基于超临界流体的增压直喷汽油机燃烧机理研究

In the present study, turbo-charged direct injection combustion fueled with suprecritical gasoline is porposed to deal with the lower thermal efficiency limited by lower compression and higher PM emissions of turbo-charged gasoline direct injection engine. By the comprehensive use of thermodynamic analysis, constant-volume experiments, engine experiments and numerical simulation, the mechanism of turbo-charged direct injection combustion fueled with suprecritical gasoline is investigated. To achieve the supercritical fuel,the waste heat of residual gas is innovatively proposed to heat the fuel with pressure higher then its critical pressure controlled by pump. the injection characterisitcs, flame characteristics and the effects of control parameters on them are studied by the constant-volume experiments, which can reveal the essential differences between the injection of liquid and supercritical fulid. The supercritical fulid injection is achieved by the modification the injection system of turbo-charged gasoline direct injection engine. The performance, combustion characteristics, emission characteristics and the control strategies based on multi-parameters are analyzed by the experiments on the turbo-charged direct injection engine fueled with suprecritical gasoline. The reduced chemical kinetic model of gasoline surrogate and the injection model are developed under the supercritical conditon. The combustion mechanism and the emission formation mechanism of turbo-charged direct injection combustion fueled with suprecritical gasoline are analyzed by the the coupled model of CFD and kinetics.

本研究为应对增压直喷汽油机压缩比较低限制热效率，微粒排放较高的问题提出了在增压直喷汽油机上实现超临界流体燃烧。综合应用热力学分析、数值模拟、定容燃烧弹实验及发动机台架试验等手段研究超临界汽油燃料增压直喷燃烧的燃烧机理。创新性的提出在燃油喷射系统的油轨中利用废气的余热能加热由喷油泵控制高压燃料（压力在临界压力以上），以获得超临界流体；在定容燃烧弹实验平台上研究超临界流体的喷射特性及控制参数的影响规律，揭示超临界流体喷射与液体喷雾的本质区别；通过对增压直喷汽油机的燃油喷射系统的改造，实现较高压缩比下的超临界流体喷射燃烧，分析超临界汽油燃料增压直喷发动机的性能，燃烧特性、排放特性及其多参数控制策略（喷射参数、进气参数、EGR）；发展超临界状态下汽油燃料替代混合物化学动力学模型和喷射模型，并利用简化动力学与CFD耦合模型分析超临界汽油燃料增压直喷燃烧的燃烧反应动力学机理及有害排放物生成机理。

本项目为应对增压直喷汽油机压缩比较低限制热效率，微粒排放较高的问题提出了在增压直喷汽油机上实现超临界流体燃烧，并开展了基于超临界流体的喷射和燃烧机理研究。首先，结合理论计算和实验评估了汽油燃料及其常用替代混合物处于超临界状态下的临界特性和物性参数，为后续的研究提供基础。其次，搭建了超临界汽油燃料喷射特性研究的实验平台，并在此基础上采用利用背光法、纹影法以及激光多普勒方法对直喷单孔/多孔喷油器的超临界喷雾特性进行了研究，揭示了燃料从亚临界跨越到超临界状态喷雾特性的变化规律。构建并验证了适用于超临界喷射的CFD模型，分析了燃油参数和环境参数对超临界喷射特性的影响规律；再次，为了研究超临界汽油燃料的燃烧和排放机理，在前期研究的基础上构建了适用于超临界汽油燃料替代混合物化学动力学模型，并验证了模型的有效性。最后，结合发动机台架实验和数值模拟，研究了直喷发动机中超临界燃烧的特性和机理，揭示了超临界燃烧在提高热效率、降低颗粒物方面的潜力。