Span-Wagner多参数状态方程（S-W方程）作为二氧化碳热力性质计算的经典模型，因其以密度和温度为独立变量，难以直接应用于工程常见的压力与温度、压力与比焓、压力与比熵等输入条件，制约了其在热力系统仿真中的推广。针对这一局限，提出一种基于割线法的逆向求解策略。该策略通过构建相应的残差函数，将工程常用参数组合转换为S-W方程的直接输入；同时，结合饱和状态参数与临界点特征，设计了适用于单相区及湿蒸汽区的迭代初始值确定方法，并重点解决了近临界温度区域内压力与温度反推计算易发散的问题。计算结果表明，该逆向求解方法的最大相对误差仅为0.0039%，验证了其在工程应用范围内求解二氧化碳热力性质的高精度与强鲁棒性，有效拓展了S-W方程的工程适用性，为二氧化碳动力系统的设计与优化提供了可靠的热物性计算工具。

The Span-Wagner multi-parameter equation of state (S-W EoS), a classic model for calculating the thermodynamic properties of carbon dioxide, uses density and temperature as its independent variables. This inherent formulation makes it difficult to apply directly to input conditions common in engineering practice, such as pressure- temperature, pressure-enthalpy, and pressure-entropy, which limits its widespread use in thermal system simulation. To overcome this limitation, an inverse solution strategy based on the secant method is proposed. This strategy transforms commonly used engineering parameter pairs into direct inputs for the S-W EoS by constructing the corresponding residual function. Furthermore, by incorporating saturation state parameters and critical point characteristics, a method for determining the initial iterative values is designed, applicable to both the single-phase and wet steam regions. The strategy specifically addresses and resolves the convergence difficulties encountered in the inverse calculation of (pressure, density) near the critical temperature. The calculation results demonstrate that the maximum relative error of this inverse method is only 0.0039%, confirming its high accuracy and robust performance in solving for the thermodynamic properties of CO? within the range of engineering applications. This approach effectively extends the engineering applicability of the S-W EoS, providing a reliable tool for the calculation of thermophysical properties in the design and optimization of CO? power systems.

新疆维吾尔自治区自然科学基金面上项目（2023D01A79）；2024新疆维吾尔自治区重大科技专项-全烧高碱煤下的锅炉快速变负荷研究（2024A01005-1）。