Figure 6 Calculated results of two-dimensional fuel mass distributions for Pattern A and C under air pressure of 1.09 MPa and at room temperature
Comparing the position of flame tip with that of the spray tip, it can be estimated that the ignition occurred at the middle of the spray and the flame propagated toward the spray tip as if the flame chased the spray development. In contrast to pattern A, as shown in Fig.8 (b), the ignition occurred in the vicinity of the spray tip with the ignition delay of around 1 ms in the case of pattern C, and the spray flame developed with time. Since the injection rate of pattern C increases with time and reaches the maximum at around 2.3 ms after start of injection, it implies that a large amount of fuel with higher injection velocity was injected into the burning region.
Combining those observations, in the case of pattern C, it can be estimated that a large amount of the fuel was enveloped by the flame at around the spray tip, which resulted in the deterioration of the air entrainment and longer combustion period as reported in [9][11].
5. EFFECT OF THE PERIODICAL FLUCTUATION OF INJECTION RATE ON FUEL DISPERSION
As written in the former section, injection rate and injection rate shaping have large effects on the spray evolution, spray shape and fuel distribution. However, it implies that, once the injection rate has determined, the spatial distribution of fuel droplets has almost determined and it is almost impossible to control the spatial distribution actively. Therefore, if we can obtain a new methodology for controlling the spatial distribution of fuel droplets without changing the fuel injection rate, at least without changing the average injection rate, it will give a powerful option for optimizing the temporal and spatial fuel distributions within the engine cylinder. In light of this, we are examining the effect of the periodical fluctuation of injection rate on the spatial dispersion of fuel droplets [15][16]. In the following, a part of the recent results is introduced.
