**3.1 Combustion characteristics**

In this section, the combustion characteristics of impinging flame at three types of injection pressure are discussed. At 40 mm of impingement distance, three types of injection pressure were employed i.e. 80, 120, and 180 MPa.

**Figure 2** shows the impinging flame at three types of injection pressure. Regarding injection rate graphs in previous work [10], luminous flames occur just before the end of injection. Furthermore, comparing three different injection pressure, the luminous flame appears earlier with higher injection pressure. It means increasing injection pressure leads to shorter ignition delay due to generate higher premixing of fuel and air. The flame luminosity was figured out at 0.9 ms after start of injection (ASOI) only during injection pressure of 120 and 180 MPa. However, it was unseen at injection pressure 80 MPa at 0.9 ms ASOI when increasing the time to 1.2 ms ASOI, the flame luminosity appeared. During the time of 1.2 ms ASOI, most brightness of flame luminosity was captured at injection pressure of 180 MPa. In this case, the luminous flame is starting to decrease then disappear. Similarly, at timing of 1.8 ms ASOI, the injection pressure of 120 MPa shows luminous flame start to decrease. However, in this timing the luminous flame continuous to develop at injection pressure of 80 MPa. It evident from **Figure 2**. that injection duration was longer with lower injection pressure than combustion duration showed finish later.
