Co-evaluation of spray kinematics and ignition behaviour: The feasibility of biofuels as direct substitutes for RP-3

Energy shortages and environmental pollution challenge aviation, with biofuels offering a promising alternative to petroleum fuels. This study aims to evaluate the feasibility of two self-developed biofuels (Fuel A: 67.97% second-generation biodiesel + 23.03% methyl tert -butyl ether + 9.00% n-butanol; Fuel B: 78.15% second-generation biodiesel + 13.61% tetrahydrofuran + 8.24% isopropanol) as substitutes for RP-3, specifically for spray dynamics and ignition. Spray characteristics were studied using shadowgraphy in a constant-volume chamber under temperatures (423–773 K), backpressures (1.4–2.8 MPa), and injection pressures (60–90 MPa). Results show both fuels have kinematic viscosity and surface tension matching RP-3, and similar spray morphology/breakup. Spray penetration is governed by injection pressure, suppressed by backpressure, and enhanced at high temperature via vapour boost. Spray cone angle increases as injection pressure drops and backpressure rises, while showing a non-monotonic “flash boiling peak–film contraction” response to temperature. Fuel A, with stronger secondary breakup, has larger cone angles. Spray projected area decreases with backpressure, increases linearly with injection pressure, and expands at high temperature, matching RP-3. Regime analysis via Re-We-Oh model confirms all conditions are in the aerodynamically dominated atomisation regime. Ignition delay times of Fuel B (superior atomisation) were measured in a shock tube and compared with RP-3, showing consistency. This study provides experimental and theoretical support for bio-alternative fuel design and aero-engine application.