Why do we truly need to advance the injection ???
Turbo Mini Forums

Now if I could figure out how to post pictures here, you'd see this:



What I said above is based on first hand experience, not just sitting on the couch with my mind wandering. Have a look at the figure: the "window opens" and "window closes" lines (plotted against the LH axis) are from the last set of experiments I did with the dyno donkey being fed by 500 cc injectors. These lines were established by, as I said, holding the engine at constant RPM and load (very light in this case) while advancing or retarding until the fuel pulse fell out of the window of opportunity. This plot, then, represents one line in the advance map.

The other lines, plotted against the RH axis, are the mechanics of what's going on: the actual valve open time and the time needed to get all the fuel in within 100 crank degrees.

What does this show? Even if the on-paper pulse initiation angle is D from above (30 ATDC - black line on my graph here), the engine can take that pulse up to 80 BTDC at idle (advanced, eh?) and in order to get the full shot of ~4 ms of fuel in, you have to excite the injectors 160 BTDC (an additional 80 advance, eh?)

This is no different from the mechanics of firing a spark plug: as engine speed increases, the spark has to be initiated earlier because burn rate is fixed. We have to excite the injectors earlier because travel time is (relatively) fixed. If burn rate, or travel time were infinite, we wouldn't need to advance timing at all. In an engine we want the peak cylinder pressure to be ~17 ATDC and yet we light the plugs anywhere from 10-50 BTDC.

Now, for the same reasons we don't have a retard curve in a distributor (don't even TRY to get me started on this subject!!) we won't need to have retard in the map table. Set the reference position for injection at TDC and advance from there.

Edited by TurboDave16V on 4th Jan, 2006.

www.starchak.ca and www.TDCperformance.ca

Edited by TurboDave16V on 4th Jan, 2006.

Now if I could figure out how to post pictures here, you'd see this:

http://www.telusplanet.net/~chichm/sales/window.jpg

What I said above is based on first hand experience, not just sitting on the couch with my mind wandering. Have a look at the figure: the "window opens" and "window closes" lines (plotted against the LH axis) are from the last set of experiments I did with the dyno donkey being fed by 500 cc injectors. These lines were established by, as I said, holding the engine at constant RPM and load (very light in this case) while advancing or retarding until the fuel pulse fell out of the window of opportunity. This plot, then, represents one line in the advance map.

The other lines, plotted against the RH axis, are the mechanics of what's going on: the actual valve open time and the time needed to get all the fuel in within 100 crank degrees.

What does this show? Even if the on-paper pulse initiation angle is D from above (30 ATDC - black line on my graph here), the engine can take that pulse up to 80 BTDC at idle (advanced, eh?) and in order to get the full shot of ~4 ms of fuel in, you have to excite the injectors 160 BTDC (an additional 80 advance, eh?)

This is no different from the mechanics of firing a spark plug: as engine speed increases, the spark has to be initiated earlier because burn rate is fixed. We have to excite the injectors earlier because travel time is (relatively) fixed. If burn rate, or travel time were infinite, we wouldn't need to advance timing at all. In an engine we want the peak cylinder pressure to be ~17 ATDC and yet we light the plugs anywhere from 10-50 BTDC.

Now, for the same reasons we don't have a retard curve in a distributor (don't even TRY to get me started on this subject!!) we won't need to have retard in the map table. Set the reference position for injection at TDC and advance from there.

www.starchak.ca and www.TDCperformance.ca

-Tyler
DO NOT TOUCH MY HORNS OF DOOM!

Marcel,

Interesting graph! I remember seeing it before but I didn't remember the advance numbers being that big.

So from now on, I'll just say that we need to increase or decrease advance. I won't talk about retard anymore (unless I'm talking about myself :) )

Anyways, do you have any suggestion on how you could automatically detect that you ran out of injection window time instead of having a wrong advance?

http://www.jbperf.com/

Edited by curta_crankn_daddy on 5th Jan, 2006.

www.starchak.ca and www.TDCperformance.ca