Blending Ammonia into Hydrogen to Enhance Safety through Reduced Burning Velocity

Laminar burning velocities (SL) of hydrogen/ammonia mixtures in air at atmospheric pressure were studied experimentally and numerically. The blending of hydrogen with ammonia, two fuels that have been proposed as promising carriers for renewable energy, causes the laminar flame speed of the mixture, SL, to decrease significantly. However, details of this have not previously available. Systematic measurements were therefore performed for a series of hydrogen/ammonia mixtures with wide ranges of mole fractions of blended ammonia (XNH3) and equivalence ratio using a heat flux method based on heat flux of a flat flame transferred to the burner surface. It was found that the mixture of XNH3 = 40% has a value of SL close to that of methane, which is the dominant component of natural gas. Using three chemical kinetic mechanisms available in the literature, i.e., the well-known GRI-Mech 3.0 mechanism and two mechanisms recently released, SL were also modelled for the cases studied. However, the discrepancies between the experimental and numerical results can exceed 50% with the GRI-Mech 3.0 mechanism. Discrepancies were also found between the numerical results obtained with different mechanisms. These results can contribute to an increase in both the safety and efficiency of the coutilization of these two types of emerging renewable fuel and to guiding the development of better kinetic models.