Effect of Intake Airflow and Fuel Injection Pressure on Swirling Flame Characteristics of Diesel and JP-8

Abstract Since swirling flames have a wide range of applications, a thorough understanding of flame characteristics across varied intake flow rates and fuel injection pressures will aid in improving next-generation burner designs. In this study, a laboratory scale swirl burner was utilized to investigate the flame characteristics of diesel and JP-8 for a solid cone pressure atomizer with a fixed swirl number of 0.53. Three different fuel injection pressures and airflow rates were tested, ranging from 0.62–0.96 MPa and 350–550SLPM, respectively. Flame images were captured through direct photography using a high speed camera and the flame characteristics were evaluated in terms of flame length, width, and angle. Additionally, to assess flame variations under different operating conditions and fuel types, spatially averaged and time-averaged grayscale intensity fluctuations were determined and compared. The results show that flame characteristics are strongly influenced by the global equivalence ratio, injection pressure, and air flow rate, while both spatially averaged and time-averaged grayscale intensity fluctuations are primarily dominated by the fuel injection pressure. At the more developed swirling flows of 450 SLPM and 550 SLPM, the flame length of diesel is longer than that of JP-8 under medium (0.79 MPa) and high (0.96 MPa) injection pressures. However, at a higher injection pressure (0.96 MPa) and less developed swirling flow (350 SLPM), the flame length of JP-8 exceeds that of diesel. In most cases, JP-8 results in a wider flame than diesel, except at 350 SLPM air flow rates and 0.96 MPa fuel injection pressure. In terms of flame angle, JP-8 exhibits a larger flame angle across all conditions. The most compact flame shape was observed at the highest air flow rate (550 SLPM) and lowest fuel pressure (0.62 MPa) for both fuels.