Detonation properties and nitrogen oxide production in ammonia–hydrogen–air mixtures

Ammonia is a promising compound for chemical storage of renewable energy produced from non-continuous sources. However, the low reactivity of ammonia requires to use ammonia–hydrogen blends as a fuel for combustion applications. The present study corresponds to a first numerical assessment of the potential of ammonia–hydrogen–air mixtures as reactive mixtures for detonation engine applications. Both ideal and curved detonation models were employed to calculate the detonation properties, entropy production, and NOx production for mixtures with varying amounts of ammonia and hydrogen under a wide range of initial thermodynamics conditions. Interestingly, our calculations show that the entropy production and the amount of nitrogen oxides produced at the Chapman–Jouguet state respectively decreases and increases with the proportion of hydrogen in the ammonia–hydrogen blend. These aspects could have a great impact on engine efficiency and air pollution and should be considered with care. Our results also demonstrate that only mixtures with relatively low amounts of ammonia, i.e., X lower than 0.25 of the fuel blend, can be employed for detonation engine application

Theoretical analysis of the condensation of combustion products in thin gaseous layers

In this paper, a theoretical analysis of the condensation of combustion products in narrow gaps between planar plates is performed. The investigation is motivated by the empirical results shown by Veiga-López [“Flame propagation in narrow channels,” Ph.D. thesis (Carlos III University of Madrid, 2020)] and the lack of a theoretical description directly applicable to them. In these experiments, he describes how discontinuous condensed water films appeared on the walls of the combustion chamber, forming dry/wet stripes parallel to the flame front at the products region. The formulation developed here is derived from a general approach for condensation, which is simplified considering the conditions of high-temperature combustion products. Notably, the liquid phase disappears from the system of equations, which exclusively contains the gaseous phase. The expressions resulting are analytical, simple, and easy to interpret. They allow us to understand qualitatively the effects of the main physical phenomena of the process, which is described by the interaction between heat exchange, mass transfer, the thermodynamic conditions, and the velocity of the combustion products. The construct is subsequently utilized to perform the numerical parametric studies, to analyze the influence of two main parameters of the problem: gap thickness and flame velocity. Despite the relative simplicity of the model, it predicts similar condensation–vaporization–condensation cycles to those observed at the laboratory