Engine starting - fuel injection
Why do it if it's not fun?
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Engine starting - fuel injection
Purely to satisfy my own curiosity:
When starting a fuel-injected engine, the usual procedure (obviously it may vary from one aircraft to another and you should check your POH) is to start with the mixture at ICO, and advance it to full-rich once the engine fires.
What is actually going on here? Fair enough for a cold engine which has been primed - presumably the priming fuel will ignite and cause the engine to fire. But how about a warm engine which hasn't been primed? How does the engine fire if it has no fuel? Or is there some gadget in the fuel injection unit which means that full-lean actually allows a bit of fuel through if you're trying to start the engine?
FFF
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When starting a fuel-injected engine, the usual procedure (obviously it may vary from one aircraft to another and you should check your POH) is to start with the mixture at ICO, and advance it to full-rich once the engine fires.
What is actually going on here? Fair enough for a cold engine which has been primed - presumably the priming fuel will ignite and cause the engine to fire. But how about a warm engine which hasn't been primed? How does the engine fire if it has no fuel? Or is there some gadget in the fuel injection unit which means that full-lean actually allows a bit of fuel through if you're trying to start the engine?
FFF
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Hot big fuel injected engines - a delight!
The fuel lines across the top of the engines get hot and turn the cool fuel remaining in them into hot vapour. This will ignite more easily so you leave it alone to get on with the job and don't add fuel until it fires.
Failure to do this causes more cool fuel through the pipes, flooding the engine with too much fuel before it gets a chance to ignite.
It's probably more complex than that - but that's the idea behind it and it works everytime.
The fuel lines across the top of the engines get hot and turn the cool fuel remaining in them into hot vapour. This will ignite more easily so you leave it alone to get on with the job and don't add fuel until it fires.
Failure to do this causes more cool fuel through the pipes, flooding the engine with too much fuel before it gets a chance to ignite.
It's probably more complex than that - but that's the idea behind it and it works everytime.
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Chilli
That's about it, except for the vapour being more flammable. It is when mixed with air, but will be mixed at the wrong ratio as injectors stay open for a time period, not a metered output. Until liquid fuel is running through the injector, the mixture in the cylinder will be too weak to ignite.
It will often take a few more cranking revolutions when warm, just to purge cool liquid fuel to the injectors. But if you did select enrichment, it would die terribly, just as it started.
The only quick way to clear a flooded injector engine is to pull the injector leads off and crank it. Full throttle whilst cranking won't make any difference.
Modern injector engines will have a water temp sensor that controls cold start enrichment for you.
That's about it, except for the vapour being more flammable. It is when mixed with air, but will be mixed at the wrong ratio as injectors stay open for a time period, not a metered output. Until liquid fuel is running through the injector, the mixture in the cylinder will be too weak to ignite.
It will often take a few more cranking revolutions when warm, just to purge cool liquid fuel to the injectors. But if you did select enrichment, it would die terribly, just as it started.
The only quick way to clear a flooded injector engine is to pull the injector leads off and crank it. Full throttle whilst cranking won't make any difference.
Modern injector engines will have a water temp sensor that controls cold start enrichment for you.
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I still can't understand why we have to have a mixture control anyway, A fuel on or off switch/lever/tap and a nice fancy electronic brain to actually do all the metering would be far more sensible.
Ah well, we can but dream!
Ah well, we can but dream!
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SSD & SAS,
I was thinking exactly the same thing!!
But then I remembered last summer and such a mount does exist in the form of a Diamond DA40TDi....True car style ignition switch on, when the diesel light goes out, start! - single lever power control on a wobbly-prop type!!
If I could afford it I would have one!!
Regards, SD..
I was thinking exactly the same thing!!
But then I remembered last summer and such a mount does exist in the form of a Diamond DA40TDi....True car style ignition switch on, when the diesel light goes out, start! - single lever power control on a wobbly-prop type!!
If I could afford it I would have one!!
Regards, SD..
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SAS, we have, it is called FADEC or it's cheaper brother LASAR. LASAR ignition is certified and offers a fast improvement on hot starting. FADEC offers even better control as it sorts the mixture out as well.
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Of course we have it, but why isn't it fitted to everything! Why do Lyco's and Conti's still come out of the factory fitted with carbs and points?
FADEC would be lovely, as would not having an expensive piece of noise polluting rubbish attached to a prop. Here I go again....
FADEC would be lovely, as would not having an expensive piece of noise polluting rubbish attached to a prop. Here I go again....
