Ammonia is one of promising energy carriers that can be directly used as carbon-neutral fuel for combustion applications. However, because of the low-burning velocity of ammonia, it is challenging to introduce ammonia to practical combustors those are designed for general hydrocarbon fuels. One of ways to enhance the combustibility of ammonia is by mixing it with other hydrocarbon fuels, such as methane, with a burning velocity is much higher than the burning velocity of ammonia. In this study, we conducted flame propagation experiments of ammonia/methane/air using a fan-stirred constant volume vessel to clarify the effect of methane addition to ammonia on the turbulent flame propagation limit. From experimental results, we constructed the flame propagation maps and clarified the flame propagation limits. The results show that the flame propagation limits were extended with an increase in mixing a fraction of methane to ammonia. Additionally, ammonia/methane/air mixtures with the equivalence ration of 0.9 can propagate at the highest turbulent intensity, even though the peak of the laminar burning velocity is the fuel-rich side because of the diffusional-thermal instability of the flame surface. Furthermore, the Markstein number of the mixture obtained in this research successfully expressed the strength of the diffusional-thermal instability effect on the flame propagation capability. The turbulence Karlovitz number at the flame propagation limit monotonically increases with the decreasing Markstein number.

氨是有前途的能量载体之一，可以直接用作燃烧应用中的碳中性燃料。然而，由于氨的低燃烧速度，将氨引入设计用于普通烃燃料的实用燃烧器中是有挑战性的。增强氨可燃性的一种方法是将其与其他碳氢化合物燃料（例如甲烷）混合，其燃烧速度远高于氨的燃烧速度。在这项研究中，我们使用风扇搅拌的恒容容器进行了氨/甲烷/空气的火焰传播实验，以阐明将甲烷添加到氨中对湍流火焰传播极限的影响。根据实验结果，我们构建了火焰传播图并阐明了火焰传播极限。结果表明，随着甲烷与氨的混合比例的增加，火焰的传播极限得到了扩展。另外，即使层流燃烧速度的峰值由于火焰表面的扩散热不稳定性，当量比为0.9的氨/甲烷/空气混合物也可以以最高湍流强度传播。此外，在该研究中获得的混合物的马克斯坦数成功地表示了扩散热不稳定性对火焰传播能力的影响的强度。火焰传播极限处的湍流Karlovitz数随Markstein数的减少而单调增加。等效值为0.9的氨/甲烷/空气混合物可以以最高湍流强度传播，即使由于火焰表面的扩散热不稳定性，层流燃烧速度的峰值位于燃料丰富的一侧。此外，在该研究中获得的混合物的马克斯坦数成功地表示了扩散热不稳定性对火焰传播能力的影响的强度。火焰传播极限处的湍流Karlovitz数随Markstein数的减少而单调增加。等效值为0.9的氨/甲烷/空气混合物可以以最高湍流强度传播，即使由于火焰表面的扩散热不稳定性，层流燃烧速度的峰值位于燃料丰富的一侧。此外，在该研究中获得的混合物的马克斯坦数成功地表示了扩散热不稳定性对火焰传播能力的影响的强度。火焰传播极限处的湍流Karlovitz数随Markstein数的减少而单调增加。在这项研究中获得的混合物的马克斯坦数成功地表达了扩散热不稳定性对火焰传播能力的影响的强度。火焰传播极限处的湍流Karlovitz数随Markstein数的减少而单调增加。在这项研究中获得的混合物的马克斯坦数成功地表达了扩散热不稳定性对火焰传播能力的影响的强度。火焰传播极限处的湍流Karlovitz数随Markstein数的减少而单调增加。