**Figure 2.**

*Impinging flame at three types of injection pressure. (a) Pinj = 80 MPa. (b). Pinj = 120 MPa. (c) Pinj = 180 MPa.*

*Effect of Injection Pressure on Local Temperature and Soot Emission Distribution of Flat-Wall… DOI: http://dx.doi.org/10.5772/intechopen.102867*

**Figure 3**(**a–c**) shows the temperature and KL factor distribution of impinging flame at different injection pressure. These figures were extracted from flame natural luminosity images by using a two-color method analysis. Brightness color in its distribution indicates temperature and KL factor. Flame luminosity was obtained to investigate the temperature and KL factor distribution, therefore both of them seem similar shapes.

#### **Figure 3.**

*Flame temperature distribution (Top) and KL Factor (Bottom) at different injection pressures. (a) Dimp = 40mm Pinj = 80 MPa. (b) Dimp = 40mm Pinj = 120 MPa. (c) Dimp = 40mm Pinj = 180 MPa.*

At high injection pressure, complicated distribution of temperature was spread to wider area. However, the phenomenon was contrarily at lower injection pressure. The temperature was contributed to heat transfer on the wall [9]. The lowest injection pressure in this study is 80 MPa where it has the highest temperature compared to other injection pressure variations. This is probably due to more flame natural luminosity was captured at lower injection pressure as shown in **Figure 2**.

**Figure 3**(**a–c**) describes the KL factor distribution at injection pressure variations. Based on liquid length data in evaporating conditions, the soot formation region was formed [10]. This liquid length existed before impingement during the injection period. A shorter period with higher injection pressure has been found through the soot formation that occurred around the center of the impingement wall as shown in **Figure 3**. Mixing the fuel and air better is an important decisive factor in the reduction of soot formation.

A similar trend of integrated flame luminosity, luminous flame area, mean temperature, and integrated KL factor was shown in **Figure 4**(**a–d**). It starts increasing and reaches the maximum point before decreasing at time variation in each injection pressure. The integrated luminosity is shown in **Figure 4(a)**. The flame luminosity

#### **Figure 4.**

*Integrated Flame luminosity, luminous flame, mean temperature, and KL factor under injection pressures. (a) Integrated flame luminosity. (b) Luminous flame area. (c) Mean temperature. (d) Integrated KL factor.*

*Effect of Injection Pressure on Local Temperature and Soot Emission Distribution of Flat-Wall… DOI: http://dx.doi.org/10.5772/intechopen.102867*

indicates soot combustion in case of insufficient oxygen by a rich mixture. Opposite relation was found between injection pressure and luminosity where higher injection pressure will have smaller and shorter luminosity. Increasing injection pressure means increasing the velocity. Therefore, air entertainment will improve spray atomization and premixing of fuel and air. **Figure 4(b)** shows the shorter flame area at higher injection as a result of premixing fuel and air.

**Figure 4(c)** describes the mean temperature of three types of injection pressure where it has a lower temperature compared to the temperature at injection pressure of 80 MPa. The differences in temperature among them were approximately 100K. We can see that flame temperature distribution at three types of injection pressure were 1.2, 1.5, and 1.8 ms ASOI as shown in **Figure 4(c)**. At the time 1.5 and 1.8 ms ASOI, the temperature distribution was almost uniform where the mean temperature will be high as shown in **Figure 4(c)**. On other hand, the reduction of soot formation may affect premixed combustion at high injection pressure with a shorter injection duration.

**Figure 4(d)** shows the integrated KL factor which is consist of the soot formation. This formation was decreasing when the injection pressure increased. Meanwhile, in **Figure 4(a–c)**, the integrated KL factor increases to peak value at maximum flame natural luminosity and flame area. As mentioned before, opposite relation between injection pressure and KL factor was found which is due to less air entertainment than

#### **Figure 5.**

*Distribution of temperature from wall surface at 1.2 ms ASOI under injection pressures and positions. (a) Position1 at 1.2 ms ASOI. (b) Position2 at 1.2 ms ASOI. (c) Position3 at 1.2 ms ASOI.*

spray atomization and fuel-air mixing decreasing. Next, it affects a high equivalent ratio. For soot production purposes, the correlation between high temperature and fuel-air mixing is interesting to discuss.
