Overview of Injection Technology and Spray Quality

While spray quantity is important to achieving NOx reduction performance, it is independent of the type of injector technology chosen. Instead, spray quality is a primary metric used in determining the injector and mixing technology that is used. Spray quality is a measure of the size, speed, and pattern of the DEF droplets that enter the exhaust stream. Two types of test equipment used to quantify spray quality are shown in Fig. 15.8. The piece of equipment shown on the left of the 

Not only are these tools important for injector development, they also provide critical information used as inputs for computational fluid dynamics (CFD) analysis. As mentioned previously, simulation plays a critical role in SCR system development. The more accurate the measurements are while quantifying an injector s spray quality, the more accurate the simulated spray quality will be which will in turn give better correlation between simulation and hardware testing. 

90 % of the measured spray has less than the measurement reported for the DvO.9 value. This description also applies to DvO.l (10 %) and DvO.5 (50 %) measurements. 

To provide clarity when calculating Sauter mean diameter (D32), an example has been provided below. The SMD measurement represents a one number descriptor used to compare different sprays and is considered industry standard for comparing spray quality. Table 15.1 provides a truncated sampling of a hypothetical spray. For this example, whole numbers are used to signify the number of droplets counted for a given diameter measurement. This data can be used to calculate the SMD for the example outlined below. Equations 15.2-15.4 show an example of how to calculate SMD based on the data provided in Table 15.1. 

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