PERWAVES - Percolating Reactive Waves in Particulate Suspensions
  1. 2019 • TEXUS 56
Physical Sciences:
  • Combustion
Sounding Rocket
J.M. Bergthorson (1), A. Higgins (1), S. Goroshin (1), J. Hoyt (1), T. Karhela (2), M. Nganbe (1), N. Provatas (1), M. Radulescu (1), P. de Goey (3), B. Schmitz (4), E. Shafirovich (5)
McGill University of Montreal
AFL - Alternative Fuels Laboratory
Macdonald Engineering Building, Rm 464
Québec H3G 1Y6
Eindhoven University of Technology
Combustion Technology
Airbus Defence and Space GmbH
Airbus-Allee 1
28199 Bremen
University of Texas at El Paso
In order to address climate change, a transition to a low-carbon economy is desirable. Many clean primary energy sources, such as solar panels and wind turbines, are being deployed and promise an abundant supply of clean electricity in the near future. 
The key question becomes how to store, transport and trade this clean energy in a manner that is as convenient as fossil fuels.  

The Alternative Fuels Laboratory (AFL) at McGill University is actively researching the use of recyclable metal fuels as a key enabling technology for a low-carbon society. 
Metal fuels, reduced using clean primary energy, have the highest energy density of any chemical fuel and are stable solids, simplifying trade and transport. The chemical energy stored in the metal fuels can be converted to useful thermal or motive power through two main routes: 
  • the Dry Cycle, where metal powders/sprays are burned with air, or the
  • Wet Cycle, where metal powders are reacted with water to produce hydrogen and heat as an intermediate step before using the hydrogen as a fuel for various power systems. 
Another advantage is that metal combustion is carbon-free.

Metals have high energy density but they do not ignite easily unless in powder form, when they burn in discrete flames. So-called discrete burning occurs when a piece of fuel ignites and burns completely due to the heat created by other fuel elements around it. Unlike traditional fires that burn through their fuel continuously, discrete fires spread by jumping from one fuel source/particle to another.

Studying combustion or dust particles. Iron, 45 µm, and Oxygen/Xenon.

It is intended to find the ideal blend of oxygen and metal powder as well the ideal size of the metal dust to create the best conditions for combustion. 

By burning metal powder under the condition of weightlessness, researchers are able to study how it burns in a chamber with evenly spaced metal powder. In contrast: on Earth a metall powder clumps together due to gravity.

The results from the burning will be analysed to create models of discrete burning to extrapolate the ideal conditions.

Prior to the rocket flight, the apparatus was extensively tested in the low gravity environment provided by a parabolic flight aircraft. Three flights were performed on the Canadian Space Agency (CSA) Falcon-20 aircraft at the National Research Centre (NRC) in Ottawa, Canada, in May 2019. A total of 46 parabolas allowed the validation of the apparatus modifications as well as the determination of optimal operating conditions for the hardware.

Also compare the ESA website article: 

Iron powder can be considered as an energy storage. Its energy can be released by burning at a time and location of convenience. 
Also, burning iron powder is a CO2-free process. Combustion turns the iron into rust which can be regenerated, leading to a circular process. 
The SOLID student team of the TU Eindhoven, The Netherlands, demonstrated the combustion process under laboratory conditions. Together with partners, the first industrial iron fuel installation was deployed at the brewery Swinkels Family Brewer in Lieshout, The Netherlands, in October 2020. A follow-up project is a 1 MW system. Plans are on the way for a 10 MW system in 2024 and to convert the first coal-fired power plant into a sustainable iron fuel plant by 2030.

TEXUS 56 was launched on 15 November 2019 at 09:35 UTC from Esrange Space Center. The rocket achieved an apogee of 256 km, providing around 6 min of microgravity. 

The experimental concept of the PERWAVES experiment is to ignite a gas/iron powder particle mixture (here an Oxygen/Xenon gas mixture and iron particles of 45 µm / 25 µm sizewithin a transparent quartz glass reactor tube, and to be able to visualize, and make measurements of the flame propagation front.

The results from the burning will be analysed to create models of discrete burning to extrapolate the ideal conditions of particles’ flow and Oxygen concentration.
11 combustion runs performed in microgravity aboard the TEXUS-56 rocket. The data was recorded by the diagnostic system and downloaded on the experiment hard-drive.

The investigation of flame propagation in iron particle suspensions in oxygen/xenon gas mixtures were performed in two consecutive sounding-rocket flights: MAXUS-9 in 2017 and TEXUS-56 in 2019. The observed independence of the flame speed on the particle burning rates has confirmed that combustion occurs in the theoretically predicted discrete flame propagation regime, which is a prerequisite for the occurrence of percolating-flame behavior. The change in the flame appearance observed with a decrease in the fuel concentration is also in accord with theoretical modeling of the percolating flame structure.

Due to the statistical nature of percolating flames, their experimental study requires a large number of trials. Such experiments are only possible on long-duration orbital and sub-orbital platforms. The importance of the problem of percolating reaction-diffusion waves, which encompasses many fields of modern science, and the considerable difficulties encountered in their theoretical research motivates future sounding-rocket and space-based experiments.

The optimal combustion particle size is in the range of 25-30 micrometres, which is close to leftovers from iron processing.

For more details, please, consult Reference Document no. [15] 

For the ESA sounding rocket campaign in 2022, a PERWAVES follow-up investigation is planed. 

A percolation theory for a system in which sources are communicating by diffusion through a scalar field has not yet been developed and the percolation thresholds are unknown. Thus, the main objective of Stage II of the PERWAVES experiment was the experimental estimation of the flame percolation threshold and observation of the percolating flame structure. Theory [7], [8] predicts that if the particles in space are positioned in regular lattices, the fuel concentration limit for discrete flame propagation would be almost twice the value of the concentration for a flame burning in the continuous regime. Propagation of the flame below this limit is only possible in a system with randomly positioned sources where the flame can explore fluctuations in the interparticle distance, i.e. percolate through the system. Thus, all flames with a fuel concentration below the (regular) discrete flame propagation limit are percolating flames. The goal of the experiment was to correlate the flame appearance with the fuel concentration to show that, as soon as fuel concentration is close or below the “regular limit”, i.e., when the flame starts to percolate, the roughness of the flame front sharply increases, demonstrating fractal appearance characteristic of percolation phenomenon.
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Figure 1: TEXUS 56 launch configuration with schematic view of ICAPS and PERWAVES.

Figure 2: PERWAVES apparatus enclosed in the payload section of the TEXUS-56 sounding rocket.

Figure 3: Transition from Maxus-9 to TEXUS-56: Summary of technical modifications performed on the experimental module during the transition from Phase I to Phase II of the PERWAVES experiment.

This video was recorded during a parabolic flight experiment on board the Falcon-20 aircraft of the Canadian National Research Centre that offers researchers up to 18 sec of zero-gravity. It shows at 30 times reduced speed iron metal dust igniting as it reaches combustion heat in slow-motion. So-called discrete burning occurs when a piece of fuel ignites and burns completely due to the heat created by other fuel elements around it. Unlike traditional fires that burn through their fuel continuously, discrete fires spread by jumping from one fuel source to another.
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