In this paper, a thermodynamic analysis for an irreversible Otto Miller Cycle (OMC) has been presented by taking into consideration heat transfer effects, frictions, time-dependent specific heats, internal irreversibility resulting from compression and expansion processes. In the analyses, the influences of the engine design parameters such as cycle temperature ratio, cycle pressure ratio, friction coefficient, engine speed, mean piston speed, stroke length, inlet temperature, inlet pressure, equivalence ratio, compression ratio, and bore-stroke length ratio on the effective power, effective power density and effective efficiency have been investigated relations with efficiency in dimensionless form. The dimensionless power output and power density and thermal efficiency relations have been computationally obtained versus the engine design parameters. The results demonstrate that the engine design and running parameters have considerable effects on the cycle thermodynamic performance. of a OMC. The results showed that the cycle efficiency increased up to 50%, as cycle temperature ratio increases from 6 to 8, the effective power raised to 11 kW from 5 kW at this range. Other parameters such as engine speed, mean piston speed, cycle pressure ratio affected the performance up to 30%, positively. However, friction coefficient and inlet temperature have negative effect on the performance. As the friction coefficient increases from 12.9 to 16.9, a performance reduction was seen up to 5%. Increase of the inlet temperature abated the performance by 40%. (C) 2016 Elsevier Ltd. All rights reserved.