Periodic Reporting for period 1 - IPROP (Ionic Propulsion in Atmosphere)
Reporting period: 2023-11-01 to 2024-10-31
Nowadays the aeronautical transport field is still widely based on internal combustion engines, even if a growing attention is paid to electric engines and in general to propulsion systems with low environmental impact. In this context, thrust generation by means of ions acceleration is a propulsion technique which could play a revolutionary role. At present, ionic propulsion is well operative in space applications but much less studied for atmospheric ones. It potentially allows to develop propulsion units with important advantages over thermochemical devices: first, the good thrust/(power consumption) ratio already attained at the current level of research, which is expected to increase dramatically as technology proceeds; moreover, the absence of any moving components and the light weight, together with the emission of naturally decaying gases without solid particles (no combustion at all).
The IPROP project aims to bring ionic air-breathing propulsion beyond the pioneering phase, exploring its capabilities and improving its performance. Cold plasma for atmospheric propulsion is a subject of recent investigations: model airplanes and vertical lifters have recently flown with this type of propulsion, but the potential of this technology is much higher.
To this purpose, a complete research program is proposed, starting from breakthroughs in fundamental research to be achieved through theoretical, numerical and laboratory studies. The following steps will lead to develop improved and optimized propulsive units, with the objective of designing and building an airship model (technological demonstrator) with ion propulsion. A further objective is the conceptual design of a full-scale stratospheric airship: a major long-term impact is expected for ion-powered airships, which could act as stratospheric platforms replacing many satellite functions, such as telecommunications, remote sensing and disaster risk management in civil protection, offering these services at much lower costs, with the benefit of being recoverable systems. A fully successful program may lead to top-level, fully ion-powered airships: thanks to the propulsive units without moving mechanical parts, powered by solar energy, they would have extremely long operation times, low maintenance and create very low pollution.
The IPROP project aims to bring ionic air-breathing propulsion beyond the pioneering phase, exploring its capabilities and improving its performance. Cold plasma for atmospheric propulsion is a subject of recent investigations: model airplanes and vertical lifters have recently flown with this type of propulsion, but the potential of this technology is much higher.
To this purpose, a complete research program is proposed, starting from breakthroughs in fundamental research to be achieved through theoretical, numerical and laboratory studies. The following steps will lead to develop improved and optimized propulsive units, with the objective of designing and building an airship model (technological demonstrator) with ion propulsion. A further objective is the conceptual design of a full-scale stratospheric airship: a major long-term impact is expected for ion-powered airships, which could act as stratospheric platforms replacing many satellite functions, such as telecommunications, remote sensing and disaster risk management in civil protection, offering these services at much lower costs, with the benefit of being recoverable systems. A fully successful program may lead to top-level, fully ion-powered airships: thanks to the propulsive units without moving mechanical parts, powered by solar energy, they would have extremely long operation times, low maintenance and create very low pollution.
1) Theoretical and numerical modeling of the ionization and drift processes.
A simplified 2D numerical model has been developed for the simulation of the ionic drift under the effect of the electric field generated between opposite electrodes, with the aim of studying the effect of different ion collectors geometries on the thruster performance. One-way models with drift-diffusion and unsteady effects are available, coupling charge flux and electrostatic Poisson equations with a Navier-Stokes equation which includes an electric forcing term (charge distribution not depending on the flow but only on the electric field). The work on two-way models with drift-diffusion is in progress, with a first code including a bidirectional coupling of Navier-Stokes, charge flux and Poisson equations.
The effects of different plasma kinetic models on the results of a corona discharge simulation have been investigated by introducing a discharge model based on the time-dependent drift-diffusion approximation in a quasi-2D finite volume approach. Simulations have been carried out considering a wire-to-wire geometry with fixed electrodes radii and distance. Electric current, number densities and EHD force yielded by different treatments of the chemical source term in the continuity equation have been compared: the results show that in a numerical simulation the kinetic model has a significant impact on the computed EHD force, indicating the need of a proper choice to accurately predict the performance of plasma thrusters. A comparison between the above mentioned results and the measurements obtained in a corresponding laboratory experiment is in preparation.
2) Physics of ionic thrusters in laboratory.
The previous knowledge about wires-to-airfoils geometries for the thrusters electrodes has been extended with a comprehensive study including several collector shapes and testing of non-uniform emitters arrangements. A different configuration for the ion thrusters – not based on airfoil collectors – is being tested now, leading to some promising preliminary results which are surely worth of further investigation. In fact, the first data indicate the chance of tripling the thrust with respect to a wire-to-airfoil of same size and voltage.
An experiment in a low-speed wind tunnel has been performed on a wire-to-airfoil thruster with the purpose of evaluating changes in performance due to simulated flight conditions and, for the first time, comparing them with a simple physical model of the drift region which is good agreement with the laboratory data.
An experiment about ionization processes between electrodes in a cylindrical geometry is in progress with the aim of creating a reference for the theoretical and numerical ionization studies.
