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A numerical study has been carried out to evaluate the suitability of using ozone to achieve stable combustion of a very lean iso-octane/air mixture in a spark-ignition engine. A CFD model has been developed to simulate the compression stroke of the engine and the model has been validated against experimental data. Such a model is able to simulate the chemical kinetics of iso-octane/air/ozone mixtures during the compression stroke, thus predicting the composition and the thermodynamic conditions of the mixture in the chamber at the spark ignition time. These conditions have been used to compute the laminar flame speed of such a mixture by employing a 1-D solver. The accuracy of the solver has been assessed by comparing the numerical results with experimental data. As regards ozonized air, no measured laminar flame speeds for iso-octane/air/ozone mixtures are available. Hence, the model has been validated against experimental data for methane/air/ozone mixtures. The model has been used to investigate iso-octane/air/ozone mixtures, with 0, 200 and 500 ppm of ozone at IVC. The stoichiometric and a lean case with ϕ = 0.5 have been compared. The results show that, during the engine compression stroke, ozone decomposition produces oxygen atoms, which attack fuel molecules producing OH-radicals. These radicals favor the low-temperature oxidation until ignition time is reached. At the ignition time, the thermodynamic conditions of the mixture, in terms of pressure and temperature, are similar for cases with and without ozone. However, with ozone, a partially oxidized mixture is obtained, which promotes an increase of the laminar flame speed to a value comparable to the case without ozone under stoichiometric conditions.

A novel heat recovery strategy for internal combustion engines is proposed. The aim is to recover thermal energy from the engine exhaust gases and through cylinder walls to heat pressurized water to supercritical conditions and to directly inject such supercritical water into the combustion chamber. Herein, this strategy is applied to a spark ignition, four‐stroke, port fuel injection engine. An in‐house solver, which includes a heat exchanger model, has been developed to conduct numerical simulations of the apparatus. At first, the engine model has been validated by comparing the results with experimental measurements. Then, a parametric analysis has been conducted to maximize the engine efficiency by varying the injection start timing, the injector diameter, and the water/fuel ratio. A single‐objective genetic algorithm has been used to select the optimal set of such parameters. Finally, a multiobjective genetic algorithm has been used to maximize the engine efficiency and minimize the exhaust gas–water heat exchanger size. The results show that the proposed approach may lead to a significant increase in the engine efficiency, up to about 12%.

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The aim of this work is the analysis of the characteristics of biodiesel combustion in industrial burners in order to optimize the overall combustion process. A CFD model has been employed to simulate the fuel atomization process and the liquid spray evaporation that occur in a burner. A pressure swirl atomizer has been considered and a "flamelet" model has been implemented to simulate the fuel combustion. The validation of the numerical model has been carried out by a comparison with the experimental data provided by NIST (National Institute for Standards and Technology) for methanol injection and combustion in a cylindrical vessel with an injector axially located. The model has been employed to analyze the behavior of biodiesel fuel, inside the NIST burner, and to make a comparison with the injection and combustion of methanol. Biodiesel has been modelled as methyl-decanoate. A parametric study, by varying the injector included half-angle and the inlet air mass flow rate, has been carried out in order to identify an optimal configuration in terms of flame temperature and pollutant distributions as a result of the combustion process.