In the effort to achieve the goal of a climate-neutral transportation system, the use of hydrogen and other synthetic fuels plays a key role. As battery electric vehicles become more widespread, e-fuels could be used to defossilize the hard-to-electrify transportation sectors and to store energy produced from renewable and non-continuous energy sources. Among e-fuels, hydrogen and ammonia are very attractive because they are carbon-neutral and their oxidation does not lead to any CO2 emissions. Furthermore, hydrogen/ammonia mixtures overcome the issues that arise as each of the two fuels is separately used. In the automotive sector, the use of either hydrogen, ammonia or their blends require a characterization of such mixtures under engine-like conditions, that is, at high pressures and temperatures. The aim of this work is to evaluate the Laminar Flame Speed (LFS) of hydrogen/ammonia mixtures by varying the thermodynamic conditions and the molar composition of the reactants. The influence of hydrogen addition on the flame structure is assessed, in terms of flame thickness, temperature and major species profiles, under engine-like conditions. To this end, one-dimensional simulations have been carried out by employing several kinetic reaction mechanisms. The results have been compared with experimental data available in the scientific literature to guarantee the accuracy of the numerical results. Finally, a parametric analysis has been carried out to study the influence of pressure, temperature, equivalence ratio and hydrogen mole fraction on LFS by considering thermodynamic conditions that have not been explored in the literature and are relevant for automotive applications. The results show that LFS increases exponentially with the hydrogen mole fraction. In a semi-logarithmic scale, a second-degree polynomial regression is proposed to fit the numerical results, whereas a linear regression is accurate enough with H2 mole fraction in the range 0 - 0.6. As expected, LFS decreases with increasing pressure, although this effect is less pronounced as pressure increases. On the other hand, the increase of LFS with temperature is higher as pressure increases and H2 mole fraction decreases.
A Numerical Study of the Laminar Flame Speed of Hydrogen/Ammonia Mixtures under Engine-like Conditions
Marco D'Amato;Vinicio Magi;Annarita Viggiano
2024-01-01
Abstract
In the effort to achieve the goal of a climate-neutral transportation system, the use of hydrogen and other synthetic fuels plays a key role. As battery electric vehicles become more widespread, e-fuels could be used to defossilize the hard-to-electrify transportation sectors and to store energy produced from renewable and non-continuous energy sources. Among e-fuels, hydrogen and ammonia are very attractive because they are carbon-neutral and their oxidation does not lead to any CO2 emissions. Furthermore, hydrogen/ammonia mixtures overcome the issues that arise as each of the two fuels is separately used. In the automotive sector, the use of either hydrogen, ammonia or their blends require a characterization of such mixtures under engine-like conditions, that is, at high pressures and temperatures. The aim of this work is to evaluate the Laminar Flame Speed (LFS) of hydrogen/ammonia mixtures by varying the thermodynamic conditions and the molar composition of the reactants. The influence of hydrogen addition on the flame structure is assessed, in terms of flame thickness, temperature and major species profiles, under engine-like conditions. To this end, one-dimensional simulations have been carried out by employing several kinetic reaction mechanisms. The results have been compared with experimental data available in the scientific literature to guarantee the accuracy of the numerical results. Finally, a parametric analysis has been carried out to study the influence of pressure, temperature, equivalence ratio and hydrogen mole fraction on LFS by considering thermodynamic conditions that have not been explored in the literature and are relevant for automotive applications. The results show that LFS increases exponentially with the hydrogen mole fraction. In a semi-logarithmic scale, a second-degree polynomial regression is proposed to fit the numerical results, whereas a linear regression is accurate enough with H2 mole fraction in the range 0 - 0.6. As expected, LFS decreases with increasing pressure, although this effect is less pronounced as pressure increases. On the other hand, the increase of LFS with temperature is higher as pressure increases and H2 mole fraction decreases.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
