瞬态工况下DPF温度特性的数值分析

Numerical analysis of temperature characteristics in diesel particulate filter under transient conditions

在柴油机颗粒捕集器(DPF)使用的过程中,工况变换造成的排气热冲击会使其内部出现较大温度梯度,导致热应力破坏.为了避免DPF使用过程中的热应力破坏,以DPF为研究对象,利用对流传热原理建立了DPF温度传递模型,研究了入口流量、载体孔目数、载体长度和颗粒物沉积量对DPF温度特性的影响.结果表明:入口流量可以极大地影响DPF的温度特性,当排气流量由173 kg·h^-1提高至1072 kg·h^-1时,载体轴向温度梯度极值下降56.2%,更大的入口流量会导致载体传热加快;当载体目数由100目提升至300目时,升温迟滞时间下降38.36%,优化孔目数结构可以有效加速载体升温,使温度分布均匀;将载体长度由270 mm增加至630 mm时,轴向温度梯度极值由1465.89 K·m^-1降低至734.78 K·m^-1,延长DPF长度有利于降低载体前端温度梯度,减缓高温排气的热应力冲击;当颗粒物沉积量分别为0、1.0、2.2、4.0和8.0 g·L^-1时,轴向温度梯度极值分别为1465.88、1478.62、1493.24、1521.16和1621.21 K·m^-1,颗粒物负载增加会导致载体温度梯度极值呈指数型增加,严重加剧载体局部温度积聚,增大热应力破坏风险.

During the use of diesel particulate filter(DPF),the thermal shock of the exhaust can make a large temperature gradient,resulting in thermal stress damage.To avoid the thermal damage of DPF,the DPF temperature transfer model was established,and the effects of flow rate,cell per square inch(CPSI),filter length and soot deposition on the temperature characteristics were investigated.The results show that the flow rate has obvious effect on the temperature characteristics of DPF.When the flow rate is increased from 173 kg·h^-1 to 1072 kg·h^-1,the axial temperature gradient is decreased by 56.2%.When the CPSI is increased from 100 to 300,the delay time is reduced by 38.36%.When the length of the filter is increased from 270 mm to 630 mm,the axial temperature gradient extreme value is reduced from 1465.89 K·m^-1 to 734.78 K·m^-1.When the soot deposition contents are 0,1.0,2.2,4.0 and 8.0 g·L^-1,the axial temperature gradient extreme values are 1465.88,1478.62,1493.24,1521.16 and 1621.21 K·m^-1,respectively.The increase of soot loading can lead to an exponential increase in the extreme value of temperature gradient,which aggravates the local temperature accumulation and enhances the risk of thermal stress damage.