Ok, maybe the wrong term. Distributed on two portions. This will work fine? Injector deadtime, valve overlap, injection advance, spark into valve overlap with fresh mixture hanging around in the ducts, resonance occurencies in the outlet concerning injection advance at certain rpms etc.

That's what comes to my mind when I hear "wasted spark".

Hubert

Ok, what I wanted to say is: in my map injection advance is set to 520°. How do you transfer this to a EFI system which is running wasted spark?
Most if not all definitions like Injection Advance are based on the assumption that the EFI part is running with half the speed of the crankshaft.

Hubert

Luhbo wrote on 08/19/09 at 20:01:45:

Injector deadtime will be twice as important to get right, apart from that it is not a problem. But some people claim that spark at valve overlap is the cause of more than one carbed Guzzi catching fire and burning down to a pile of crap. Right or wrong, I have no idea. Carefully choosing the injection advance should decrease the risk.

Luhbo wrote on 08/19/09 at 21:38:59:

While I dislike the wasted spark idea in theory (or for purity) I must admit I don't think it will be much of a problem, neither spark or fueling. At least not until you want to squeeze the absolute last hidden powers from the engine, completely impossible without a good brake dyno and lots of invested time.

Your 520° [trailing edge] is a very wierd figure as it is, if we do some timing maths. At idle it will inject the whole shot on closed valve, but as pulsewidths get longer and rpm increases, it ends up injecting some of it all the way back in the previous cycle's intake stroke and the rest at closed valve. How wierd is that? Actually this will be the case as soon as at 3500 rpm if you give it a handfull of throttle.

Running the ECU in 'two-stroke' mode as some call it, let's say we use the corresponding value 260°. This means we'll get the first shot of the two injections at closed valve and the other one ending at maximum valve lift. I wouldn't be too surprised if that even turns out to be of benefit.

raz wrote on 08/20/09 at 02:54:12:


In fact it's not weird, it's just a dilemma. The charged fuel needs some time to evaporate, finding this time while laying around in front of the closed valve. A dilemma I call it because it's obvious that with higher rpms and wider throttle this time gets shorter and shorter. In fact it is the case that at WOT you'd need the complete two crank revolutions to get the required amount of fuel completely delivered. Lambda 0.8, original airbox and open Mistral cans can push you so far In this case you'll have to face other problems arising.

That's one of the unsolved problems btw. which high reving direct injections engines have to deal with.

And thanks for puting in the expression "Two Stroke Mode". It surely helps to keep the discussion focused. I don't know whether I would have posted again if the discussion whether a spark should be wasted or not would have went on 

Hubert

Quote:


Dammit, screwed up again 

Obviously a little knowledge is a dangerous thing

Probably not. To vague I think. Just think of an humble start for instance.
I'd set the ECU into "Start Mode" after power up or better after it detects zero RPM (no pulses). In this mode the processor does not only count the phase pulses (the teeth) but also measures the time between them. In case the processor sends a Spark signal AND detects more or less simultaneously a sudden and remarkably shorter time between the pulses it might have been the spark TDC. On the other hand if time between pulses becomes longer then the engine is probably nearing a compression TDC.
As soon as the RPM has jumped to the second row the program falls back into normal running mode and behaves as usual, as today.

Hubert