An experimental study on spray auto-ignition of RP-3 jet fuel and its surrogates

Jet fuel is widely used in air transportation, and sometimes for special vehicles in ground transportation. In the latter case, fuel spray auto-ignition behavior is an important index for engine operation reliability. Surrogate fuel is usually used for fundamental combustion study due to the complex composition of practical fuels. As for jet fuels, two-component or three-component surrogate is usually selected to emulate practical fuels. The spray auto-ignition characteristics of RP-3 jet fuel and its three surrogates, the 70% mol n-decane/30% mol 1,2,4-trimethylbenzene blend (Surrogate 1), the 51% mol n-decane/49% mol 1, 2, 4-trimethylbenzene blend (Surrogate 2), and the 49.8% mol n-dodecane/21.6% mol iso-cetane/28.6% mol toluene blend (Surrogate 3) were studied in a heated constant volume combustion chamber. Surrogate 1 and Surrogate 2 possess the same components, but their blending percentages are different, as the two surrogates were designed to capture the H/C ratio (Surrogate 1) and DCN (Surrogate 2) of RP-3 jet fuel, respectively. Surrogate 3 could emulate more physiochemical properties of RP-3 jet fuel, including molecular weight, H/C ratio and DCN. Experimental results indicate that Surrogate 1 overestimates the auto-ignition propensity of RP-3 jet fuel, whereas Surrogates 2 and 3 show quite similar auto-ignition propensity with RP-3 jet fuel. Therefore, to capture the spray auto-ignition behaviors, DCN is the most important parameter to match when designing the surrogate formulation. However, as the ambient temperature changes, the surrogates matching DCN may still show some differences from the RP-3 jet fuel, e.g., the first-stage heat release influenced by low-temperature chemistry.