Trade-off studies between NOx and CO2 to evaluate the future development strategies for aircraft engine

The fuel efficiency of civil aviation has improved significantly by more than 70%, hence reducing aviation’s CO2 emissions. Among the 70% fuel reduction, more than half has been achieved due to engine technology development, e.g., advanced engine cycles and technologies. To reduce fuel consumption, engine designer and manufacturers are striving to increase operating pressure and turbine inlet temperature; however, this increase causes adverse effects on NOx emissions for a given combustion technique. Especially at higher operating temperature and pressure, this trade-off between fuel consumption and NOx emission is highly nonlinear. This study tends to quantify the aviation’s climate impact from CO2 and NOx emissions by considering the nonlinear variations of CO2 and NOx caused by the nature of engine cycles. The analysis starts with engine modelling combined with emission calculations to understand the trade-off between CO2 and NOx emissions when varying the design variables, like overall pressure ratio and turbine inlet temperature. A typical turbofan engine with a high bypass ratio is considered. We then apply the exchange rate of CO2 and NOx emissions to the baseline emission inventory, the well-known AERO2K dataset. The state-of-the-art climate assessment tool, AirClim, is used to calculate the changes of climate impact concerning the exchange rate of CO2 and NOx emissions. Accordingly, we quantify the development trend of aviation's climate impact from CO2 and NOx concerning the intrinsic feature of an engine cycle. This research can provide us with insights into the engine development strategy that could be adapted to optimize the engine not only to reduce fuel consumption but also for climate impact reduction.