Injection timing: strange behavior

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PierreL
Experienced MS/Extra'er
Posts: 250
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Injection timing: strange behavior

Post by PierreL »

Hello everybody,
I have a strange behavior of inj. timing.

What i did is to let the engine idle at +- 2.200 t/min, with a constant PW.
Then i changed the inj timing value from +360 to -360 step 10, and burn to the msbox on every change.
And observed the AFR.Here is an image of the log (and the log itself)

What i found bizarre is that AFR does not vay continuously, but sometimes jumps upwards when i change the timing, then downwards for the next change...

Does anybody have an explanation about that ?

Many thanks,
Pierre
inj timing.JPG
PS: Engine is monocylinder
PierreL
Experienced MS/Extra'er
Posts: 250
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Re: Injection timing: strange behavior

Post by PierreL »

Sorry, it was my mistake: burning to the controller did make him loose the synchronisation.

I repeated the test without burning (just "apply") and it is now far better.

On the image here below, man can see that the best results are for an angle around 200°
ok.JPG
elutionsdesign
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Re: Injection timing: strange behavior

Post by elutionsdesign »

I assume you are using the highest AFR as "best"? Did you find any variance with rpm?
Graduate of EFI University.

I build, repair, install and tune Megasquirt systems in North Dakota and beyond!
pit_celica
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Re: Injection timing: strange behavior

Post by pit_celica »

In my understanding, the best injector timing is where the AFR is the lowest (more rich). This means that you have too much fuel for given air flow to stay at a steady RPM and load point. Remember that injector timing is usually used to gain fuel economy.

So, based on your datalog, I think that 290° of injection timing would be optimal for this RPM/load point. But, this log do not contain any load data (TPS or MAP). So, you still need to verify that this test was done at a steady load.

I do not understand why you've done this test at a steady PW? What was your goal doing it this way?

Sam
PierreL
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Re: Injection timing: strange behavior

Post by PierreL »

pit_celica wrote:In my understanding, the best injector timing is where the AFR is the lowest (more rich). This means that you have too much fuel for given air flow to stay at a steady RPM and load point. Remember that injector timing is usually used to gain fuel economy.

So, based on your datalog, I think that 290° of injection timing would be optimal for this RPM/load point. But, this log do not contain any load data (TPS or MAP). So, you still need to verify that this test was done at a steady load.

I do not understand why you've done this test at a steady PW? What was your goal doing it this way?

Sam
Hi Sam,
I'm in a pure alpha-n configuration: i only use the TPS.
The test was done at a constant tps (idle)
And i did arrange a little bit the VE table so the PW remains constant even if rpm change a little bit.
My goal was effectively to make sure that only the injection timing has an impact on the AFR.
Isn't it right ?
Thank you,
Pierre
pit_celica
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Re: Injection timing: strange behavior

Post by pit_celica »

Ok, what you did is right. It's just the goal you are aiming that isn't.

You are playing with injection timing to get the max efficiency of the injected fuel (better fuel economy). At a steady RPM/Load (TPS in your case), you should have a steady mass airflow. If you have a steady fuel PW in addition to all other conditions, AFR should stay steady. The fact that AFR is varying means that the combustion efficiency is changing and more/less fuel is burned.

So, more burned fuel and less unburned fuel is a good thing and this should yield to better fuel economy/more power. The injection timing where you have the better efficiency is where the AFR is the richer for a given VE or PW value. This means that for a given RPM/Load point, you can reduce the fueling to get back to your leaner AFR target.

I hope it make some sense to you.

Sam
PierreL
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Re: Injection timing: strange behavior

Post by PierreL »

Thank you Sam,
I abolutely agree, and this is why i will use the angle where the AFR is the lowest, which mean the richest mixture.
Is evreything ok like that ?
Pierre
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