(3-12) Relationship between Fuel Injection Rate and Spray Characteristics of the Swirl Nozzle for Gasoline Engine((FS-1)Fuel Sprays 1-Gasoline sprays)

The experiments on the instantaneous fuel flow rate and the spray characteristics, velocity and Sauter mean diameter, are introduced in this paper. Five swirl nozzles, which are used for gasoline direct injection engines and are the same design however differed in the static flow rate as 600, 700, 800, 900 and 1000 cc/min respectively, are utilized. Alternative fuel of normal-heptane instead of gasoline is employed for all experiments. The flow rate measurements have been performed under the injection pressure of 7.0 MPa and injection frequency of 16.7 Hz. The amount of fuel at each injection is set as certain values for all nozzles so that valve-opening duration is changed from 0.7 to 3.51 ms for each nozzle. A laser Doppler anemometer (LDA) is applied to measure the centerline velocity of the test section within a quartz-glass pipe of 3.5 mm inner diameter. The instantaneous fuel flow rate and integrated mass are simulated using measured centerline velocity. For the spray measurement, a phase Doppler anemometer (PDA) is applied to obtain the droplet velocity and diameter distribution pattern. The experiments are made under the fuel injection amount of 24.4mg/cycle for 700 and 1000 cc/min nozzles and 8.6 mg/cycle for all the nozzles. An example of flow rate results is shown in Fig. 1, where the fuel injection amount is set to 8.6 mg/cycle for the nozzles of 700 and 1000 cc/min. In the graph, the abscissa axis is the phase angle. The phase angle of 360 degree is corresponding to one injection period. The result shows that for the nozzle of 700 cc/min, its instantaneous flow rate is larger than that of 1000 cc/min at initial stage (from 53 to 56 degree) but is smaller that that of nozzle of 1000 cc/min as injection processes. After 60 degree, sharp decreasing flow rate is observed for the nozzle of 1000 cc/min. This feature is related with the valve opening duration, valve moving speed and the flow coefficient at the nozzle passage. Negative fuel flow rate during 62 to 67 degree and after 78 degree are observed in the figure. They are caused by the oscillating flow inside the pipe of test section and it is related with the inner diameter and length of the pipe and/or fuel flow line volume. Figure 2 shows the radial distribution of mean velocities for all nozzles. The measuring position is at z = 25 mm and injection amount is 8.6 mg/cycle. It can be seen that the position of the maximum mean velocity is shift to the outer position with increasing the static flow rate of the nozzle except for the 1000 cc/min nozzle. It is considered that the results are related with the spray angle because increasing in the instantaneous fuel flow rate causes the different spray angle and the different maximum velocity. At last, the time dividing analysis for intermittent spray is also presented.