AdioSS

I just woke up after nearly 14 hours of sleeping & remember dreaming about this. I very rarely remember my dreams, but this seems like something that could work.

Ok, the OEMs have been working with deactivating cylinders in attempt to boost fuel economy during light loads for a long time. We all know about the Cadillac V8-6-4, right? And more recently GM's Active Fuel Management (AFM) & Mopar's Displacement On Demand (DoD). These shut down individual cylinders by killing their fuel injectors & closing their valves. I'm sure spark may also be cut off? I really don't know all the details of how this is working because my life interests & hobbies have changed since this stuff started being implemented. My "hot rod" hasn't moved under its own power since like 2006 []

Anyway, back to my idea/dream. When DoD shuts down a cylinder from producing power there are still considerable pumping losses due to the rod & piston still pumping. The rings are still dragging along the cylinder wall, the trapped gas in the cylinder keeps getting compressed & expanded, & all the other actions being performed in & around the engine keep going. Now what if this cylinder could be turned from a drag on the system to something that could help the system?

I'm talking about converting the unused cylinders effectively into positive displacement superchargers. Some compressors are basically engines that only compress air that are driven by other engines. By reversing the valve timing on the dead cylinders & probably doing something different with the exhaust the dead cylinders could act as superchargers when they are not being used as a regular cylinder. Now, I'm not sure about the levels of efficiency of one vs the other, but it seems to me that there might be some gains in this over dead cylinders.

Kevin Blown 95 TA

It might be the level of complexity that makes that idea impractical. As for the dead pistons causing pumping loses, yeah there is some, but don't forget that if the live cylinders have to pump a dead one up with compression, it will still have compression forcing it back down again, just not as much as if it were firing. I'm not sure about the exhaust valve being open on those, though. Can't remember how that plays into it when the cylinders deactivate.

engineermike

First, try and understand the basic concepts of speed-density and why cylinder deactivation and VCT improve mileage. Once you figure that out, it will become obvious why turning dead cylinders into superchargers will not improve anything.

On the flip side, if you could figure out a way to get additional live-cylinder exhaust expansion out of the dead cylinders, then you would be on to something. One of the shortcomings of the IC engine is that the compression ratio and expansion ratio are locked at he same number. The expansion ratio really wants to be much higher to get more energy out of the hot gasses, but instead we just release it to atmosphere. Some fancy cam and SC tricks (Miller cycle) have been attempted to try and improve on this, with limited success. If you could figure out a way to incorporate this into the dead cylinders, then you could become very rich.