Comparing Figs. 12 and 13 shows that the soot distribution is similar to the luminous flame, both with and without the CCD jet. Between the pictures of with and without the CCD jet, there are similar flame shapes and soot until 0.6 msec, when the CCD jet has not reached the flame. After the CCD jet reaches the injected fuel, the flame and soot disappear rapidly. This indicates that the CCD jet causes a rapid mixture of soot and surrounding air, resulting in quick oxidation of the soot.
Figure 14 shows the averaged areas of luminous flames and the shadow of soot with and without the CCD jet for the conditions in Figs. 12 and 13. With the CCD jet both luminous flame and soot areas diminish earlier than without the CCD jet. The areas change similarly, and the soot behavior may be estimated from the flame pictures. The Case 2, which has shorter distance between the nozzle and CCD orifice than in Case 1, resulted in similar soot reduction characteristic as in Case 1.
Figure 15 shows pictures for Case 3 where the distance between the main nozzle and CCD orifice is the shortest. Figure 16 shows the changes in luminous flame area. Without the CCD jet, the spray flame injected from the center of the combustion chamber remains for a long time, spreading along the wall. With the CCD jet, the jet penetrates the flame, and there are no apparent differences with and without the CCD jet, different from Cases 1 and 2.
These results indicate that impingement of the jet promotes oxidation of soot, but that when the jet is close to the spray flame, it only penetrates the flame with no combustion enhancement. Similarly, experiments changing the direction of impingement were performed.
Fig.15 Photographs of combustion flames with and without CCD jets for Case 3.
