Novel liquid-piston-coupled adaptable continuous compressed air ejection system: Thermodynamics design and optimization

Cold launch technology based on pneumatic ejection experiences rapid development with extensive applications in recent years. From small unmanned aerial vehicles to large-scale rail vehicle launches, compressed air ejection technology plays an indispensable role. Compared with traditional thermal launch systems, cold launch technology offers advantages including simpler structure, lower operational costs, and enhanced mobility. It effectively reduces site constraints while extending launch equipment service life. However, current compressed air ejection systems face limitations in performing continuous ejections within short intervals, particularly for missions requiring rapid preparation. This paper proposes a novel adaptive continuous compressed air ejection system coupled with liquid piston and an innovative dual air storage tank delayed activation strategy for quick-opening/closing valve operation control. A comprehensive transient thermodynamic model of the compressed air ejection system is developed, employing a segmented modeling methodology to address the transient effects induced by rapidly actuated quick-opening/closing valves. The numerical calculation results demonstrate that the delayed opening quick-opening/closing valve operational strategy proposed in this paper can significantly reduce maximum load on the ejection mechanism (decrease by 19.6%) while maintaining impact object exit velocity (decrease by 1.2%). When the number of cylinders in numerical calculation increases from 1 to 7, the exit velocity of the impact object increases by 8.3 m/s, while the force acting on a single cylinder decreases by 19.89%. The numerical calculation results reveal that increasing the diameter of cylinder can enhance impact object exit velocity, yet further improvement becomes constrained by quick-opening–closing valve's airflow limitations when exceeding critical dimensions. Multi-objective optimization results of numerical calculation demonstrate that for the 30-ton impact object ejection mission, the optimal operating point exit velocity, maximum acceleration per cylinder, and energy utilization efficiency are 19.21 m/s, 9.19 m/s² and 56.17%, respectively.