Characterization of Liquid Impinging Jet Injector Sprays for Bi-Propellant Space Propulsion: Comparison of PDI and High-Magnification Shadowgraphy

[EN] Impinging jet sprays are investigated in the reference case of like-doublet injector, for application to bi-propellant combustion. Green propellants are considered, namely ethanol as a fuel and hydrogen peroxide as an oxidizer, that is well represented by water. This study reports original comparisons between standard spray characterization (PDI) and high-magnification shadowgraphy of the spray (2.5 x 3.2 mm, 2.5 µm per pixel) based on short laser backlight illumination (5 ns). Shadowgraphy images describe accurately the inner spray structure and provide the size and velocity of droplets. This diagnostic is used to analyse the influence of jet momentum (driven by injection pressure) on impinging jet atomization, as well as the evolution of spray topology, drop size distribution and average diameter along the spray centreline. The application of shadowgraphy to the dense region of water and ethanol sprays shows the different atomization behaviour of these two fluids with respect to their surface tension. Elliptical droplets are characterized inside the spray, which confirms the interest of a direct visualization of droplets in such dense sprays.The authors wish to acknowledge the support of CNES (French Space Agency).Boust, B.; Michalski, Q.; Claverie, A.; Indiana, C.; Bellenoue, M. (2017). Characterization of Liquid Impinging Jet Injector Sprays for Bi-Propellant Space Propulsion: Comparison of PDI and High-Magnification Shadowgraphy. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat Politècnica de València. 488-495. https://doi.org/10.4995/ILASS2017.2017.5001OCS48849

Étude expérimentale et modélisation des pertes thermiques pariétales lors de l'interaction flamme–paroi instationnaire

Throughout this work, unsteady flame–wall interaction is studied experimentally in both laminar and turbulent regimes, in order to improve current knowledge and provide reference data for modelling and simulation. First, an equation for thermal head-on flame quenching is derived from the energy balance in quenched zone. Based on heat conduction, this model is confirmed by simulating the combustion of gaseous mixture in a spherical vessel. Additionally, a model for wall heat losses is developed in collaboration with RENAULT, based on a new approach of heat conduction resulting from gas–wall collisions. This model is validated in both laminar and turbulent regimes, and improved in order to account for the influence of gas dynamics on wall heat losses in combustion chambers.Au cours de ces travaux, l'interaction flamme-paroi instationnaire a été étudiée expérimentalement en régime laminaire et turbulent, pour comprendre les phénomènes mis en jeu et fournir des données de référence pour la modélisation et la simulation. D'une part, le coincement frontal d'origine thermique a été décrit à l'aide d'un modèle basé sur un bilan d'énergie dans les gaz frais. Cette modélisation purement conductive du coincement de flamme a été confirmée par une simulation de la combustion de prémélange dans une enceinte sphérique. D'autre part, un modèle de pertes thermiques pariétales a été proposé via une approche originale de la conduction thermique, qui apparaît comme le résultat statistique du rebond des molécules de gaz sur la paroi. Développé en collaboration avec RENAULT, ce modèle validé en régime laminaire et turbulent a fait l'objet d'améliorations pour tenir compte de l'aérodynamique locale qui pilote les échanges thermiques aux parois des chambres de combustion

Etude expérimentale et modélisation des pertes thermiques pariétales lors de l'interaction flamme-paroi instantannaire

Au cours de ces travaux, l'interaction flamme-paroi instationnaire a été étudiée expérimentalement en régime laminaire et turbulent, pour comprendre les phénomènes mis en jeu et fournir des données de référence pour la modélisation et la simulation. D'une part, le coincement frontal d'origine thermique a été décrit à l'aide d'un modèle basé sur un bilan d'énergie dans les gaz frais. Cette modélisation purement conductive du coincement de flamme a été confirmée par une simulation de la combustion de prémélange dans une enceinte sphérique. D'autre part, un modèle de pertes thermiques pariétales a été proposé via une approche originale de la conduction thermique, qui apparaît comme le résultat statistique du rebond des molécules de gaz sur la paroi. Développé en collaboration avec RENAULT, ce modèle validé en régime laminaire et turbulent a fait l'objet d'améliorations pour tenir compte de l'aérodynamique locale qui pilote les échanges thermiques aux parois des chambres de combustion.Throughout this work, unsteady flame wall interaction is studied experimentally in both laminar and turbulent regimes, in order to improve current knowledge and provide reference data for modelling and simulation. First, an equation for thermal head-on flame quenching is derived from the energy balance in quenched zone. Based on heat conduction, this model is confirmed by simulating the combustion of gaseous mixture in a spherical vessel. Additionally, a model for wall heat losses is developed in collaboration with RENAULT, based on a new approach of heat conduction resulting from gas wall collisions. This model is validated in both laminar and turbulent regimes, and improved in order to account for the influence of gas dynamics on wall heat losses in combustion chambers.POITIERS-BU Sciences (861942102) / SudocSudocFranceF

