Combustion machine learning: Principles, progress and prospects

Inverse heat transfer method applied to capacitively cooled rocket thrust chambers

Large-eddy simulations are carried out for the coaxial injection of liquid nitrogen and preheated hydrogen at supercritical pressures. The conditions are similar to that in typical liquid-propellant rocket combustors. By using nitrogen as a model gas, the mixing process is studied without the interference with chemical reactions. An analysis of the thermodynamic conditions that arise in the shear layer reveals that local phase separation may occur if the injection condition is transcritical. A novel volume-translation method on the basis of the cubic Peng–Robinson equation of state is introduced for the use in multispecies large-eddy simulations and is tested for both trans- and supercritical injection conditions. The new thermodynamic model corrects the deficiencies of the Peng–Robinson equation of state in the transcritical regime at minimal extra computational cost. Two independently developed large-eddy simulation codes are used for the simulations and the results are compared. The outcome indicates t...

Large-Eddy Simulation of Coaxial LN2/GH2 Injection at Trans- and Supercritical Conditions

Turbulent combustion will remain central to the next generation of combustion devices that are likely to employ blends of renewable and fossil fuels, transitioning eventually to electrofuels (also referred to as e-fuels, powerfuels, power-to-x, or synthetics). This paper starts by projecting that the decarbonization process is likely to be very slow as guided by history and by the sheer extent of the current network for fossil fuels, and the cost of its replacement. This transition to renewables will be moderated by the advent of cleaner engines that operate on increasingly cleaner fuel blends. A brief outline of recent developments in combustion modes, such as gasoline compression ignition for reciprocating engines and sequential combustion for gas turbines, is presented. The next two sections of the paper identify two essential areas of development for advancing knowledge of turbulent combustion, namely multi-mode or mixed-mode combustion and soot formation. Multi-mode combustion is common in practical devices and spans the entire range of processes from transient ignition to stable combustion and the formation of pollutants. A range of burners developed to study highly turbulent premixed flames and mixed-mode flames, is presented along with samples of data and an outline of outstanding research issues. Soot formation relevant to electrofuels, such as blends of diesel-oxymethylene ethers, hydrogen-methane or ethylene-ammonia, is also discussed. Mechanisms of soot formation, while significantly improved, remain lacking particularly for heavy fuels and their blends. Other important areas of research, such as spray atomization, turbulent dense spray flames, turbulent fires, and the effects of high pressure, are briefly mentioned. The paper concludes by highlighting the continued need for research in these areas of turbulent combustion to bring predictive capabilities to a level of comprehensive fidelity that enables them to become standard reliable tools for the design and monitoring of future combustors.

Challenges for turbulent combustion

A systematic approach to high-fidelity modeling and efficient simulation of supercritical fluid mixing and combustion

A comparison of the numerical predictions of several groups modeling the reacting flow inside a gaseous methane/gaseous oxygen single-element rocket combustion chamber is conducted. The focus is pl...

Numerical Investigation of Reacting Flow in a Methane Rocket Combustor: Turbulence Modeling

Time-resolved flow field and thermal loads in a single-element GOx/GCH4 rocket combustor

The flow and combustion in a GCH4/GOX single-element rocket combustor is analysed by several groups using different numerical models and tools. The tools and simulation setups vary with respect to modeling fidelity and computational expense. A short overview of the tools and the individual simulation setups is given. The focus of the paper is the comparison of the results obtained by the different groups as well as with experimental data. This encompasses the study of specific features of the combustor flow among the different simulations, as well as the validation with typical rocket engine design and performance parameters, such as wall heat flux and combsution pressure, gained from hot firing tests.

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Numerical Investigation of Flow and Combustion in a Single Element GCH4/GOx Rocket Combustor

Under rocket-relevant conditions, real-gas effects and thermodynamic nonidealities are prominent features of the flow field. Experimental investigations indicate that phase separation can occur, de...

Single-Phase Instability in Non-Premixed Flames Under Liquid Rocket Engine Relevant Conditions

Propellant injection and turbulent combustion in high-pressure engines is often dominated by real-gas effects. However, previous studies suggested that the departure of the fluid properties from an ideal gas behavior has only a limited effect on the laminar flame structure. This is due to the fact that chemical reactions take place in the flame zone where the temperature is sufficiently high and molecular interactions are negligible, i.e., the ideal gas assumption is valid. On the other hand, various experimental and numerical studies of injection processes at high-pressure conditions demonstrated that real-gas effects can have a strong impact on the turbulent flow. Mixing is influenced by the rapid change of fluid properties. In this work, we exploit the gap in the fidelity of the thermodynamics model needed to describe the laminar flame structure and that needed to describe the turbulent flow field. We then propose a new real-gas flamelet model with increased numerical performance. The computational cost of the new formulation is not significantly higher than that of an ideal gas simulation. The performance of the method is analyzed and the error that is introduced by our assumptions is assessed by comparison to more complete modeling. Finally, the method is used to simulate a turbulent jet flame emanating from a coaxial injector at supercritical pressure and cryogenic oxidizer temperature. The results are compared with experimental OH∗ images giving evidence of the suitability of the present method.

Julian Zips

Papers

Numerical Investigation of Reacting Flow in a Methane Rocket Combustor: Turbulence Modeling

Time-resolved flow field and thermal loads in a single-element GOx/GCH4 rocket combustor

Numerical Investigation of Flow and Combustion in a Single Element GCH4/GOx Rocket Combustor

Single-Phase Instability in Non-Premixed Flames Under Liquid Rocket Engine Relevant Conditions

Efficient Thermo-Chemistry Tabulation for Non-Premixed Combustion at High-Pressure Conditions