Fuel injected engines

[shumway76]

Having flown both carburettor & fuel injected versions of C172, I am just curious, why is it for the fuel injected C172 (R & S) the engine is started with mixture at cutoff, which is moved to full rich immediately the engine "catches".
What is the theory behind it?

[S-Works]

It's generally a Lycoming thing. My fuel injected 172 with the 6 cylinder Rolls engine is started at full rich.

[ShyTorque]

From my time flying behind a fuel injected Lycoming, I recall that it's because the heat from the engine after shutdown can cause fuel to expand in the supply pipework and dribble into the manifold. Starting at cutoff allows that fuel to be drawn into the engine and burnt without over-richening the mixture in the first few induction strokes.

But I'm possibly recalling it incorrectly because that was over twenty years ago. :}

[stickandrudderman]

It reduces the risk of over-fuelling and therefore potential for flooding or fire in the inlet manifold.

[miroc]

My C172S is started from cold with throttle only 1cm in, mixture full forward, 3-4 seconds fuel pump, and it catches very quickly regardless of outside temperature. Successfully done yesterday at LJPZ - 32 deg C.

That's a cold start. If warm or only partly warm, there is a problem how to find the right mixture for the actual conditions.

One of the solutions is to over prime the engine a bit, cut off the mixture, throttle full and hit the starter. That creates a very rich nonburnable mixture first but with every cycle/revolution the mixture gets leaner and leaner to the point where it catches because the mixture is just right. In that moment you need to supply gas - by forwarding the mixture quickly. Throttle must be pulled back immediately.

That could be the theory behind it...

Unfortunately that did not work for me yesterday, I do not know why. At the end I needed ground power unit to start that engine The engine was partly warm because I had to taxi to the fuel pump. First start of the day was no problem, after refuelling I played one hour with it. Very embarrassing.

Miroc

[IO540]

why is it for the fuel injected C172 (R & S) the engine is started with mixture at cutoff, which is moved to full rich immediately the engine "catches".

The actual procedure is engine and airframe (fuel system layout) dependent, but in general you don't actually do that. You prime the system by running the fuel pump with the throttle a little open and with the mixture fully open, for a few seconds(*), and then you shut the mixture, fuel pump off, and start the engine.

The engine starts on the fuel which you pumped into the system.

When it starts, you move the mixture to full rich, leave it there for a few secs until the engine is running nicely, and then lean it aggressively (to peak EGT if you have EGT instrumentation) to minimise risk of plug fouling.

(*) on my installation (TB20, IO540-C4), one primes till there is a tiny movement on the analog fuel flow gauge. It is close to 5 seconds.

[flybymike]

The only way to hot start a fuel injected turbo TSIO 520 Continental is by the use of carefully selected !$%^&*:*:}:{ swear words in conjunction with every conceivable movement of all available levers.

[Pilot DAR]

One of the injected Lycoming Lake Amphibians I fly seemed able to get a "hung start" if you advanced the Mixture too quickly following the start. The engine just stumbled along for a minute or so, with either opening or closing the throttle causing the engine to falter. For some engines, "getting the touch" is helpful....

My C172S is started from cold with throttle only 1cm in, mixture full forward, 3-4 seconds fuel pump

If this is the injected Lycoming version of the 172S, are you sure this is the Cessna recommended procedure? It's not for the one I've been flying....

At the end I needed ground power unit to start that engine ....... after refuelling I played one hour with it.

Though I'm not aware of stated starter motor cycle limits for the 172, I would, none the less suggest that it is possible to overheat and damage a starter motor with continued cranking. By way of example, I can tell you that many piston engines, and small turbines have starter motor limitations like: 30 seconds cranking, 30 seconds waiting, 30 seconds cranking, 30 seconds waiting, 30 seconds cranking, 30 MINUTES waiting. It is possible to melt armature windings when over working starters....

Injected Lycomings can be a bit fussy to start, but are generally nicer than some injected Continentals.....

[IO540]

Starting some FI engines can be "fun" but I do recommend digging out the POH and trying to follow that.

A lot of pilots are using a procedure passed down from somebody else, or out of some pilot forum...

In my TB20 it works every time, for both cold and hot starts.

However one thing which helps a lot with hot (or "warm" :) ) starts is a high speed starter. I have a Skytec 149-NL (http://www.skytecair.com/) (I think; mine is the older 12/24V jumper selectable model which draws less current than the original Skytec) and it turns the engine so fast you barely need any petrol :)

[Pilot DAR]

Skytec) and it turns the engine so fast

A bit of thread drift.....

Yes, some starters turn the engine over at higher RPM. This is helpful to a point. There is no longer a Skytec on my O-200, as it turned it over so fast (+300 RPM) that it through out the magneto impulse couplings, changing the timing during the start, and causing backfiring.

