Hongfa Huo

Counterflow Diffusion Flames of Oxygen and N-Alkane Hydrocarbons (CH4-C16H34) at Subcritical and Supercritical Conditions

This article presents an investigation of counterflow diffusion flames of oxygen and n-alkanes (CH4-C16H34) over the entire thermodynamic fluid regime and a wide range of flow strain rates. The formulation incorporates fundamental thermodynamics and transport theories, along with detailed chemistry. An improved two-point flame-controlling continuation method is employed to capture the complete flame response along the S-curve. Two selected members of the n-alkane family, methane and n-heptane, are studied in detail. The results confirm that the flame thickness () and the global heat-release rate () of oxygen/hydrocarbon systems are closely related to the pressure-weighted strain rate, and . The latter correlation is further modified to account for the pressure effect on peak flame temperature, for the oxygen/methane system, for the oxygen/n-heptane system. The inlet temperature appears to have a negligible effect on flame characteristics. General similarities are developed in the mixture-fraction space in terms of flame temperature, species concentrations, flame thickness, and heat-release rate for all pressures under consideration. This suggests that the flame behaviors at high pressure can be evaluated by their counterpart at low pressure. The common features for the n-alkane family are identified. The flame properties of a given hydrocarbon fuel can be predicted from those of another hydrocarbon fuel at the same flow conditions. The results contribute to the establishment of a tabulated chemistry library for the modeling of supercritical combustion of oxygen and hydrocarbon fuels.

Comprehensive Study of Cryogenic Fluid Dynamics of Swirl Injectors at Supercritical Conditions

A comprehensive study is conducted to enhance the understanding of swirl injector flow dynamics at supercritical conditions. The formulation is based on full-conservation laws and accommodates real...

A Three-Dimensional Analysis of Swirl Injector Flow Dynamics at Supercritical Conditions

1 Graduate Research Assistant, Georgia Institute of Technology, Email: xwang343@gatech.edu. 2 Mechanical Engineer, GE Global Research Center, Niskayuna, NY, 12309 3,4 Postdoctoral fellow, School of Aerospace Engineering 5 William R. T. Oakes Professor and Chair, School of Aerospace Engineering, Fellow AIAA. 1 American Institute of Aeronautics and Astronautics A Three-Dimensional Analysis of Swirl Injector Flow Dynamics at Supercritical Conditions

Large-Eddy Simulation of Supercritical Combustion: Model Validation Against Gaseous H2–O2 Injector

Supercritical combustion has attracted significant interest due to its applications in high-pressure combustion devices. Validation of supercritical combustion modeling, however, has not been well reported because of the lack of experimental data with sufficient spatial and temporal resolution as well as the complexity associated with modeling and simulations. The present work begins to bridge this gap with a systematic examination of gaseous H2–O2 combustion of a shear coaxial injector at supercritical conditions, using both large-eddy simulation and detached-eddy simulation approaches. The formulation accommodates the full conservation laws and real-fluid thermodynamics and transport theories. Turbulence/chemistry interactions are treated by means of the flamelet and flamelet/progress-variable approaches. A nonpremixed jet flame (Sandia flame D) was first considered for code validation at ideal-gas conditions. The gaseous H2–O2 combustion at supercritical conditions was then studied systematically using...

Large Eddy Simulation of Supercritical Combustion of Liquid Oxygen and Kerosene of a Bi-Swirl Coaxial Injector

Supercritical combustion of Liquid OXygen (LOX) and kerosene with a bi-swirl coaxial injector is studied using Large-Eddy Simulation (LES) associated with Flamelet model. The injector configuration is derived from main injectors of the RD-0110 engine. Swirling oxygen at 120 K and swirling kerosene at 300 K are introduced from the injector to the combustion chamber at compressed liquid states. The operating pressure is 10 MPa. A three-component surrogate consisting of n-decane/n-propylbenzene/n-propylcyclohexane (74%/15%/11% by mole) is used to represent kerosene. A detailed chemistry kinetics with 209 species and 1673 elemental reactions is employed to establish the flamelet library. The injector near-field flow and flame structures are examined and discussed in detail to enhance understanding of supercritical combustion of liquid oxygen and kerosene with a bi-swirl coaxial injector. Suggestions are also made for future studies of supercritical combustion of dual-liquid propellants associated with bi-swirl coaxial injectors.

