Is Carnot engine the only form of reversible engine? Is it possible to have a different form of reversible engine that goes through different processes? For a standard Otto cycle working with ideal gas, theoretically the two processes involving isochoric pressure change can be reversible processes. Does it mean that the Otto cycle can also have same efficiency as Carnot cycle? Since temperature of the working fluid is changing during isochoric pressure change, does it mean there are infinite number of heat reservoirs being used at different temperatures so that there is no finite temperature difference at every point of the isochoric process?