On the importance of species selection for the formulation of fuel surrogates

Fuel surrogates are mixtures of simple compounds that emulate the combustion characteristics of more complex fuels, with the primary objective to enable detailed combustion modeling of very complex real fuels. Current efforts in surrogate development aim at optimizing the compositions of pure hydrocarbons to emulate multiple combustion related properties. In doing so, weights are assigned when defining optimization problem to reflect the importance of each property. In this study, we report on the relative importance of species selection and their weights on the overall performance of the optimized surrogate. Using experimental data of a reference jet fuel as target, we designed a study using a surrogate optimizer that imposes orthogonal perturbations on the surrogate components and weights and analyzed their impact on the optimized surrogate mixtures. Results from 3600 cases show that perturbations of surrogate components, rather than weights, induce far greater variability in the optimized composition and target property agreement. While the Derived Cetane Number (DCN) agreement shows a greater variability from the weight perturbation, the main reason for such high sensitivity is due to the wide range of values for pure component DCN of the individual components, which is also a result of the surrogate component selection. Further, the results show that the selection of surrogate components nearly predefines the overall shape of the distillation curves regardless of the weight values. The current study quantitatively supports the idea that appropriate selection of surrogate components that capture the physical and chemical characteristics of actual constituents of target fuel will increase the possibility of successful surrogate formulation and will mitigate the impact from arbitrary weight assignment.

燃料替代物是简单化合物的混合物，其模拟更复杂燃料的燃烧特性，主要目的是能够对非常复杂的实际燃料进行详细的燃烧建模。当前在替代物开发方面的努力旨在优化纯烃的组成以模拟多种与燃烧相关的特性。在这样做时，在定义优化问题时会分配权重以反映每种特性的重要性。在这项研究中，我们报告了物质选择及其权重对优化后的替代物整体性能的相对重要性。以一种参考喷气燃料的实验数据为目标，我们使用一种替代物优化器设计了一项研究，该优化器对替代物成分和权重施加正交扰动，并分析了它们对优化后的替代物混合物的影响。3600个案例的结果表明，替代物成分的扰动，而非权重，在优化后的组成和目标特性一致性方面引起更大的变化。虽然衍生十六烷值（DCN）的一致性在权重扰动下显示出更大的变化，但这种高敏感性的主要原因是由于各个组分的纯组分DCN值范围很广，这也是替代物组分选择的结果。此外，结果表明，替代物组分的选择几乎预先确定了蒸馏曲线的整体形状，而与权重值无关。当前的研究从数量上支持了这样一种观点，即适当选择能够捕捉目标燃料实际成分的物理和化学特性的替代物组分将增加成功配制替代物的可能性，并将减轻任意权重分配的影响。