Long term electricity storage by oxygen liquefaction and LNG oxy-combustion

The paper proposes an innovative scheme exploiting oxygen liquefaction as a means for storing excess electricity generation from renewable sources. Liquid oxygen is then used in an oxy-combustion process with LNG to generate electricity when renewable energy generation is below the demand. An equivalent round trip efficiency is defined to make it possible comparing the system performances with hybrid plants including conventional generation and storage. The proposed scheme exhibits very high equivalent round trip efficiency, giving the system operators the opportunity to integrate more and more renewable energy generation inside power systems. Liquefied carbon dioxide and water are byproducts of the process. The size of the plant and of the storage tanks needed for a 4 TWh yearly demand with a peak around 800 MW is compatible with state-of-the-art systems used for LNG storage in similar size gas power plants

Progress on the Development of an Iodine-fed Hall Effect Thruster

The paper deals with the results of an ongoing activity carried out by the Department of Civil and Industrial Engineering (DICI) and the Department of Chemistry and Industrial Chemistry (DCCI) of the University of Pisa (UniPi) in collaboration with SITAEL SpA, aimed at the development of technologies for Iodine-fed Hall Effect Thrusters. A feeding system architecture is described and the results of reduced order numerical models of the feeding system are illustrated, in both steady and unsteady state conditions. An activity for iodine interaction with materials is in progress. The experimental setups for material characterization tests are described. Material samples can be heated from room temperature up to 300 °C and exposed to iodine at high (soakage test) or low (flow test) concentration, simulating the condition at which the materials will undergo in the propulsion system, in the vacuum facility or in the spacecraft. Calibration and preliminary soakage test results are illustrated. On the thruster unit side, the candidate thruster and cathode are presented along with the modifications needed to operate them on iodine. Finally, a description of the foreseen test campaign and associated facilities is presented

Fundamental Scaling Laws for Electric Propulsion Concepts - Part 2: MPD Thrusters

As a second part of multi-phase study aimed at highlighting the fundamental scaling laws relevant to the main types of plasma thrusters, this paper focuses on magnetoplasmadynamic thrusters. The basic principles underlying the operation of different types of plasma devices are first recalled. The ideal scaling trends of self-field and applied-field MPD thrusters are outlined. Real thruster behaviour is then considered and the role of the "onset" phenomena as the principal performance-limiting factor in this class of thrusters is highlighted. Different theories on the onset are reviewed. A general stability criterion proposed by Tikhonov is discussed. Results of recent activities carried aut by the authors to obtain a better insight into the onset problem are then described. Large-scale magnetohydrodynamic instabilities have been shown to develop whenever the current rises beyond a threshold value. These instabilities have features of helical kink modes and their occurrence can be described by the Kruskal-Shafranov criterion. The growth of these modes is deemed to be the cause of the large loss of efficiency observed in MPD thrusters when operating at high current. The connection between Tikhonov's criterion and the Kruskal- Shafranov limit is discussed. This insight may suggest better ways to control or postpone the onset so as to achieve higher efficiency levels

A New Hypersonic High Enthalpy Wind Tunnel

A hypersonic high enthalpy, arc heated, blow-down wind tunnel has been recently developed at Centrospazio in order to perform experiments in the low to medium Reynolds number range (10^4 - 10^6). The tunnel is capable of delivering Mach 6 flows up to 2-5 MJ/kg in specific total enthalpy on an effective test section 60 mm in diameter. It operates in pulsed quasi-steady mode, with running times ranging from 10 to 30 ms. The uniformity of the potential core of the flowfield has been experimentally assessed in different operational points of the facility, demonstrating good steadyness and repeatability of the test conditions. Activities are presently ongoing aimed at defining the wind tunnel overall capabilities by investigating in detail its characteristics as well as at expanding its operational envelope

Experimental Investigation of Shock Wave/Boundary Layer Interactions over an Artificially Heated Model in Hypersonic Flow

Experimental tests have been carried out to analyze the effect of wall-to-total temperature ratio on the characteristics of a fully laminar shock-wave/boundary-layer interaction in a Mach 6 high enthalpy flow. Test cases were run in a new high-enthalpy arc-heated wind tunnel developed at Centrospazio in the framework of the ESA/FESTIP program. In order to heat-up the model surface a high temperature radiator movable on a remotely controlled displacement system was employed. As the investigation was focused on local dynamic and thermal loads, the model was instrumented with pressure transducers and thin film gauges. The experimental results were compared with numerical simulations carried out at CIRA on the same test cases. Pressure measurements showed a fair agreement with numerics, even if the accuracy of the measurements did not allow to discriminate the differences within the different wall temperature cases numerically calculated. Heat flux data are consistently higher than what calculated by CIRA: further investigation is presently under way to identify the reason of this difference, however the main reason is believed to be related to relaxation phenomena of the frozen flow on the model surface. Additional investigation aimed at evaluating the importance of this effect are presently underway

Experimental characterization for hypersonic testing

The preliminary experimental characterization of the flow field developing in the test section of a small high enthalpy arc-heated Mach 6 tunnel has been carried out in terms of Mach number and local flow velocity angle. Measurements have mainly been obtained in cold flow conditions (no arc), though a limited number of tests has also been performed in hot flow conditions (Ttot=1800 K). To this purpose Pitot and yawmeter probes have been employed: in particular a theoretical model for using uncalibrated conical yawmeters in hypersonic flow has been developed. Total temperature measurements could not be obtained with the necessary accuracy due to problems of response time and survivability of thermocouples. The test campaign is presently underway and will include total temperature measurements performed by means of a fast-response total temperature probe based on transient thin-film heat flux gauge technology. List of Symbols A nozzle area h heat transfer coefficient k Newtonian coefficient M Mach number n local surface normal vector p pressure &q heat flux r nozzle radius R gas constant (288 J kg-1 K-1 for air) T temperature V velocity α,β local velocity vector angles χ Mach unsteadiness factor γ specific heat ratio ρ density θ angle between undisturbed flow and local surface normal Θ vibrational excitation temperature constan

A New Hypersonic High Enthalpy Wind Tunnel

A hypersonic high enthalpy, arc heated, blow-down wind tunnel has been recently developed at Centrospazio in order to perform experiments in the low to medium Reynolds number range (10^4 - 10^6). The tunnel is capable of delivering Mach 6 flows up to 2-5 MJ/kg in specific total enthalpy on an effective test section 60 mm in diameter. It operates in pulsed quasi-steady mode, with running times ranging from 10 to 30 ms. The uniformity of the potential core of the flowfield has been experimentally assessed in different operational points of the facility, demonstrating good steadyness and repeatability of the test conditions. Activities are presently ongoing aimed at defining the wind tunnel overall capabilities by investigating in detail its characteristics as well as at expanding its operational envelope

Development of a Model of Distributed Turboelectric Propulsion System for Transport Aircrafts

The paper deals with the first efforts in developing a model of distributed turboelectric propulsion system for transport aircrafts. A description of all the sub-systems is given: electric power is generated by a power system based on a turbo-alternator; the power is transmitted to a distributed thrust system, consisting of several electric motors moving fans for thrust generation, or to a battery package for electric energy storage. The model of the power system (to be completed) includes the turbo-alternator, the transmission line (with losses) and the electric energy storage system. The model of the thrust system includes the treatment of the boundary layer ingestion by the fans. The first results obtained by the models are illustrated