Influence of Operating Conditions and Residual Burned Gas Properties on Cyclic Operation of Constant-Volume Combustion

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Effect of Fuel Properties on the Combustion of Storable Bipropellants : Alkanes, Ethanol with Hydrogen Peroxide

International audienceRecently, the interest in storable propellants for rocket engines has been driven by the need of cost reducing of space launch: safety, easier handling, and gain in mass structure. Therefore, reduced hazards liquid propellants are considered such as hydrogen peroxide in association with green fuels (kerosene or ethyl alcohol) for propulsion. To this purpose, test benches at lab-scale have been developed at PPrime Institute (Poitiers, France): the one used in the present study is dedicated to the combustion of non-hypergolic propellants at moderate mass-flow rate (ACSEL test bench). The spray is generated by impingement of liquid jets in two configurations: either like doublet or unlike triplet. Both configurations are being studied and implemented in reactive tests with HTP875 (High Test Peroxide of 87.5% by weight) as oxidizer and, respectively, ethanol, iso-octane, and n-decane (as a pure alkane substitute of a kerosene) fuels. The injector plate is implemented in a 105 mm long combustion chamber with different nozzle throat diameters. Tests cover a range of equivalence ratio based on stoichiometry from 0.6 to 2.1 with imposed total mass flow of 15 to 20 g/s. A comparison of the combustion performances and stability is proposed in terms of chamber pressure, total mass-flow rate, equivalence ratio, and characteristic velocity. A focus is given to the effect of the fuel properties on the combustion at steady regime, considering first the effect of the miscibility of the fuel and the oxidizer, and secondly its volatility

Optimization of a Catalytic Chamber for H2O2 Decomposition Based on Beads

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Effect of Injector Design on the Combustion of Ethanol and Hydrogen-Peroxide Sprays

International audienceThis paper describes the injection and combustion behavior of liquid reactants---ethanol and hydrogen peroxide---in relevant conditions for storable bi-propellant space thrusters. Particularly, this study points out the comparison between two fundamental injector designs based on impinging-jet atomization. First, like-doublet injection generates separate sprays of oxidizer and fuel that need to undergo vaporization, mixing, and chemical reaction. Second, unlike-triplet injection generates a unique spray of bipropellant mixture that only has to vaporize before burning. The effect of these two injection processes is compared in terms of spray pattern, drop size and velocity, as well as combustion efficiency. For this purpose, direct and [Math Processing Error]-filtered visualizations of the reacting flow are performed, and the characteristic velocity is computed from experiments at combustion pressure 0.6 MPa and overall equivalence ratio in the range 0.5--2.2

Experimental Comparison of Hydrogen Peroxide Catalysts for a Hydrogen Peroxide/n-Decane Bipropellant Combustor

International audienceThis paper presents an experimental comparison of the catalytic activity of different alumina-based catalysts for highly concentrated hydrogen peroxide (85% w.) decomposition. Three pellet-shaped catalysts with manganese oxide or platinum active phases were considered. Their performances were investigated by measuring the temperature increase in the catalytic bed after several injections of 100  μL of hydrogen peroxide in a constant-volume chamber. This setup evidenced a loss of reactivity after several injections, which was due to water poisoning. Pellets were, then, tested in a small-scale catalytic chamber plugged into a combustor. Hydrogen peroxide was injected at various mass flow rates (from 4.5 to 9.0  g⋅s−1) through the catalytic chamber. The temperature evolution at the exhaust was recorded via a thin thermocouple (1 mm) and used to compare the activity of the different catalysts. The specific surface area, the active phase amount, and the platinum dispersion were measured after the tests. Catalysts experienced a decrease of those values, evidencing the ageing of the catalytic material. Preliminary combustion tests were performed for all catalysts in a hydrogen peroxide/n-decane bipropellant combustor. Results were compared to evaluate the influence of the efficiency of the catalytic system on combustion performance

Development of 1D Model of Constant-Volume Combustor and Numerical Analysis of the Exhaust Nozzle

Pressure gain combustion cycles are under the spotlight due to their higher theoretical cycle thermal efficiency compared to conventional machines. Under this prism, a constant-volume combustor (CVC) prototype supplied with a mixture of air and liquid iso–octane was developed. The efforts of the current study were focused on both creating a 1D model of the experimental test rig for the CVC analysis and a 3D numerical simulation of the exhaust system. The goal of the study was to retrieve the total outlet quantities of the combustor, which would otherwise be difficult to assess experimentally, and to investigate the pulsating flow field at the outlet. First, a thorough description of the reduced order model was accompanied with the model’s validation using the available experimental data of the chamber. Then, the resulting outlet stagnation properties of the CVC were imposed as spatially averaged transient boundary conditions to the 3D exhaust flow domain. The unsteady Reynolds–averaged Navier–Stokes equations were solved for a sufficient number of periods, and the assessment of the out-take system in terms of losses and attenuation was conducted. In conclusion, the analysis of the combustor’s outflow will pave the way for an effective future design of the CVC exhaust system