It has pulsed injectors just
>>like (well, similar to) your Saturn.
>
>
> Thanks for the info. It is about time the major aircraft engine makers
> got out of the stone age.

Even some of the stone age stuff is improving.

http://www.radialengines.com/fuel_injection/index.htm

[Private]

"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

I also own a couple of >96 S1 series Saturns and am very happy with their
economy and utility, however I think you are mistaken regarding the fuel
injection.

AFAIK the 91-94 SOHC engines used a single electric injector mounted in the
throttle body. The 95> and all DOHC engines use one injector per cylinder
located in the port close to the valve, however while this is called
sequential port injection the injectors pulse once per revolution (@60
degrees BTDC) or twice per cycle so are actually pulsing on both the intake
and exhaust cycle. It seems counter-intuitive to me, but it works well so
the Saturn engineers must know something we don't. The ignition is also a
waste spark type that simultaneously fires two cylinders, one near the top
of the compression stroke and one near the top of the exhaust stroke.

[[email protected]]

Matt wrote "


>Even some of the stone age stuff is improving.

>http://www.radialengines.com/fuel_injection/index.htm


Thanks Matt, I always wonder why it takes sooo long for a simple idea
to get put into motion. 11,000 - 12,000 grand seems high but The "FAA"
blessing accounts for more then half of it I bet.

Ben
www.haaspowerair.com

[Eduardo K.]

In article <_EOdg.194434$P01.165735@pd7tw3no>,
Private > wrote:
>
>
>AFAIK the 91-94 SOHC engines used a single electric injector mounted in the
>throttle body. The 95> and all DOHC engines use one injector per cylinder
>located in the port close to the valve, however while this is called
>sequential port injection the injectors pulse once per revolution (@60
>degrees BTDC) or twice per cycle so are actually pulsing on both the intake
>and exhaust cycle. It seems counter-intuitive to me, but it works well so
>the Saturn engineers must know something we don't. The ignition is also a
>waste spark type that simultaneously fires two cylinders, one near the top
>of the compression stroke and one near the top of the exhaust stroke.
>
>

Your engine is multiport but not sequential. Seq-multiport inyection fire
each injector individually and only when the valve is open. It improves
idle and part throttle economy. At medium to high loads injector are
open most of the time anyway, so when they open is not as critical
so the advantages of sequential are not important..



--
Eduardo K. |
http://www.carfun.cl | Freedom's just another word
http://e.nn.cl | for nothing left to lose.
|

[Eduardo K.]

In article >,
Aaron Coolidge > wrote:
>
>I have yet to see a fuel-injected car that fires its injectors at exactly
>the right time as the intake valve opens. The injector is a little solenoid,
>and has ~5 mS response time opening - longer when closing. A 3600 RPM car
>engine is running at 60 Hz, ie, one revolution per 16.67 mS.
>
>On my analog fuel injection car (1977), all the injectors run in parallel.
>Pulse width is varied according to RPM. The airflow meter biases the pulse
>width a tiny bit. The injectors create a little cloud of finely atomized
>gasoline which gets sucked into the cylinder as the intake valve opens.
>Interestingly enough, although it's port FI, there is a single injector
>in the intake manifold just aft of the throttle body. It turns on at full
>throttle to further enrichen the mix, and also gives a shot of fuel when
>starting the engine presumably for priming (there is no choke, of course).
>It's the height of 70's technology which the Japanese licensed from the
>Germans (Hitachi copy of L-Jetronic).
>

Bosch Motronic cars fire the inyectors individually so they are open while
the intake valve is. You are correct that at a mid to upper range
injectors are open more that what the intake valve is open. It just poodles
behind it.


--
Eduardo K. |
http://www.carfun.cl | Freedom's just another word
http://e.nn.cl | for nothing left to lose.
|

[Matt Barrow]

> wrote in message
oups.com...
> Matt wrote "
>
>
>>Even some of the stone age stuff is improving.
>
>>http://www.radialengines.com/fuel_injection/index.htm
>
>
> Thanks Matt, I always wonder why it takes sooo long for a simple idea
> to get put into motion. 11,000 - 12,000 grand seems high but The "FAA"
> blessing accounts for more then half of it I bet.

Probably 80%+; most of it is off the shelf parts, but when you put all those
OTS part together, in an FAA bureaucratic world....

[Matt Barrow]

> wrote in message
oups.com...
> Matt wrote "
>
>
>>Even some of the stone age stuff is improving.
>
>>http://www.radialengines.com/fuel_injection/index.htm
>
>
> Thanks Matt, I always wonder why it takes sooo long for a simple idea
> to get put into motion. 11,000 - 12,000 grand seems high but The "FAA"
> blessing accounts for more then half of it I bet.

Combine the above with, say, this: http://www.wacoclassic.com/sales.html

I think I've found my next Big-Boy-Toy :~)

[soxinbox]

The continuous injection causes gas vapors to build up while the valve is
closed, and these vapors tend to float into the intakes of the other
cylinders. This is why the rear cylinders burn richer than the front in
typical 6 cyl fuel injected aircraft engines. The sequential injection in
car engines eliminates this problem. The fuel injected aircraft engine is
not much better than, if not worse than, the central ( throttle body )
injection system.

