The ICAO Post-COVID forecasts estimate a 2.4%-4.1% increase for a low to high revenue passenger-kilometres growth rate. Air traffic growth inevitably increases aviation's combustion and acoustic emissions, hence aggravating aviation's environmental impact locally and globally. HOPE will deliver an integrated aircraft propulsion system comprising two multi-fuel ultra-high bypass ratio (UHBR) turbofan engines, a fuel cell based auxiliary propulsion and power unit (FC-APPU) driving an aft boundary layer ingestion (BLI) propulsor based on tube-wing aircraft configuration.

The HOPE system:

1. minimises the combustion and noise emissions during landing and takeoff (LTO), hence the impact on air quality and noise annoyance near airports, without the trade-off of cruise emissions;
2. retrofits the existing aircraft configuration, allowing the substantial emission reduction to be achieved within a short time;
3. de-risks the use of hydrogen solely in existing tube-wing aircraft configurations;
4. smoothens aviation’s energy transition through assessment and exploitation of several greener propulsion technologies at different maturity level.

HOPE emission goals consist of LTO NOx: -50%, CO: -50%, soot: -80%, perceived noise: -20% (~3 dB per operation), and climate impact: -30%, compared to state-of-the-art technology in 2020 (A320neo). To this end, HOPE will:

1. Design an integrated aircraft propulsion system accommodating multi-fuel (kerosene/sustainable aviation fuel +hydrogen) UHBR turbofan engines, FC-APPU, and an aft BLI propulsor;
2. Explore the novel idea of combining a BLI propulsor with FC-APPU for zero-emission taxiing;
3. Model, experiment, and demonstrate for the first time a low emission multi-fuel combustion technology burning H2+kerosene/SAF for future UHBR turbofan engine;
4. Assess societal impact, environmental burden, and cost benefits of the reduced noise and emissions by HOPE technology;
5. Formulate policy and recommendations to introduce HOPE technology.