Fengquan Zhong

Heat Transfer of Aviation Kerosene at Supercritical Conditions

The heat transfer characteristics of China no. 3 kerosene were investigated experimentally and analytically under conditions relevant to a regenerative cooling system for scramjet applications. A test facility developed for the present study can handle kerosene in a temperature range of 300-1000 K, a pressure range of 2.6-5 MPa, and a mass How rate range of 10-100 g/s. In addition, the test section was uniquely designed such that both the wall temperature and the bulk fuel temperature were measured at the same location along the flowpath. The measured temperature distributions were then used to analytically deduce the local heat transfer characteristics. A 10-component kerosene surrogate was proposed and employed to calculate the fuel thermodynamic and transport properties that were required in the heat transfer analysis. Results revealed drastic changes in the fuel flow properties and heat transfer characteristics when kerosene approached its critical state. Convective heat transfer enhancement was also found as kerosene became supercritical. The heat transfer correlation in the relatively low-fuel-temperature region yielded a similar result to other commonly used jet fuels, such as JP-7 and JP-8, at compressed liquid states. In the high-fuel-temperature region, near and beyond the critical temperature, heat transfer enhancement was observed; hence, the associated correlation showed a more significant Reynolds number dependency.

Thermal Cracking and Heat Sink Capacity of Aviation Kerosene Under Supercritical Conditions

pressurerangeof3–4.5MPa,andaresidencetimerangeof0.6–3s.Thechemicalheatsinkwasdeterminedthrougha control volume analysis of the fuel flow. Compositions of the cracked gaseous and liquid products were analyzed via gas chromatography. Based on the results of fuel conversion, the temperature range for the active cracking was observedtobeapproximately800–1000K,beyondwhichthecrackingapproachescompletion.Itwasalsofoundthat the variation of the chemical heat sink with temperature can be nonmonotonic and a maximum endothermicity was seen to occur in the temperature range of 900–960 K, depending on the residence time. For the current operation conditions, the maximum chemical heat sink reached 0:5 MJ=kgat a fuel conversion of 45%. Composition analysis ofthegaseousproductindicatedthatthesaturatedhydrocarbonssuchasmethanebecamedominantastemperature

Numerical Study of Turbulent Flow and Convective Heat Transfer Characteristics in Helical Rectangular Ducts

Three-dimensional turbulent forced convective heat transfer and its flow characteristics in helical rectangular ducts are simulated using SST k-omega turbulence model. The velocity field and temperature field at different axial locations along the axial direction are analyzed for different inlet Reynolds numbers, different curvatures, and torsions. The causes of heat transfer differences between the inner and outer wall of the helical rectangular ducts are discussed as well as the differences between helical and straight duct. A secondary flow is generated due to the centrifugal effect between the inner and outer walls. For the present study, the flow and thermal field become periodic after the first turn. It is found that Reynolds number can enhance the overall heat transfer. Instead, torsion and curvature change the overall heat transfer slightly. But the aspect ratio of the rectangular cross section can significantly affect heat transfer coefficient.

NUMERICAL SIMULATION OF IGNITION AND COMBUSTION OF ETHYLENE IN A SUPERSONIC MODEL COMBUSTOR WITH A REDUCED KINETIC MECHANISM

The unsteady process of ignition and combustion of ethylene at varied fuel/air equivalence ratios in a Mach 2.5 supersonic model combustor is studied numerically. The reacting turbulent flow is solved using the shear stress transport (SST) k–ω turbulence model and a reduced kinetic mechanism obtained with sensitivity analysis and the assumption of quasi-steady-state from a detailed mechanism of ethylene. The present results reveal that ignition of ethylene first takes place in the cavity due to the local low speed and high static temperature. At a low equivalence ratio of 0.32, combustion is established and stabilized downstream of the cavity. However, as the equivalence ratio increases to 0.6, the combustion downstream of the cavity generates sufficient heat release to cause pressure and the flame to propagate upstream and to generate a shock train upstream of the injection point. Formation of the shock structure results in subsonic flow in the vicinity of the injection and combustion with higher efficiency stabilized mainly in the fuel/air mixing shear layer. The time evolutions of fuel jet and C2H2 qualitatively agree well with the experimental results, of which high-speed schlieren photos and chemiluminescence images of CH* are obtained at similar flow conditions.

Numerical Study of Impingement Cooling of Aviation Kerosene at Supercritical Conditions

In the present paper, numerical study of flow and heat transfer properties of RP-3 kerosene at liquid and supercritical conditions in an impingement model is conducted with renormalization group (RNG) k - epsilon turbulence model and a ten-species surrogate of kerosene. The independence of grids is first studied, and the numerical results are compared with experimental data for validation. Characteristics of flow and heat transfer of kerosene flow in the impingement model are studied with different inlet mass flow rates and different inlet temperatures. The velocity and temperature field show similar profile compared to that of air impingement. The heat transfer rates increase first with the increasing of inlet temperature and then decrease suddenly when the inlet temperature is 500 K.

