Performance and size optimization of the turbine-less engine integrated solid oxide fuel cells on unmanned aerial vehicles with long endurance

Fuel cells are applied to power sources on unmanned aerial vehicles with long endurance to save fuel and increase endurance. A turbine-less engine integrated with solid oxide fuel cells was proposed in our previous work. With the variation of fuel cell area, the specific fuel consumption and the engine weight both sharply changes, which severely affected the endurance of aircraft equipped with the engine. Therefore, the mathematical models considering the performance and weight were built to demonstrate the effect of the fuel cell size on the performance of the engine, and the key part was validated by experimental data. The main conclusions are as follows: the coupling effect between the equivalent ratio and the fuel cell stack number is strong. The endurance increment ratio for the aircraft compared with the endurance of the aircraft with turbojet engines first increases and then decreases with increasing fuel cell stack number or the equivalence ratio. In a big operating zone, the hybrid engine has a high endurance increment ratio. The maximum value is 0.152. Meanwhile, the fuel cell stack number is 3.7, and the equivalence ratios are respectively 0.356 and 0.137 in the reformer and combustor. The rated specific fuel consumption rate are 27.9 (g/s)/kN. In addition, the maximal thrust and thrust variation range of the engine increase by about 46% and 383–403%, compared with those of the turbojet engine.