We show in this work that a finite-time-thermodynamics model of an irreversible Otto cycle is suitable to reproduce performance results of a real spark ignition heat engine. In order to test our model we have developed a computer simulation including a two-zone combustion model and compared the evolution of the performance parameters of the simulated engine as functions of the rotational speed ͑͒ with those obtained from a simple theoretical scheme including chemical reactions. A theoretical Otto cycle with irreversibilities arising from friction, heat transfer through the cylinder walls, and internal losses properly reproduces simulation results by considering extreme temperatures and mass inside the cylinder as functions of. Furthermore we obtain realistic values for the parameters characterizing global irreversibilities, their evolution with , and a clearer understanding of their physical origin not always well established in theoretical models.

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The cycle-by-cycle variations in heat release for a simulated spark-ignited engine are analyzed within a turbulent combustion model in terms of some basic parameters: the characteristic length of the unburned eddies entrained within the flame front, a characteristic turbulent speed, and the location of the ignition kernel. The evolution of the simulated time series with the fuel-air equivalence ratio, φ, from lean mixtures to over stoichiometric conditions, is examined and compared with previous experiments. Fluctuations on the characteristic length of unburned eddies are found to be essential to simulate heat release cycle-to-cycle variations and recover experimental results. Relative to the non-linear analysis of the system, it is remarkable that at fuel ratios around φ 0.65, embedding and surrogate procedures show that the dimensionality of the system is small.

By performing quasidimensional computer simulations and finite-time thermodynamic analysis we study the effect of spark advance, fuel ratio, and cylinder internal wall temperature in spark ignition engines. We analyze the effect of these parameters on the power output and efficiency of the engine at any rotational speed,. Moreover, we propose the optimal dependence on of the spark advance angle and the fuel ratio with the objective to get maximum efficiency for any fixed power requirement. The importance of engine power-efficiency curves in order to perform this optimization procedure and also of the evaluation of macroscopic work losses in order to understand the physical basis of the optimization process is stressed. Taking as reference results from simulations with constant standard values of spark advance, fuel ratio, and cylinder internal wall temperature, the optimized parameters yield to substantial increases in engine performance parameters.