【作者】 王滨；

【导师】 王定标；

【作者基本信息】 郑州大学 ， 化学工程， 2019， 硕士

【摘要】 在我国的一些北方地区,时常出现的极端低温情况,使得汽车性能变差。汽车燃油辅助加热器作为完全独立于发动机的加热装置,能够充分改善汽车冷启动。因此关于如何提高汽车燃油辅助加热器性能的研究具有重要的意义。本文利用数值模拟方法探究了各结构参数对汽车燃油辅助加热器性能的影响,并对原始模型进行了结构改进。主要工作与成果如下:（1）应用FLUENT软件对某汽车燃油辅助加热器进行了燃烧模拟,并对Y=0截面的温度场分布以及各组分分布进行了分析。结果显示,汽车燃油辅助加热器温度场均匀指数为50.48%,出口氮氧化物质量分数为2.25×10^-7,出口平均CO质量分数为0.046,出口平均O₂质量分数为0.039。模型内部温度场分布不均匀,火焰筒内后燃现象比较严重,整体CO、氮氧化物排放量不高但还有降低的空间。另外,由Y=0截面温度场和氮氧化物分布云图可以看出,在温度较高处,氮氧化物浓度比较高,可以推断出氮氧化物主要是由于局部温度过高所致,即产生的氮氧化物多为热力型。（2）分析了各结构参数对于汽车燃油辅助加热器的单一性能（即温度场均匀指数、出口氮氧化物含量）的影响。结果发现,仅改变喷口半径R时,温度场均匀指数及出口氮氧化物含量总体均呈下降趋势。仅增大一二次风进风量比时,温度场均匀指数呈上升趋势,出口氮氧化物含量呈下降趋势。受导流板缩口位置的影响,仅改变喷口距离L_k时,燃烧室温度场均匀指数波动较大,出口氮氧化物含量呈现先减小后增大的趋势。仅改变燃烧室长度L_r时,温度场均匀指数及氮氧化物排放均有总体上升的趋势。（3）鉴于某些具体的工程应用中对于汽车燃油辅助加热器的单一评价方式考虑得比较全面,且各单一性能指标可能产生互相影响的情况,本文针对已模拟计算过的不同结构参数的模型建立了一种综合性能评价方法,计算了选取的20个模型的综合性能得分并进行排序。综合评价指标中考虑的单一评价指标在温度场均匀指数、出口氮氧化物含量这两个评价指标的基础上加入了出口CO含量以及出口O₂含量。结果显示,综合性能最优的模型各结构参数为R=1.0mm、一二次风进风量比为0.0605、L_k=31mm、L_r=157mm。（4）针对改变结构参数对于解决汽车燃油辅助加热器后燃现象严重、温度分布不均匀效果不明显的问题,本文提出了一种改进的新结构,并选取三种新结构的参数,分析选择了流场效果最好的一种进行下一步模拟分析,并与改进前综合性能最优的模型进行了对比。结果表明,改进后的汽车燃油辅助加热器内部流体在燃烧室内形成了循环流动,燃烧室内温度场均匀指数比改进前提高了23.43%,柴油雾化更均匀,NOx排放降低了98.10%,CO降低了6.35%,O₂利用率提高了11.34%。更多还原

【Abstract】 For Chinese northern regions,the performance of automobile could decay with extreme low temperature circumstance.In consideration of this problem,the fuel automotive heater which is completely independent of engine-based heating device is used to improve the performance of vehicle starting.Therefore,it has great significance to research on how to enhance the performance of automotive fuel-assisted heater.In this paper,the influence of various structural parameters on performance was analyzed with numerical simulation,meanwhile improved model was proposed on the basis of original model by results.The main work is as follows:（1）The performance of combustion was simulated with FLUENT software,furthermore the distribution of temperature field and each component on Y=0 cross section were analyzed.The results show that the uniformity index of temperature is50.48%,the average mass fraction of NOx,CO and O₂,respectively,is 2.25×10^-7,0.046 and 0.039 in the outlet cross section.According to above data,not only be the distribution of internal temperature field proved uniform,but also the post-combustion phenomenon in the flame tube is serious.In addition,there is still margin decline though the overall emission load of NOx is low.Besides it can be inferred that nitrogen oxides are mainly caused by excessive local temperature from the temperature field of Y=0 cross section and the NOx distribution cloud chart,because it can be seen that high-concentration nitrogen oxides appear at higher temperature.（2）The effect of the single performance of the automotive fuel auxiliary heater with various structural parameters（temperature field uniformity index,and outlet nitrogen oxide content）were analyzed.It was found that when the nozzle radius R was changed,the temperature field uniformity index and the outlet nitrogen oxide content shows a downward trend.When the ratio of the amout of premariy and secondary air-intake is increased,the temperature field uniformity index is increasing,and the export nitrogen oxide content is decreasing.Influenced by the position of the deflector,when the nozzle distance L_k is changed,the temperature field of the combustion chamber fluctuates greatly,and the nitrogen oxide content of the outlet first decreases and then increases.When only the length L_r of the combustion chamber is changed,the temperature field uniformity index and the nitrogen oxide emission have an overall upward trend.（3）In view of the fact that the more single evaluation methods for automotive fuel auxiliary heaters are considered in some specific engineering applications,and each single performance index may affect each other,this paper aiming at the models of different structural parameters that have been simulated before established a comprehensive performance evaluation method,and the comprehensive performance scores of the selected 20 models were calculated and sorted.The single evaluation index considered in the comprehensive evaluation index added the export CO content and the export O₂ content besides the temperature field uniformity index and the export nitrogen oxide content.The result shows that the structural parameters of the model with the best overall performance are R=1.0mm,and the ratio of the primary air inlet is 0.0605,and L_k=31mm,and L_r=157mm.（4）In order to solve the problem that the function of changing the structural parameters to improve the temperature uniformity of automobile fuel auxiliary heater is not obvious,this paper proposed a new structure model with three different structural parameters and selected the best one.Further simulation analysis was carried out using the new structure and compared with the model with the best comprehensive performance before improvement.The result shows that the internal fluid of the improved automobile fuel auxiliary heater forms a circulating flow in the combustion chamber.The uniform index of the temperature field in the model combustion chamber is increased by 23.43%,the atomization of the diesel is more uniform,and the NOx emission is reduced by 98.10%.CO emmision is reduced by6.35%,and O₂ utilization is increased by 11.34%.更多还原