I'm having trouble working this knowing that if I allow too much adiabatic expansion, the water vapor will condense to a liquid. I believe that the Clapeyron Equation is used to keep the steam in its phase.  (dP / dT) = L / (T * dV)

Steam at 180 psi is piped into an 80cm cylinder with a piston that has a total travel length of 1.8 m. At what distance along the cylinder should I stop the addition of steam and allow the adiabatic expansion to take place if I want to have the Carnot Engine operating at it's highest efficiency? By highest efficiency I mean the largest adiabatic expansion possible without converting the steam into liquid. This is of course balanced against the initial volume of steam added.

Could someone point me in the direction of solving this problem?