In the context of reducing carbon dioxide ([Formula: see text]) emissions, hydrogen is gaining momentum as a possible fuel for Internal Combustion Engines (ICEs). In-cylinder direct injections allow for a higher specific power density while enabling different levels of charge stratification. The high-pressure injection leads to the onset of under-expanded jets, characterized by complex patterns of shock waves and expansion fans. In ICEs simulations, such physics needs to be correctly solved to obtain a reliable assessment of the mixture formation. In this paper, the main features of hydrogen under-expanded jets are examined under the conditions typically found in turbocharged engines. Improved correlations are provided for the assessment of the Mach disk height and diameter, up to a Nozzle Pressure Ratio (NPR) equal to 60. The dependency of the hydrogen-air mixing on the cylinder temperature has been analyzed, and the unsteady jet dynamics has been examined by continuously varying the combustion chamber pressure. To the authors’ knowledge, no studies of this kind can be found in the literature for the specific case of hydrogen. Lastly, a preliminary investigation of the jet-jet interaction (a Coanda-like effect) is reported. This phenomenon is observable when multi-hole injectors are employed, and it may have a great impact on the mixture formation.
This historical moment is characterized by a great awareness regarding the need to reduce the Greenhouse Gas emissions (GHG), which are responsible for the climate change and its detrimental consequences. Green hydrogen produced by means of Power-to-Gas technologies from renewables is gaining momentum as a possible clean fuel for the future mobility. In such a context, traditional injectors for hydrocarbon fuels are currently being tailored to be used with hydrogen. The short time available for the injection process leads to the employment of a high inlet pressure, resulting in the formation of an under-expanded jet. In this work, the main characteristics of these jets are analyzed by means of Computational Fluid Dynamics (CFD) for a Nozzle Pressure Ratio (NPR) equal to 10. Then, to provide insights regarding the dependence of the air-hydrogen mixing on section shape of the nozzle, comparisons have been performed by changing the nozzle cross-section (circular, rectangular, and elliptical), keeping constant the mass flow rate to highlight the different levels of axial penetration and radial spread observed when varying the aspect ratio (1.5, 5.0, 8.0).
The European Green Deal for halving greenhouse gases emissions by 2030, compared to those of 1990s, and the resulting conversion in road transport from 2035 imply the need for the automotive field. Hydrogen-fueled internal combustion engines show a good potential to satisfy the transition towards the carbon neutrality. In particular, direct injection of hydrogen in spark-ignited internal combustion engines have great efficiency potentialities, nonetheless the design optimization of the injection systems needs extensive analysis for the evaluation of the hydrogen-air mixing processes under different engine operating conditions. Transient simulations of the gas-exchange process and fuel injection and mixing are fully described within this paper for two different commercial CFD codes namely, AVL-Fire and Ansys-Fluent. Both codes use the finite-volume approach to discretize the governing equations. Numerical results from the two commercial codes have been compared against the experimental data provided by the Argonne National Laboratories in terms of contours of fuel mole-fractions and velocity-field vectors, resulting from applying laser-based techniques on an optically accessible, single-cylinder engine.
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