Pavlo

How?

Are injectors on/off/on/off...... all the time or just on during inlet stroke for a period of time?

P

ScoobyDuck

iTrader: (1)

Paul,

would have thought that the Cam position sensor has some role in this - so the ECU knows that it's on an inlet stroke & thus says TURN ME ON SCOTTY @ what ever duty cycle is requiered?!?

Steve

Pavlo

If so, at what frequency?

Short of getting a scope on the injectors my puny brain has trouble.

I am measureing between 2.1 and 2.7ms on idle (see-sawing due to lambda measurement).

Paul

ustolemyname??stevieturbo

iTrader: (1)

Sequential injection requires a cam sensor, as ideally, the injector is only squirting while the inlet valve is open, which will require a cam sensor, to let the ecu know when the valves will be open.
As for converting ms to duty, not sure if there is a straightforward conversion. I think it would also depend on rpm.

Pavlo

I did wonder if it only squirted once per rev. and that 50% duty cycle would mean 50% of the inlet stroke, so 90deg.

But people warn about going above 85% dutycycle, but if the above is true, it doesn't make much sense. But itw would explain how IDC of over 100% are possible, just leave the injector on for over 180deg, without looking at cam timing, I would guess the inlet is open a little past BDC.

P

ustolemyname??stevieturbo

iTrader: (1)

I suppose the readings of 100+ do refer to the injector remaining open for longer than the inlet valve is open, but again, 100% means the injector is no longer pulsing, so a reading of over 100 doesnt really make sense. Depends on how the dc is actually being measured

Pavlo

And thus the circle was complete!

Do the injectors pulse more than once per inlet cycle?

I suspect they do, if so, what's the frequency?

Paul

ustolemyname??stevieturbo

iTrader: (1)

Frequency depends entirely on rpm. The injector should only be open while the valve is open. If perhaps that time may extend beyond and inject when the valve is closed, then somehow, depending on what is measuring the dc, it must be giving a false reading of 100+
The actual duty cycle cannot be more than 100% as this is just fully open.

EvilBevel

Is RPM * Injector ms/1200 too easy an answer ?

Pavlo

aaaarrrghhh, people know this FFS!

I would assume that the injector fires at a fixed frequency, say 100 hertz or something.

OR

The injector fires once for every crank sensor pulse, beginning at around TDC.

OR

THe injector just stays on, but the more I think about it the more I realise this is poor, and the pulsing creates the mist like a water sprinkler.

edit to add, EvilBevil to the rescue, thanks

Paul

[Edited by Pavlo - 8/27/2002 5:17:49 PM]

EvilBevel

Phew, thought the FFS was meant at my reply

I'm trying to remember where the 1200 came from, but I'm pretty sure it's 1/4th of 4800 (four cylinder) ... hmmm ... <ponders> revs per minute... <ponders some more>

Andy.F

At 6000 RPM the engine rotates at 100 revs per second, that equals 10ms per revolution. A complete (2 rotation) cycle takes 20ms.

Therefore if an injector pulse time is 15ms at 6000 rpm it equal to a 75% duty cycle (15/20)

When you approach approx 90% duty cycle at say 7000 rpm then the closed interval in this case is only 1.7ms, this can be where you get issues as the injector can't mechanically close and open in this time window. As you ask for more duty it tends to run 87% 88% 89% 90% - step change - 100% nothing in between.

Note an injector may happily open-close in 1.7ms but not close-open ! The power applied will give a quicker open action than close action. For the same reasons the injector pulse width will not equal the injector open time. The difference is greatest at either very small or very large duty cycles.

Hope this helps not confuses !

ScoobyDuck

iTrader: (1)

maybe to the rescue .. but some of us are still miles out to sea !

ustolemyname??stevieturbo

iTrader: (1)

So it is pulsing while the inlet is open,as oopposed to just plain open. Makes sense I suppose.
Id guess the injector will start pulsing way before tdc, as it should probably start just slighty before the inlet valve opens? Depends on what map is in the ecu, as to when injection starts and ends. This is user settable on the motec, though havent delved that far.

Andy.F

Think about it guys, a 380cc/min injector x4 will need to be open 100% ie never shut, in order to produce 300bhp

ustolemyname??stevieturbo

iTrader: (1)

Strange, that on a cossie, 380cc injectors would supply enough fuel for around 350bhp ( possibly more? ) I think bosch greens or blues are about that?? or am I way off?

Andy.F

LOL 380 injectors in my world will supply enough for 360 bhp too but we are on scoobynet here and we have to have a 20% factor of safety for everything

I believe the dark green 803's are rated at 380cc

[Edited by Andy.F - 8/27/2002 5:51:59 PM]

ustolemyname??stevieturbo

iTrader: (1)

Any idea how much your 5th injector flows?? Cossies are sequential too, so why can an equivalent sized injector allow more power?

Andy.F

Don't think they do allow more power, it's just that everyone runs the scoobs so rich that they confine 380's to less than 300bhp.

As far as I'm aware my OEM 5th injector doesn't actually run. I will check this out soon. My 6th injector is a 0.6mm ERL water injection atomiser and is rated at 138cc at 5 bar I think.

MorayMackenzie

Scooby and Cossie injector capacities are, IIRC, measured differently. The Cossy ones are, IIRC, measured at a fixed fuel pressure and a fixed duty cycle (80%iirc). IIRC, scooby injectors are rated at 100% duty cycle, hence a cossy injector rated at flow capacity X will, indeed, outflow a scooby injector with he same rating.

Andy.F

Interesting Moray, that rings a bell actually

Strange thing is, my scoob produces more power on its 380's than my cossie did on 380's
Must be due to the scoob having a far superior engine to start with
Or perhaps I just didn't try hard enough with the cossie

Pavlo

water injection nozzles it is then....

I wonder if you could adjust the fuel map such that you run the extra nozzles on constant feed right through the rev range. So in effect you would have to knock out 138cc of fuel flow right through the fuel map.

(can someone please sanity check the below)
At 800rpm idle, 4 x 380cc/min at 2.5ms:
4cyl * 800rpm / 2cycles per rev = 1600 squirts per min.
2.5ms * 1600 = 4000ms = 4 sec = 0.0667minutes
380cc/min * 4 cyl * 0.0667min = 101.33cc/min.

138cc\min @ 5bar = 97.5cc\min @ 2.5bar (standard ish idle FP )

So the above being true, it would just about be possible to run a lowish flow nozzle 100% of the time.

Paul

Andy.F

Paul

Havn't checked your maths but when considering fuel flow at idle, account for manifold vacuum. It is reasonable to consider that the injectors run with a constant fuel differential pressure of 3 bar.

Regarding running a constant single injector, yes it could work (andy means yes it does work )

Pavlo

At idle my car is mapped for 17:1, I am sure it goes to 14.7:1 (stoich) once the ecu has learn from the lambda over time. But you could possibly run, dare I say 2 extra injectors all the time with no pressure switches or anything.

I forgot (how ironic) about differential injector FP.

Paul