柴油机颗粒排放测量全流稀释定容采样系统设计研究

国际及欧美相关标准规定,全流稀释系统是柴油机排放型式认证试验唯一的基准系统。对柴油机颗粒排放全流稀释定容采样系统进行研究,发现其核心是用于稳定系统流量的临界文丘里喷管的设计。当临界文丘里喷管前后的压比达到一定值时,喉口处的气流速度达到当地声速,此时流量达到最大且保持恒定,不再随环境参数的变化而变化,即处于临界状态。该流量是柴油机气态排放和颗粒排放计算中的关键参数之一,是排放测试设备的关键技术。

Design of a Sampling System of Diesel Particulate Full-Flow Dilution Constant Volume

In this paper only the Full Flow Dilution System is designed and introduced. Full flow dilution is normally used only for measurement on heavy duty engines. The main purpose of the CVS facility ( Constant Volume Sampling) is to provide a constant mass flow though the dilution tunnel during the period of the whole test cycle, while the exhaust gas flow rate before dilution is varying. This is realized by using critical flow venturi- nozzles and by controlling the critical flow inlet conditions to constant values, i.e. pressure and tempera- ture. That means, by controlling the inlet conditions of the critical flow of venturi- nozzles a over- critical pressure difference between inlet and outlet of the venturies can be reached, such, sound velocity is generated in the smallest cross section of the critical flow venturi, variations of system pressure after the venturi nozzle do not affect the system flow any more.