A simplified Mean Value Model of the combustion process for the simulation of Energetic Systems.

Current environmental issues require continuous improvements of the performance of energetic systems, which are mainly based on combustion processes. In order to find solutions for maximizing the energy output while minimizing the fuel consumption and pollutants emissions, the optimization of the combustion processes within the plants plays a fundamental role. The purpose of this work was the creation of a flexible code for the fast simulation of combustion processes calculating the chemical equilibrium composition and adiabatic flame temperature of the mixture of products from the combustion of a generic CnHmOr fuel. Seven dissociation reactions have been taken into consideration, yielding eleven products species: CO2, CO, H2O, H2, O2, N2, OH, NO, O, N, H. The non-linear system of equations describing the equilibrium conditions has been numerically solved via the non- linear optimization tools of the Matlab® environment, using the Gauss-Newton and Levenberg-Marquardt algorithms. The adiabatic flame temperature and chemical composition of combustion products can be evaluated for both constant-volume and constant- pressure systems. A 0-D Simulink® model of the compression and expansion strokes of an Internal Combustion Engine (ICE) was then developed, using the described calculation code. The combustion process has been modeled as a sequence of instantaneous constant-volume reactions which involve a fraction of the total amount of fuel. At each simulation step the model evaluates temperature, pressure, volume and chemical composition at the equilibrium conditions through the well-known conservation equations. The fraction of burned fuel at each simulation time step is determined by a fuel burning rate (FBR) curve, which can be used to describe different combustion processes. The Matlab® calculation code has been validated by comparison with results obtained from the open literature, and proved to be accurate and robust. The Simulink® model demonstrates the potential applications of the developed program in the simulation of combustion-based energy systems, allowing the evaluation of changes in the thermodynamic state variables and equilibrium composition of the system.