NETL researchers have completed some of the first in-situ measurements of ammonia-fueled flames. The foundational combustion research will be used to validate computer models needed to design next-generation energy systems using ammonia as a carbon-free fuel.

“Fuels that create zero carbon dioxide emissions such as ammonia, among other decarbonization strategies, will be critical for combatting the effects of climate change,” said NETL’s Clint Bedick. “However, to develop optimized ammonia combustion systems, validated modeling tools are needed. For that, you need real-world data.”

The researchers leveraged NETL’s cutting-edge Advanced Combustion Laboratory in Pittsburgh, Pennsylvania, to measure temperatures and concentrations of various compounds, including nitrogen oxides (NOx), that are formed during fuel combustion. The work supports the Lab’s Hydrogen with Carbon Management Program and Turbines subprogram. For their experiments, Bedick and his team used fuel mixtures representative of cracked ammonia, which is composed of ammonia and hydrogen, and an ammonia-natural gas blend.

“While ammonia is a carbon-free fuel, the formation of NOx remains a concern,” Bedick said. “Ammonia is one molecule of nitrogen and three molecules of hydrogen, and that fuel-bound nitrogen can lead to NOx formation pathways resulting in 1,000s of parts per million of the highly reactive gas. This is undesirable because NOx can cause environmental problems such as acid rain and negative health effects.”

Recent research by NETL and others has uncovered a potentially viable method toward low-NOx combustion of ammonia through the “rich-quench-lean” (RQL) strategy. In this strategy, a rich-burn phase, in which there is substantially more fuel than air in the mixture, is utilized to partially oxidize the fuel, while simultaneously converting a large portion of the unburnt fuel to hydrogen through thermal cracking. Further downstream, a secondary air injection phase burns out the hydrogen and remaining ammonia, while minimizing fuel-NOx formation.

“A major component to making the RQL strategy work is the development and validation of chemical kinetic mechanisms,” Bedick said. “Prior to this NETL research, there were few examples of in-situ, quantitative species measurements. Our results matched model predictions well overall, providing much needed validation data in an environment which can be represented by simple one-dimensional models.”

Work is underway to refine the research, but these initial data hold great promise for the research community and could one day lead to clean energy systems that use ammonia as a fuel without generating significant amounts of NOx. 

“This advancement is significant because, while ammonia can be used in a clean energy economy as a hydrogen carrier, direct utilization as a fuel is favored for power generation, once the issue of NOx formation is mitigated through next-generation computer modeled designs,” Bedick said.

NETL is a U.S. Department of Energy national laboratory that drives innovation and delivers technological solutions for an environmentally sustainable and prosperous energy future. By its world-class talent and research facilities, NETL is ensuring affordable, abundant and reliable energy that drives a robust economy and national security, while developing technologies to manage carbon across the full life cycle, enabling environmental sustainability for all Americans.