Using finite-time thermodynamics, the relations between the power output, thermal efficiency and compression ratio have been derived. The effect of the specific heat of the working fluid, being temperature dependent, on the irreversible cycle performance, is significant. The conclusions obtained in this investigation are in full agreement with those of published studies for other cycles and may be used when considering the designs of actual diesel-engines. (c) 2005 Elsevier Ltd. All rights reserved.