This paper aims to give numerical modelling of a composite cylinder which is found in a four-stroke, direct injection diesel engine. In this study, a new generated special software COMPCYL is developed and used as an optimization program. Stress-strain analysis of the designed composite structures is made by using the finite element method. By using this code, the carbon fiber/carbon matrix type composite structures are tested due to maximum internal pressure and temperature distributions. For each ply critical stress-strain distributions are determined and the failure analysis is made (C) 2000 Elsevier Science Ltd. All rights reserved.