Firstly I'd like to add that even small amounts of water injection
significantly change MBT.
Now for the justification.
This stuff is all from the PDF document I submitted here several times which covers Ionization Gap Sensing in combination with feedback ignition timing and PPP control.
From page 100 of 207:
"
Figure 3 A large part of the test cycle is displayed. The spark advance controller is shut off around cycle 100 and advance is held constant. The water spraying starts around cycle 250 which leads to increased PPP and decreased torque output. The spark advance controller is switched on at about cycle 400, controlling PPP back to MBT leading to increased output torque. The water spraying stops around cycle 550 and the parameters asymtotically go back to their initial conditions, when the water still in the system, e.g. deposited on the walls, decreases."
I need to resize this image to fit screen. Admin
Now if I could just rig up
my Saabs ECU to do that.
ops:
Anyhow, they were spraying a relatively small amount of water, but were running at part throttle, so it may have been a very high water/air ratio.
Nevertheless it should be noted that adding WI effectively moves the Peak Pressure Position (PPP) back about 5 degrees, at least on these experiments.
This is also the largest flaw I saw on the NACA studies. All of their conditions were at MBT
without water injection. So of course, when the water moves the PPP back 5 degrees you can run more boost and less fuel. It's just like pulling timing 5 degrees.
Darn that flame development angle. :twisted:
Adrian~