Fuel injection explanation

"Brian C." wrote in
:

Here is how I start up a Cessna 172-S (IO-360 180HP):

Cold start (oil temp below green arc): Master on, Trottle foward,
mixture foward, fuel pump for 3 sec (look for rise in fuel flow
indicator), throttle to 1/4 inch (about 1000 RPM), Ignition

Warm start (Oil temp in the green arc): Master on, Throttle foward,
mixture foward, fuel pump for 1 sec., mixture back to cut-off,
Ignition. When engine fires, smoothly but quickly retard the throttle
to about the 1000 RPM range, and quickly follow with mixture to full
rich.

Hot start (Oil temp in green arc and engine shut down within last 30
minutes): Master on, Throttle foward, mixture foward, mixture back to
cut-off,

Why mixture forward followed by mixture back to cutoff?

Here is how I start up a Cessna 172-S (IO-360 180HP):

Cold start (oil temp below green arc): Master on, Trottle foward,
mixture foward, fuel pump for 3 sec (look for rise in fuel flow
indicator), throttle to 1/4 inch (about 1000 RPM), Ignition

Warm start (Oil temp in the green arc): Master on, Throttle foward,
mixture foward, fuel pump for 1 sec., mixture back to cut-off,
Ignition. When engine fires, smoothly but quickly retard the throttle
to about the 1000 RPM range, and quickly follow with mixture to full
rich.

Hot start (Oil temp in green arc and engine shut down within last 30
minutes): Master on, Throttle foward, mixture foward, mixture back to
cut-off,

Why mixture forward followed by mixture back to cutoff?




When the plane was shut down last, it was accomplished by pulling the
mixture to cutoff and starving the engine of gas. By pushing the mixture
full foward for the hot start, The fuel in the lines primes the engine
without the need for additional priming with the aux. fuel pump. The engine
catches almost as soon as you engage the starter with a hot start.

FWIW, the cold start procedures in your POH differ from the procedure in mine.
However, it sounds like the hot start procedures are the same.

As to your question about where the engine gets its fuel to hot start ... Even
though you killed the engine with the mixture control, a bit of fuel will still
leak out of the injector lines and into the intake after the engine is shut
down. That is usually *more* than enough to start and run the engine for a few
seconds. In fact it's enough fuel that the engine will flood if it's hot and
the mixture is set rich.

Hot starts on FI engines are problematic. On mine, I almost always (but not
always) get it to light off and run using the POH procedures (throttle at fast
idle, mixture cut off, no boost pump, crank until start, enrichen mixture).
However, some of my Musketeer bretheren with the same Lyc. IO-360 have better
luck with intentionally flooding the hot engine using the boost pump and
mixture control before starting. Then they use the procedure for a flooded
engine. I have once or twice resorted to this when I couldn't get a hot start
with the normal POH procedure.

Also FWIW, I really don't like fuel injection on airplane engines. Sure it's
great not to have to worry about carb heat. But instead I worry about hot
starts and plugged injectors. As far as the "advantage" of quicker throttle
response for FI, I say big deal. Your supposed to throttle up gently on all
engines, so I just don't see FI as an advantage here. Still, the Lyc IO-360
seems to be a pretty good engine and it and I have come to an understanding
about hot starts.

Best regards,

Steve Robertson
N4732J 1967 Musketeer Super III

wrote:



The POH is very specific about cold starting: The auxiliary fuel pump
should be turned on and the mixture control pushed in until you see a
rise in the fuel pressure, then the pump is shut off and the mixture
control returned to idle cuttoff.

The POH states that if the engine is hot, the auxiliary fuel pump is
NOT to be used.

Consequently, hot starts are extremely problematic and I can see why:
you are trying to start an engine that was shut down by pulling the
mixture control to idle cuttoff, which starves the engine for fuel,
then trying to restart it with the mixture control in exactly the same
position. Where does the engine get it's fuel to run under those
circumstances? Some people suggest that the POH should be ignored and
the fuel lines primed as per cold starts.

I'm just asking. I'm always ecstatic when I find that the engine is
cold because I know it will start right up using the cold engine start
procedure. Hot starts....

Corky Scott

On Tue, 22 Jun 2004 08:56:08 -0400, Steve Robertson
wrote:

Also FWIW, I really don't like fuel injection on airplane engines. Sure it's
great not to have to worry about carb heat. But instead I worry about hot
starts and plugged injectors. As far as the "advantage" of quicker throttle
response for FI, I say big deal. Your supposed to throttle up gently on all
engines, so I just don't see FI as an advantage here. Still, the Lyc IO-360
seems to be a pretty good engine and it and I have come to an understanding
about hot starts.

