NASA-funded university study uses simulation to consider ammonia as a fuel
The University of Central Florida (UCF) has a long history of working in the aerospace field. Way back in 1968, a $12,500 grant was given to the university from NASA. More recently, in 2013, it was awarded $55 million to research the impact of space weather events on satellites and orbiting objects—dubbed the GOLD mission. UCF also partners with SpaceX and Blue Origin, houses NASA’s Center for Lunar and Asteroid Surface Science, and was once home to my all-time favorite space-themed college mascot—Citronaut. This year, the university formed a team of university and industry partners to study the use of ammonia as a jet-engine fuel. Ansys is one of the corporate partners for the NASA-funded project, and its simulation tools look to play a big part in the development.
NASA’s University Leadership Initiative is built to fund U.S. university projects for research and development of NASA’s Strategic Implementation Plan. Most of these goals are big, moonshot-level shifts to the way we think about aviation and space exploration.
The UCF-led project is titled “Zero-Carbon Engine Core with Supercritical Carbon Dioxide Power Cycle for Onboard Power.” Its aim is to shift to ammonia jet fuels. This will include a series of design tradeoffs, but the eventual payoff of the effort might be a more sustainable future. Some of the simulation tools needed to understand computational fluid dynamics already exist and can be applied to the project, and others will need to be developed.
Ammonia as a Fuel
Fuel is a constant concern for both air and space travel. The sustainability of using fossil fuels is flagged because of the climate change risks involved with the fuel and the eventual exhaustion of supply.
Ammonia as a fuel for aircraft is not a new idea, even if the idea has not yet been successfully implemented on a large commercial scale. NASA’s X-15 Aircraft was fueled by anhydrous ammonia and liquid oxygen. It made 199 flights in 1959. A report from the University of Ontario in 2017 looked at several alternative fuels and methods of synthesizing ammonia as a fuel. Reaction Engines in the United Kingdom is building a reactor that will take pure ammonia and crack it into hydrogen and nitrogen. Presumably, the UCF team will follow the same method as Reaction Engines, catalytically cracking the ammonia into hydrogen and nitrogen and then burning the hydrogen. The hydrogen is burned for power and exhausted as nitrogen and water.
Ammonia can be stored as a liquid and will produce considerably fewer emissions than petroleum-based fuels. Airports could store the ammonia in tanks similar to jet fuel, so there aren’t huge changes to the infrastructure required. A side effect of converting the ammonia could also provide cooling and help prevent overheating or burnout in the jet engines. Disadvantages to using ammonia as a fuel, besides the ever-present odor, are the high ignition temperature, low flame velocity and slow chemical kinetics, according to a 2020 article published in Energy Research called “A perspective on the use of ammonia as a clean fuel: Challenges and solutions.” Ammonia is also highly corrosive and toxic, presenting challenges for tanks and lines that will contact the material.
These disadvantages are mostly design challenges that engineers will have to overcome if adopting ammonia in a design. The larger and less technical advantage is inertia, as well as the cost of widespread adoption. While low relative to outfitting airports with cryogenic liquid hydrogen systems, there will still be a large cost required to retrofit kerosene tanks with ammonia tanks. Even with the benefits to sustainability and carbon emission gains, mandating a new fuel source for jet engines is going to encounter some mental resistance.
Simulation as a Partner
Simulation tools are built to give engineers insight into engineering problems. As engineers, we know that running simulations further up the design process will give us better overall results and help to plan processes and production when required. Good simulation results should save us time, raise efficiency and have strong fidelity of results. It’s fantastic to see Ansys included as a partner in the NASA grant, an acknowledgment by the university and industry members that simulation will enhance the project. Integrating a simulation supplier early in the process will ensure that the systems and components can be designed with the fine details of that supplier’s simulation tools in mind.
The Ansys products called out include Ansys Chemkin-Pro, built to model “complex, chemically reacting systems.” Modules are built for Combustion Analysis and Emissions Analysis, but it’s really the Reaction Workbench that will do most of the work here. The Reaction Workbench creates “a tailored fuel model that matches physical or chemical properties of real fuel.” We are decades into the exploration of replacement fuels for gasoline, and Chemkin-Pro has a Model Fuel Library with the combustion characteristics of alternative fuels. The UCF project might also be a great help for Ansys, creating new data that can be used in the fuel database.
Ansys Fluent is the other main tool called out in the announcement. It is one of the big hitters in CFD and brings a big set of pre-existing tools for a study of this magnitude. There are combustion options here to complement the Ansys Chemkin-Pro options, but there’s also a larger array of simulation tactics that can be used. Modules for fluid mixing, gas turbines and hypersonic speed already exist in the software. More tangential concerns when changing to ammonia, such as turbulence modeling and fluid-structure interactions, are also available and might be a part of the due care testing for the project. If any structural issues are found, it’s comforting to know that Ansys Mechanical is at the ready using the same formats as the fluid simulation products.
What Does It All Mean?
This project is big-picture engineering, working to apply an alternate fuel to air travel. This is a great creative application of engineering, taking products that are already in the field and using them in a different way. Shifting our reliance on petroleum-based fuels to more sustainable alternatives is moonshot-level and will require several hundred small details to be championed.
Regardless of our political ideologies, it’s becoming clear that climate change is one of the issues of our lifetime. As engineers, we need to be able to look at problems from all angles and be willing to take in new information that potentially shifts our approach.
A university with a strong track record of NASA partnerships like UCF is positioned well to be successful at adopting ammonia, not just for the first five years of this project but hopefully through a few more iterations of the grant. Pulling together a strong partnership of university and industry engineers and bringing in a simulation provider can only improve the project’s chances.
