Hydrogen Production from Ammonia-Rich Combustion Under High Temperature and High Pressure Conditions

Abstract

Hydrogen is a promising fuel in the upcoming era where carbon-neutral is emphasized. However, the safety and cost issues of onboard storage restrict the massive application of hydrogen in internal combustion engines (ICEs) on vehicles. Considering that ammonia is a carbon-free hydrogen carrier, hydrogen production by ammonia reforming can be a potential way for supplying hydrogen onboard. This paper presents an investigation on the hydrogen production from ammonia-rich combustion on a rapid compression machine (RCM) over conditions with varying pressures (22-36 bar), temperatures (1200-1300 K), and equivalence ratios (1.75-2.25). Both major combustion reactants (NH3) and products (H2 and N2) were analyzed using a fast sampling system and gas chromatography (GC). Chemical analysis was also conducted for interpreting experiments. The results showed that current ammonia mechanisms were inadequate to predict the ignition delay time and the hydrogen production under fuel-rich conditions. The experimental hydrogen production increases with the increasing initial temperature, which can be ascribed to the increase of reaction rate constants of key reactions related to hydrogen. The hydrogen production was found to first increase and then decrease with the increasing initial pressure, which was failed to be interpreted by simulations. A moderate fuel-rich equivalence ratio also contributed to higher hydrogen production, in which the combined impact between key radical pool buildup (NH3 and NH2) and the reaction ratios of key reactions (NH2+H->NH+H2) was responsible.

Keywords: Hydrogen production, Reforming combustion, Sampling, Reaction ratio