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This paper presents the authors’ most recent research regarding the feasibility of cooling a 1 kN scaled-down experimental rocket engine, running on gaseous oxygen and gaseous methane, for a ground test. The cooling segment of a rocket engine has always been a delicate problem, increasing the development time and costs of development. Since a series of problems can occur during the first ignition of a rocket engine prototype, removing as many potential issues from the initial test, such as using liquid methane for the cooling system, could result in a more stable experiment. Using water as the cooling agent can contribute to a more accelerated TRL increase of the engine’s subcomponents while reducing the risks taken for a whole assembly test. Thus, the combustion chamber, nozzle, and injector can be tested separately from the final cooling method, which can be added subsequently. In the present work, both a steady and transient CFD combustion simulation of a multicomponent compound, consisting of gaseous oxygen and gaseous methane was conducted in the combustion chamber of a small-scale rocket engine. The simulation is based on PDF-flamelet approach for the oxygen and methane combustion, along with real gas equations for the cooling agent. [ABSTRACT FROM AUTHOR]

The oxidation of H 2 diluted in N 2 with and without 10 % H 2 O or 20 % CO 2 additions are studied at fuel-lean conditions at 100 atm and 500–1000 K in a supercritical-pressure jet-stirred reactor. The mole fractions of H 2 and O 2 are quantified by using micro-gas chromatography (µ-GC). Experiment shows that H 2 oxidation is inhibited at lower temperatures (850–950 K) while it is promoted at higher temperatures (950–1050 K) with 10 % H 2 O additions or 20 % CO 2 additions. In addition, the effect of H 2 O is more significant than that of CO 2. Five models are employed in simulations of the observables. Unfortunately, all of these models fail to capture the effect of H 2 O and CO 2 additions on H 2 oxidation. Pathway and sensitivity analyses of H 2 show that the reactions of H + O 2 + (M) = HO 2 + (M) and H 2 O 2 + (M) = 2OH + (M) dominate the radical production (HO 2 and OH) and H 2 oxidation at 100 atm. A further perturbation of pre-exponential coefficients and collisional factors of these reactions indicates that collisional factors of H 2 O and CO 2 have small effect under the experimental conditions, while a smaller reaction rate for H 2 O 2 + (M) = 2OH + (M) may explain the inhibiting effect of H 2 O and CO 2 additions at lower temperatures. Real-fluid corrections on intermolecular interactions and mixing rules should be further investigated to explain the effect of H 2 O and CO 2 additions. [ABSTRACT FROM AUTHOR]

Numerical predictions of the fuel heating and cavitation erosion location indicators occurring during the opening and closing periods of the needle valve inside a five-hole common rail Diesel fuel injector are presented. These have been obtained using an explicit density-based solver of the compressible Navier-Stokes (NS) and energy conservation equations; the flow solver is combined with two thermodynamic closure models for the liquid, vapour and vapour-liquid equilibrium (VLE) property variation as function of pressure and temperature. The first is based on tabulated data for a 4-component Diesel fuel surrogate, derived from the Perturbed-Chain, Statistical Associating Fluid Theory (PC-SAFT) Equation of State (EoS), allowing for the variation of the physical and transport properties of the fuel with the local pressure and temperature to be quantified. The second thermodynamic closure is based on the widely used barotropic Equation of State (EoS) approximation between density and pressure only and neglects viscous heating. The Wall Adapting Local Eddy viscosity (WALE) LES model was used to resolve sub-grid scale turbulence while a cell-based mesh deformation Arbitrary Lagrangian–Eulerian (ALE) formulation is used for modelling the injector's needle valve movement. Model predictions are found in close agreement against 0-D estimates of the temporal variation of the fuel temperature difference between the feed and hole exit during the injection period. Two mechanisms affecting the temperature distribution within the fuel injector have been revealed and quantified. The first is ought to wall friction-induced heating, which may result to local liquid temperature increase up to fuel's boiling point while superheated vapour is formed. At the same time, liquid expansion due to the depressurisation of the injected fuel results to liquid cooling relative to the fuel's feed temperature; this is occurring at the central part of the injection orifice. The spatial and temporal temperature and pressure gradients induce significant variations in the fuel density and viscosity, which in turn, affect the formed coherent vortical flow structures. It is found, in particular, that these affect the locations of cavitation formation and collapse, that may lead to erosion of the surfaces of the needle valve, sac volume and injection holes. Model predictions are compared against corresponding X-ray surface erosion images obtained from injector durability tests, showing good agreement.