"Capt. Geoffrey Thorpe" <The Sea Hawk at wow way d0t com> wrote in message
news:Y4qdnUbiTJtM6OrZnZ2dnUVZ_sidnZ2d@wideopenwest .com...
> "J. Severyn" > wrote in message
> ...
>>
>> "karl gruber" > wrote in message
>> ...
>>>
>>> For the most part, only diesel engines have direct injection.
>
> <...>
>> But there are a few new gasoline engines that do use direct injection.
>> The
> <...>
>> It would be nice to see this technology transferred to aero engines as it
>> looks like it improves fuel economy and gets more power for the same size
>> engine. Well, don't hold your breath....unless you jump over to
>> rec.aviation.homebuilt
>
> The fuel economy improvements are seen at lighter loads. At aircraft type
> loads (60+%) and at altitude you can't run lean and/or stratified so you
> don't gain much economy.
>
> The improvment in power from the increased volumetric effciency and charge
> cooling would still apply.
>
>
> Geoff.
>

[karl gruber]

Sox,

It's just the opposite.

The front cylinders run richer than the rear.

It's called "the occult migration of fuel!"

Karl
"Curator" N185KG
Gami ser# 0019


"soxinbox" > wrote in message
...
> The continuous injection causes gas vapors to build up while the valve is
> closed, and these vapors tend to float into the intakes of the other
> cylinders. This is why the rear cylinders burn richer than the front in
> typical 6 cyl fuel injected aircraft engines. The sequential injection in
> car engines eliminates this problem. The fuel injected aircraft engine is
> not much better than, if not worse than, the central ( throttle body )
> injection system.
>
> "Capt. Geoffrey Thorpe" <The Sea Hawk at wow way d0t com> wrote in message
> news:Y4qdnUbiTJtM6OrZnZ2dnUVZ_sidnZ2d@wideopenwest .com...
>> "J. Severyn" > wrote in message
>> ...
>>>
>>> "karl gruber" > wrote in message
>>> ...
>>>>
>>>> For the most part, only diesel engines have direct injection.
>>
>> <...>
>>> But there are a few new gasoline engines that do use direct injection.
>>> The
>> <...>
>>> It would be nice to see this technology transferred to aero engines as
>>> it looks like it improves fuel economy and gets more power for the same
>>> size engine. Well, don't hold your breath....unless you jump over to
>>> rec.aviation.homebuilt
>>
>> The fuel economy improvements are seen at lighter loads. At aircraft type
>> loads (60+%) and at altitude you can't run lean and/or stratified so you
>> don't gain much economy.
>>
>> The improvment in power from the increased volumetric effciency and
>> charge cooling would still apply.
>>
>>
>> Geoff.
>>
>
>

[soxinbox]

I guess it would depend on the engine. Mine feeds intake air front to back,
so that some of the vapor rich air from the front cylinder feeds the middle
and rear cylinder.

"karl gruber" > wrote in message
...
> Sox,
>
> It's just the opposite.
>
> The front cylinders run richer than the rear.
>
> It's called "the occult migration of fuel!"
>
> Karl
> "Curator" N185KG
> Gami ser# 0019
>
>
> "soxinbox" > wrote in message
> ...
>> The continuous injection causes gas vapors to build up while the valve is
>> closed, and these vapors tend to float into the intakes of the other
>> cylinders. This is why the rear cylinders burn richer than the front in
>> typical 6 cyl fuel injected aircraft engines. The sequential injection in
>> car engines eliminates this problem. The fuel injected aircraft engine is
>> not much better than, if not worse than, the central ( throttle body )
>> injection system.
>>
>> "Capt. Geoffrey Thorpe" <The Sea Hawk at wow way d0t com> wrote in
>> message news:Y4qdnUbiTJtM6OrZnZ2dnUVZ_sidnZ2d@wideopenwest .com...
>>> "J. Severyn" > wrote in message
>>> ...
>>>>
>>>> "karl gruber" > wrote in message
>>>> ...
>>>>>
>>>>> For the most part, only diesel engines have direct injection.
>>>
>>> <...>
>>>> But there are a few new gasoline engines that do use direct injection.
>>>> The
>>> <...>
>>>> It would be nice to see this technology transferred to aero engines as
>>>> it looks like it improves fuel economy and gets more power for the same
>>>> size engine. Well, don't hold your breath....unless you jump over to
>>>> rec.aviation.homebuilt
>>>
>>> The fuel economy improvements are seen at lighter loads. At aircraft
>>> type loads (60+%) and at altitude you can't run lean and/or stratified
>>> so you don't gain much economy.
>>>
>>> The improvment in power from the increased volumetric effciency and
>>> charge cooling would still apply.
>>>
>>>
>>> Geoff.
>>>
>>
>>
>
>