Academic literature on the topic 'Combustion transcritique'
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Dissertations / Theses on the topic "Combustion transcritique":
Gaillard, Pierre. "Interfaces diffuses et flammes transcritiques LOX/H2." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066510/document.
In cryogenic engines, the propellants are refrigerated and stored liquid in order to limit the dimension of the tanks. They are pressurized by turbopumps before their injection in the combustion chamber. To increase the efficiency of the engines, the chamber pressure is increased and can be above the critical pressure of the propellants. This combustion regime is called transcritical. It exhibits some properties of diphasic injection with a high density core jet but does not have a phenomenon of atomization. The study of the oxygen transition from dense to light has been the main objectives of this thesis. In supercritical regime, the width of this transition decreases with the pressure till it reaches the critical pressure where it becomes infinitely thin. The lack of discretization in the zone of strong gradients leads to numerical instabilities. This situation is analog from a numerical point of view to a liquid-vapor interface. Thus, in this thesis we have extented the diffuse interface methods to the supercritical regime. The second gradient method introduced by van der Waals has allowed the simulation of subcritical and supercritical flames. The multifluid approach has been implemented in the solver CEDRE for the computation of a large eddy simulation of the experimental bench MASCOTTE in supercritcal conditions
Ruiz, Anthony. "Simulations Numériques Instationnaires de la Combustion Turbulente et Transcritique dans les Moteurs Cryotechniques." Phd thesis, Institut National Polytechnique de Toulouse - INPT, 2012. http://tel.archives-ouvertes.fr/tel-00691975.
Lechner, Valentin. "Experimental study of LOX/CH4 flames in rocket engines." Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPAST040.
Using methane as a fuel in rocket engines would have many advantages but the combustion with pure oxygen at high pressure remains poorly understood. From a thermodynamic point of view, methane and oxygen share very similar critical point values, making it challenging to predict propellant mixing, flame anchoring, stability and structure. Moreover, when methane is injected in excess, aerosols can be produced, which can clog the lines, damage the turbine, and reduce the efficiency.Therefore, a thorough update of the knowledge of LOX/CH4 combustion is necessary. These challenges are tackled within the consortium composed of EM2C laboratory, ONERA, CNES, and ArianeGroup. Two test campaigns are carried out at the MASCOTTE facility from ONERA, aiming to study three central topics: the flame structure, wall heat transfers, and aerosol production. To this end, various experimental diagnostics are implemented simultaneously during high-pressure hot-fire tests.Various imaging diagnostics are implemented to analyze the flame structure and the dense liquid jets. Despite the acquisition difficulties encountered in these extreme conditions, the analyses reveal a complex flame structure. In the subcritical regime, atomization and evaporation mechanisms dominate. The flame is much more opened and longer than at higher pressures, where diffusive mixing mechanisms prevail. Characterizing flame anchoring remains a challenge. A water ice ring surrounding, and masking, the flame foot has been identified. Formation mechanisms are proposed, and a growth/destruction temporal cycle is highlighted. Its presence strongly affects flame visualizations, and may lead to misinterpretations of its topology.Laser-induced phosphorescence (LIP) is implemented for the first time at MASCOTTE. Various LIP methods exist, but they are not well suited to the MASCOTTE conditions: wide temperature range, thermal transients, and two-phase flow environment favoring laser absorption/diffusion. Therefore, a specific method, the Full Spectrum Fitting method (FSF method), has been developed. It exploits the spectral dependence on temperature, enabling instantaneous measurements from 100 to 900 K with a precision of 17 K, with no dependence on the laser excitation energy. A detailed data analysis highlights the predominant wall heat transfer modes, studies the influence of the operating points, and compares the experimental data with a wall heat transfer model, which is particularly well suited for deducing the convective properties of the flow.Three diagnostics are used to characterize aerosols. An intrusive probe samples particles and burnt gases downstream of the flame. The particles are sampled on TEM grids and analyzed by Transmission Electron Microscopy. Detailed images of the aerosol morphology reveal that the particles are soot. Combustion products are analyzed by gas chromatography. This makes it possible to identify soot precursor molecules such as benzene and acetylene. Soot are quantified temporally by laser extinction. A dedicated post-processing method is developed and various hypotheses are discussed to explain the spatial variations of the soot production downstream of the flame
Gonzalez, Flesca Manuel. "Contributions en simulation, expérimentation et modélisation destinées à l’analyse des instabilités de combustion hautes fréquences des moteurs fusées à ergols liquides." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLC088/document.
