SYNOPSISIn this work we present a simplified irreversible Otto engine model which includes power losses and a chemical combustion reaction at the end of the adiabatic compression. The heat released in the combustion reaction is taken as a fluctuant quantity around its mean value. The fluctuations are simulated by means of a Gaussian stochastic process for a rich-air intake mixture and by two non-linear deterministic noisy maps in the case of poor-air mixtures. The fluctuant combustion heat drives the Otto engine model producing in turn fluctuant power output and fluctuant cycle efficiency. We analyse the size of the fluctuant outputs in terms of the fluctuant input.