Dynamic Cylinder Deactivation

[christofoo]

This thread didn't die, and I'm still getting foam flecked PM's from t vago, so I want to try delving back into whether or not DCD will improve FE.

But I want to try simplifying my argument again, largely for previously mentioned reasons.

So, here goes:

==============================

DCD vs lean-burn: Why does lean-burn work and DCD not?

Suppose the lean-burn engine is operating at 25% (er, how to say this?) leanness, by which I mean stoichiometric AFR X 1.25.

Compare to DCD with 25% of cylinders deactivated, 75% at stoichiometric AFR. All else being equal, including valve timing.

If you think I'm wrong, explain to me:

1. Is there a difference in air mass flow rate?
2. Is there a difference in manifold vacuum?
3. Whatever else you think requires consideration.

[Frank Lee]

Because lean burn does not incur pumping losses.

[t vago]

Originally Posted by christofoo

This thread didn't die, and I'm still getting foam flecked PM's from t vago, so I want to try delving back into whether or not DCD will improve FE.

Originally Posted by t vago

Your latest foray into that charlatan's thread illustrates my point rather well. How many edits and "oops" did you do there? Learn more about what you're trying to comment on.

Apparently, in your universe, this counts as "foam-flecked." Alright, prima donna, let's have at it.

Originally Posted by christofoo

But I want to try simplifying my argument again, largely for previously mentioned reasons.

So, here goes:

==============================

DCD vs lean-burn: Why does lean-burn work and DCD not?

Suppose the lean-burn engine is operating at 25% (er, how to say this?) leanness, by which I mean stoichiometric AFR X 1.25.

Compare to DCD with 25% of cylinders deactivated, 75% at stoichiometric AFR. All else being equal, including valve timing.

If you think I'm wrong, explain to me:

1. Is there a difference in air mass flow rate?
2. Is there a difference in manifold vacuum?
3. Whatever else you think requires consideration.

Lean Burn works because intake manifold is lowered, compared to an engine running at stoichiometric. DCD does not work, compared to Lean Burn, because you're placing a drag on the engine (in the form of non-firing cylinders that are still pumping air - therefore consuming more fuel than necessary).

Figure the rest of it out on your own, professor.

[christofoo]

Originally Posted by Frank Lee

Because lean burn does not incur pumping losses.

High AFR means extra air, which doesn't contribute to combustion, getting pumped through the engine. Can you elaborate?

[christofoo]

Originally Posted by t vago

...

Lean Burn works because intake manifold is lowered, compared to an engine running at stoichiometric. DCD does not work, compared to Lean Burn, because you're placing a drag on the engine (in the form of non-firing cylinders that are still pumping air - therefore consuming more fuel than necessary).

Figure the rest of it out on your own, professor.

Same number of pistons, same mass of air? (answer the question please?), same RPM. Please elaborate.

[Frank Lee]

I have elaborated in the past. The short version is, pumping air through cylinder(s) in which no combustion takes place consumes power. Ever notice how powerful the motors on air compressors need to be?

[christofoo]

Originally Posted by Frank Lee

I have elaborated in the past. The short version is, pumping air through cylinder(s) in which no combustion takes place consumes power. Ever notice how powerful the motors on air compressors need to be?

Maybe link to your elaboration? I still don't see how over-stoich-AFR, i.e. pumping extra air through the cylinder that doesn't contribute to combustion, is different. I see an energy conservation argument here.

[t vago]

Would you agree, christofoo, that the very act of sucking in air into a cylinder counts as work being consumed?

[christofoo]

Originally Posted by t vago

Would you agree, christofoo, that the very act of sucking in air into a cylinder counts as work being consumed?

Agreed. This is also true going above stoich-AFR.

[t vago]

Originally Posted by christofoo

Agreed. This is also true going above stoich-AFR.

It doesn't matter whether the AFR is rich, at stoich, or lean. Take as a given the fact that a cylinder has to consume work to suck in air (or an air/fuel mix).

Now, how much work does each cylinder consume? Not looking for numbers, but a general answer.