Spray quality

Note that the traces are somewhat ragged (individual spectra have different intensities due to fluctuations in spray quality). Addition of trifluoroacetic acid caused a huge boost in ion current at 30 s, due to its ability to protonate neutrals to form [M + H]+ ions (as well as catalyze the hydrolysis)—the ion count per data point jumped from 3000 to a momentary value of 48,000 (Fig. 3 shows only 0-15,000 counts, to keep the rest of the data on scale). To smooth out these fluctuations and to focus in on the relative abundances of the ions of interest, we normalized the data to the total intensity of the three key ions (Fig. 4) the product traces disregard the other product, to take account of the different ionization efficiencies of these two ions. 

Physical properties of the three test fuels are presented in Table I. Except for the surface tension of No. 6 fuel oil, which was a typical value, all properties were measured for the specific samples tested. The primary differences between the SRC-II middle distillate and the No. 2 fuel were the higher specific gravity, surface tension, and viscosity of the SRC-II. The No. 6 grade fuel, a residual fuel oil, had a much higher viscosity than either of the distillate fuels. Both the SRC-II and No. 2 fuel oil were sprayed at a nominal temperature of 80°F to simulate usage in a non-preheat combustion system. The No. 6 fuel oil was sprayed at temperatures ranging from 150° to 240°F in order to assess spray formation processes and spray quality over a broad range of viscosities. 

Mean droplet size as measured from the holograms and photographs was consistent with the visual observations of spray formation and spray quality. 

For comparable fuel flow rates, the Sonicore atomizer could provide a spray with smaller SMD. Increasing the air-to-fuel ratio improved spray quality and can be used to compensate for increased fuel viscosity. 

Both droplet size data and visual spray quality correlated with fuel viscosity for both atomizer types. 

Advanced nozzle designs, such as twin-fluid, pre-orifice and air-inclusion nozzles, can also be used. Most are designed to reduce spray drift. Atomisation in twin-fluid nozzles occurs because the interaction of air and liquid. Different spray qualities can be produced by changing both liquid and air pressures. Low spray volume rates (75-1501/ha) and high work rates (ha/hour) are possible. 

For a fixed-orifice conventional hydraulic pressure nozzle operating with a given spray liquid, the only way in which flow rate through the nozzle can be changed is by varying the pressure at the nozzle. However, variations in operating pressure result in changes to both the spray volume distribution pattern (pattemation), the droplet size (spray quality) and velocity distributions (see Table 4.2). 

In this type of nozzle, spray liquid and air are mixed together as they pass through chambers in the nozzle body to form a spray that is delivered from a modified flood or reflex type nozzle. The flow of air contributes directly to the spray droplet formation process. By controlling air and liquid pressures, liquid flow rate and spray quality from the nozzle can be varied independently. Droplets generated from such nozzle designs can contain air inclusions if they are above... 

Multinational companies have shown interest in the development of application technologies, but commitment has not been sustained where intellectual property rights (IPR) in large markets could not be established. Disappointingly few farmers worldwide are aware of alternatives to conventional hydraulic sprayers, which inefficiently use large volumes of water, but remain by far the most important method of pesticide application. Worse still, recent emphasis in application research has focused on the reduction of spray drift (especially in Europe and North America). The most common solution to be implemented to date has been to increase droplet size spectra (without necessarily improving spray quality) thus spray application has probably become generally more inefficient. 

Hall, K. J., N. Western, P.J. Holloway, D. Stock, Effects of adjuvant oil emulsions on foliar retentionand spray quality, in Proceedings of the Brighton Crop Protection Conference—Weeds, 1997, pp. 549-554. 

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... 

Fig. 15.7 Role of injector spray quality in SCR system optimization...

Fig. 15.8 Spray quality measurements equipment. Left PDPA. Right Pattemator...

Fig. 15.10 Spray quality calculations—droplet distribution curve and DvO.9...

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. 

There are multiple spray measurements used to quantify an injectors spray quality. Some of these measurements include DIO (arithmetic mean), D32 (Sauter mean diameter), D31 (evaporative mean diameter), DvO.9, and droplet distribution curve. Figure 15.9 provides a description and equation used to calculate SMD, DIO, and D31. Figure 15.10 shows a typical droplet distribution curve with an overlay to show the DvO.9 calculation. The DvO.9 value represents the point where... 

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. 

Fig. 15.13 Spray quality comparison—droplet size (pressure swirl injector)...

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