VNT与EGR耦合对不同海拔燃用含氧燃料柴油机工作过程的影响

Because the intake manifold pressure may be higher than the exhaust manifold pressure in turbocharged diesel engines operating at high-altitude conditions, there are design challenges for effectively using exhaust gas recirculation (EGR) technologies. Moreover, due to the fundamental trade-off between nitrogen oxides (NOx) and particulate matter (PM) emissions, emissions control of the diesel engines at high-altitude conditions becomes more complex. The combination use of EGR, variable nozzle turbine (VNT), and oxygenated fuels can expand the application regions of EGR, enhance the transient response of the EGR system and air-to-fuel ratio. This measure can help solve the trade-off difficulty for NOx and PM emissions control, and also can alleviate the performance deterioration of the diesel engines at high altitude. Therefore, a high-pressure common-rail diesel engine with coordinated controls of EGR and VNT is selected in this research to study the nonlinear coupling relationship between VNT vane opening and EGR rate as well as its variation trend at different altitude levels with multi-component oxygenated fuels that are produced by biodiesel, ethanol, and diesel（BED） mixed with certain proportions. This study will also address the effects of the coupled system of EGR and VNT on the combustion and emissions characteristics, power capability, and fuel economy of the diesel engines fueled with pure diesel and BED blends, as well as their variation trends at different altitude levels. Moreover, this research will explore the effects of the coupled system of EGR and VNT on the working processes of the diesel engines running with oxygenated fuels at different altitude conditions in order to provide a theoretical basis for high-efficiency and low-emissions combustion diesel engines at high altitude regions.

由于涡轮增压柴油机在高原运行时进排气逆差问题突出，难以实现排气再循环(EGR)技术，加之氮氧化合物(NOx)和微粒（PM）生成此消彼长，使高海拔下柴油机的排放控制更加复杂。将EGR、VNT（可变喷嘴截面涡轮增压器）与含氧燃料掺烧技术结合，可拓宽EGR的适用工况，提高EGR响应与空燃比，有助于解决NOx与PM排放的矛盾，并有利于减小海拔上升导致的柴油机性能恶化的程度。因此选择EGR与VNT耦合的高压共轨柴油机作为研究机型，将生物柴油和生物乙醇按一定比例与柴油混合成多组分含氧燃料（BED），研究VNT开度与EGR率的非线性耦合关系以及随海拔的变化规律，研究EGR与VNT耦合系统对燃用纯柴油与BED燃料的燃烧特性、排放特性、动力性以及经济性的影响机理以及随海拔变化的规律。探索EGR与VNT耦合系统对不同海拔下燃用含氧燃料柴油机的工作过程的影响，为在高原地区实现高效低污染燃烧提供理论依据。

将 EGR（废气再循环）、VNT（可变喷嘴截面涡轮增压器）与含氧燃料掺烧技术结合，可解决进排气逆差，拓宽EGR 的适用工况，提高 EGR 瞬态响应与空燃比，有助于解决 NOx 与 PM 排放的矛盾，并有利于减小海拔上升导致的柴油机性能恶化的程度。由于EGR与VNT均由排气能量驱动，大气压力的变化也对空燃比与EGR率有不同程度的影响，三者的协调控制机理直接影响柴油机工作特性，高原环境下三者的影响关系与控制机理更加复杂 。因此，选择带 EGR 与 VNT的高压共轨柴油机作为研究机型，将生物柴油和生物乙醇按一定比例与柴油混合成多组分含氧燃料（BED燃料），通过台架测试与试验设计方法，研究了 VNT开度与 EGR 率的非线性耦合关系以及随海拔的变化规律，研究了大气压力、EGR 、VNT 耦合关系对空气系统的影响规律；采用一维与三维联合仿真分析方法，结合台架测试，研究了大气压力、EGR 、VNT 耦合关系对燃用纯柴油与 BED 燃料的燃烧特性与燃烧化学反应动力学的影响规律；通过台架测试与试验设计方法，研究了大气压力、EGR 、VNT 耦合关系对燃用纯柴油与 BED 燃料的排放特性、动力性以及经济性的影响机理以及随海拔变化的规律应用支持向量机建模与遗传算法优化，在全工况范围内，进行了高压共轨柴油机经济性与排放性能的多目标综合优化。探索了EGR 与 VNT 耦合系统对不同海拔下燃用不同燃料柴油机的工作过程与性能的影响规律以及优化方法，为在高原地区实现高效低污染燃烧以及运行在不同海拔地区、匹配VNT与EGR系统的高压共轨柴油机标定策略提供理论依据。