Supercritical LOX/Methane Combustion of a Shear Coaxial Injector

A good understanding of the flow dynamics and the flame stabilization mechanism in a liquid rocket engine is essential for the development of high-performance liquid rocket engines. The current work attempts to improve the understanding of LOX/CH4 combustion dynamics at conditions similar to contemporary liquid rocket engines. Three-dimensional Large-Eddy Simulation (LES) of LOX/Methane combustion in a shear coaxial injector is performed, focusing on the identification of the flame stabilization mechanism of the non-premixed LOX/Methane flames at supercritical conditions. The flamelet and the flamelet/progress-variable approaches are considered. Extreme caution is exercised to improve the numerical accuracy of the dual-time stepping preconditioning scheme to ensure that the primary quantities in the governing equations are indeed conserved at locations where the typical density ratio is up to 100. The mixing and the flame dynamics at supercritical conditions in the vicinity of the shear coaxial injector are studied. The flame anchoring/lift-off and the corresponding mechanisms are also systematically studied.

Pressure and Geometry Scaling of Gaseous Hydrogen/Gaseous Oxygen Shear-Coaxial Injectors

The effects of pressure and geometry scaling on the flow and combustion characteristics of gas–gas injectors have been studied both numerically and experimentally. The chamber operating conditions cover a pressure range of 0.1–10 MPa, and the length varies from 0.125 to 0.25 m. The large-eddy simulation technique is used to achieve turbulence closure. Simulations of both pure mixing and combustion in model and prototype combustors at two different pressures are conducted to examine the flow,mixing, and combustion similarities for both the pressure and geometry scaling. Then hot-firing tests covering a pressure range of 0.92–6.1MPa are conducted tomeasure the wall temperature. The temperature-increase profile indicates that all the combustion cases are similar. Finally the geometry scaling is also investigated experimentally with two geometrically similar combustors. Results show that similar temperature-increase profiles were obtained for the two combustors. Results of both numerical calculations and experimental measurements suggest that there are similarities of mixing and combustion flowfields for different chamber pressures and geometries when the injection and geometry conditions satisfy the given criteria, i.e., the injection temperature, velocity, and mixture ratio are fixed, gaseous hydrogen/gaseous oxygen shear coaxial injection, and the injector and combustor are geometrically similar.

Cryogenic Fluid Dynamic Response of Swirl Injector to External Forcing at Supercritical Conditions

The present study explores the effects of externally imposed excitations on the cryogenic fluid dynamics of pressure swirl injectors at supercritical conditions. The external forcing is imposed through periodic oscillations of the mass flow rate at the injector tangential inlet over a broad band of frequencies. The flow field evolution, film thickness, and the spreading angle at the nozzle exit, are investigated and compared with the results obtained from flow without external forcing. The results indicate that low frequency forcing results in coherent flow structures at the frequency of the external forcing, whereas very high-frequency forcing does not affect the flow field significantly due to large viscous dissipation of the high-frequency fluctuations. Due to the conservation of mass and momentum, external forcing does not lead to much variation in the time-averaged film thickness and spreading angle, however, their instantaneous quantities become more regular and periodic when external forcing is enforced. The effect of the forcing magnitude was also investigated. When the forcing magnitude is very large, the film thickness and spreading angle at the injector exit deviate from the low forcing magnitude cases.

Wall Heat Transfer Measurements in High-Pressure Combustion Devices

AbstractTo investigate the wall heat transfer characteristics in a combustion chamber over a broad range of pressure conditions, a method of taking a series of wall temperature measurements in a heat sink combustion chamber, and calculating the wall temperature and heat flux from the temperature data, was introduced. The temperature and heat flux at the inner wall of the combustion chamber can be obtained using this method. The key parameters of the test article are presented, and the technique requirements for thermocouples are described. A two-dimensional (2D) axisymmetric numerical calculation method was developed to obtain the wall temperature and heat flux from the measured temperatures. The method was applied to a firing test of a single-element gaseous hydrogen/gaseous oxygen shear-coaxial injector chamber to demonstrate the details of the method. Furthermore, the heat transfer characteristics of a single-element combustion chamber at chamber pressures of 0.92 MPa to 6.1 MPa were investigated using...

Several Fundamental Issues in Large Eddy Simulation of Supercritical Mixing and Combustion

Large-Eddy Simulations (LES) of supercritical cold flow in a swirl injector with axi-symmetric configuration, and supercritical flames for LOX/methane stabilized after a splitter plate have been performed with various grid resolution. LES is used for turbulence closure. Three to four level of grid resolution is used to examine the grid sensitivity in both cold and reaction flows at supercritical conditions. One level of grid resolution corresponds to a 50% grid size decrease for all directions. In addition, the effect of ideal-gas and real-gas thermodynamic and transport property evaluations, sub-grid scale (SGS) models, and turbulent combustion models are also studied under reacting conditions. The results identify that the most important factor for accurate solutions is the grid resolution with the current numerical methodology. Turbulent combustion models are the second most important modeling factor. The effect of SGS models and property evaluation is much less important. To make high-fidelity modeling of supercritical mixing and combustion less expensive, so that they can be widely used in solving practical problems associated with supercritical mixing and combusting , appropriate models are needed to alleviate the grid resolution requirement.