The Peer review has evaluated this group as Excellent
The group activity is devoted to fundamental research on internal combustion engines, placing emphasis on the development and application of advanced 1D-multiD numerical models. The main topics which are matter of current investigation are: 1) S.I. engines fuelled with gasoline, natural gas, hydrogen and bio-ethanol; 2) turbocharged Diesel engines; 3) HCCI (Homogeneous Charge Compression Ignition) engines; 4) exhaust after-treatment systems for Diesel and Otto engines. The major aim of such activities is the development of innovative numerical tools to predict the performances and emissions of modern engines and to optimize efficiency, fuel consumption and conversion of pollutant emissions in the after-treatment system. Since the early nineties, the research group has been developing an advanced 1D fluid dynamic code for engine simulation, named GASDYN, which is well known to the international academic and industrial community, being at the forefront of 1D engine modeling. The GASDYN code has been recently coupled to an open-source CFD code, named OpenFOAM, to carry out integrated 1D-3D simulations of i.c. engines. OpenFOAM is also developed and applied by the research group, to study the combustion process of direct injection diesel, gasoline and HCCI engines. A primary role has been played by the group in the field of the computational engine modelling, publishing continuously original contributions to the referring conference of the international automotive community (SAE World congress, held annually in Detroit) since 1998. The 1D simulation GASDYN is able to calculate the thermo-fluid dynamic processes from the intake to the exhaust system, including typical elements such as cylinders, valves, junctions, catalytic converters, particulate filters, deNOx traps, silencers. The solution of the conservation equations at the basis of the 1D model, considering a one-dimensional, compressible, unsteady flow, with transport of species and chemical reactions, is obtained by means of conservative, shock-capturing, symmetric numerical methods. In particular, the GASDYN code pioneered the tracking of reacting chemical species along the exhaust aftertreatment system since 1997. The main innovative aspects of the code are related to: i) the prediction of the combustion process in the cylinder of Diesel and Otto engines by means of quasi-D multi-zone models, including chemical models for the prediction of NO, HC, CO, CO2 and soot emissions. Specific predictive models for hydrogen and natural gas combustion have been developed and detailed chemical mechanisms, developed by the Department of Industrial Chemistry of Politecnico di Milano, have been embedded to predict auto-ignition (HCCI engines) and knock in S.I. engines; moreover, a predictive thermodynamic multi-zone combustion model for the Diesel engine has been realised; ii) the transport of reacting chemical species along the ducts of the intake and exhaust manifold and after-treatment system; in particular, the cryogenic injection of hydrogen in the intake system as well as the post-oxidation of HC and CO in the exhaust ducts due to secondary air injection has been modelled; 27 iii) dedicated sub-models to predict the conversion of the pollutant emissions in the three-way catalytic converter, the oxidation catalyst, the diesel particulate filter, the selective catalytic reduction system; in particular, the conversion efficiency and temperature of the after-treatment system can be evaluated for steady and transient operating conditions, including the warm-up and light-off of the system during a European driving cycle; iv) the simulation of S.I. and C.I. turbocharged engines, with detailed models for the compressor and the turbine (with variable nozzle geometry or waste-gated), for the cooled EGR valve and the intercooler; v) the modelling of intake and exhaust silencers with complex geometry (perforates, sound absorbing material, flow reversals, etc.) and the prediction of radiated noise. For what concerns the group activity related to the opensource CFD code OpenFOAM, it is focused on advanced developments and applications for engine modelling. In this contest a primary role has been played internationally as referring institution of such community for internal combustion engine simulations, combustion and spray (www.foamcfd.org). Current developments of the OpenFOAM code are concerned with: i) Definition of automatic mesh motion with topological changes for engine simulation, allowing the possibility of attaching or detaching boundaries, adding or removing cell layers and using sliding mesh interfaces. ii) Implementation of Lagrangian library for spray modelling including the most advanced submodels for: atomization (LISA), injection, breakup (TAB, KHRT, Reitz-Diwakar,…), collision (Trajectory, O’Rourke), evaporation (Frossling), heat transfer (Ranz-Marshall), wall film, turbulent dispersion. iii) Development and application of advanced turbulent combustion models for premixed and diffusive flames (Chemkin C++ implementation, ODE solvers library for direct integration, Diesel combustion models (EDM, characteristic time combustion model and complex chemistry approach). Implementation of ISAT technique (In-Situ Adaptive Tabulation), turbulence/chemistry interaction accounted by the PaSR (Partially Stirred Reactor) model.