[wsmempson]

The starting procedures on my Lycoming engined IO540 Saratoga are;

COLD

mixture fully lean
Select tank
throttle cracked open 1/2 to 1 inch
fuel pump on
mixture to fully rich until fuel flow registering the mixture to fully lean.
crank engine until it catches, then mixture fully rich and set idle at 1,200 rpm
Thereafter, leaning on the ground etc as appropriate

HOT

mixture fully lean
select tank
Throttle fully open
fuel pump on
crank engine until it catches, then simultaneously mixture to fully rich and pull back the throttle to set idle at 1,200 rpm. (this really needs three or four hands to be done well....)

WARM

mixture fully lean
select tank
Throttle fully open
fuel pump on
open the mixture for 1 second to fully rich then back to fully lean
crank engine until it catches, then simultaneously mixture to fully rich and pull back the throttle to set idle at 1,200 rpm.

The hot and cold procedures seem to work every time; for the warm (not hot, but not really cold) you simply have to develop a feel for what works for your engine.

[A and C]

The Lycoming and Continental engines use totally deferent ways of metering the fuel and until you understand how these metreing units work you can't really make much sense of the advice given above.

I would recommend a trawl of the engine manufactures websites, Lycoming & Continental both publish some very good data that will help you understand the way these thing work and why the operating technique differs between the engine types.

[Tinstaafl]

Like others have written, you really need to refer to the manual for the aircraft. However....

There are generally two camps in the injected world: All injected Lycomings I've come across uses a lean start, and all injected Continentals I've flown used a rich start.

I fly PA31s a lot (inj. Lycoming) and the manual's method generally works fine with a slight caveat: When the engine is hot/warm it can sometimes be a bit of guess work about how much/how little (or not) to prime depending on time spent since shutdown and which aircraft I'm in. I find it best to prime for a second or two with the throttle fully open/mixture rich then pump off & crank with mixture at ICO. As the engine catches reduce throttle to idle while advancing the mixture. Using this flooded start method seems to reduce the variables of finding a combustible mixture vs vapour locks vs priming to a single procedure. In these aircraft it gives me a start every time.

When I flew lots of Continentals, I used to run the pump for 15 seconds or so with mixture ICO when the engine was hot. That reduced (but didn't always eliminate) vapour locks. Then start as per the manual ie primed & mixture rich. Often I'd have to tickle the pump on HI or ON for a moment to prevent the engine from stopping, then pump OFF to prevent over-rich, on again as the engine started to die, off again. After a few iterations the engine(s) would run fine once the vapour locks were pushed through the lines.

[Mark 1]

I have a Mattituck (Lycoming clone) IO-360.
Their recommendation is similar to that shown above for other Lycomings, and it works pretty well for me.
Some aircraft are fitted with a purge valve, which, when opened, allows fuel to be pumped through the entire system as far as the distribution block and returned to the fuel tank. In principle this allows you to start with fresh cool fuel in the lines, but in practice not many people use it as it adds a potential critical failure mode into the system if the valve fails.

Here are Mattituck's recommendations:

How do I start my fuel Injected Lycoming style TMX IO-360?
Procedure for a cold engine:
(1) Set propeller governor control in "Full RPM" position (where
applicable).
(2) Turn fuel valve "On".
(3) Open throttle wide open, move mixture control to "Full Rich"
turn boost pump on, approximately 3 to 5 seconds, turn boost pump off,
then return throttle to "Closed" and return mixture control to
"Idle Cut-Off".
(4) Open throttle 1/4 to 1/2 of travel. Keep you hand on the throttle during the staring
process to make movement toward the idle position after the engine has started an easy
immediate thing to be able to do.
(4) Set magneto selector switch (consult airframe manufacturer's
handbook for correct position).
(5) Engage starter.
(6) Engine starts.
(7) Retard throttle towards idle position.
(8) Move mixture control slowly and smoothly to "Full Rich".
(9) Check oil pressure gage. If minimum oil pressure is not indicated
within thirty seconds, stop engine and determine trouble.
Procedure for a hot engine that was shut down with in a few minutes ago:
(1) Set propeller governor control in "Full RPM" position (where
applicable).
(2) Turn fuel valve "On".
(3) Open throttle wide open, move mixture control to "Full Rich"
return throttle to "Closed" and return mixture control to
"Idle Cut-Off".
(4) Open throttle 1/4 to 1/2 of travel. Keep you hand on the throttle during the staring
process to make movement toward the idle position after the engine has started an easy
immediate thing to be able to do.
(4) Set magneto selector switch (consult airframe manufacturer's
handbook for correct position).
(5) Engage starter.
(6) Engine starts.
(7) Retard throttle towards idle position.
(8) Move mixture control slowly and smoothly to "Full Rich".
(9) Check oil pressure gage. If minimum oil pressure is not indicated
within thirty seconds, stop engine and determine trouble.
Procedure for a hot engine that was shut down more than a couple of minutes ago:
(1) Set propeller governor control in "Full RPM" position (where
applicable).
(2) Turn fuel valve "On".
(3) Open throttle wide open, move mixture control to "Full Rich"
turn boost pump on, approximately 1 second or less, turn boost pump off,
then return throttle to "Closed" and return mixture control to
"Idle Cut-Off".
(4) Open throttle 1/4 to 1/2 of travel. Keep you hand on the throttle during the staring
process to make movement toward the idle position after the engine has started an easy
immediate thing to be able to do.
(4) Set magneto selector switch (consult airframe manufacturer's
handbook for correct position).
(5) Engage starter.
(6) Engine starts.
(7) Retard throttle towards idle position.
(8) Move mixture control slowly and smoothly to "Full Rich".
(9) Check oil pressure gage. If minimum oil pressure is not indicated
within thirty seconds, stop engine and determine trouble.

