Phase-transition-induced flame structure evolution and combustion performance in a center-staged aero-engine combustor

Transcritical kerosene injection is increasingly relevant to high-performance aero-engine combustors, yet the coupled impacts of phase state, flame dynamics, and performance remain insufficiently quantified under controlled conditions. This study experimentally investigates transcritical RP-3 injection in a single-cup, center-staged combustor by combining real-gas thermodynamic analysis with multi-diagnostic combustion characterization. The main-stage kerosene injection state is parameterized by T _f-m/ T _c and p _f-m/ p _c, spanning 0.465–1.034 and 0.14–1.29, respectively, while maintaining a constant fuel flow rate. Flame structure and heat-release-related dynamics are captured via CH* chemiluminescence, complemented by synchronously acquired high-frequency dynamic pressure, and combustor performance is evaluated using outlet temperature-field measurements, OTDF , and combustion efficiency. Results indicate a distinct “concentrated-diffused-reconcentrated” evolution of the V-shaped flame as the fuel state transitions from liquid to two-phase and then to supercritical. Quantitative CH* statistics show a non-monotonic mean intensity with an inflection near the liquid-phase endpoint, whereas the peak intensity increases monotonically as T _f-m and p _f-m rise. In the two-phase region, both CH* and dynamic-pressure FFT spectra exhibit broadband characteristics without a pronounced narrowband peak, and time-domain CH* signals show intermittency rather than sustained periodic oscillations, suggesting that, under the present single-cup combustor and tested acoustic boundary, no dominant frequency-locked thermoacoustic mode is observed within the investigated conditions. Consistently, the outlet temperature field becomes less uniform in the two-phase region and recovers under supercritical injection; correspondingly, CO and UHC emissions decrease in the liquid-phase region, rise in the two-phase region, and decrease again under supercritical injection, whereas NOx increases toward the two-phase region and then decreases under supercritical conditions; combustion efficiency also degrades in the two-phase region and improves again in the supercritical region. These findings support an engineering recommendation to avoid two-phase injection operation and favor single-phase liquid or supercritical injection for more stable, uniform, and efficient combustion.