【作者】 薛建波；

【导师】 王桂华； 李国祥；

【作者基本信息】 山东大学 ， 动力机械及工程， 2007， 硕士

【摘要】 欧洲Ⅲ／欧洲Ⅳ法规增加了对轻型汽油车的低温冷启动过程的HC和CO排放测试，该测试也称为Ⅵ型试验。已报道的试验结果表明：在-7℃环境温度下，按欧Ⅲ标准排放检测循环试验的汽油机在冷启动过程前195秒采样时间内的THC比常温下的测试结果高了15倍左右。为满足欧Ⅲ排放法规的要求，本文提出通过利用汽车加热器在冷启动前提升汽油机的体温的方案，重点解决-7℃环境温度下的冷启动排放问题。方法是：利用汽车加热器在发动机冷启动前预热汽油机水套内的冷却液以提高发动机体温，同时加热器的燃气借道三效催化器排出，这可方便而有效地提高三效催化器的入口温度。这样既提高了燃烧室壁温、减少了冷激效应的影响、改善了混合气形成，减少启动过程中HC和CO在缸内的产量，又保证了发动机在冷启动的开始阶段三效催化器可以很快达到起燃温度，有效转化有害排放。显然这种方法对于减轻汽油机冷启动过程的排放是非常有效的措施。该方法要求汽车加热器的排放水平应远优于汽油机的情况，为此本课题利用西迪阿特公司的通用流体力学模拟软件STAR—CD对D5LC空气加热器的燃烧室进行了数值模拟，分析了燃烧室内部流场的分布情况、燃烧室内部结构对流场形成的影响、燃烧过程的温度场和排放生成的情况，为实现燃烧室内高效低污染燃烧提供了理论基础。计算结果表明：在二次风进气弯管的切向进气道处流速达到最大值，符合二次风的设计思想；强化扰动使得流动区域内的已燃气体与新鲜空气充分混合；二次风流速很大，和一次风存在比较明显的流速差，导致在二级缩口处相遇的时候形成负压区而产生回流，一方面保证了火焰的稳定性，另一方面可以使得混合气在燃烧室尽可能的停留较长的时间，保证混合气的充分混合和燃料的充分燃烧。在欧Ⅲ低温冷启动模拟实验台架上进行了汽油机与加热器联合运行以后冷启动阶段排放水平的初步测试。实验结果表明该方案能够有效降低汽油机冷启动阶段的THC、CO、NOx等有害排放量。原机的THC主要产生于冷启动及暖机过程(约为前90秒)，THC的排放峰值基本对应于发动机的减速段。本实验中，使用加热器对发动机预热之后，冷启动阶段THC的排放大幅降低，在催化器前可以降低THC排放58.7％，在催化器后可以降低THC排放53.8％。原机及使用加热器后CO的峰值均出现在减速段。CO主要产生于启动初期，催化转换器起燃以后CO基本被氧化。冷启动时混合气较浓，空燃比较小，催化转换器尚未起作用，因此形成大量CO。在冷启动及暖机阶段，使用了加热器之后在催化器前可以降低CO排放8.15％，在催化器之后减少20.02％。NOx排放的峰值对应于发动机中、大负荷工况。这主要是由于随着发动机负荷增大，喷油量增加，缸内空燃比不均匀，且燃烧温度提高所致。在冷启动及暖机阶段，使用了加热器之后，催化器前的NOx排放量降低了73.6％，催化器后的NOx降低了71.4％。更多还原

【Abstract】 The Euro III and Eoro IV emission regulations require the emission test of the HC and CO of the light gasoline engines during the cold-start period,which are named IV experiment.The HC exhaust emission of the gasoline engine used in the Euro III emission regulations cycling test during the former 195 second of the cold-start period at the environment temperature of -7°C is 15 times more than that at the normal temperature,which is indicated on the coverd experimental report. In this paper, in order for gasoline vehicles to meet the Euro III emission regulation, an air heater was used to increase the cooling water’s temperature before cold-start of the gasoline, which was hoped to solve the problems of quicken light-off of catalyst and reduce exhaust emissions at -7°C ambient temperature.The plan is using an air heater to increase the cooling water’s temperature before cold-start of the gasoline,and the emission of the air heater is vented via the catalyst to improve the intake temperature of the catalyst.The plan which is a effectual measure to decrease the cold-start period emission can improve the cylinder wall temperature,cut down the quench effect, mend mixture and decrease the emission in the cylinder during the cold-start period.And also the way can improve the tempertature of the catalyst which has high transfer efficiency.And also this plan demand that the emission of the air heater is better than that of the engine.So the Other task is doing the simulation of the flow and combustion of the chamber of the air heater produced by Hebei Hongye Machinery Co.Ltd using the CFD software-STAR-CD.By analyzing the fluent,combustion, temperature field and the emission concentration field of the chamber ,to obtain the theory to design the air heater with low pollution and high efficiency. The simulation displayed that the highest velocity appears at the tangential air inlet flue.of the secondary air which accords with the planning programming.This can make the mixture more homogeneous and supply enough oxidant for the afterburning.The secondary air’s velocity is higher head and shoulders above than the first air, which forms the negative pressure field and results in back flow when they encounter.So the mixture can obtains combustion stability and complete combustion. The experiment on engine test bench which can simulate and test the cold start characteristics of gasoline vehicles was done. The result indicated that this method can effectively reduce the exhaust emission of CO, HC and NOx during the cold-start period. Most of the HC emission is produced during the cold-start and the warming-up period which may be the former 90s.and the peak is at the speed-down moment of the engine.This experiment reduced 58.7% of the total HC emission before the catalyst and reduced 53.8% of the total HC emission behind the catalyst after the engine warm-up using the air heater.The peak of the CO emission which was most produced during the cold-start period and was oxidated after the catalyst initiation was at the speed-down moment no matter using the air heater or not. The overrich mixture ,lower air-fuel ratio and the catalyst not-initiation may be the reasons of the mass CO emission produced during the cold-start period. This experiment reduced 8.15% of the total CO emission before the catalyst and reduced 20.2% of the total CO emission behind the catalyst after using the air heater.For more fuel injected, inhomogeneous cylinder air-fuel ratio and higer combustion temperature are along with the higer working conditions of the engine, the peak of the NOx emission corresponds to the medium and higher working conditions of the engine. This experiment reduced 73.6% of the total NOx emission before the catalyst and reduced 71.4% of the total NOx emission behind the catalyst after the engine warm-up using the air heater.更多还原