NASA National Aeronautics and Space Administration NASA Carbon Neutral Fuels for Advanced Air Mobility (AAM) Exploring electric energy and fuels from renewable energy for sustainable aviation By Dr. Pankaj Dhussa

1. Carbon Neutral Fuels for Advanced Air Mobility (AAM)
Exploring electric energy and fuels from renewable energy for sustainable
aviation
Challenge
In 2016, aviation was responsible for 2.5% of global CO2
emissions
1% of world’s jet fuel needs come from low-carbon or
zero-carbon fuels
Thermal management in future aircraft will be a
significant challenge for all battery, hybrid, and
turboelectric architectures
Expected Impacts
Minimize the adverse impact of aviation fuels on the
environment
Assess how NASA could potentially contribute to a
paradigm-shift in energy sources for AAM with a
focus on sustainability
Solutions
Conducted a set of studies addressing the high-level system of
systems perspective for carbon neutral fuels for AAM to:
Explore the box to be drawn around the system
Create a baseline case
Compare alternative energy storage types
Assessed the feasibility, viability, and desirability for further
research activities and solutions
Results
Emerging needs identified through the activities:
Detailed thermal management models need to be integrated into
the parametric vehicle designs
Optimization of a future aircraft and the airspace operations must
be coupled and evaluated by higher level metrics ($/(pax*mile),
gCO2/(pax*mile), door-to-door time,…).
The average customer today is very different from 30 years ago,
and the average customer 30 years from now, will be very
different from today. New metrics are needed that capture those
differences.
Comparison of Some Energy Storage Alternatives
Does not include tank or integration penalties
Next Steps
Several difficult questions need to be addressed:
• Why will future customers travel and to where?
• What matters more to them? Cost, environmental impact, speed,
comfort…?
• What other external factors will create opportunities or barriers?
A map that captures the interactions and strengths of the various
drivers would provide insight into how things have evolved to reach
today’s state and where things may be heading. The weighting factors
on these drivers change over time, are subject to feedback and bi-
direction influence, and are linked to demographic, economic, and
cultural shifts, as well as technology development.
POC: Lee Kohlman, NASA Glenn Research Center
Specific Energy
Energy Density
Vaporization Cooling
Ratio
Relative Minimum
Boiling Temperature
Liquid Hydrogen
Liquid Methane
Liquid Ethane
Jet A
Butanol
Methanol
Liquid Anhydrous Ammonia
Select Fuel
Characteristics
Liquid
Hydrogen
Liquid Methane
Liquid Ethane
Liquid Anhydrous Ammonia
Jet A
Butanol
Ethylene
Liquid Propane
Liquid Butane
Gasoline
Propanol
Ethanol
Methanol
Battery (Li-S)
0
2
4
6
8
10
12
14
16
0 10 20 30 40 50 60
Energy
Density
(MJ/L)
Specific Energy (MJ/kg)
Energy Storage Characteristics of Selected Fuels
(40% Fuel, 95% Battery Efficiency)
Example UAM Sizing Result- 6 Passenger Quad
More data is needed to refine results (batteries are based on SotA circa 2015)
Understanding Our Own Biases Due to
Perspective and Role
Specific Energy: MJ/kg
(LHV/mass)
Energy Density: MJ/L
(LHV/volume)
Vap. Cooling Ratio: MJ/MJ
(heat of vaporization/specific energy)
Boiling Temperature: 1/K