Efficiency at Maximum Power of Low-Dissipation Carnot Engines

We study the efficiency at maximum power, eta*, of engines performing finite-time Carnot cycles between a hot and a cold reservoir at temperatures T(h) and T(c), respectively. For engines reaching Carnot efficiency eta(C) = 1 - T(c)/T(h) in the reversible limit (long cycle time, zero dissipation), we find in the limit of low dissipation that eta* is bounded from above by eta(C)/(2 - eta(C)) and from below by eta(C)/2. These bounds are reached when the ratio of the dissipation during the cold and hot isothermal phases tend, respectively, to zero or infinity. For symmetric dissipation (ratio one) the Curzon-Ahlborn efficiency eta(CA) = 1 - root T(c)/T(h) is recovered.