Oval and elliptical chain rings work just fine as they are with a centrally located axle. At least in the sense that they make for a varying effective gear ratio that is largest when the oval is vertical and smallest when it's horizontal. Whether they actually result in a faster or more efficient ride is debatable - some riders like them but they've never gained much of a following.

Clearly you're not willing to actually think about either my or HKL's arguments based on the geometry of the situation nor accept the experience of those who have ridden with such chain rings. Envision the distance that a single tooth of the ring moves for a given angular rotation of the crank. If that tooth is near the long axis of the oval it moves farther than if the tooth is near the short axis. The chain engages that tooth and therefore has to move exactly as far as the tooth does. If you still can't see it then I suggest you find someone with oval rings and borrow their bike. Ride at a reasonably constant speed and you'll immediately feel the variation in the angular rotation speed of the cranks.