Auto ignition of a nitrogen-based monofuel as a function of pressure and concentration

• The auto ignition of aqueous urea ammonium nitrate (UAN) monofuel is measured for the first time.
• The role of water in stabilizing and inhibiting the ignition is demonstrated.
• The AIT of aqueous UAN increases with pressure due to increase of water vaporization temperature.
• The boundary conditions that facilitate auto ignition of this fuel are outlined.

Conversion of hydrogen into a transportable and environmentally friendly chemical fuels can facilitate the implementation of renewable energy sources in our energy portfolio. In this paper we analyze a liquid mono-fuel composed of an aqueous solution of ammonium nitrate and urea (UAN), a commercial fertilizer commodity and a hydrogen carrier. In order to implement this fuel, additional information regarding its safety and combustion behavior is needed. We report on an important safety parameter of UAN, namely the auto ignition temperature (AIT). The AIT was measured in an original experimental system based on an ASTM standard under applied pressure at different water contents. The water content impacts the crystallization temperature which allows utilization of the fuel at different weather conditions. Specifically, the role of water in stabilizing and inhibiting the ignition is demonstrated, where ignition occurs in a gaseous phase after nearly complete water evaporation. Additionally, the influence of initial pressure on the ignition process was investigated. The AIT increases with pressure due to the increased water vaporization temperature. This study outlines the boundaries that support auto ignition and useful combustion of this fuel.