Effect of PID Control of Longitudinal Ventilation on Performance Improvement of Combined Smoke Exhaust System in Tunnel Fires

In the combined smoke exhaust system for tunnel fires, the critical velocity for longitudinal mechanical auxiliary ventilation is usually a fixed value. However, the uncertain development speed and scale of the fire often result in an excessive critical velocity, hindering early-stage personnel evacuation and rescue. To address this challenge, this study introduces the proportional-integral–differential (PID) control algorithm for regulating longitudinal mechanical auxiliary ventilation velocity in combined smoke exhaust system. Initially, we conduct a theoretical analysis of the PID control algorithm's application in combined smoke exhaust system. Subsequently, through numerical simulations, we demonstrate the system's stability in varying fire scenarios characterized by different development speeds during development periods and heat release rates during stable periods. And then, an analysis is conducted on the impact of the control system on the smoke exhaust system performance. The results reveal that the control system can maintain good smoke stratification downstream of the fire source, especially during fire development period, facilitating early personnel evacuation and rescue. Moreover, the smoke exhaust efficiency of the combined system is significantly enhanced. Finally, a detailed implementation plan for deploying this control method in practical engineering applications is presented.