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My 1986 Golf GTi has the most fantastic reliable mechanical fuel-injection. And it has driven 180,000 miles (and still going strong!)
I find it odd that aviation engines haven't caught up with automotive technology.
Regards
Adam
I find it odd that aviation engines haven't caught up with automotive technology.
Regards
Adam
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My new car has all sorts of clever computers controlling the engine.
A bit fell off, the computer couldn't cope with controlling what was left, and the whole system collapsed. Not in the air, thanks.
A bit fell off, the computer couldn't cope with controlling what was left, and the whole system collapsed. Not in the air, thanks.
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GtW
FADEC will drop into a safe mode if something falls off. It may restrict the power a bit, but it won't shut down.
Modern car ECUs also have this, calling it a limp home mode. Car rpm gets limited to about 50%.
You could argue that the far superior engine management will result in reduced vibration, so bits are less likely to fall off in the first place.
FADEC and powerful car management systems will even give individual cylinder timing and fuelling control, to optimise power/efficiency/cylinder temp.
While people keep buying replacement Lycs and Contis that paid off their development costs 25 years ago, the makers aren't going to just shell out $m developing something else.
Unless we all start installing diesels and FADEC equiped alternatives, but then the legislators won't let that happen as it might not be safe.
Then again, some people argue that the Mk 1 Escort was a good car
FADEC will drop into a safe mode if something falls off. It may restrict the power a bit, but it won't shut down.
Modern car ECUs also have this, calling it a limp home mode. Car rpm gets limited to about 50%.
You could argue that the far superior engine management will result in reduced vibration, so bits are less likely to fall off in the first place.
FADEC and powerful car management systems will even give individual cylinder timing and fuelling control, to optimise power/efficiency/cylinder temp.
While people keep buying replacement Lycs and Contis that paid off their development costs 25 years ago, the makers aren't going to just shell out $m developing something else.
Unless we all start installing diesels and FADEC equiped alternatives, but then the legislators won't let that happen as it might not be safe.
Then again, some people argue that the Mk 1 Escort was a good car
Fuel injected engines are easy to start if very cold or very hot. It is the inbetween that they can be a pain.
. Follow the POH recommended procedure. If it does not start in a reasonable time stop cranking and give the engine a big shot of prime. Now you will know the engine is flooded so crank it with the throttle wide open and the mixture ICO. Every engine will start everytime although it may take a bit of cranking. As the engine starts to fire smoothly pull back the throttle and bring up the mixture. 
. Follow the POH recommended procedure. If it does not start in a reasonable time stop cranking and give the engine a big shot of prime. Now you will know the engine is flooded so crank it with the throttle wide open and the mixture ICO. Every engine will start everytime although it may take a bit of cranking. As the engine starts to fire smoothly pull back the throttle and bring up the mixture.
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Hot fuel injected engines...just as bad as cold ones.
Hot - Eng. over 60degrees or OAT +30degrees, prime for a few seconds then Aux Fuel Pump On, Start, Mix rich then pump off. Always seems to work for me!
I always end up having problems with cold engines
Hot - Eng. over 60degrees or OAT +30degrees, prime for a few seconds then Aux Fuel Pump On, Start, Mix rich then pump off. Always seems to work for me!
I always end up having problems with cold engines
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One cannot offer general advice on this subject. Different engine installations are different. The pipe layouts differ, the fuel pump position and operation does too, etc.
The procedure in the POH should work - if it doesn't then one should find out why it doesn't.
I think any FI engine can be started using the straight cold start procedure - the problem is the amount of cranking that's needed to do it.
The procedure in the POH should work - if it doesn't then one should find out why it doesn't.
I think any FI engine can be started using the straight cold start procedure - the problem is the amount of cranking that's needed to do it.
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The recommendation I got given for the Twin Comm was if cold, prime until fuel flow indicated, then wait for 3 seconds, then ICO & crank.
If warm, "prime" till fuel flow indicated, normally very short period, which made sure that the lines were full of fuel rather than vapour, then ICO & crank.
In both cases, the throttles were "cracked" open less than 1/4". Over the period I had the aircraft, it always worked, regardless of how cold, or hot, the engines were.
If warm, "prime" till fuel flow indicated, normally very short period, which made sure that the lines were full of fuel rather than vapour, then ICO & crank.
In both cases, the throttles were "cracked" open less than 1/4". Over the period I had the aircraft, it always worked, regardless of how cold, or hot, the engines were.
