液态多组分实际及替代燃料燃烧的官能团匹配相平衡模型研究方法开发

Combustion phenomena of petroleum-based fuels have not been completely understood due to their complex compositions. Surrogate fuels are simpler mixtures of components of which the combustion kinetics and physical properties are well archived. Studying the combustion of surrogate fuels has become a necessary approach to the combustion of understand petroleum-based fuels. Fuels usually enter the combustion system as a liquid. Therefore the ignition and consequent combustion behaviors are coupled with the composition distribution due to phase transition. Typically, people have been using the phase equilibrium parameters of the surrogate components themselves to model the vaporization process. However, this approach may not adequately reflect the "functional groups" provided by the petroleum-based fuels. This could make the surrogate fuel less advantageous in terms of the combustion chemistry it managed to match in the first place..This study will use RP-3 aviation kerosene as a target fuel, basing on its functional group distribution during phase transition, to develop a methodology that can establish the phase equilibrium model of its surrogate fuel. The methodology may include distillation of a RP-3 fuel, gas chromatograph of two phases, identification of important functional groups from the combustion kinetic models of the surrogate fuel, and modification of the thermodynamic activity coefficient functions for non-ideal solutions. This study aims to provide fundamental contribution onf the methodology to develop activity coefficient functions of surrogate fuel components that can be used in modeling the phase transition in droplet and spray combustion.

石油燃料因为组分复杂造成其燃烧现象至今为止仍无法全面的了解，替代燃料为较少组分及燃烧化学及物理性质明确的混合物，研究其燃烧现象成为了解石油燃料燃烧的必要手段。石油燃料通常以液态进入应用系统的燃烧室，其引燃及后期的燃烧现象与相变化耦合造成的组分分布息息相关。目前在替代燃料的模型发展上，一般使用替代燃料组分自身的相平衡参数进行模拟，此模型未必能贴近石油燃料挥发过程所提供给气相燃烧化学的官能团，可能使替代燃料在这样的相变化燃烧过程中，失去本有的燃烧化学优势。.本研究将尝试以国内航天煤油RP-3为目标燃料，以其燃料挥发过程的官能团为基础，发展替代燃料相平衡模型的开发方法。其中将包括液态RP-3的蒸馏、两相多浓度的气相色谱分析、替代燃料燃烧化学模型中重要官能团的分析、及适度修改热力学中非理想溶液多组分的活度系数关系式，以供替代燃料使用。希望能为石油燃料液滴及喷雾燃烧的相变化模型做出基础方法的贡献。

本项目聚焦于石油燃料液滴及喷雾燃烧的相平衡模型开发方法：首先，开展了液态航空煤油RP-3的蒸馏实验，通过气相色谱质谱联用分析（GC-MS）、核磁共振（NMR）、神经网路+红外光谱等方法获取蒸发过程中的重要官能团（CH3、CH2、CH、C(烷烃)、C（芳香烃））含量信息，发现在实际复杂燃料蒸发过程气液相中平均分子量会不断增大，但官能团含量基本保持不变，而现有的替代燃料模型无法模拟这一特性。其次，通过匹配真实的官能团演变得到了基于UNIFAC方法的24组分模型燃料，能够很好地复现实际蒸发过程气液相中的官能团演变，并预测燃烧标（平均分子量、碳氢比、衍生十六烷值、临界碳烟指数）和物理性能（液相密度、表面张力、动力学黏度）的变化。最后，通过官能团匹配（Functional Group Matching, FGM）方法将详细24组分模型燃料简化为四组分模型燃料，并提出了一种“人工”活度系数模型（“Artificial” Activity Coefficient Model, AACM）对四组分模型的活度系数进行修正，使得４组分模型燃料能够在整个蒸馏过程中很好地再现24组分替代燃料的预测结果。本项目提出的这一套具有“人工”活度系数的替代燃料相平衡模型开发方法对燃料型号和组分数没有限制，在不牺牲模型预测精度的同时提高了模型计算效率和耦合现有化学动力学机理的应用潜力，具有重要科学意义。该替代燃料相平衡模型后续可耦合气相动力学模型和湍流模型，完成复杂燃料液滴及喷雾燃烧的建模工作。