Advances reported in detonation-based systems and solid-fuel scramjets
By Waruna Kulatilaka and Shyam Menon|December 2024
The Propellants and Combustion Technical Committee works to advance the knowledge and effective use of propellants and combustion systems for military, civil and commercial aerospace systems.
Among the year’s advancements, milestones related to cutting-edge combustion concepts such as rotating detonation engines, RDEs, and solid-fuel scramjets gained attention due to potential performance enhancements and the ability to simplify engine components while increasing the power-to-weight ratio.
The coveted pressure gain combustion in RDEs continued to elude researchers. In January, researchers from the Royal Military College, University of Ottawa and National Research Council of Canada’s Aerospace Research Centre reported in an article in the Journal of Propulsion and Power, JPP, on a quasi-two-dimensional approach to simulate the injectors of RDEs. Their streamline and particle-tracking analyses confirmed that over-expansion shock waves in the injectors were responsible for significant stagnation pressure losses that overcame pressure gains from detonation. The study suggests that careful injector sizing and design may be key to achieving net pressure gain combustion in RDEs.
RDEs also offer a revolutionary technology for land-based power generation, offering potential improvements in efficiency and emissions reduction. In an April JPP article, researchers at the National Energy Technology Laboratory and West Virginia University described their multiyear survey of machine learning approaches to improve capabilities for real-time monitoring of RDEs, a major step toward active control of these engines in laboratory and industrial settings. By evaluating various convolutional neural networks for image classification, object detection and time series classification, they identified methods capable of real-time detonation wave analysis.
In rotating detonation rocket engines, injecting rocket propellants in both gaseous and liquid phases offers a wide array of choices. Liquid/liquid injection systems provide the highest theoretical advantage but operate at the most arduous conditions. In August, Purdue University researchers described their investigation of cryogenic systems with direct injection of liquid oxygen with kerosene or cryogenic methane fuels. Their work on these propellant combinations, published in JPP, resulted in successful detonation of both fuels. Additional work focused on storable liquids — hydrogen peroxide oxidizer with hydrocarbon fuels.
In July, University of Central Florida researchers concluded their investigation of liquid fuels for detonation applications. In a paper published in the Proceedings of the Combustion Institute, they described the droplet burning behavior at varying amounts of nitrogen dilution at stoichiometric and rich equivalence ratios, illustrating how these parameters affect the detonation characteristics of liquid fuels.
With increasing attention to hypersonic flight and related propulsion systems, a team of researchers at Virginia Tech investigated a simpler method for achieving this goal with solid-fuel scramjets. In March, they conducted experimental and computational work, achieving flameholding and sustained combustion at considerably lower total temperatures than those previously reported. Additionally, they developed the first known fully optically accessible solid-fuel scramjet. Their work, described in a journal article published in JPP, led to a greater understanding of the flowfield within the combustor, improving flameholding and flammability limits.
Contributors: Kareem Ahmed, Stephen Heister, Kristyn Johnson-May, S. She-Ming Lau-Chapdelaine, Andrew Nix and Gregory Young
