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In this work, a quasi-dimensional, multi-zone combustion model is analytically presented, for the prediction of performance and nitric oxide (NO) emissions of a homogeneous charge spark ignition (SI) engine, fueled with biogas-H2 blends of variable composition. The combustion model is incorporated into a closed cycle simulation code, which is also fully described. Combustion is modeled on the basis of turbulent entrainment theory and flame stretch concepts. In this context, the entrainment speed, by which unburned gas enters the flame region, is simulated by the turbulent burning velocity of a flamelet model. A flame stretch submodel is also included, in order to assess the flame response on the combined effects of curvature, turbulent strain and nonunity Lewis number mixture. As far as the burned gas is concerned, this is treated using a multi-zone thermodynamic formulation, to account for the spatial distribution of temperature and NO concentration inside the burned volume.

In this work, a new CO emissions formation model is developed based on the dynamics of a representative pool of radicals in the post-flame combustion gases. The ultimate target is the derivation of a kinetics-based CO model, formulated by a single differential equation, that can run very fast in any engine diagnostic/post-processing tool which analyzes in-cylinder processes in the framework of big data acquired at the engine test bench or during engine operation in the field. Specific objectives in the development of the current model are (i) inclusion of the effect of engine operating conditions on the CO emissions formation mechanism, (ii) ease of implementation in any diagnostic code/platform, (iii) fast running times toward real-time capability, and (iv) robustness. The presently developed CO model consists of a single Ordinary Differential Equation (ODE) that can be solved analytically, without the need of a stiff chemical kinetics solver.

In this work a quasi-dimensional multi-zone combustion diagnostic tool for homogeneous charge Spark Ignition (SI) engines is analytically developed for the evaluation of heat release, flame propagation, combustion velocities as well as engine-out NOx and CO emissions, based on in-cylinder pressure data analysis. The tool can be used to assess the effects of fuel, design and operating parameters on the SI engine combustion and NOx and CO emissions formation processes. Certain novel features are included in the presently developed combustion diagnostic tool. Firstly, combustion chambers of any shape and spark plug position can be considered due to an advanced model for the calculation of the geometric interaction between a spherically expanding flame and a general combustion chamber geometry.