An investigation of the fuel heating, vapor formation, and cavitation erosion location patterns inside a five-hole common rail diesel fuel injector, occurring during the early opening period of the needle valve (from 2 μm to 80 μm), discharging at pressures of up to 450 MPa, is presented. Numerical simulations were performed using the explicit density-based solver of the compressible Navier–Stokes (NS) and energy conservation equations. The flow solver was combined with tabulated property data for a four-component diesel fuel surrogate, derived from the perturbed chain statistical associating fluid theory (PC-SAFT) equation of state (EoS), which allowed for a significant amount of the fuel’s physical and transport properties to be quantified. The Wall Adapting Local Eddy viscosity (WALE) Large Eddy Simulation (LES) model was used to resolve sub-grid scale turbulence, while a cell-based mesh deformation arbitrary Lagrangian–Eulerian (ALE) formulation was used for modelling the injector’s needle valve movement. Friction-induced heating was found to increase significantly when decreasing the pressure. At the same time, the Joule–Thomson cooling effect was calculated for up to 25 degrees K for the local fuel temperature drop relative to the fuel’s feed temperature. The extreme injection pressures induced fuel jet velocities in the order of 1100 m/s, affecting the formation of coherent vortical flow structures into the nozzle’s sac volume.

Graphical abstract Highlights • Hydrothermal flames in a counterflow configuration are studied. • The classic flamelet model is extended to account for the real-fluid effects. • The extended flamelet model is evaluated in both a priori and a posteriori analyses. • Good agreement is achieved between the detailed chemistry and flamelet results. Abstract In this article, hydrothermal flames were studied and an extended flamelet model was developed accounting for the real-fluid effects. The newly formulated real-fluid flamelet/progress variable (FPV) model was evaluated in a laminar counterflow configuration through both a priori and a posteriori analyses. At supercritical conditions, the ideal-gas model results showed a higher flame temperature and intermediate species mass fractions compared to the real-fluid model results in both the detailed chemistry (DC) and FPV approaches. To thoroughly evaluate the real-fluid flamelet library, the a priori tests were carried out under atmospheric and supercritical conditions with different strain rates. The comparisons of tabulated quantities and reference values from DC simulations showed that the real-fluid FPV model can correctly predict the thermal properties and species mass fractions in hydrothermal flames. Finally, the a posteriori analysis showed overall good agreement between the FPV and DC results, verifying the newly proposed real-fluid FPV approach. [ABSTRACT FROM AUTHOR]

In the present numerical study, implicit large eddy simulations (LES) of non-reacting multi-components mixing processes of cryogenic nitrogen and n-dodecane fuel injections under transcritical and supercritical conditions are carried out, using a modified reacting flow solver, originally available in the open source software OpenFOAM®. To this end, the Peng-Robinson (PR) cubic equation of state (EOS) is considered and the solver is modified to account for the real-fluid thermodynamics. At high pressure conditions, the variable transport properties such as dynamic viscosity and thermal conductivity are accurately computed using the Chung transport model. To deal with the multicomponent species mixing, molar averaged homogeneous classical mixing rules are used. For the velocity-pressure coupling, a PIMPLE based compressible algorithm is employed. For both cryogenic and non-cryogenic fuel injections, qualitative and quantitative analyses are performed, and the results show significant effects of the chamber pressure on the mixing processes and entrainment rates. The capability of the proposed numerical model to handle multicomponent species mixing with real-fluid thermophysical properties is demonstrated, in both supercritical and transcritical regimes.

This paper introduces a new model for real gas thermodynamics, with improved accuracy, performance, and robustness compared to state-of-the-art models. It is motivated by the physical insight that in non-premixed flames, as encountered in high pressure liquid propellant rocket engines, mixing takes place chiefly in the hot reaction zone among ideal gases. We developed a new model taking advantage of this: When real fluid behavior only occurs in the cryogenic oxygen stream, this is the only place where a real gas equation of state (EOS) is required. All other species and the thermodynamic mixing can be treated as ideal. Real fluid properties of oxygen are stored in a library; the evaluation of the EOS is moved to a preprocessing step. Thus decoupling the EOS from the runtime performance, the method allows the application of accurate high quality EOS or tabulated data without runtime penalty. It provides fast and robust iteration even near the critical point and in the multiphase coexistence region. The model has been validated and successfully applied to the computation of 0D phase change with heat addition, and a supercritical reactive coaxial LOX/GH 2 single injector. [ABSTRACT FROM AUTHOR]

