Investigation of Aqueous Ammonia/Hydrogen Blends for Use In Advanced Dual-Fuel Combustion

Abstract Aqueous ammonia (NH4OH, a solution of 29.1% NH3 in water) and aqueous ammonia/hydrogen (NH4OH/H2) premixed blends were explored using a dual-fuel strategy with #2 diesel directly injected. Diesel fuel was substituted (at constant energy) with NH4OH and NH4OH/H2 blends at constant fuel energy while maintaining phasing using the diesel SOI timing. NH4OH/H2 blends were evaluated to investigate the efficacy of hydrogen for improving ignition quality and flame speed of the premixed mixture, and to determine if aqueous ammonia/hydrogen blends could be used as substitutes to represent the performance of anhydrous ammonia. The hydrogen concentration in the blends was adjusted to match adiabatic flame temperature (TAd) to anhydrous ammonia. Substitution of diesel fuel energy for aqueous ammonia was limited to 50% by energy at low-loads due to combustion instability, and challenges maintaining intake runner temperature at mid-loads due to significant enthalpy required to vaporize the aqueous ammonia. NH4OH/H2 blends exhibited improved combustion stability and led to over 4% decrease in unburned-to-supplied premixed energy, but were not suitable surrogates for NH3 combustion due to controlled end-gas autoignition (c-EGAI) and hydrogen preignition issues.