The size effect of micro turbojet engine combustors makes them highly susceptible to non-uniform circumferential exit temperature distributions, which severely compromises the service life of hot-section components and overall engine reliability. To investigate its causes and influence mechanisms, this paper conducts a systematic study based on a self-developed micro turbojet engine and its dedicated measurement and control platform, utilizing a combination of experimental and numerical simulation methods. First, the exit temperature distribution characteristics across the full rotational speed range were acquired through whole-engine hot-fire tests, verifying the existence of circumferential temperature non-uniformity. The results reveal the evolution law: the temperature non-uniformity is most pronounced at low rotational speeds, whereas intensified airflow mixing at high speeds (80,000–100,000 r/min) drives the temperature distribution toward uniformity. Second, based on fluid-thermal coupled simulations, the matching and influence relationships between uneven fuel flow distribution and the exit temperature field were investigated. It was found that localized fuel deviations trigger a step-wise enlargement of the circumferential temperature difference and a decrease in combustion efficiency. To verify this matching relationship, an independent cold-flow test of the fuel distribution ring was conducted, confirming the accurate correspondence between the localized flow reduction at a specific fuel nozzle and the localized low-temperature zone at the exit. The formulation of this matching relationship provides a data-driven basis for the online condition monitoring and fault troubleshooting of micro engines. Finally, building upon these findings, the influence of the large mixing hole diameter on the flow-thermal coupling of the combustor was further investigated. The results indicate that excessively large diameters (≥ 8 mm) tend to induce jet interference, while excessively small diameters (≤ 3 mm) result in thermal constraint failure. Medium diameters, such as 6 mm, achieve a favorable balance between combustion efficiency and temperature uniformity. The revelation of these flow-thermal coupling mechanisms provides a theoretical reference for the subsequent optimization design of the combustor's aerodynamic structure.
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