Hydrogen is the energy vector that will lead us toward a more sustainable future. It could be the fuel of both fuel cells and internal combustion engines. Internal combustion engines are today the only motors characterized by high reliability, duration and specific power, and low cost per power unit. The most immediate solution for the near future could be the application of hydrogen as a fuel in modern internal combustion engines. This solution has advantages and disadvantages: specific physical, chemical and operational properties of hydrogen require attention. Hydrogen is the only fuel that could potentially produce no carbon, carbon monoxide and carbon dioxide emissions. It also allows high engine efficiency and low nitrogen oxide emissions. Hydrogen has wide flammability limits and a high flame propagation rate, which provide a stable combustion process for lean and very lean mixtures. Near the stoichiometric air–fuel ratio, hydrogen-fueled engines exhibit abnormal combustions (backfire, pre-ignition, detonation), the suppression of which has proven to be quite challenging. Pre-ignition due to hot spots in or around the spark plug can be avoided by adopting a cooled or unconventional ignition system (such as corona discharge): the latter also ensures the ignition of highly diluted hydrogen–air mixtures. It is worth noting that to correctly reproduce the hydrogen ignition and combustion processes in an ICE with the risks related to abnormal combustion, 3D CFD simulations can be of great help. It is necessary to model the injection process correctly, and then the formation of the mixture, and therefore, the combustion process. It is very complex to model hydrogen gas injection due to the high velocity of the gas in such jets. Experimental tests on hydrogen gas injection are many but never conclusive. It is necessary to have a deep knowledge of the gas injection phenomenon to correctly design the right injector for a specific engine. Furthermore, correlations are needed in the CFD code to predict the laminar flame velocity of hydrogen–air mixtures and the autoignition time. In the literature, experimental data are scarce on air–hydrogen mixtures, particularly for engine-type conditions, because they are complicated by flame instability at pressures similar to those of an engine. The flame velocity exhibits a non-monotonous behavior with respect to the equivalence ratio, increases with a higher unburnt gas temperature and decreases at high pressures. This makes it difficult to develop the correlation required for robust and predictive CFD models. In this work, the authors briefly describe the research path and the main challenges listed above.

This paper deals with a numerical and experimental characterization of a high-pressure diesel spray injected by a common-rail injection system. The experiments considered a free non-evaporating spray and they were performed in a vessel reproducing the practical density that characterizes a D.I. diesel engine at injection time. The fuel was supplied at high pressure by a common-rail injection system with a single hole tip. The computations have been carried out by using both the TAB model and a hybrid model that allows one to describe both liquid jet atomization and droplet breakup. In order to validate the breakup model, an extensive comparison between data and numerical predictions has been carried out in terms of spray penetration, Sauter mean diameter, near and far spray cone angles, and spray structure.

The aim of this work is to set up a methodology for simulating Common Rail high-pressure injectors based on coupling a lump-model with CFD two-phase multi-dimensional computations. The unit simulated is the Bosch injector. The injector lump-model resulted in the definition of the three sub-models for hydraulics, mechanics and electro-magnetics. The second-order differential governing equations have been solved in Matlab/Simulink environment and are properly coupled together with the one-dimensional partial differential equations that describe the unsteady pipe flow. A detailed library of thermo-mechanical properties for ISO-4113 oil and diesel fuel is included. Cavitation effects on discharge coefficient in the main orifices were accounted for by using results from CFD steady two-phase flow simulations. The evaluation of the model capability was assessed by using detailed experiments carried out at different practical injector operating conditions. Instantaneous and integrated injected flow rate, and injector needle lift were measured and collected for comparison with simulation. CFD steady computations revealed to be unavoidable in driving the lump-model toward a high reliability of injector performances over the whole range of injection pressures and energizing times.

In this paper three-dimensional Large Eddy Simulations (i.e., LES) by using a PLIC-VOF method have been adopted to investigate the atomization process of round liquid jets issuing from automotive multi-hole injector-like nozzles. LES method is used to compute directly the effect of the large flow structure, being the smallest one modelled. A mesh having a cell size of 4 μm was used in order to derive a statistics of the detached liquid structures, i.e. droplets and ligaments. The latter have been identified by using an algorithm coded by authors. Cavitation modeling has not been included in the present computations. Two different mean injection nozzle flow velocities of 50 m/s and 270 m/s, corresponding to two mean nozzle flow Reynolds numbers of 1600 and 8700, respectively, have been considered in the calculations as representative of laminar and turbulent nozzle flow conditions. The numerical results clearify the role of both the boundary layer relaxation and the inner liquid jet turbulence in determining the onset of jet surface perturbations. Simulations indicate that, at the high Oh and We numbers typical of automotive injection conditions, the nozzle flow regime likely determines the same statistics of the detached liquid structures, while it changes the fragmentation rate of the liquid jet considerably.

DI Diesel engine are widely used both for industrial and automotive applications due to their durability and fuel economy. Nonethe- less, increasing environmental concerns force that type of engine to comply with increasingly demanding emission limits, so that, it has become mandatory to develop a robust design methodology of the DI Diesel combustion system focused on reduction of soot and NOx simultaneously while maintaining a reasonable fuel economy. In recent years, genetic algorithms and CFD three-dimensional combustion simulations have been successfully applied to that kind of problem. However, combining GAs op- timization with actual CFD three-dimensional combustion simulations can be too onerous since a large number of calculations is usually needed for the genetic algorithm to converge, resulting in a high computational cost and, thus, limiting the suitability of this method for industrial processes. In order to make the optimization process less time-consuming, CFD simulations can be more conveniently used to generate a training set for the learning process of an artifical neural network which, once correctly trained, can be used to forecast the engine outputs as a function of the design parameters during a GA optimization performing a so-called virtual optimization.In the current paper, a numerical methodology for the multi-objective virtual optimization of the combustion of an automotive DI Diesel engine, which relies on artificial neural networks and genetic algorithms, was developed

A numerical methodology to simulate the high pressure spray evolution and the fuel-air mixing in diesel engines is presented. Attention is focused on the employed atomization model, a modified version of the Huh and Gosman, on the definition of a turbulence length scale limiter and of an adaptive local mesh refinement technique to minimize the result grid dependency. All the discussed models were implemented into Lib-ICE, which is a set of libraries and solvers, specifically tailored for engine simulations, which runs under the open-source CFD technology OpenFOAM®.To provide a comprehensive assessment of the proposed methodology, the validation procedure consisted into simulating, with a unique and coherent setup of all models, two different sets of experiments: a non-evaporating diesel fuel spray in a constant-volume vessel with optical access and an evaporating non-reacting diesel fuel spray in an optical engine. The first of these experiments were carried out by the authors by analyzing optical pictures of the jets taken at different instants by imaging technique. A Common-Rail-based injection apparatus was used for injecting commercial diesel fuel at pressures ranging from 50 to 123 MPa inside a constant volume vessel at engine-like density conditions and operating in single shot mode. Literature data were then used to validate the vapor fuel-air mixing at engine conditions.