Addition of Ammonia to a Bluff-Body Stabilized Flame and Its Effect on NOx Emissions and Static Stability

Ammonium carbamate is a material of interest in the field of aircraft thermal management for on-board electronics systems. However, the use of this material creates both ammonia and carbon dioxide, which must be either stored or consumed. One method of addressing this issue would involve consuming the ammonia in the combustion process of the propulsion system. However, a concern is the effect of the ammonia on the combustion process, especially on combustion efficiency, flame stability, and pollutant emissions. The present study examines these effects through combustion rig experiments as well as model predictions. Ammonia was injected into a bluff-body stabilized propane flame, and emissions were sampled and analyzed using a Fourier transform infrared (FTIR) spectroscopy instrument. Lean blowout data was also recorded. Ammonia injection increased the NOX emissions and increased the equivalence ratio at lean blowout. Chemical kinetic modeling of the experiments shows that almost all of the NH3 converted into NH2 intermediate, which leads to the formation of NO precursors such as NH and HNO. The thermal decomposition of HNO is the primary source of NOX formation at the current experimental conditions. A notional engine was also modeled with a simplified PSR-PFR chemical reactor network using a detailed JP-8 surrogate chemical kinetic model. Simulations were performed using a full three-level statistical design of experiments with six variables over the operating range of the engine. Results show that ammonia addition in the inlet stream has a limited effect on NOX production while increasing CO formation.