Kinetic Modeling Analysis on Laminar Burning Velocity of Ammonia/Dimethyl Ether-air Premixed Flames
Ph.D. Student Tao Cai
Department of Mechanical Engineering, University of Canterbury
Time & Place
Tue, 08 Jun 2021 11:20:08 NZST in E12, Engineering Core
Ammonia (NH3), as a hydrogen energy carrier and carbon-free fuel, is being increasingly considered as a potential candidate for transportation and power generation systems to replace conventional fossil fuels. However, unlike hydrogen and hydrocarbon fuels, the laminar burning velocity is comparatively low, making it difficult to be directly applied in practical applications. This work considers blending dimethyl ether (DME) to promote the flame speed of NH3 flames using the 1D freely propagating flame model in Chemkin-Pro 2019, with the emphasis being placed on the underlying enhancement mechanism. For this, the reaction mechanism is first validated by comparing the calculations with the available experimental data. It is shown that the presence of DME significantly enhances the laminar burning velocity SL of NH3 flames, which is almost comparable to methane/air flames when the blended ratio is 0.5. Reaction pathway and sensitivity analyses indicate that adding DME can lead to major reaction steps and sensitivities being changed, thus affecting the overall reaction rate. Furthermore, the thermal, chemical, and diffusion effects are determined, with the first two playing a positive role in enhancing the flame speed. Furthermore, the inlet pressure is found to significantly affect the SL of binary mixtures, but its influence on NH3/air flames is minimal. This difference is because the relative importance of termination versus branching reactions in binary flames is more remarkable. The overall reaction order, characterizing the laminar burning flux over elevated pressure, is empirically determined to distinguish the importance of chain branching and termination reaction steps, which shows a decreasing trend with increasing the inlet pressure. This work could provide a guideline on the selection of fuel flexibility and shed light on the fundamental flame enhancement mechanism.
Supervisor: Prof Dan Zhao