Implementation of a multi-zone numerical blow-by model and its integration with cfd simulations for estimating collateral mass and heat fluxes in optical engines

Nowadays reducing green-house gas emissions and pushing the fossil fuel savings in the field of light-duty vehicles is compulsory to slow down climate change. To this aim, the use of new combustion modes and dilution strategies to increase the stability of operations rich in diluent is an effective technique to reduce combustion temperatures and heat losses in throttled operations. Since the combustion behavior in those solutions highly differs from that of typical market systems, fundamental analyses in optical engines are mandatory in order to gain a deep understanding of those and to tune new models for improving the mutual support between experiments and simulations. However, it is known that optical accessible engines suffer from significant blow-by collateral flow due to the installation of the optical measure line. Thus, a reliable custom blow-by model capable of being integrated with both mono-dimensional and three-dimensional simulations was developed and validated against experimental data. The model can work for two different configurations: (a) stand-alone, aiming at providing macroscopic data on the ignitable mixture mass loss/recover through the piston rings; (b) combined, in which it is integrated in CFD engine simulations for the local analysis of likely collateral heat release induced by blow-by. Furthermore, once the model was validated, the effect of the engine speed and charge dilution on the blow-by phenomenon in the optical engine were simulated and discussed in the stand-alone mode. © 2021 by the authors. Licensee MDPI, Basel, Switzerland

Il perfetto cortigiano, specchio della magnificenza perduta del Rinascimento italiano

descrizione del testo e della sua importanza nella costruzione di una cultura europea del Rinascimentodescription of the text and its importance in the construction of the European Renaissance cultur

A numerical methodology based on CFD and plasma chemical kinetics simulations: a focus on the cyano radical

Anticipating the effect of implementing new fuel blends and combustion strategies is crucial in order to deal with the short-medium term green transition envisaged for passenger car fleets. In spark ignition engines, the use of alternative low-carbon fuel blends including biofuels, e-fuels and hydrogen, together with the stabilization of ultra-lean and highly diluted combustion conditions may accomplish both fuel economy and pollutant emission targets. In this framework, studying the very early ignition phase in terms of produced radicals is fundamental in order to optimize operating strategies. To this aim, optical analysis in dedicated engine configurations is a powerful device to extensively characterize those phenomena. The use of numerical tools further enhances investigative possibilities, as they provide insight into plasma-fluid interactions as well as related production of radicals and allow significant extensions of operative conditions along with the reduction of costs and efforts associated with experimental campaigns. This work is focused on the presentation of a numerical methodology supported by UV-visible emission spectroscopy on an optically accessible spark ignition direct injection engine. Focusing on the spark plug zone, the numerical tool traces the cyano radical (CN), which can be a key marker for ignition processes if considering its high sensitivity to the presence of CO2 and N2, namely the main components of charge diluent (e.g., when applying exhaust gas recirculation). The core of the methodology is a white-box zero-dimensional model for the simulation of non-equilibrium plasma chemical kinetics, accounting for the collisions with electrons and reaction schemes. The local mixture composition of the gaseous phase to be provided to the code is determined by means of three-dimensional CFD engine simulations performed with AVL-FIRE. Besides evaluating the effect of air-fuel ratio on CN, which is largely demonstrated in the literature (leaner mixtures feature lower CN production due to the smaller amount of carbon available for the CN-paths), the effect of the injection timing was investigated. Two different values of injection timings were tested for both stoichiometric and lean conditions at the same spark timing. The CN analysis showed that experimental data and numerical results are well correlated. The key role of the mixture local stratification on the CN production as a result of the injection timing was identified and discussed