Experimental studies on the combustion characteristics of alternative jet fuels

Conventional Jet-A and six alternative jet fuels, including three Fischer–Tropsch “Synthetic Paraffinic Kerosene” (SPK) fuels and three “Hydrotreated Renewable Jet” (HRJ) fuels, have been experimentally investigated to obtain their fundamental combustion characteristics in terms of Derived Cetane Number (DCN), autoignition response, laminar flame speed, and extinction stretch rate for premixed combustion. The ignition delay times and DCNs for each jet fuel and selected binary blends of Jet-A and alternative jet fuel were determined by using a Fuel Ignition Tester in accordance with the ASTM D7170 method. In addition, the autoignition response for fuel/air mixtures was recorded and compared in a heated Rapid Compression Machine, conducted at an air-to-fuel mass ratio of 13 and under a compressed pressure of 22 bar. By changing the compression ratio and initial temperature, the trend of autoignition behavior over a range of compressed temperatures was studied. Atmospheric laminar flame speeds and extinction stretch rates were also measured in the premixed twin-flame configuration by using a counterflow burner. The flame data at two unburned mixture temperatures of 400 K and 470 K were reported respectively over an equivalence ratio range of ϕ = 0.7–1.4 for the laminar flame speeds and of ϕ = 0.9–1.6 for the extinction stretch rate measurements. The comparison of fundamental combustion properties for Jet-A and various alternative jet fuels provides insights into understanding the impact of fuel properties on combustion performance and developing a cost-effective combustion testing program that includes fundamental characterization.