Road-to-Stratosphere clearing technology allows for clean rocket fuel

A new study by UC Riverside shows that the chemicals used in electric car batteries can give us carbon-free fuel for space flight.

In addition to reducing emissions, this chemical has many advantages over other rocket fuels, but it does not require high energy, low cost, and refrigerated storage.

The chemical, ammonia borane, is currently used to store hydrogen in fuel cells that run electric vehicles. UCR researchers now understand how this combination of boron and hydrogen releases enough energy to launch rockets and satellites.

“In addition to electric vehicles, we are the first to demonstrate that in addition to electric vehicles, ammonia boron is used to make rockets,” said UCR Chemical Engineer and first author of the new study. Their demo has now been published Journal of Physical Chemistry C.

The most commonly used rocket fuels are known to be hydrocarbon based and have a variety of negative environmental impacts. They can poison the soil for decades, cause cancer, produce acid rain, ozone depletion, and greenhouse gases such as carbon dioxide.

In contrast, once burned, ammonia boron releases healthy compounds such as boron oxide and water. “The damage to the environment is minimal,” Biswawas said.

Compared to hydrocarbon fuels, ammonia boron emits more energy, which can be costly because less fuel is needed to power the same flight.

In order to release energy from the fuel and allow it to burn, stimuli and oxidizers are added to provide more oxygen to the fuel. Fuel cells often use stimuli for this purpose. They increase the burn rate, but remain the same before and after the reaction.

“Spacecraft need a lot of energy in a short period of time, so it is not good to use a stimulus because it does not contribute to the energy you need. Student and co-author of the study, currently working at UCR.

The decomposition of natural ammonia boron disrupts its overall ability to react with most oxidizers. However, the researchers found an oxidizer that modulates the decomposition and oxidation mechanisms of this fuel, allowing it to extract its total energy content.

“This is similar to the use of catalytic converters to completely burn hydrocarbon fuels,” Gildell said. “Here, we are able to create more complete combustion of chemicals and increase the overall reaction force, using the oxide itself chemistry, without the need for a stimulus.”

In addition to producing unwanted products, some rocket fuels require storage at cold temperatures. “NASA used very low-liquid liquid hydrogen,” Gildell said. “Therefore, it requires a lot of space for maintenance as well as cryogenic conditions.”

In contrast, this fuel is stable at room temperature and can withstand high temperatures. In this study, the researchers created fine ammonium borne particles, which can be depleted in very wet areas within a month.

The research team is currently studying how different amounts of ammonium boron particles age in different environments. In order to improve stability in humid conditions, they are developing methods to protect the oil particles.

The study is being co-sponsored by UCR Professor of Chemical Engineering Michael R. Zekarias and funded by the University Research Fellowship Program of the US Defense Risk Reduction Agency and the Bureau of Naval Research. The agencies provided the funds for the production of clean, efficient flight fuel.

Quantum chemistry calculations needed to support experimental observations in this study were conducted in collaboration with UCR Materials Scientists Hyuna Kwon and Bryan M. Wong.

“We have determined the basic chemistry that promotes this combination of fuels and oxidizers,” Biswawas said. “We look forward to seeing how it works at a high level right now.”