resulted image is very clear and spray periphery is easily determined by image analyzing program.
If low frame rates are used, the injection delay time gets important in synchronizing the camera system with spray first images. The uncertainty gets lower when higher frame rates are used. In order to capture the initial stages of spray and reduce the uncertainty about the timing, high frame rates, 16000 and 32000 fps with continuous recording are used in this study. The corresponding time uncertainties are below 0.0625 and 0.03125 ms which are acceptable for spray evolution.
When the corrected images are obtained, the image geometries must be converted to the real geometries. Converting the measured distance into the real distance was calculated as follows: at first, a known distance between two points on the image was measured and a converting parameter was obtained. Then the measured distance of the spray was converted into actual distance.
The measurements were carried out by following the same procedure presented in Figure 6. In this paper, spray tip penetration length is measured from the injector tip to spray tip, which is defined as the intersection of the spray contour—determined by chosen threshold level — and spray axis. The spray cone angle measurement is obtained separately from the spray length measurements. It is measured between the tangent lines fitted through the upstream half of the spray contour. Besides penetration and cone angle, two other characteristics were also investigated for different chamber conditions. The first one was spray width that was measured at the widest point perpendicular to the spray axis and the second was spray area that was calculated by the colored pixels chosen with predetermined threshold level.
Fuel mass measurements were carried out at 50, 80, 100, 120 MPa injection pressures with 2.0 ms injection duration. In the study of Payri et al., 2000 μs injection duration was used as a quasisteady condition in nozzle characterization.