Different techniques for measuring thrust, electrical parameters and flow characteristic are being tested in this phase of the research program, also including particle image velocimetry measures on electrodes systems of different sizes, shapes and materials.
3) Testing ionic thrusters against environmental conditions.
For this recently opened branch of the project, different laboratory configurations are being prepared for testing the ion thrusters performance against wide changes of the external conditions such as air pressure, temperature, humidity, radiations. These experiments will also include insulation tests and studies of the electrodes aging.
4) Further activities
As a preliminary work for the future work packages, some activities dealing with the design of a demonstrator airhsip and the following stratospheric applications have already started.
A novel design technique for airships featuring ion-thrusters has been presented, with a first application to the sizing of a low-altitude demonstration mission.
Development has also begun on ultra-lightweight power supply units to power the demonstrator's on-board ion thrusters.
A simplified 2D numerical model has been developed for the simulation of the ionic drift under the effect of the electric field generated between opposite electrodes, with the aim of studying the effect of different ion collectors geometries on the thruster performance. One-way models with drift-diffusion and unsteady effects are available, coupling charge flux and electrostatic Poisson equations with a Navier-Stokes equation which includes an electric forcing term (charge distribution not depending on the flow but only on the electric field). The work on two-way models with drift-diffusion is in progress, with a first code including a bidirectional coupling of Navier-Stokes, charge flux and Poisson equations.
The effects of different plasma kinetic models on the results of a corona discharge simulation have been investigated by introducing a discharge model based on the time-dependent drift-diffusion approximation in a quasi-2D finite volume approach. Simulations have been carried out considering a wire-to-wire geometry with fixed electrodes radii and distance. Electric current, number densities and EHD force yielded by different treatments of the chemical source term in the continuity equation have been compared: the results show that in a numerical simulation the kinetic model has a significant impact on the computed EHD force, indicating the need of a proper choice to accurately predict the performance of plasma thrusters. A comparison between the above mentioned results and the measurements obtained in a corresponding laboratory experiment is in preparation.
2) Physics of ionic thrusters in laboratory.
The previous knowledge about wires-to-airfoils geometries for the thrusters electrodes has been extended with a comprehensive study including several collector shapes and testing of non-uniform emitters arrangements. A different configuration for the ion thrusters – not based on airfoil collectors – is being tested now, leading to some promising preliminary results which are surely worth of further investigation. In fact, the first data indicate the chance of tripling the thrust with respect to a wire-to-airfoil of same size and voltage.
An experiment in a low-speed wind tunnel has been performed on a wire-to-airfoil thruster with the purpose of evaluating changes in performance due to simulated flight conditions and, for the first time, comparing them with a simple physical model of the drift region which is good agreement with the laboratory data.
An experiment about ionization processes between electrodes in a cylindrical geometry is in progress with the aim of creating a reference for the theoretical and numerical ionization studies.
Different techniques for measuring thrust, electrical parameters and flow characteristic are being tested in this phase of the research program, also including particle image velocimetry measures on electrodes systems of different sizes, shapes and materials.
3) Testing ionic thrusters against environmental conditions.
For this recently opened branch of the project, different laboratory configurations are being prepared for testing the ion thrusters performance against wide changes of the external conditions such as air pressure, temperature, humidity, radiations. These experiments will also include insulation tests and studies of the electrodes aging.
4) Further activities
As a preliminary work for the future work packages, some activities dealing with the design of a demonstrator airhsip and the following stratospheric applications have already started.
A novel design technique for airships featuring ion-thrusters has been presented, with a first application to the sizing of a low-altitude demonstration mission.
Development has also begun on ultra-lightweight power supply units to power the demonstrator's on-board ion thrusters.
In the field of theoretical and numerical modeling of the electric discharge leading to propulsive effects, the results beyond the state of the art include a fast 2D code for the study of some ion collector geometries and a study about the effects of different plasma kinetic models in corona discharge simulations. The work in this field continues along several directions, all of which require further research.
In the field of exploration of innovative electrode geometries and ionization concepts in laboratory, detailed results have been obtained about a wide class of airfoil collectors coupled with non-uniform arrangements of the ion emitters. An optimized thruster has been tested in a wind tunnel determining its behaviour in presence of a low and realistic flight velocity and interpreting these results by means of a simple theoretical model. Finally, collectors of new geometry have been recently introduced, leading to remarkable improvements in the thrusters performance, as for example tripling the thrust with respect to an optimized wire-to-airfoil system under the same conditions. The research is in progress, in order to lead to thrusters suitable for the intended applications.
In the field of exploration of innovative electrode geometries and ionization concepts in laboratory, detailed results have been obtained about a wide class of airfoil collectors coupled with non-uniform arrangements of the ion emitters. An optimized thruster has been tested in a wind tunnel determining its behaviour in presence of a low and realistic flight velocity and interpreting these results by means of a simple theoretical model. Finally, collectors of new geometry have been recently introduced, leading to remarkable improvements in the thrusters performance, as for example tripling the thrust with respect to an optimized wire-to-airfoil system under the same conditions. The research is in progress, in order to lead to thrusters suitable for the intended applications.