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In 2019, aviation was responsible for 2.6% of world CO 2 emissions as well as additional climate impacts such as contrails. Like all industrial sectors, the aviation sector must implement measures to reduce its climate impact. This paper focuses on the simulation and evaluation of climate scenarios for air transport. For this purpose, a specific tool (CAST for "Climate and Aviation -Sustainable Trajectories") has been developed at ISAE-SUPAERO. This tool follows a methodology for the assessment of climate impacts adapted to aviation. Firstly, models for the main levers of action, such as air traffic, aircraft energy consumption and energy decarbonization, are provided using trend projections from historical data or assumptions from the literature. Second, the evaluation of scenarios is based on aviation carbon budgets, which are also extended to non-CO 2 effects using the concept of GWP*. Several scenario analyses are performed in this paper using CAST allowing different conclusions to be drawn. For instance, the modelling of the scenarios based on the more recent ATAG (Air Transport Action Group) commitments shows that aviation would consume 6.5% of the world carbon budget for +1.5 • C. Some illustrative scenarios are also proposed. By allocating 2.6% of the world carbon budget to aviation, it is shown that air transport is compatible with a +2 • C trajectory when the annual growth rate of air traffic varies between − 1.8% and +2.9%, depending on the technological improvements considered. However, using the same methodology for a +1.5 • C trajectory shows that a drastic decrease in air traffic is necessary. Lastly, analyses including non-CO 2 effects emphasize the importance of implementing specific strategies for mitigating contrails.

The aircraft environmental control system (ECS) is the second-highest fuel consumer system, behind the propulsion system. To reduce fuel consumption, one research direction intends to replace conventional aircraft with more electric aircraft. Thus, new electric architectures have to be designed for each system, such as for the ECS. In this paper, an electric ECS is modeled and then sized and optimized for different sizing scenarios with the aim of minimizing fuel consumption at the aircraft level. For the system and for each component, such as air inlets and heat exchangers, parametric models are developed to allow the prediction of relevant characteristics. These models, developed in order to be adapted to aircraft design issues, are of different types, such as scaling laws and surrogate models. They are then assembled to build a preliminary sizing procedure for the ECS by using a multidisciplinary design analysis and optimization (MDAO) formulation. Results show that the ECS design is highly dependent on the sizing scenario considered. An approach to size the ECS globally with respect to all the sizing scenarios leads to an ECS that accounts for around 200 N of drag, 190 kW of electric power, and 1500 kg of mass for the CeRAS aircraft.

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