Fuel injector timing

[wrench459]

Old school or atlest mine had the injector starting to open at 60 degrees btdc when it closed no clue.
As I'm learning about low slope,high slope and breakpoint and digging around in an Ford pcm for a possiable conversion. My head is spinning!
There's one place where I can control the injector on time in crank rotation.
Does 300 degrees of on time sound about right? This is a simple street car with a small cam.

[GTJIM]

Older FI just gang-squirts the fuel in - some cylinders against closed intake valves and others open!

Timed (sequential) injection has to be a bit more economical - so the fuel arrives at the same valve opening point for each cylinder.

I don't think it matters too much when the injection cycle starts - but it would seem that finishing the fuel supply just before or at valve closing would be a reasonable idea. Remember that increased fuel demands are met by lengthening the injector open phase - so end-pulse timing is variable ... just to add another uncontroled item to the mix.

.... BUT: maybe on a street motor working at less than WOT it may even be an idea to try injecting the fuel against a closed valve to get vapourisation before the valve fully opens at low fuel demands...

Lots to think about - though, I am sure the car manufacturers have done a bit of experimenting. Might be some SAE papers on it ... somewhere on the WWW

http://www.sae.org/servlets/index

There! I searched for 'fuel injection timing' .. and got 81,698 hits - so there is bound to be some info there.

[wrench459]

Would not the fuel sitting around just before the intake valve opens help any?
For an example a cam that the intake valve starts to open at 17 btdc.
I would think the cooling effect on the overlap would help out some.
When I look at the base fuel table which is master of all. I see that the mixture can be set to lower than lambda.
Sneaky right?

[GTJIM]

Originally Posted by wrench459 Would not the fuel sitting around just before the intake valve opens help any?

I just thought that the valve/port would still be hot enough to vapourise the fuel - and have it ready to be swept into the port by airflow as soon as the inlet valve opened. That would surely help getting fully vapourised fuel/air mix into the cylinder at low throttle openings.

However - do you ever use 'low throttle openings' ?

[markandson]

Originally Posted by wrench459 Would not the fuel sitting around just before the intake valve opens help any? For an example a cam that the intake valve starts to open at 17 btdc. I would think the cooling effect on the overlap would help out some. When I look at the base fuel table which is master of all. I see that the mixture can be set to lower than lambda. Sneaky right?

With the reading I have done trying to tune my system I too am confused but I think in general it is not advisable to inject against a closed valve. Less than lambda is possible under light load and decel conditions.

[Bill Hoffmann]

Originally Posted by GTJIM I just thought that the valve/port would still be hot enough to vapourise the fuel - and have it ready to be swept into the port by airflow as soon as the inlet valve opened. That would surely help getting fully vapourised fuel/air mix into the cylinder at low throttle openings.

I believe GM multipoint fuel injection works exactly this way - it injects twice, once just before the valve opens and again after. At least this is what I remember reading when the system first came out in the 80s or so.

Bill

[guyopel]

The ' 75 Opel inj. sys. fired injectors at closed intake valves and GM muiti-ports sys. fire all inj. at the same time for startup and until eng. temps. were up .. this worked but later they went to syn. port inj. for fuel mileage . HTH Keep up you work ! Dan .

[wrench459]

Originally Posted by markandson Less than lambda is possible under light load and decel conditions.

Hey Jeff
I'm dealing with percentages of lamdba for the commanded a/f ratio.
So less than lamdba oh lets say .85 will result in a 12.44 a/f ratio.
But this is in theory and not for the faint of heart. On decel I'm planning on killing the injectors just like the stock systems do. Now only if I can get the decay rate correct so that on tip-in there wont be a big bang.
Under light load my thinking is to keep the adaptive fuel control some what close to stock only tighten up the limits. I don't like the idea of the pcm adding or subtracting 30% of fuel before it flags a problem.

[markandson]

Originally Posted by wrench459 Hey Jeff I'm dealing with percentages of lamdba for the commanded a/f ratio. So less than lamdba oh lets say .85 will result in a 12.44 a/f ratio. But this is in theory and not for the faint of heart. On decel I'm planning on killing the injectors just like the stock systems do. Now only if I can get the decay rate correct so that on tip-in there wont be a big bang. Under light load my thinking is to keep the adaptive fuel control some what close to stock only tighten up the limits. I don't like the idea of the pcm adding or subtracting 30% of fuel before it flags a problem.

So when you say less than lambda you are talking rich not lean, which when I re-think the actual words you used, is correct.

[wrench459]

Crud I was basing the A/F ratio off of pure gasoline which has a stoich of 14.64.
Todays pump fuels are more than likely an E10 blend with a stoich of 14.20 .
How about the 300 degrees of injector on time , did I get that right?

[ghcoe]

Probably anything you want to know about fuel injection can be found here.

www.MSefi.com • Index page

Sequential injection is just for better fuel economy. For performance you use Bank fire injection. Sequential will give you performance problems at higher RPM. You would have to have some high flow rate injectors to be able to run at a high rpm because of the short window of opportunity. It is true that the injector on bank fire shoots gas on the closed valve. This allows the fuel to vaporize some before the valve opens. On bank fire I do not think there is a timing for the injection. It is just a timed pulse for all cylinder that can be triggered by any cylinder. Sequential needs a cam trigger that tells the ECM that number 1 cylinder is coming up on the compression stroke, no degrees. The rest of the injectors are fired in a timed sequence determined by the ECM at what RPM the engine is running at.

[wrench459]

After looking into this a little more.
Its seems there two different approaches each with its own sets of problems. I don't think sfi or speed density matters as much as when the injector fires. One school of thought has all (100%) of the fuel in the intake before the intake valve opens. The other school injects the fuel as the intake valve is opening. The first one has to deal with a much larger transient(fuel puddling)than the latter. The second has to deal with running out of time and max. out the duty cycle of the injector. When the injector goes static its running on fuel pressure not the pcm.
After checking several different sources they all say the same thing "it is what it is" Happy Tuning
BTW the 300 number I stated before was when the injector CLOSED. Zero degrees is TDC on the power stroke so I'll need to open up the number close to 380 to deal with the overlap of the cam.. Live and learn.