  We investigate a stochastic heat engine based on an over-damped particle
diffusing on the positive real axis in an externally driven time-periodic
log-harmonic potential. The periodic driving is composed of two isothermal and
two adiabatic branches. Within our specific setting we verify the recent
universal results regarding efficiency at maximum power and discuss properties
of the optimal protocol. Namely, we show that for certain fixed parameters the
optimal protocol maximizes not only the output power but also the efficiency.
Moreover, we calculate the variance of the output work and discuss the
possibility to minimize fluctuations of the output power.
