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The potential environmental benefits of hybrid electric regional turboprop aircraft in terms of fuel consumption are investigated. Lithium-air batteries are used as energy source in combination with conventional fuel. A validated design and analysis framework is extended with sizing and analysis modules for hybrid electric propulsion system components. In addition, a modified Bréguet range equation, suitable for hybrid electric aircraft, is introduced. The results quantify the limits in range and performance for this type of aircraft as a function of battery technology level. A typical design for 70 passengers with a design range of 1528 km, based on batteries with a specific energy of 1000 Wh/kg, providing 34% of the shaft power throughout the mission, yields a reduction in emissions by 28%. Keywords Hybrid electric propulsion

With civil aviation growing at around 4.7% per annum, the environmental footprint of aviation is increasing. Moreover, the use of kerosene as a fuel accelerates the depletion of non-renewable fossil fuels and increases global warming. Hence, the aviation industry has to come up with new technologies to reduce its environmental impact and make aviation more sustainable. An electrically assisted propulsion system can combine the benefits of an electrical power source with a conventional turbofan engine. However, the additional electrical system increases the weight of the aircraft and complexity of the power management system. The objective of this research is to analyze the effect of an assistive electrical system on the performance of a turbofan engine for an A320 class aircraft on a short-range mission. The developed simulation model consists of an aircraft performance model combined with a propulsion model. The power management strategy is integrated within the simulation model. With the proposed propulsion system and power management strategy, the electrically assisted propulsion system would be able to reduce fuel burn, total energy consumption, and emissions for short-range missions of around 1000 km.

Aviation is an important contributor to the global economy, satisfying society’s mobility needs. It contributes to climate change through CO2 and non-CO2 effects, including contrail-cirrus and ozone formation. There is currently significant interest in policies, regulations and research aiming to reduce aviation’s climate impact. Here we model the effect of these measures on global warming and perform a bottom-up analysis of potential technical improvements, challenging the assumptions of the targets for the sector with a number of scenarios up to 2100. We show that although the emissions targets for aviation are in line with the overall goals of the Paris Agreement, there is a high likelihood that the climate impact of aviation will not meet these goals. Our assessment includes feasible technological advancements and the availability of sustainable aviation fuels. This conclusion is robust for several COVID-19 recovery scenarios, including changes in travel behaviour.

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Since its discovery, the flameless combustion (FC) regime has been a promising alternative to reduce pollutant emissions of gas turbine engines. This combustion mode is characterized by well-distributed reaction zones, which potentially decreases temperature gradients, acoustic oscillations, and NOx emissions. Its attainment within gas turbine engines has proved to be challenging because previous design attempts faced limitations related to operational range and combustion efficiency. Along with an aircraft conceptual design, the AHEAD project proposed a novel hybrid engine. One of the key features of the proposed hybrid engine is the use of two combustion chambers, with the second combustor operating in the FC mode. This novel configuration would allow the facilitation of the attainment of the FC regime. The conceptual design was adapted to a laboratory scale combustor that was tested at elevated temperature and atmospheric pressure. In the current work, the emission behavior of this scaled combustor is analyzed using computational fluid dynamics (CFD) and chemical reactor network (CRN). The CFD was able to provide information with the flow field in the combustor, while the CRN was used to model and predict emissions. The CRN approach allowed the analysis of the NOx formation pathways, indicating that the prompt NOx was the dominant pathway in the combustor. The combustor design can be improved by modifying the mixing between fuel and oxidizer as well as the split between combustion and dilution air.

This paper presents performance assessment of the proposed hybrid engine concept using Liquid Natural Gas (LNG) and kerosene. The multi-fuel hybrid engine is a new engine concept integrated with contra rotating fans, sequential dual combustion chambers to facilitate "Energy Mix" in aviation and a Cryogenic Bleed Air Cooling System (CBACS). The current analysis focuses on three aspects: 1) effects of the CBACS on the HPT cooling air requirement and the associated effects on the cycle efficiency; 2) performance optimization of the hybrid engine; 3) assessment of the emission reduction by the hybrid engine. An integrated model framework consisting of an engine performance model, a turbine cooling model, and a Cryogenic Heat Exchanger (CHEX) model is used to perform the analyses. The parametric analysis shows that using the CHEX, the bleed air temperature can be reduced significantly (up to 600 K), which reduces the turbine cooling air requirement by more than 50%, while increasing the LNG temperature by 300K. Consequently, the cycle efficiency improves even further. Depending on the fuel flow distribution between two combustors. The CO 2 emission from the hybrid engine is lower by 15% to 30%. The mission analysis along with the Multi-Fuel Blended Wing Body aircraft shows a reduction in NOx emissions by 80% and CO 2 emission by 50% when compared to B-777 200ER.

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