This paper presents a joint experimental and numerical study on premixed laminar ammonia/methane/air flames, aiming to characterize the flame structures and NO formation and determine the laminar flame speed under different pressure, equivalence ratio, and ammonia fraction in the fuel. The experiments were carried out in a lab-scale pressurized vessel with a Bunsen burner installed with a concentric co-flow of air. Measurements of NH and NO distributions in the flames were made using planar laser-induced fluorescence. A novel method was presented for determination of the laminar flame speed from Bunsen-burner flame measurements, which takes into account the non-uniform flow in the unburned mixture and local flame stretch. NH profiles were chosen as flame front markers. Direct numerical simulation of the flames and one-dimensional chemical kinetic modeling were performed to enhance the understanding of flame structures and evaluate three chemical kinetic mechanisms recently reported in the literature. The stoichiometric and fuel-rich flames exhibit a dual-flame structure, with an inner premixed flame and an outer diffusion flame. The two flames interact, which affects the NO emissions. The impact of the diffusion flame on the laminar flame speed of the inner premixed flame is however minor. At elevated pressures or higher ammonia/methane ratios, the emission of NO is suppressed as a result of the reduced radical mass fraction and promoted NO reduction reactions. It is found that the laminar flame speed measured in the present experiments can be captured by the investigated mechanisms, but quantitative predictions of the NO distribution require further model development.

Summary Fuel cell vehicles face complicated road conditions, which may impact on the output performance of fuel cell stacks. In the present study, the water transport in the gas diffusion layer (GDL) of proton exchange membrane fuel cell (PEMFC) under vibration conditions are investigated. A stochastic method is employed to reconstruct the 3‐D GDL with experimentally validated varying porosities. The volume of fluid (VOF) method is adopted to investigate the two‐phase problems. Sinusoidal vibration source terms are superposed, which can vary with required amplitudes and directions. Over time, the water transport process takes three steps: water intrusion, water accumulation, and water removal. The water intrusion tends to start from the sides of the GDL, then spreads into the central area. Compared with the no‐vibration case, the water saturations are higher in both the vertical and horizontal vibration cases. The vibration will enhance the water transport through GDL layers. As such, the higher the vibration amplitude and frequency, the larger the water saturation. Accordingly, the water saturation of the GDL vary sinusoidally over time. The water breakthrough paths are identified and compared during the water removal processes. Vibration in the horizontal direction is much easier to promote the water transport inside a layer compared with vibration in the vertical direction. More substantial water saturation in the GDL layers will restrict the gas transfer paths. Consequently, less oxygen will participate in the reaction, which will further impact on the fuel cell performance.

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