2.2.2. Injection Rate Measurement

There are two methods which can be used to measure the injection rate. The Zeuch method obtains the injection rate after injecting fuel into the pressure vessel. With the Bosch-Tube method, fuel is injected into the pipe to detect the pressure change in the injection rate meter. Then, the injection rate is measured. In this study, the Bosch-Tube method was used [5]. The Bosch-Tube measurement principle involves feeding the fuel into the pipe with a cross-sectional area A and selecting the fuel control volume in the pipe flowing at the speed of sound as c, when the fuel in the pipe moves at a speed of u. The characteristics of the fuel moving inside can be expressed as shown in Figure 3. By knowing the sonic velocity and fuel density in the pipe and ascertaining the pressure change in the chamber, the injection rate can be calculated.


**Figure 3.** Control volume in the pipe to measure the injection rate.

**Figure 4.** Injection rate measurement; (**a**) Injection rate measuring device, (**b**) Schematic diagram.

**Table 2.** Experimental conditions for measuring injection rate.


As shown in Figure 4, the injection rate measurement system consists of a measuring tube with a length of about 12.6 m, needle valve, accumulator, pressure gauge, and regulator. The injector is installed on the adapter in the injection rate measuring device and is connected to the common-rail to supply high-pressure fuel. When fuel injection starts, the injection rate is measured by passing the fluid through the pressure sensor (Kistler, Model:6052c, Winterthur, Switzerland) that is mounted on the adapter. The experimental conditions for the injection rate are expressed in Table 2.
