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This kind of cylinder deactivation is called DFCO ... engine braking
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DFCO or Deceleration Fuel Cut-Off, aka Engine braking.
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That's cylinder deactivation on all cylinders.
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True, if in full DFCO. However, all the cylinders are not deactivated in this case.
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Guess what, it slows you down.
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True, when cylinder deactivation is on all cylinders.
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The air does not expand because of the residual heat.
It expands because it's been compressed in the compression stroke - costing energy - and the piston is going down because it's connected to the crankshaft.
Sure you'll get some of that compression energy back, but never all of it.
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Agreed.
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Cylinder deactivation works if you can control the valves so the compression stroke is no longer a compression stroke, and very little energy is wasted moving the piston about.
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Works better this way no doubt.
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There could be some advantage in increasing the load at the same rpm for the remaining cylinders - and better BSFC.
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Possibly.
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Don't expect miracles though ...
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I never do.
There are however, differences in the effect of engine braking when comparing petro to diesel engines.
Engine braking - Wikipedia, the free encyclopedia
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Petrol (gasoline) engines
The term engine braking usually refers to the braking effect caused by the closed-throttle partial-vacuum in petrol (gasoline) engines when the accelerator pedal is released. While some of the braking force is due to friction in the drive train, this is negligible compared to the effect from the vacuum.
When the throttle is closed, the air flow to the intake manifold is greatly restricted. The concept can be illustrated by the amount of effort required to blow/suck through a thin tube vs. a thicker one. It is the work the engine has to do against this restricted air flow that provides the braking effect.
[edit] Diesel engines
Diesel engines do not have engine braking in the above sense. Unlike petrol engines, diesel engines vary fuel flow to control power rather than throttling air intake and maintaining a constant fuel ratio as petrol engines do. As they do not maintain a throttle vacuum, they are not subject to the same engine braking effects.
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Like I posted earlier.
"It may have
some merit."
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