I doubt that the throttle response from carburator to fuel injection
would be discernable. Carburators have a system called the
accelerator pump which literally injects fuel directly into the
venturi when the throttle is snapped open. It's a one time shot to
prevent stumble when you stamp on the accelerator pedal. After that,
the full throttle fuel enrichment system takes over, as long as you
are demanding full throttle, or above normal throttle.

Fuel injection, the type that has individual injectors for each
cylinder, can't do that. The amount of fuel injected has to respond
according to how it's been designed to operate. In todays cars, the
injectors are designed to be able to inject the proper amount of fuel
according to a number of parameters and sensors, all controlled by a
computer. But unless you're flying behind a FADEC system, the fuel
injection systems for Lycoming and Continental are not that
sophisticated.

With the non computer controlled injection systems being used in
aviation right now, the only advantage you get over carburators is not
much worry about carb ice and somewhat better fuel distribution per
cylinder which may permit you to use mixture settings on the lean side
of peak.

Hot starting is not one of the advantages.

Getting a much better fuel burn is not really going to happen until
computers get involved with controlling the injectors.

When you consider that most of the life of the engine is spent
cruising at the leanest safe settings, both carburated engines and
fuel injected engines end up being fairly close together in fuel burn
because both are optimized for that operation.

That's as I understand things.

I did not know that Lycoming counted on a certain amount of post
engine shut down bleed through from the injectors to allow a hot non
primed restart. With a carburator, hot starts are (or should be) non
events as the moment the engine is turning it's sucking fuel from the
carburator.

Corky Scott

Steve Robertson wrote:

As to your question about where the engine gets its fuel to hot start ... Even
though you killed the engine with the mixture control, a bit of fuel will still
leak out of the injector lines and into the intake after the engine is shut
down.

Interesting. Since the reason usually advanced for using the mixture to shut down is
that the engine will be starved for fuel and consequently will not fire if the prop
is moved on the ground, it seems that fuel injection is less safe than carburetion.
At least in this regard.

George Patterson
None of us is as dumb as all of us.

"G.R. Patterson III" wrote in message
...

Steve Robertson wrote:

As to your question about where the engine gets its fuel to hot start
.... Even
though you killed the engine with the mixture control, a bit of fuel
will still
leak out of the injector lines and into the intake after the engine is
shut
down.

Interesting. Since the reason usually advanced for using the mixture to
shut down is
that the engine will be starved for fuel and consequently will not fire if
the prop
is moved on the ground, it seems that fuel injection is less safe than
carburetion.
At least in this regard.

I asked an examiner this question...he said it was correct, but that
it only takes a few hours for all the fuel to evaporate so it's likely
to be fine after that!

Paul

Steve Robertson wrote:
As to your question about where the engine gets its fuel to hot start ...
Even
though you killed the engine with the mixture control, a bit of fuel will
still
leak out of the injector lines and into the intake after the engine is shut
down.

In article , G.R. Patterson III
wrote:
Interesting. Since the reason usually advanced for using the mixture to shut
down is
that the engine will be starved for fuel and consequently will not fire if
the prop
is moved on the ground, it seems that fuel injection is less safe than
carburetion.
At least in this regard.

A better answer might be that retarding the mixture creates too lean a
mixture for ignition.
For example, if the engine does not quit with the mixture retarded
(chugs, diesels), you can then advance the throttle and create a leaner
mixture.

Steve Robertson wrote in message ...
Also FWIW, I really don't like fuel injection on airplane engines. Sure it's
great not to have to worry about carb heat. But instead I worry about hot
starts and plugged injectors.

That's why God invented engine monitors. I can't imagine owning an
injected engine without an engine monitor.

-Robert, IO-360-A3B6 Mooney driver

In article ,
wrote:
When you cold start an IO-360, you are supposed to run the auxiliary
fuel pump with the mixture control knob pushed in until you see a rise
in fuel pressure, then shut off the pump and pull the mixture contol
knob back to shut off, and start the engine, pushing the mixture to
full rich when the engine starts.

I get more reliable starts by moving the mixture to idle cutoff before
turning off the pump. That seems to preload the fuel pressure so that
when it catches there's fuel available. Also it takes a moment (or longer
if it's cold) for the fuel you just squirted in to vaporize, so wait a few
seconds before cranking.

Now that I've had a lot of practice (IO-540) I don't even push the mixture
full rich on start. I just push it in an inch or so to the position where
I run it on the ground. It's so lean that it stumbles above about 1500 RPM.

For hot starts I use the procedure someone else explained. No priming with
the fuel pump, just full throttle and mixture at idle cutoff, then crank
until it starts and quickly (I keep my pinky and ring finger over the ball
of the throttle and my thumb on the mixture -- crazy Comanche knob order)
pull the throttle and advance the mixture.

--
Ben Jackson

http://www.ben.com/