基于DOE虚拟优化柴油机EGR及多次喷射策略

Optimization of EGR and Bulti-injection for Diesel Engine Based on DOE

以某轻型车用高压共轨柴油机为研究对象,将DOE(Design of Experiment)试验设计方法与CFD(Computational Fluid Dynamics)数值模拟相结合,进行柴油机EGR(Exhaust Gas Recirculation)及多次喷射策略参数的虚拟优化。建立了完整的缸内燃烧过程的仿真模型,并用试验测得的缸内压力数据对模型进行验证,验证表明该模型可以较为准确地反映柴油机的工作情况。利用该仿真模型对EGR率及多次喷射策略参数进行虚拟优化,结果表明,EGR的引入可以大幅度降低缸内最高温度与NOx排放量。预喷燃油的燃烧对燃烧室起到预热作用,提高了主喷时的缸内温度和压力,缩短了滞燃期,同时稀释了缸内的氧气浓度,抑制了NOx的生成。后喷可以再次提高燃烧末期时燃烧室的温度,能有效对缸内Soot进行氧化。EGR与多次喷射相结合可以显著降低NOx和Soot的排放,并改善其trade-off关系,且当预喷油量为5%,主预喷时间间隔为20℃A,后喷油量为10%,主后喷时间间隔为20℃A时,发动机的综合性能较佳。

Taking a light-duty diesel engine as prototype, combined with DOE and CFD, EGR and multi-injection strategy were researched. A complete combustion model was established, and it was validated that the model can simulate the performance and working process of diesel engine with tested cylinder pressure. Results indicate that in-cylinder max. temperature and NOx emission can be reduced obviously by introducing EGR. Pilot injection can restrict NOx emission because of its pre-heated to cylinder. This preheated effect can improve the cylinder temperature and pressure, shorten ignition delay period and dilute the concentration of oxygen. Post injection can improve in-cylinder temperature again at the end of combustion, and it can reduce Soot emission effectively. NOx and Soot emission can be reduced remarkably and their Trade-off can be improved by EGR combined with multi-injection strategy. The good engine performance can be achieved when pilot injection quality equals to 5%, pilot injection timing equals to 20 ℃A, post injection quality equals to 10%, post injection timing equals to 20 ℃ A.