This research concerns some of the issues raised by high frequency combustion instabilities in rocket engines. These instabilities are known to have detrimental effects leading, in some cases, to the destruction of the propulsion system. To avoid the appearance of such instabilities it is important to gain an understanding of the processes driving such dynamical phenomena. One has to consider the complex coupling between injection, combustion and the acoustic resonances of the system. The present work contributes to this objective by developing three items.The first deals with numerical simulations of non-reactive and reactive jets submitted to different modulation conditions to understand the interaction between jets, flames and their environment. Numerical simulations of non-reactive round jets as well as more complex flames formed by coaxial injectors operating under transcritical conditions were carried out using large eddy simulation (LES) adapted to real gas situations by making use of the AVBP-RG flow solver. Round jets were submitted to transverse velocity fluctuations. It has been found that for all amplitudes and frequencies of modulation, the modulated jet is deformed and oscillates. This behavior can be represented by a model. The coaxial flames were submitted to mass flow rate and pressure modulation. For these cases it has been found that the modulation induces variations of the global heat release rate. A mathematical relationship between the modulated parameters and the heat release rate has been proposed.The second item includes experimental investigations. For this purpose a New Pressurized Coupled Cavities (NPCC) laboratory test rig has been developed. The possible coupling between the plenum and the thrust chamber was studied. A model, linking pressure and velocity fluctuations between the plenum and the thrust chamber, has been developed. The laboratory test rig was also used to gather some knowledge on the levels of damping and the damping coefficients could be determined.The last item of this document deals with the development of a reduced order dynamical model which includes some of the driving and damping mechanisms of high frequency combustion instabilities. This dynamical description was implemented in a high frequency stability code (STAHF). This code was used to examine a 87 MW liquid rocket engine (BKD operated at DLR, Germany) exhibiting high frequency oscillations. After the adjustment of some control parameters, STAHF was able to retrieve some the features observed in experiments carried out at DLR
Ruiz, Anthony. "Unsteady Numerical Simulations of Transcritical Turbulent Combustion in Liquid Rocket Engines." Thesis, Toulouse, INPT, 2012. http://www.theses.fr/2012INPT0009/document.
In the past fifty years, most design parameters of the combustion chamber of Liquid Rocket Engines (LREs) have been adjusted without a detailed understanding of combustion phenomena, because of both limited experimental diagnostics and numerical capabilities. The objective of the present thesis work is to conduct high-fidelity unsteady numerical simulations of transcritical reacting flows, in order to improve the understanding of flame dynamics in LRE, and eventually provide guidelines for their improvement. First real-gas thermodynamics and its impact on numerical schemes are presented. As Large-Eddy Simulation (LES) involves filtered equations, the filtering effects induced by real-gas thermodynamics are then highlighted in a typical 1D transcritical configuration and a specific real-gas artificial dissipation is proposed to smooth transcritical density gradients in LES. Then, a Direct Numerical Simulation (DNS) study of turbulent mixing and combustion in the near-injector region of LREs is conducted. In the non-reacting case, vortex shedding in the wake of the lip of the injector is shown to play a major role in turbulent mixing, and induces the formation of finger-like structures as observed experimentally in similar operating conditions. In the reacting case, the flame is attached to the injector rim without local extinction and the finger-like structures disappear. The flame structure is analyzed and various combustion modes are identified. Finally, a LES study of a transcritical H2/O2 jet flame, issuing from a coaxial injector with and without inner recess, is conducted. Numerical results are first validated against experimental data for the injector without recess. Then, the recessed configuration is compared to the reference solution and to experimental results, to scrutinize the effects of this design parameter on combustion efficiency
Yang, Songzhi. "Modeling of Diesel injection in subcritical and supercritical conditions." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLC045/document.
To satisfy latest stringent emission regulations, important progress is still be expected from internal combustion engines. In addition, improving engine efficiency to reduce the emission and fuel consumption has become more essential than before. But many complex phenomena remain poorly understood in this field, such as the fuel injection process. Numerous software programs for computational fluid dynamics (CFD) considering phase change (such as cavitation) and injection modelling, have been developed and used successfully in the injection process. Nevertheless, there are few CFD codes able to simulate correctly transcritical conditions starting from a subcritical fuel temperature condition towards a supercritical mixture in the combustion chamber. Indeed, most of the existing models can simulate either single-phase flows possibly in supercritical condition or two-phase flows in subcritical condition; lacking therefore, a comprehensive model which can deal with transcritical condition including possible phase transition from subcritical to supercritical regimes, or from single-phase to two-phase flows, dynamically. This thesis aims at dealing with this challenge. For that, real fluid compressible two-phase flow models based on Eulerian-Eulerian approach with the consideration of phase equilibrium have been developed and discussed in the present work. More precisely, a fully compressible 6-equation model including liquid and gas phases balance equations solved separately; and a 4-equation model which solves the liquid and gas balance equations in mechanical and thermal equilibrium, are proposed in this manuscript. The Peng-Robinson equation of state (EoS) is selected to close both systems and to deal with the eventual phase change or phase transition. Particularly, a phase equilibrium solver has been developed and validated. Then, a series of 1D academic tests involving the evaporation and condensation phenomena performed under subcritical and supercritical conditions have been simulated and compared with available literature data and analytical results. Then the fully compressible two-phase flow models (6-Equation and 4-Equation systems) have been employed to simulate the cavitation phenomena in a real size 3D nozzle to investigate the effect of dissolved N2 on the inception and developing of cavitation. The good agreement with experimental data proves the solver can handle the complex phase change behavior in subcritical condition. Finally, the capability of the solver in dealing with the transcritical injection at high pressure and temperature conditions has been further validated through the successful modelling of the engine combustion network (ECN) Spray A injector