【作者】 刘瑞祥；

【导师】 高希彦；

【作者基本信息】 大连理工大学 ， 动力机械及工程， 2005， 博士

【摘要】 本研究的目标是联合使用高过滤效率的红外再生微粒陶瓷过滤器和废气再循环(EGR),同时降低柴油机的微粒排放和NOx排放。试验结果表明:本文研究开发的柴油机微粒陶瓷过滤器平均过滤效率在95%以上,达到欧Ⅲ及以上微粒排放标准;基于宽范围氧传感器(UEGO)的闭环控制柴油机EGR系统能有效地降低NOx排放,NOx的降低率最高可达42%,平均降低率约为30%。 首先通过试验对柴油机微粒过滤器的过滤特性和再生特性进行了基础研究。过滤试验表明:壁流陶瓷具有良好的过滤效率,平均过滤效率在95%以上。壁流陶瓷的压降近似线性增长。在6120柴油机台架上,排气烟度为3BSU时,单个过滤器持续工作时间达2个小时以上,两个过滤器同时使用,具有较长的再生间隔时间,可以满足实际车辆的需要。再生试验表明:微粒沉积量对再生过程有重要的影响。微粒量多,再生温度高,过多将导致陶瓷内部熔融;微粒量少则再生温度低,过少则导致再生不稳定甚至终止。微粒物质量在适当范围内时,具有最好的再生性能综合指标。过滤器利用柴油机排气作为再生气流。再生气流对再生过程有很大的影响,具体表现为再生气流的氧含量对燃烧的影响和气流流动对热量传输的影响。再生气流流量小,由于氧气不足再生缓慢;流量大,则因为排气温度低于燃烧温度,再生气流具有冷却作用,也会导致再生困难。调节再生气量是控制再生过程的关键问题,需要进一步的优化。 通过调整加热器流通孔的分布密度和调整电热丝在辐射盘上的分布密度,以及采用双层壳体过滤器,过滤器再生性能综合指标得到进一步提高。 从多孔介质理论出发,推导了壁流陶瓷压力降与柴油机运行参数间的关系。由试验数据应用线性回归解出待定系数,得到壁流陶瓷压力降与柴油机转速和排气温度的关系。由上述关系确定的再生时机能将微粒物质量控制在适当的范围内,解决了实际应用中过滤器再生时机的确定这一关键技术难题。 从流体力学基本原理出发,结合柴油机的特点,推导出了再生调节阀开度与负荷、排气温度和背压间的函数关系。实际应用时,分两步来确定再生调节阀开度。首先根据基准负荷调节阀开度MAP确定对应基准负荷的再生调节阀开度,然后根据实测的负荷由开度修正公式进行修正。这样确定的再生调节阀开度能实现再生时氧气流量基本不变的目标,满足实际应用的要求,解决了实际应用中过滤器再生废气量控制这一关键技术难题。 由ECU自动控制再生调节阀开度时,在柴油机稳态工况和瞬态工况下进行了再生试验。再生温度变化平缓,陶瓷中心峰值温度被控制在1000℃以下,径向温度梯度低于30℃/cm,再生效率平均可达80%以上,再生过程稳定,再生成功率97%以上。 在微粒过滤器的基础上,建立了具有清洁再循环废气的、基于宽范围氧传感器(UEGO)的闭环控制柴油机EGR系统。用UEGO测得的空燃比作为反馈信号进行闭环控制,使EGR系统的控制与柴油机的混合比和燃烧状况紧密地结合在了一起,基本消除了柴油机制造公差、磨损、燃油成分改变、以及环境条件的变化对NOx降低效果的影响,能充分发挥EGR系统降低NOx的潜力。UEGO在柴油机上的应用正顺应了最新的研究动向——柴油机的λ控制技术,可以认为,基于UEGO的EGR系统是柴油机λ控制技术的一个重要组成部分。 在柴油机稳态工况下,通过试验测定了不同空燃比时,NOx、HC、CO、烟度和油耗的变化。通过对测试数据的分析,确定了最佳空燃比MAP。更多还原

【Abstract】 This study presents the exhaust gas recirculation (EGR), coupled with a high-collection efficiency particulate ceramic filter (DPF) to simultaneously control particulate and NOx emissions from diesel engine.Experiments are carried out using 6120 Diesel engine equipped with DPF. The results indicate that the filter’s average particulate cleaning efficiency is above 95 percent, the back pressure increases approximate linearly. And the filtration period of single filter is more than 2 hours at 3 BSU soot emission level, therefore two filters working simultaneously can work enough time continuously before the back pressure comes to the certain guideline value. Effect of trapped particulate amounts on the regeneration process is notable. The more the amount of particulates trapped is, the higher the temperature in ceramic during the regeneration process is, but excessive particulates amount will cause melting inside the ceramic. The less the amount of particulates trapped is, the lower the temperature in ceramic during the regeneration process is, but too little particulates amount will cause unstable regeneration process, even stop the regeneration. When the particulates amount is between 23g and 25g, the best regeneration performance can be obtained.By adjusting the distribution of both holes and electric heater components, and adopting double-layer filter, the regeneration performance can be further improved.Based on the porous medium theory, the formula which relates the pressure drop of the wall-flow ceramic and the engine conditions is deduced, the wall-flow ceramic pressure drop depends on two variables, the engine speed and the exhaust gas temperature. The coefficients are determined by disposing experimental data using the linear regression method, then, the pressure drop can be calculated using the formula and the two measured values of engine speed and exhaust gas temperature. The particulates amount on the occasion of regeneration determined by the former formula can be controlled in range of 22gm and 28gm. The key technical problem of how to determine regeneration occasion in the practical application is solved efficiently.The valve used to adjusting the regeneration gas flow is referred to as the regeneration valve. On the basis of fluid mechanics principle, considering the character of the engine, the formula which relates the regeneration valve opening and engine load, the exhaust gas temperature and back pressure is also deduced. Two steps are involved to determine the regeneration valve opening in practical application. First, determine the regeneration valve opening according to standard valve opening MAP. Secondly, correct the regeneration valve opening using the opening correction formula according to experimental load. Thus determined regeneration valve opening realizes the aim that the oxygen flux keeps almost unchangeable during the regeneration process, satisfies the requirement in practical application, and solves the key technical problem of how to determine the exhaust flux in the filter during the regeneration process.Regeneration experiments are carried out at both steady and transient engine operation conditions while the regeneration valve opening is controlled by ECU. The results show that the regeneration temperature distribution is even, the peak temperature in the ceramic centeris controlled under 1000℃, and the radial temperature gradient is under 30℃/cm , the regeneration process is steady, the average regeneration efficiency can reaches above 80 percent, and the regeneration success ratio reaches above 97 percent.A new EGR system, which is based on universal exhaust gas oxygen (UEGO) sensor and controlled by a closed loop, is developed. The system uses the filtered clean recirculation exhaust gas. Using the air-fuel ratio measured by UEGO as the feedback to control EGR,更多还原