Real-Gas Effects and Phase Separation in Underexpanded Jets at Engine-Relevant Conditions

Traxinger, Christoph; Banholzer, Matthias; Pfitzner, Michael

doi:10.2514/6.2018-1815

Cited by 16 publications

(17 citation statements)

References 53 publications

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“…Recently Traxinger et al (2018) attempted to shed more light on the effect of real gas modelling within the context of supercritical under-expanded jets, however no quantitative data was reported for the near-nozzle shock structure of under-expanded n-hexane jets investigated by them. To sum up, it should be noted that the ideal gas EoS and fluid properties used in the present study might not be able to capture perfectly all the characteristics of under-expanded hydrogen jets formed by high-pressure (P 0 >30 bar cases) injection of supercritical fluids at their initial state.…”

Section: Discussionmentioning

confidence: 99%

LES and RANS modelling of under-expanded jets with application to gaseous fuel direct injection for advanced propulsion systems

Hamzehloo

Aleiferis

2019

International Journal of Heat and Fluid Flow

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A density-based solver with the classical fourth-order accurate Runge-Kutta temporal discretization scheme was developed and applied to study under-expanded jets issued through millimeter-size nozzles for applications in highpressure direct-injection (DI) gaseous-fuelled propulsion systems. Both large eddy simulation (LES) and Reynoldsaveraged Navier-Stokes (RANS) turbulence modelling techniques were used to evaluate the performance of the new code. The computational results were compared both quantitatively and qualitatively against available data from the literature. After initial evaluation of the code, the computational framework was used in conjunction with RANS modelling (k-ω SST) to investigate the effect of nozzle exit geometry on the characteristics of gaseous jets issued from millimeter-size nozzles. Cylindrical nozzles with various length to diameter ratios, namely 5, 10 and 20, in addition to a diverging conical nozzle, were studied. This study is believed to be the first to provide a direct comparison between RANS and LES within the context of nozzle exit profiling for advanced high-pressure injection systems with the formation of under-expanded jets. It was found that reducing the length of the straight section of the nozzle by 50% resulted in a slightly higher level of under-expansion (~2.6% higher pressure at the nozzle exit) and ~1% higher mass flow rate. It was also found that a nozzle with 50% shorter length resulted in ~6% longer jet penetration length. At a constant nozzle pressure ratio (NPR), a lower nozzle length to diameter ratio resulted in a noticeably higher jet penetration. It was found that with a diverging conical nozzle, a fairly higher penetration length could be achieved if an under-expanded jet formed downstream of the nozzle exit compared to a jet issued from a straight nozzle with the same NPR. This was attributed to the radial restriction of the flow and consequently formation of a relatively smaller reflected shock angle. With the conical nozzle used in this study and a 30 bar injection pressure, an under-expanded hydrogen jet exhibited ~60% higher penetration length compared to an under-expanded nitrogen jet at 100 μs after start of injection. Moreover, the former jet exhibited ~22% higher penetration compared to a nitrogen jet issued through the conical profile with 150 bar injection pressure.

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Section: Discussionmentioning

confidence: 99%

LES and RANS modelling of under-expanded jets with application to gaseous fuel direct injection for advanced propulsion systems

Hamzehloo

Aleiferis

2019

International Journal of Heat and Fluid Flow

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“…A major implication for engine operation is that increasing P at a given P inj well beyond the limit of the choked flow is essentially counterproductive, because it lowers the likelihood of autoignition and increases the risk of jet impingement at the walls, which would cause a hike in UHC and CO emissions, 1,4 as well as the risk of phase separation in the fuel stream, 24 which would inhibit mixing. 60 Increasing the pressure levels at fixed P was found to lead to the formation of jets with virtually identical global air-to-fuel ratios and mixing state distributions. The implication here is that, at a given P, P inj should be determined on the basis of the desired fuel injection rate and P ch on the basis of the desired mixture reactivity, which is partly determined by the reactants' concentration and by extension P ch .…”

Section: Discussionmentioning

confidence: 92%

“…A major implication for engine operation is that increasing Π at a given P inj well beyond the limit of the choked flow is essentially counterproductive, because it lowers the likelihood of auto-ignition and increases the risk of jet impingement at the walls, which would cause a hike in UHC and CO emissions, 1,4 as well as the risk of phase separation in the fuel stream, 24 which would inhibit mixing. 60…”

Section: Discussionmentioning

confidence: 99%

The effect of high-pressure injection variations on the mixing state of underexpanded methane jets

Sakellarakis

Vera-Tudela

Doll

et al. 2020

International Journal of Engine Research

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This work presents a joint experimental and numerical study of global characteristics and mixing behavior of underexpanded methane jets at high-pressure conditions in a Constant Volume Chamber. Injection pressures of 200, 250, and 300 bar and pressure ratios of 4, 5, 6, 8, and 10 at each of those pressures have been investigated. Tracer LIF with acetone as tracer has been applied to experimentally quantify the mixing of methane and quiescent air. In order to exploit the symmetry of the configuration, accompanying simulations have been carried out in Reynolds-Averaged Navier-Stokes framework with the k – w SST turbulence model and real-gas modelling based on the Soave-Redlich-Kwong Equation of State has been employed to account for high-pressure corrections in thermodynamic and caloric properties. The experiments confirm the hyperbolic decay of axial fuel concentration and the Gaussian shape of traverse concentration profiles in the self-similar region of the jets, while simulation results match well with experimentally determined fuel concentration fields. It is found that scaling laws proposed in literature for steady-state jet propagation can qualitatively interpret the effect of injection variations on jet tip penetration and volume. Increasing pressure ratio at fixed injection pressure leads to the formation of slightly richer jets, with slightly smaller mass percentage in the range of air-to-fuel ratios most favorable to autoignition. By contrast, increasing pressure ratio at fixed chamber pressure leads to virtually identical Probability Distribution Functions of local air-to-fuel ratios and the same is observed when employing a fixed pressure ratio at higher pressure levels.

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“…This framework relies on the assumption of a local instantaneous thermodynamic equilibrium. For further details, please refer to Traxinger et al [28,30].…”

Section: Thermodynamic Modelingmentioning

confidence: 99%

Numerical Investigation of Injection, Mixing and Combustion in Rocket Engines Under High-Pressure Conditions

Traxinger

Zips

Stemmer

et al. 2020

Notes on Numerical Fluid Mechanics and Multidisciplinary Design

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The design and development of future rocket engines severely relies on accurate, efficient and robust numerical tools. Large-Eddy Simulation in combination with high-fidelity thermodynamics and combustion models is a promising candidate for the accurate prediction of the flow field and the investigation and understanding of the on-going processes during mixing and combustion. In the present work, a numerical framework is presented capable of predicting real-gas behavior and nonadiabatic combustion under conditions typically encountered in liquid rocket engines. Results of Large-Eddy Simulations are compared to experimental investigations. Overall, a good agreement is found making the introduced numerical tool suitable for the high-fidelity investigation of high-pressure mixing and combustion.

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Real-Gas Effects and Phase Separation in Underexpanded Jets at Engine-Relevant Conditions

Cited by 16 publications

References 53 publications

LES and RANS modelling of under-expanded jets with application to gaseous fuel direct injection for advanced propulsion systems

LES and RANS modelling of under-expanded jets with application to gaseous fuel direct injection for advanced propulsion systems

The effect of high-pressure injection variations on the mixing state of underexpanded methane jets

Numerical Investigation of Injection, Mixing and Combustion in Rocket Engines Under High-Pressure Conditions

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