Piston engine energy utilization for variable-altitude applications: A review of two-stage turbocharging technologies

Amid environmental challenges and development pressures in high-altitude regions, sustainable engine solutions are urgently needed for both aviation and ground transportation. Altitude-induced air density reduction causes 8–13 % power loss per km of altitude and significant emissions deterioration in piston engines—problems that demand effective technical solutions. This systematic review examines two-stage turbocharging systems operating in high-altitude environments, focusing on aviation applications from moderate to near-space elevations and ground transportation in mountainous regions. The review systematically analyzes various turbocharging configurations, key parameters, matching methods, and inter-stage flow phenomena to establish a comprehensive framework for altitude-adaptive two-stage turbocharging. These systems provide notable advantages in control flexibility, altitude adaptability, and improvements in fuel economy and emission control, with optimized configurations achieving up to 95 % sea-level power restoration at 5.5 km altitude and enabling unmanned aerial vehicles to reach 20 km with pressure ratios exceeding 23. While delivering superior performance compared to single-stage alternatives, these gains come with implementation challenges including increased system cost, weight, and packaging complexity. By synthesizing previously fragmented research across system configurations, parameter optimization, and flow dynamics, this work provides both theoretical foundations and practical design guidance for sustainable high-altitude engine systems. Future development pathways include compact architectures, electrification integration, renewable fuels, and advanced propulsion systems aimed at addressing performance and environmental demands across challenging altitude profiles. This work fills critical knowledge gaps in high-altitude engine technology and supports sustainable transportation development in environmentally sensitive mountain environments.