An Experimental Study of Chilton-Colburn Analogy Between Turbulent Flow and Convective Heat Transfer of Supercritical Kerosene

In this paper characteristics of turbulent flow and convective heat transfer of supercritical China RP-3 kerosene in a horizontal straight circular tube are studied experimentally and the validity of Chilton-Colburn analogy is examined. Using a three-stage heating system experiments are conducted at a fuel temperature range of 650-800 K a pressure range of 3-4 MPa and a Reynolds number range of 1 x 10(5) -3.5 x 10(5). The Nusselt number and skin friction coefficient are calculated through control volume analysis proposed in this paper. Heat transfer enhancement and deterioration were observed in the experiments as well as the similar change of skin friction coefficient. The present results show that Chilton-Colburn analogy is also valid for turbulent flow and heat transfer of supercritical kerosene in horizontal straight circular tubes.

Experimental Study of Ignition and Flame Characteristics of Surrogate of Cracked Hydrocarbon Fuels in Supersonic Crossflow

The ignition and flame characteristics of ethylene and blend fuel (surrogate of thermal cracked kerosene) are studied experimentally on a direct-connect supersonic combustor facility. The blend fuel consists of H2, CH4, C2H4, C2H6, C3H6and C3H8with molar fractions according to the result of gaseous compositions of thermal cracked kerosene. CH* luminance in the combustion is filmed by a high-speed camera, and unsteady process of ignition as well as flame formation and proportion is captured. Meanwhile the image of CH* luminance is one-dimensional treated along the axis of combustor and the relative amount of heat release rate of combustion is obtained. The experimental results show that with equivalence ratio increasing the flame of ethylene is changed from the cavity stabilization mode to the jet-wake stabilization mode and the combustion efficiency increases. In contrast, the total heat release and combustion efficiency of the blended fuel decrease. 漏 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

CH* Luminance Distribution Application and a One-Dimensional Model of the Supersonic Combustor Heat Release Quantization

Abstract One-dimensional model is an important way to evaluate the performance and flow characteristics of dual-mode scramjet combustor. Current work is based on a modified one-dimensional model assisted by measurements acquired on a direct-connected scramjet facility. CH* images and gas-sampling facility have been employed to quantify heat release for optimizing one-dimensional model. The results show that modified one-dimensional model gives a better evaluation of axis parameters distribution, especially for Mach number, which is the standard parameter to evaluate combustion mode. The ram/scram mode derived by the analytical results has been investigated. Intensive heat release is beneficial to obtain more stable pre-combustion shock and subsonic flow in the recirculation zone.

Numerical Study of Unsteady Properties of Ethylene/Air Turbulent Jet Diffusion Flame with Detached Eddy Simulation

Abstract In this paper, unsteady process of ignition and combustion of turbulent plane-jet diffusion flame of ethylene/air is numerically simulated with detached eddy simulation (DES) and a reduced kinetic mechanism of ethylene. The kinetic mechanism consisting of 25 species and 131 steps is reduced from a 25 species/131 steps detailed mechanism via the method of error-propagation-based directed relation graph (DRGEP). The DES results of averaged temperature profiles at varied downstream locations are compared with the DNS results of Yoo et al. [11] and satisfactory agreement between them is found. Ignition and combustion of ethylene plane-jet diffusion flame is simulated and dynamic changes of temperature field and OH radical are obtained. The present numerical study shows that DES method with a qualified reduced mechanism of hydrocarbon fuels can effectively simulate temporal and spatial evolution of ignition and combustion process.

Large Eddy Simulation of Ignition and Combustion of Ethylene/Air Turbulent Jet Diffusion Flame with Reduced Kinetic Mechanism

In this paper, unsteady process of ignition and combustion of turbulent plane-jet diffusion flame of ethylene/air at varied fuel/air ratios is numerically simulated with Large Eddy Simulation (LES) and a reduced kinetic mechanism of ethylene. The kinetic mechanism consisting of 25species and 131steps is reduced from a 71species/395steps detailed mechanism via the method of error-propagation-based directed relation graph (DRGEP) and sensitivity analysis. The LES results of height of flame lift-up and averaged temperature profiles at different downstream locations are compared with the DNS result of Yoo (2011) and satisfactory agreements are found. Unsteady processes of ignition and combustion of ethylene plane-jet diffusion flame are simulated with varied fuel injection velocities. Dynamic evolutions of temperature field as well as CH2 and OH radicals are obtained, which are found to be strongly related to turbulence eddies caused by jet/air mixing layer. The present numerical study shows that LES method with reduced mechanism of hydrocarbon fuels can effectively simulate temporal and spatial evolution of ignition and combustion process.