[flybymike]

On wonders what magic trickery has been achieved which enables us to start our fuel injected motor cars, be they hot or cold, without all this carry on.

[Jan Olieslagers]

FADEC fadec fadec fadec

(once was too short)

[FlyingStone]

On wonders what magic trickery has been achieved which enables us to start our fuel injected motor cars, be they hot or cold, without all this carry on.

Simple answer: ECU + piezo-electric injectors.

If you go into details of how modern car engine is started, you'll see that most of them are equipped with sensor, which senses the position (angle) of crankshaft, so you know which cylinder will fire first, you can adjust the ignition timing as you wish - 20° before TDC, TDC, etc. You can also adjust the precise amount of fuel which is injected into each cylinder and on top of that you can adjust the timing of the injection, if neccessary (Common Rail diesel engines) you can inject the fuel multiple times during intake stroke for better distribution throughout the cylinder. In most cases, the fuel is injected directly into the cylinder.

But in "modern" aircraft FI engine, you have continuous injection into intake ports, no sensors, you have a fixed ignition timing (except during start where ignition is retarded towards TDC to increase the torque created by the engine to ease the start - wouldn't be very good idea at high power settings). You also don't know which cylinder will fire first, so it may take a turn or two to get to the cylinder on power stroke, ...

As said by others, just read the manual, procedures laid out by manufacturer usually work pretty well in all conditions. There is really big difference between some Lycoming (fuel pump off, mixture idle cut-off) and Continental (boost pump on, mixture rich) engines, but in the end if you do what the aircraft's and engine's manual says, you should be able to start it regardless of conditions.

[IO540]

It's not FADEC.

In 1983 I had an XR3i which used the Bosch K-Jetronic (http://www.diagnostic-assistance.co.uk/mech_inj.htm) FI system. Started perfectly every time.

There were FI cars years before that, with no electronics in sight.

I think it is just the 1950s engine design, with fuel injection into the manifold, and no CHT-based fuel controls helping with warmup. It is fine in terms of specific fuel consumption, because one runs them at / near peak EGT in cruise and (assuming the ignition timing is about right at that condition) that is as efficient as an engine is going to get, for a given compression ratio. I recall seeing an analysis done by an engine designer showing that those old engines are more efficient, at cruise power of say 65%, than any petrol car engine made since.

[david viewing]

Just a note to say that in the 172R (160HP) at least, you can 'feel' the correct throttle position for starting by operating the fuel pump with the mixture rich and and the throttle closed.

With the throttle completely closed no fuel flows, but as you advance it flow appears and once the gauge moves that's enough. Then pull the mixture full lean and start as per POH, leaving the throttle set and advancing the mixture as it catches. The throttle position will be about right for fast idling. (all the above for cold start).

With warm start, my experience is to always attempt start without priming unless you know it's really cold. Only if it really won't go (after say 5-10 revs)consider some prime as per above.

However, they are all different!

[Mark1234]

Wrt the K-Jetronic - that's also a continuous flow system with injectors in the inlet manifold upstream of the valves. Essentially it's a big, distributed carburettor. Yep, it worked fine, and started with no problems, until it didn't. Then it was a king sized **** to get going again, quite adjustment sensitive.

That said, I have no real idea why injected aero engines are so temperamental. The obvious difference however is that they tend to be air cooled; therefore having wider temperature ranges, and bigger tolerances. Bit like beetle's, which can also be a right royal pain.

[FlyRon]

Though I'm not aware of stated starter motor cycle limits for the 172, I would, none the less suggest that it is possible to overheat and damage a starter motor with continued cranking. By way of example, I can tell you that many piston engines, and small turbines have starter motor limitations like: 30 seconds cranking, 30 seconds waiting, 30 seconds cranking, 30 seconds waiting, 30 seconds cranking, 30 MINUTES waiting. It is possible to melt armature windings when over working starters....For the Lycoming IO-360 the recommended starter duty cycle is:
Crank the starter for 10 sec followed by a 20 sec cool down period. This cycle can be repeated 2 times, followed by a 10 minutes cool down period before resuming crancking. After cool down, you can repeat these 3 cycles of 10 sec followed by 20 sec cool down.