Document Type : Original Article

Authors

• Seyed Ali Salari ¹
• Fathollah Ommi ²

¹ PhD Candidate, Faculty of Mechanical Engineering Department, Sharif University of Technology.

² Faculty of Aerospace Group, Mechanical Engineering Department, Tarbiat Modares University.

Abstract

The performance of naturally aspirated aircraft engines declines significantly with increasing altitude due to reduced air pressure and density, affecting power, torque, in-cylinder pressure, and combustion temperature. This study presents a comparative analysis of the carbureted (Rotax 912 ULS) and fuel-injected (Rotax 912iS) versions of the Rotax 912 engine using GT-SUITE simulations across altitudes up to 9,150 meters. Results indicate that the carbureted engine suffers an 80% reduction in power at high altitudes due to its fixed fuel-air mixture, while the fuel-injected engine maintains more stable performance by dynamically adjusting fuel delivery. The EFI system also preserves higher in-cylinder pressure and combustion stability under oxygen-scarce conditions. Although EFI mitigates performance loss more effectively than carburetion, both configurations exhibit significant degradation at high altitudes, highlighting the inherent limitations of naturally aspirated engines. These findings underscore the importance of advanced altitude compensation methods—such as turbocharging or optimized EFI mapping—for enhancing reliability and efficiency in high-altitude aviation operations.

Keywords

• Aircraft engines
• Rotax 912
• Fuel injection
• Altitude effects
• GT-SUITE simulation
• Internal combustion