Quote:
Originally Posted by t vago
So, we have a set amount of produced work, now per firing cycle instead of per cylinder. We have a set amount of pumping work being consumed per firing cycle, instead of per cylinder. We produce a set amount of available work per firing cycle, instead of per cylinder.
We shut off one cylinder via DCD. The remaining cylinders are still producing work. You pointed out that the remaining cylinders are producing less work per firing cycle, than before.
So, we need to increase the amount of fuel to the remaining cylinders, so they can provide the amount of available work as before, while also covering the slack of the deadbeat cylinder caused by DCD.
Hm... The other cylinders are already operating at stoich, right? So we must also increase the amount of oxygen going to the running cylinders! Okay, so we lowered intake manifold vacuum by a bit. Good deal! We just lowered the pumping work for all of the cylinders, right?
Waitaminute... We just increased the amount of fuel to the remaining cylinders. We did this to cover the deadbeat cylinder, which is still consuming pumping work. The pumping work per cylinder may be less than before, since we just lowered intake manifold vacuum, but we also increased the work produced by the remaining working cylinders.
Right?
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Very good, hang on, we're starting to converge now.
Which is greater, the increase in fuel consumption or reduced pumping loss? Let's back up and set the problem up to work out the same way you analyzed lean burn. Start by taking the fuel that would have gone to cylinder 1, and distribute that fuel to the other 3 cylinders. Cylinder 1 is cut, now we're consuming the same amount of fuel per cycle with 3 cylinders that we would have consumed with 4.
But, as you pointed out, the fuel per cylinder has gone up, so manifold vacuum must go down to get more oxygen into each cylinder to maintain stoich AFR.
Agreed?