Ion propulsion, the genesis of emerging research

Publication Date

19 September 2023

A matter of encounters

Can scientific curiosity, human encounters and chance be decisive factors in exploring a line of research hitherto neglected by the scientific community?

The work currently being carried out by Nicolas Binder in the Aerodynamics and Propulsion Department (DAEP) seems to support this hypothesis.

A specialist in fluid dynamics and aeronautical propulsion, the researcher first became interested out of scientific curiosity following the research work of a student engineer, Nicolas Monrolin (E2015).

“We weren’t working on the incremental aspects of a conventional engine, we were beyond that, and I was curious to see what would happen next”, Nicolas tells us. Then he kept in touch, because they got on well together and because their research work focused on breakthrough propulsion systems.

Then, in 2018, the researcher attended the brilliant thesis defence of his former student, now at the IMFT. A week after his thesis supervisor, Franck Plouraboué called ISAE-SUPAERO looking for a high-speed wind tunnel. After a number of unsuccessful attempts, he finally came across Nicolas Binder, the person in the lab interested in this disruptive work.

This thesis was the starting point for the creation of a real multi-physics electro-hydro-dynamics unit at DAEP. For me, at first it was a matter of scientific curiosity, then we started to work together, setting up projects in twos and then in threes with the Institut P' in Poitiers. We finally joined the European IPROP consortium on ionic propulsion with the École Polytechnique, the Van Kármán Institute in Belgium, the University of Milan, which was leading the project, and other Italian universities, to develop a complete line of research, and that's when things started to take off.

Nicolas Binder

The Institute as a benchmark in conventional propulsion

Expertise in conventional propulsion is one of the strengths of the Turbomachinery and Propulsion research group at DAEP. This expertise provides a reference base for assessing the performance of experiments.

The principle of ionic propulsion is to create a plasma around two electrodes of different sizes, between which a high voltage is applied. Ions escape from this plasma and are accelerated by the intense electric field towards the second electrode. These ions undergo a large number of collisions with the neutral air molecules, which slow them down, creating an ion cloud between the two electrodes. This electrically charged zone is the source of the thrust force applied to the electrodes. The aim of this research is to understand all the parameters that currently make this process ineffective. For the moment, this device generates a drag greater than the thrust it induces at modest flight speeds. There is a lot of work to be done on this subject to increase thrust density at low speeds, and above all to see if it develops favourably at high speeds, as the equations seem to show.

There is a chance that the thrust process is activated by the presence of the external flow at high speed, but we still need time to develop the measuring instrument, because this is truly exploratory research. Trying to measure this thrust at high speed has never been done before, and this test bench here at ISAE-SUPAERO is unique.

Nicolas Binder

IPROP, a European project to take things further

The IPROP project is part of the Horizon Europe Pathfinder framework, and aims to raise the level of maturity of atmospheric ion thrusters for aeronautics. Ionic thrusters, which have no moving parts, offer robustness and silent propulsion. This is an emerging field of investigation in the context of the electrification of aircraft and low-carbon air transport.

In the European consortium, ISAE-SUPAERO is responsible for the high-speed experimental part and is working closely with IMFT and Franck Plouraboué, who specialises in numerical simulation. In addition to this collaboration, the École Polytechnique is working on a new electrode device capable of sending more ions into the flow in an attempt to increase thrust density. These electrodes will be tested on the ISAE-SUPAERO test bench to carry out ambitious electric field measurements and laser measurements of the flow.

The French team is in charge of the external velocity coupling part of the flow and the development of new electrodes. Each team is developing its own specific area of expertise, which will be brought together at the ISAE-SUPAERO facility. Indications are beginning to emerge, and the trends are encouraging, but they are not yet precise enough to be published.

The other universities are working on the design of a small-scale demonstrator incorporating these optimised propulsion systems. Ultimately, the aim of the project is to design a full-scale stratospheric airship with a high degree of autonomy using solar-powered ion thrusters. These airships could replace many satellite functions, such as telecommunications or telediction, at lower cost and with the advantage of being recoverable, all with a reduced environmental impact.

If the initial results prove encouraging, it will then be possible to launch research into co-propulsion. The ionic system could be coupled to a conventional propulsion system, switched off at take-off and activated at altitude in cruise mode when thrust requirements are lower. It could reduce the need for internal combustion engines, whose efficiency could be greatly improved. But there are certainly many applications that we haven't yet thought of, which could be envisaged at high speed and high altitude.

Nicolas Binder

The study of this technology opens up a wide scientific field covering fundamental research into ion production, its coupling with airflow, electrode optimisation, aircraft integration, and even more if chance gets involved.