Effects of Ammonia Addition on the Sooting Characteristics of Ethylene Counterflow Diffusion Flames with Oscillating Strain Rates

• Published in: Energy & fuels 2023-12, Vol.37 (24), p.19950-19958
• Main Authors: Zhang, Jizhou, Xu, Lei, Yan, Fuwu, Zhou, Mengxiang, Wang, Yu
• Format: Article
• Language: English
• Subjects: Non-Carbon-Based Fuels
• ISSN: 0887-0624; 1520-5029
• DOI: 10.1021/acs.energyfuels.3c03158

Cofiring ammonia (NH3) and hydrocarbon fuels is a promising solution in the short and medium terms to achieve a decarbonized energy system. However, this approach faces challenges related to the formation of combustion-generated pollutants such as soot. This work is designed to examine the soot-formation behavior of an NH3/ethylene mixture in both steady and unsteady flames, considering the necessity of incorporating unsteady effects to accurately model soot formation in turbulent ammonia–hydrocarbon-cofired flames. A highly controllable counterflow diffusion flame burner with acoustic forcing was established to generate unsteady flames with strain rate oscillations at imposed frequencies and amplitudes. A high-repetition-rate particle image velocimetry system and a laser-induced incandescence system were employed to track the temporal evolution of the flow and soot fields, respectively. The results showed clear evidence of unsteady effects on soot formation, including phase lag and amplitude attenuations, in the present NH3-doped flames. The study also examined the influence of NH3 addition on the unsteady soot response and its dependence on the oxidizer condition, with various oxygen mole fractions (X O) of 0.25, 0.30, and 0.35. Interestingly, the experimental data demonstrate that the unsteady soot response in the NH3-doped flames is strongly controlled by the soot responses under steady conditions. This finding is consistent with our previous observations on ethylene diffusion and partially premixed flames. These results are believed to be relevant for the development of a high-fidelity flamelet-based soot model to simulate turbulent ammonia–hydrocarbon-cofired flames.