Physical and Chemical Effects of Ammonia on Gas Emissions and Soot Formation in Laminar Coflow Ethylene Diffusion Flames

Abstract

As a noncarbon fuel, ammonia is being explored as a potential alternative. This study delves into the physical and chemical impacts of ammonia in laminar coflow ethylene diffusion flames. Initially, an experiment is conducted to scrutinize the flame characteristics, including temperature, in these flames. Subsequently, a new C 2 H 4 −NH 3 −PAH model is developed and verified through ignition delay times, laminar flame speeds, and species profiles. Building on this model, the study analyzes the physical and chemical effects of ammonia on temperature, gas emissions (CO, CO 2 , NO, NO 2 , HCN, and N 2 O), formation of polycyclic aromatic hydrocarbons (PAHs), and the nucleation, condensation, growth, and oxidation of soot in laminar coflow ethylene diffusion flames. The findings reveal that under constant ethylene flow rates the use of ammonia has minimal impact on flame temperature. Moreover, ammonia decreases CO and CO 2 emissions primarily due to its dilution effect. However, gas emissions such as NO, NO 2 , HCN, and N 2 O significantly increase due to the chemical effect of ammonia. Furthermore, soot precursors noticeably decrease with the addition of NH 3 because of the inhibition of PAH formation through ammonia's dilution effect. Nevertheless, the chemical effect of ammonia plays a counterproductive role in reducing precursor formation, resulting in increased emissions of precursors A1−A4 due to the decreased free radicals. In the assessment of the nucleation, condensation, growth, and oxidation of soot in laminar coflow ethylene diffusion flames, the study indicates a substantial drop (25.7%) in the inception rate of A60 compared to A0 when using ammonia. It is noteworthy that the primary reason for the reduced soot formation with ammonia lies in the decrease of the inception rate through the dilution effect of ammonia and the inhibition of the hydrogen abstraction carbon addition (HACA) surface growth rate because the chemical effect of ammonia reduces free radical H and CH 3 concentrations.