The kinetic modeling of the pyrolysis and combustion of liquid transportation fuels is a very complex task for two different reasons: the challenging characterization of the complex mixture of several hydrocarbon isomers and the complexity of the oxidation mechanisms of large hydrocarbon and oxygenated molecules. While surrogate mixtures of reference components allow to tackle the first difficulty, the complex behavior of the oxidation mechanisms is mostly overcome by reducing the total number of involved species by adopting a lumping approach. After a first investigation of the different liquid fuels (gasoline, kerosene, and diesel fuels), a short discussion on the lumping techniques allows to highlight the advantages of this approach. The lumped POLIMI pyrolysis and oxidation mechanism of hydrocarbon and oxygenated fuels is then used for generating several skeletal mechanisms for typical surrogate mixtures, moving from pure n-heptane up to heavy diesel fuels. These skeletal models are simply reduced with a reaction flux analysis, and they involve between 100 and 200 species. While these sizes already allow detailed computational fluid dynamics (CFD) calculations in internal combustion engines, further reduction phases are necessary when the interest is toward more complex CFD computations. To maintain the standard structure of the skeletal mechanisms, successive reduction phases are not considered. Moreover, new regulations pushed toward a greater use of renewable fuels. For these reasons, the skeletal models are also extended to biogasolines including methanol, ethanol, and n-butanol. Similarly, skeletal models of diesel and biodiesel fuels, including methyl esters, are also provided. Several comparisons with experimental data and complete validations in the operating range of internal combustion engines are also reported. The whole set of comparisons with experimental data obtained in a wide range of conditions not only validate the reduced models of specific transportation fuels but also the complete kinetic scheme POLIMI 1404

A wide-range experimental and theoretical investigation of ammonia gas-phase oxidation is performed, and a predictive, detailed kinetic model is developed.

The low- and high-temperature oxidation mechanisms of n-heptane have been extensively studied in recent and past literature because of its importance as a primary reference fuel. Recent advanced analytical methods allowed for the identification of several intermediate oxygenated species at very low-temperature conditions in jet-stirred reactors. On these bases, new classes of successive reactions involving hydroperoxide species, already discussed for propane and n-butane oxidation, were included in the low-temperature oxidation mechanism of n-heptane. These new reactions allowed for the improvement of the overall mechanism, not only obtaining a satisfactorily agreement with reaction products, such as organic acids, diones, and ketones, but also in terms of system reactivity. Moreover, deeper attention was also paid to the formation of ketohydroperoxides, rarely experimentally measured. Because of n-heptane importance as a primary reference fuel, the overall POLIMI kinetic mechanism is validated in a wide range of conditions, in both the high- and low-temperature regimes. Moreover, the reliability of the updated oxidation mechanism is further proven in a couple of more complex applications, such as the autoignition of nheptane droplets in microgravity conditions and the oxidation of lean n-heptane/air mixtures in homogeneous charge compression ignition (HCCI) engines

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When it comes to handling large hydrocarbon molecules and describing the pyrolysis and combustion behavior of complex mixtures, the potential and limitations of detailed chemistry require a careful investigation. Indeed, as they involve a large number of species and reactions, detailed kinetic mechanisms often make the model predictions computationally expensive, thus strongly restricting their potential. Therefore, the automatic generation of detailed mechanisms with several thousands of molecular species and elementary reactions, very useful in many circumstances and a prerequisite to derive reduced models, may become useless from a more general application viewpoint. In order to overcome these limitations, in this paper a proper strategy to obtain suitable mechanisms for multidimensional computational fluid dynamics (CFD) applications is presented and discussed. It couples the advantages of two reduction techniques: chemical lumping of species and reactions and a flexible and reliable reduction technique aimed at eliminating unimportant species and reactions. It is shown that a central advantage of semidetailed kinetic models, already reduced with a chemical lumping, is their easier and more effective applicability to successive automatic reductions. Kinetic schemes of n-heptane and n-dodecane oxidation, reduced to 100 and 120 species, respectively, are obtained and compared with experimental data and with the complete original model. These dimensions easily allow the successive use of these reduced kinetic models particularly when the aim is to embody them within computational fluid dynamic models. In particular, simulations of steady-state, axisymmetric, laminar diffusion flames were performed comparing the original and the reduced kinetic mechanisms. The results demonstrated not only the reliability of the reduced mechanisms, but, more importantly, highlighted the great computational advantages, especially in terms of CPU times, of reduced kinetics for the simulation of multidimensional systems. Similar or even more apparent benefits are expected when reducing lumped kinetic schemes of combustion of real transportation fuels, such as gasoline, jet, and diesel fuels

Nowadays, detailed kinetics is necessary for a proper estimation of both flame structure and pollutant formation in compression ignition engines. However, large mechanisms and the need to include turbulence/chemistry interaction introduce significant computational overheads. For this reason, tabulated kinetics is employed as a possible solution to reduce the CPU time even if table discretization is generally limited by memory occupation. In this work the authors applied tabulated homogeneous reactors (HR) in combination with different turbulent-chemistry interaction approaches to model non-premixed turbulent combustion. The proposed methodologies represent good compromises between accuracy, required memory and computational time. The experimental validation was carried out by considering both constant-volume vessel and Diesel engine experiments. First, the ECN Spray A configuration was simulated at different operating conditions and results from different flame structures are compared with experimental data of ignition delay, flame lift-off, heat release rates, radicals and soot distributions. Afterwards, engine simulations were carried out and computed data are validated by cylinder pressure and heat release rate profiles.