Quote:
Originally Posted by ThermionicScott
It's probably a good thing that emissions testing continues to evolve to mirror real-world driving. I wonder if we'll see a move toward more rolling cylinder deactivation, rather than bigger displacements for the sake of it. Perhaps we'll even see it on hybrids, once the emissions standards really tighten up.
Heck, I could probably be happy as a clam driving my Outback around on one or two cylinders most of the time, if it weren't for the NVH that would cause.  |
As I understand it, there are two good reasons we see 3 cylinder 1.0's and 1.2's rather than 4 cylinder, and I can speculate on a few more.
1) 3 cylinder and 5 cylinder engines have some inherent efficiency advantages due to the timing of the exhaust pulses over the more balanced 4 and 6 cylinder engines.
2) Volume of a cylinder goes up cublicly while surface area goes up by the square as you increase cylinder size. For this reason, a 1.0L 3 cylinder has less frictional surface and less surface through which to lose heat and therefore thermodynamic efficiency. A 1.0L 2 cylinder or even 1 cylinder would be even better in this respect, but it would probably rattle your teeth out.
Speculation on my part, but due to the flame speed of gasoline combustion, there will be a (maybe more than one?) Goldilocks zone for cylinder bore and stroke at a given RPM. If a cylinder's stroke gets shorter, you need to compensate by increasing the RPM to keep piston speed in that zone or you'll lose efficiency, and (if I remember correctly) friction goes up by the square of RPM, which you'd really want to avoid.
This is not something I've read anywhere, just something I've put together myself after thinking about it a good deal. Someone please correct me if I'm wrong.