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Hello, guys,
I'm back. I am digging into the Kook paper (Tas link). About ignition delay, the informaiton is fairly convincing that substantial lowering of the oxygen partial pressure causes a delay in ignition, and also slows the burn rate. See figs. 12, 13, and 14 for that. (I note in passing that the dilution gas is not real exhaust gas.)
Of far greater interest is the effect of lowered oxygen concentration on NOx formation and engine efficiency. The evidence is very good that total NOx correlates well with their rate equation 2 (see fig. 10). The critical parameter seems to be the energy density in the flame front.
Two thoughts--
1) If the cylinder pressure is raised while keeping oxygen concentration low (low concentration, high partial pressure) then you have the prospect of rapid ignition and burn (depends on partial pressure) while the flame front temperature and NOx stay low (depends on oxygen concentration).
2) Instead of diluting the air, you could dilute the fuel and also lower the flame front temperature. What do you think?
I am still reading, will have comments on efficiency later.
Thanks, Tas, for the education. Let's proceed.
Ernie Rogers
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