Multi-Stage Thermal Relief Start-Up Strategy for Gaseous Fueled Micro Turbojets Considering Heat Accumulation Effects

To address the issues of start-up over-temperature and sharp reduction in creep life caused by the lack of droplet evaporation latent heat cooling effect when adapting micro turbojet engines (MTEs) to gaseous fuels (GFs), this study optimized the start-up control strategy based on the heat accumulation effect (HAE). By establishing a 160 kgf-class MTE GF experimental platform, the nonlinear coupling mechanism between the “supply-and-burn” characteristic of GFs and the lag of rotor aero-thermodynamic response was deeply analyzed. The study found that traditional linear fuel supply strategies ignore the closed-loop energy balance under the small volume effect of the combustor, which easily causes the exhaust gas temperature (EGT) to remain above the safety threshold for a prolonged period. Unlike conventional continuous ramping strategies, this study proposes a novel open-loop multi-stage thermal relief start-up strategy. By introducing speed dwell windows in the early ignition and mid-acceleration stages, dynamic thermal relaxation intervals were constructed to achieve a “deep washout” of the accumulated thermal load. Experimental results indicate that although the optimized strategy slightly increases the instantaneous peak temperature due to the adjustment of the acceleration slope, it effectively cuts off the over-temperature time. Specifically, the over-temperature duration is reduced from 17.2 s to 11.4 s (a 33.7% reduction), and the over-temperature severity index decreases from 756.76 °C·s to 451.70 °C·s (a 40.3% reduction). This strategy successfully achieves the smooth start-up of the GF MTE, providing an efficient and reliable start-up control paradigm for the transition of micro power systems to low-carbon/zero-carbon fuels.