Theoretical Study of the Effects of Hybridization on the Emission and Performance Characteristics of a Turbocharged Aircraft Piston Engine

In recent years, numerous studies have focused on reducing emissions from modern reciprocating engines without compromising their performance characteristics. One promising approach is to use Mild-Hybrid engines as an alternative proposal to the conventional reciprocating ones. This study aims to investigate how the hybridization will impact the main performance variables and the pollutant emissions of a turbocharged, modern aircraft spark-ignition (SI) engine—specifically, the ROTAX 914. The engine is analyzed under three distinct operating conditions at three different altitudes, defined by different combinations of engine speed and throttle position, using conventional aviation fuel (AVGAS 100LL). The analysis is conducted using GT-POWER, an advanced engine simulation software that allows for complete engine modeling and parameterization across a wide range of operating conditions. The accuracy of the simulated engine model is validated by comparing its output to experimental data obtained from the engine’s technical manuals. Key performance indicators examined in this study include brake power (We), brake torque (Mσ), brake specific fuel consumption (BSFC), and emissions of nitrogen monoxide (NO) and carbon monoxide (CO). Therefore, the proposed model can be employed to investigate the operational behavior of the ROTAX 914 UL aircraft engine when integrated into a hybrid aircraft propulsion system, in which the engine is connected in series with an electric battery. In particular, the model enables parametric studies on the effects of varying engine–battery hybridization levels—defined as the respective contributions of the engine and the battery to the total propulsive power available at the aircraft propeller—on the main performance variables and emissions of the ROTAX 914 UL engine in different altitudes. The primary objective is to assess the effects of series hybridization on engine operation and its most significant emissions. This is accomplished by operating the ICE at a lower operating condition, because it is connected with a battery, which helps the engine deliver the required output power sooner. The results suggest that increasing the power output delivered by the battery, so the ICE is operating in lower loads, can significantly enhance the performance and environmental efficiency of a turbocharged aircraft SI engine at different flight altitudes. In conclusion, series hybridization presents a promising solution for improving present-day reciprocating SI engines.