车用催化转化器的CO空速特性

CO Airspeed Performance of Vehicle Catalytic Converter

根据三元催化转化器的CO空速特性试验 ,得出了CO空速特性试验曲线 .应用流体附面层理论和质量传输的基本原理分析了三元催化转化器蜂窝孔内的CO气体流动和质量传输的过程 ,解释了三元催化转化器CO空速特性的内在机理 .认为随着空速的增加 ,开始时CO的体积分数附面层厚度直线降低 ,CO传质系数kf 直线上升 ,加快了CO向催化剂表面的传质速度 ,有更多的CO被输送到催化剂表面 ,增加了CO反应物的体积分数 ,加快了CO的转化率 ,而与此同时气体流过三元催化转化器所需的时间在直线减小 ,CO参加化学反应的时间在直线减小 ,空速对CO传质系数的正面影响和对化学反应时间的负面影响都呈线性变化 ,二者作用相互抵消 ,总体表现为CO的转化率没有什么变化 .而随空速的进一步增加 ,CO的体积分数附面层厚度降低变得缓慢 ,并趋向于稳定 ,同时CO传质系数kf 的上升速度也开始变得缓慢 ,并趋于稳定 ,也就是说CO向催化剂表面的传质速度趋于稳定 ,在催化剂表面的CO的体积分数不再随着空速的增加而增加 ,CO的化学反应速度基本维持不变 ,而与此同时CO参加化学反应的时间还是在直线减小 ,所以CO的催化转化率表现为下降趋势 .

CO airspeed performance has been tested and its curve is gotten.This paper uses the flow boundary layer theory and mass transfer theory to analyze the CO gas flow state and CO mass transfer course in catalytic converter honeycomb holes,and illustrate the intrinsic mechanism of CO airspeed performance.It points out:at the beginning when the airspeed ( Φ ) increases,the thickness of CO density boundary layer decreases linearly,the CO mass transfer coefficient ( k f) increases linearly,the CO mass transfer speed to catalyst surface increases,and more CO mass is transferred to the catalyst surface,it increases the CO reactant density and increases the CO converter ratio.At the same time when the airspeed ( Φ ) increases,the time of CO going through the catalytic converter decreases linearly,the time of CO chemical reaction decresses.The positive action of airspeed to the CO mass transfer coefficient ( k f) is canceled by the negative action of airspeed to the chemical reaction time,the general action of airspeed to CO converter ratio keeps fixed.Then when the airspeed ( Φ ) increases further,the decreasing of CO density boundary layer thickness becomes less,the increasing of CO mass transfer coefficient ( k f) also becomes less and goes to stability.The CO mass transfer speed keeps almost fixed and the CO density on catalyst surface increases no more,the CO chemical reaction maintains the same speed,but the time of CO chemical reaction decreases linearly all the same,generally the CO converter ratio decreases.