Ammonia combustion appears as a meaningful way to retrieve stored amounts of excess variable renewable energy, and the spark-ignition (SI) engine has been proposed as a practical conversion system. The present work aims at elucidating the combustion characteristics of ammonia blends in engine-relevant turbulent conditions. To that end, laminar and turbulent flame experiments were conducted in a constant-volume vessel at engine-relevant conditions of 445 K and 0.54 MPa to assess the combustion behavior of ammonia/hydrogen/air, ammonia/methane/air and methane/hydrogen/air mixtures observed in an all-metal single-cylinder SI engine. Results show that the respective accelerating or decelerating effects of hydrogen or methane enrichment observed in the SI engine could not be sufficiently explained by the measured laminar burning velocities of the mixtures. Since the latter are very low, the studied combustion regimes are at the boundary between the thin and broken reaction zones regimes, and thus strongly influenced by flame-turbulence interactions. The quantification of the flame response to turbulence shows much higher effects for ammonia blends, than for methane-based fuels. The aforementioned opposite effects of ammonia enrichment with hydrogen or methane are observed on the turbulent burning velocity during the turbulent flame experiments and correlated to the thermochemical properties of the reactants and the flame sensitivity to stretch. The latter may explain an unexpected bending effect on the turbulent-to-laminar velocity ratio when increasing the hydrogen fraction in the ammonia/hydrogen blend. Nevertheless, a very good correlation of the turbulent velocity was found with the Karlovitz and Damköhler numbers, that suggests that ammonia combustion in SI engines may be described following the usual turbulent combustion models. This encourages further investigations on ammonia combustion for the optimization of practical systems, by means of dedicated experiments and numerical simulations.

氨燃烧似乎是检索存储的过量可变可再生能源的一种有意义的方式，而火花点火（SI）发动机已被提议作为一种实用的转换系统。本工作旨在阐明与发动机相关的湍流条件下氨混合物的燃烧特性。为此，在恒定体积的容器中以445 K和0.54 MPa的发动机相关条件进行了层流和湍流火焰实验，以评估氨/氢气/空气，氨/甲烷/空气和甲烷/氢气/的燃烧行为。在全金属单缸SI发动机中观察到的空气混合物。结果表明，SI发动机中观察到的氢或甲烷富集的相应加速或减速效果无法通过所测量混合物的层流燃烧速度来充分解释。由于后者非常低，因此研究的燃烧状态位于稀薄反应区和破碎反应区之间的边界，因此受到火焰-湍流相互作用的强烈影响。火焰对湍流响应的量化显示，与基于甲烷的燃料相比，氨混合气的影响要大得多。在湍流火焰实验期间，观察到了氨气富集氢气或甲烷的相反作用，其对湍流燃烧速度的影响与反应物的热化学性质和火焰拉伸敏感性相关。当增加氨/氢共混物中的氢含量时，后者可以解释对湍流与层流速度比的意外弯曲作用。但是，湍流速度与Karlovitz和Damköhler数之间存在很好的相关性，这表明SI发动机中的氨燃烧可以按照通常的湍流燃烧模型进行描述。这鼓励通过专门的实验和数值模拟对氨燃烧进行进一步研究，以优化实际系统。这表明，SI发动机中的氨燃烧可以按照通常的湍流燃烧模型来描述。这鼓励通过专门的实验和数值模拟对氨燃烧进行进一步研究，以优化实际系统。这表明，SI发动机中的氨燃烧可以按照通常的湍流燃烧模型来描述。这鼓励通过专门的实验和数值模拟对氨燃烧进行进一步研究，以优化实际系统。