Efficiency at maximum power of a chemical engine

A cyclically operating chemical engine is considered that converts chemical energy into mechanical work. The working fluid is a gas of finite-sized spherical particles interacting through elastic hard collisions. For a generic transport law for particle uptake and release, the efficiency at maximum power nu(mp) takes the form 1/2 + c Delta mu + O(Delta mu(2)), with 1/2 a universal constant and Delta mu the chemical potential difference between the particle reservoirs. The linear coefficient c is zero for engines featuring a so-called left/right symmetry or particle fluxes that are antisymmetric in the applied chemical potential difference. Remarkably, the leading constant in nu(mp) is non-universal with respect to an exceptional modification of the transport law. For a nonlinear transport model, we obtain nu(mp), with theta > 0 the power of Delta mu in the transport equation. (C) 2013 AIP Publishing LLC.