Nitrogen injection under conditions close vicinity of the liquid-gas critical point is studied numerically. The fluid thermodynamic and transport properties vary drastically and exhibit anomalies in the near-critical regime. These anomalies can cause distinctive effects on heat-transfer and fluid-flow characteristics. To focus on the influence of thermodynamics on the flow field, a relatively low injection Reynolds number of 1 750 is adopted. For comparisons, a reference case with the same configuration and Reynolds number is simulated in the ideal gas regime. The model accommodates full conservation laws, real-fluid thermodynamic and transport phenomena. Results reveal that the flow features of the near-critical fluid jet are significantly different from their counterpart. The near-critical fluid jet spreads faster andmixes more efficiently with the ambient fluid along with a more rapidly development of the vortex pairing process. Detailed analysis at different streamwise locations including both the flat shear-layer region and fully developed vortex region reveals the important effect of volume dilatation and baroclinic torque in the near-critical fluid case. The former disturbs the shear layer and makes it more unstable. The volume dilatation and baroclinic effects strengthen the vorticity and stimulate the vortex rolling up and pairing process. [ABSTRACT FROM AUTHOR]

An investigation of the fuel heating, vapor formation, and cavitation erosion location patterns inside a five-hole common rail diesel fuel injector, occurring during the early opening period of the needle valve (from 2 μm to 80 μm), discharging at pressures of up to 450 MPa, is presented. Numerical simulations were performed using the explicit density-based solver of the compressible Navier–Stokes (NS) and energy conservation equations. The flow solver was combined with tabulated property data for a four-component diesel fuel surrogate, derived from the perturbed chain statistical associating fluid theory (PC-SAFT) equation of state (EoS), which allowed for a significant amount of the fuel's physical and transport properties to be quantified. The Wall Adapting Local Eddy viscosity (WALE) Large Eddy Simulation (LES) model was used to resolve sub-grid scale turbulence, while a cell-based mesh deformation arbitrary Lagrangian–Eulerian (ALE) formulation was used for modelling the injector's needle valve movement. Friction-induced heating was found to increase significantly when decreasing the pressure. At the same time, the Joule–Thomson cooling effect was calculated for up to 25 degrees K for the local fuel temperature drop relative to the fuel's feed temperature. The extreme injection pressures induced fuel jet velocities in the order of 1100 m/s, affecting the formation of coherent vortical flow structures into the nozzle's sac volume. [ABSTRACT FROM AUTHOR]

• Identification of phase instability for diffusion flames on both stable and middle branches. • Analysis of mass and heat diffusion and its impact on presence of unstable phase. • Sensitivity study on the effects of pressure, inlet temperature and diffusion model. The single-phase instability of high-pressure, steady, laminar counterflow diffusion flame is studied using the Vapor–Liquid Equilibrium (VLE) theory. The a posteriori study focuses on the identification of the potentially unstable regions emerging throughout the full combustion states represented by the high-pressure counterflow diffusion flame solution; a specific emphasis is placed on the middle branch solutions which are characteristic of intermediary combustion states. The a posteriori analysis provides useful bounds on the multicomponent phase separation. We use a mixture-fraction space flamelet formulation with real-fluid thermodynamics; the results compare favorably to both a spatial-based flamelet and a two-dimensional direct numerical simulations (DNS) solution, at high-pressure conditions. The a posteriori , single-phase instability for a high-pressure LO2/GH2 flame is investigated by investigating the effects of operating pressure and inlet temperature on the flame structure; then the analysis is extended to a LO2/GCH4 flame to evaluate the fuel effect. It is found that a single-phase instability can appear at both the fuel and oxidizer inlets, and its location and extent is determined by the water vapor concentration and, more importantly, temperature. For the flamelets in the upper burning branch, the size and location of unstable region is nearly invariant to the scalar dissipation rate, while for the flamelets in the middle branch, the instability region near the fuel inlet expands significantly with the decrease of chemical reactivity. [ABSTRACT FROM AUTHOR]

In the present numerical study, implicit large eddy simulations (LES) of non-reacting multi-components mixing processes of cryogenic nitrogen and n-dodecane fuel injections under transcritical and supercritical conditions are carried out, using a modified reacting flow solver, originally available in the open source software OpenFOAM®. To this end, the Peng-Robinson (PR) cubic equation of state (EOS) is considered and the solver is modified to account for the real-fluid thermodynamics. At high pressure conditions, the variable transport properties such as dynamic viscosity and thermal conductivity are accurately computed using the Chung transport model. To deal with the multicomponent species mixing, molar averaged homogeneous classical mixing rules are used. For the velocity-pressure coupling, a PIMPLE based compressible algorithm is employed. For both cryogenic and non-cryogenic fuel injections, qualitative and quantitative analyses are performed, and the results show significant effects of the chamber pressure on the mixing processes and entrainment rates. The capability of the proposed numerical model to handle multicomponent species mixing with real-fluid thermophysical properties is demonstrated, in both supercritical and transcritical regimes. [ABSTRACT FROM AUTHOR]