【作者】 张宁；

【导师】 刘杰；

【作者基本信息】 北京交通大学 ， 动力机械及工程， 2018， 硕士

【摘要】 近年来,能源危机和环境污染两大问题尤为严重,传统的化石燃料已经不能满足当前的发展要求,因此寻找替代燃料显得非常重要。天然气以其储量丰富、经济清洁及能量密度高等优点,成为了最具竞争力的替代燃料,与纯天然气火花点火发动机相比,柴油/天然气双燃料发动机相对原柴油机只进行了少量的改造,但是却获得了更高的热效率。目前,国内外对于柴油/天然气双燃料发动机燃烧特性优化已做了大量工作。然而,在研究中只考虑单参数轮换的方法,如试验柴油的数量、EGR率、喷嘴数量、柴油机喷油持续时间、喷油器位置和预混天然气浓度等。优化燃烧室和喷油参数多采用多目标优化方法,因为大多数的参数之间往往存在trade-off关系。针对目前的柴油机燃烧模型对柴油微引天然气双燃料发动机中复合燃烧过程的预测能力较差的现状,提出了一种PaSR耦合湍流火焰传播模型的双燃料发动机复合燃烧模型,并对双燃料发动机燃烧过程开展了模拟研究,同时提出了一种非支配遗传算法耦合燃烧室网格自动生成算法的人工智能燃烧室结构参数自动优化方法,并依据此方法优化了燃烧室结构参数与喷油参数的匹配。主要研究结果如下:首先,双燃料发动机与纯柴油发动机相比NO_x排放明显降低,CH₄及CO排放显著升高,导致双燃料发动机的热效率低于纯柴油发动机。其次,使用原有柴油机燃烧模型时,模拟得到的缸压和放热率与试验结果相差较大,而使用改进后的双燃料发动机复合燃烧模型时,试验和模拟得到的缸压和放热率结果吻合较好,同时NO_x和CH₄排放预测结果基本一致。再次,采用非支配遗传算法NSGA-Ⅱ对燃烧室中的凸台高度h、燃烧室缩口圆心到中心线的距离R₁和燃烧室底部圆弧圆心到中心线的距离R₂进行了优化,能够使NO_x和CH₄排放量及燃料消耗率ISFC三者相比于原机都同时降低,当甲烷排放接近于零时,燃油消耗率明显降低,NO_x略微增加。最后,采用非支配遗传算法NSGA-Ⅱ对喷油夹角和喷油参数进行优化,结果表明,当喷油时刻大幅度提前时,能够明显降低CH₄排放,油束夹角的减小会引起CH₄的升高。更多还原

【Abstract】 With the increasingly serious environmental pollution and the increase of the global energy demand,traditional fossil fuels can not meet the requirement of the economic development.Therefore,exploitation and utilization of alternative fuels is particularly important.Natural gas is one of the most promising alternative fuels because of its abundant reserve,clean combustion and high energy density.Compared with the pure natural gas spark ignition engine,diesel/natural gas dual fuel engine can achieve higher thermal efficiency with only minor modification to the original diesel engine and it becomes more and more popular.A lot work has been done with optimization of the combustion characteristics of the diesel/natural gas dual fuel engine.However,only one parameters were considered in most of the research,such as the quantity of pilot diesel,EGR rate,nozzle number,injection duration of pilot diesel,position of fuel injector and the concentration of the premixed natural gas.It is necessary to optimize the combustion chamber and the fuel injection parameters with multiobjective optimization method,because most of the paremeters has trade off relations.In study,a compound combustion model was developed with the combination of the PaSR combustion model and turbulent flame propagation model,and the combustion process in the dual fuel engine was investigated.In addition,a non-dominated genetic algorithm coupled with the automatic generation algorithm of combustion chamber for the automatic optimization of combustion chamber structure parameters was proposed,and based on this method,the matching of the combustion chamber geometric parameters and fuel injection parameters was optimized.The main results are as follows:First of all,compared with the diesel engine,the NO_x emissions of the dual fuel engine is significantly reduced,and the CH₄ and CO emissions increase significantly,resulting in the thermal efficiency of the dual fuel engine is lower than that of the diesel engine.Secondly,using the original model of diesel combustion engine,simulated cylinder pressure and heat release rate and the experiment results differ greatly,and the use of dual fuel engine combustion model improved,experimental and simulated cylinder pressure and heat release rate results,while NO_x and CH₄ emission prediction results.Thirdly,using non-dominated genetic algorithm NSGA-II optimizes the combustion chamber including the combustion chamber height h,necking circle to the center line of the distance R₁ and the bottom of the combustion chamber to the center line of the are center distance of R₂,compared with the original machine,there are some spots of the NO_x and CH₄ emissions and the fuel consumption rate of ISFC decreasing at the same time,when the methane emission is close to zero,the fuel consumption rate decreased significantly,NO_x increased slightly.Finally,the non-dominated genetic algorithm NSGA-II is used to optimize the fuel spray angle and fuel injection parameters.The results show that when the injection time is significantly earlier,the CH₄ emissions can be significantly reduced,and the decrease of the the fuel spray angle will lead to the increase of CH₄.更多还原