The torque created using an oval chain ring I have seen the explanation on "How bicycle gear works?" but this seem to be using a standard round chain ring. I would like to know if there is any difference when an oval chain ring is used. As I can clearly see, one can have an oval chain ring on a fixed/single gear bike. There fore there is no slaking or tightening of the chain. So I would say that there is no difference in gear ratio during the complete rotation of the oval-chain-ring. So the torque will remain the same. 
Is there an answer to my problem? and if there is could you proved any equations
 A: If you consider the chain ring as delivering torque about a point where the chain to the rear sprocket and front chain ring is tangential (the top portion of the chain is always under tension when delivering power) you'll see that torque is not constant. In the pedal cycle, when the bulge of the chain ring is tangent to the chain the virtual lever will produce less force for a given torque. When the dip is tangential you'll produce more force (torque = force * distance).
Conversely you could express this as requiring more torque (to drive the rear wheel) when the bulge is tangential and requiring less torque when the dip is tangential.
This is used to compensate for the lack of power you can produce at the 12/6 pedal position. In effect the chain ring is actually normalizing your power output throughout the revolution of the pedals.
The slackness of the lower chain is taken up by the pulleys and springs in the rear mech.
In a fixed gear bike I'd suggest there may simply be a little extra slack in the bottom portion of the chain and/or an additional chain tensioner.
A: The principal benefit of elliptical chainrings is to reduce the resisting torque when the pedals are oriented vertically (one foot higher than the other) and increase the generated torque when the pedals are oriented horizontally (both feet at the same height). This is because a person can produce much more torque in the horizontal case by shifting weight to the forward foot.
Elliptical chainrings are not as particularly common because they are more complicated to produce and complicate the design of chain tensioners.
A: I've been trying to work out this same issue in my head and think I finally came up with an explanation that is easy to convey. With an oval chainring, you have the same number of teeth in contact with the chain at any given time, whether the ovality or bulge is perpendicular to the chain pull direction or parallel to it, thus eliminating the need for a tensioner (to illustrate this, take an oval chainring and divide it in half in any direction and the two halves will be symmetrical). So how does it work then? Think of lever arms and torque. The longer the lever arm, the more torque it produces. Think of the chain ring less as a round ring and more like 30 (assuming you are using a 30 tooth chainring) individual levers protruding from the pivot point or bottom bracket. At the bulgiest part of the ring, the lever arms are longer. If these are positioned so that they are pulling perpendicular to the chain direction when your crank arms are in a position where your foot is capable of producing the most power then you will get maximum power on your pedal stroke. This is essentially timing the mechanical efficiency of the longer lever arm to the point when the most power is produced. But if you do that, the pedal stroke will feel uneven and "pulsey". This is where the engineers and manufacturers start to tweek the formula with different clocking positions. The ovality is not set at 90 degree increments to the crank arms. You don't want "Lots of torque, Very little torque, Lots of torque, very little torque" You want to even out the torque output at the wheel despite the differing levels of torque input from the rider due to foot position in the crank cycle. In this way, the torque at the wheel remains constant even though the rider may be standing up and mashing the pedals. With a round ring, the uneven power input can result in uneven power output at the wheel and therefore possible loss of traction in bursts equal to the distance crank revolution in which you are producing the most power. With the oval chainring, this power output is evened out so that the power output of the wheel remains constant. So in short, it does not increase your power. It times it such that it is constant throughout the pedal stroke.
