Weixing Zhou

Performance cycle analysis of an open cooling cycle for a scramjet

Abstract In a conventional regeneratively cooled scramjet, fuel directly enters the combustor after cooling. It is proposed in this article that high-temperature and high-pressure fuel out of the first cooling passage can be used for secondary cooling after expanding through the turbine and transferring enthalpy from fuel to work. A fuel heat sink (cooling capacity) is thus repeatedly used to indirectly increase the fuel heat sink. Instead of carrying excess fuel for cooling or looking for any new coolant, the fuel flow for cooling is reduced, and fuel onboard is adequate to satisfy the cooling requirement for the whole hypersonic vehicle. First are defined cooling and expansion and, second, cooling an open cooling cycle (OCC) for the scramjet. This article provides a brief description of the assessment of the performance potential and scientific feasibility of a scramjet with OCC using fundamental thermodynamic principles. The results show that OCC yields higher performance gain over regenerative cooling, because of the increase in the fuel heat sink and additional power output.

Experimental method study on heat flux measurement on sharp leading edge

The heat-flux measurement is the precondition of the structure and cooling system design for hypersonic aircraft, while no experiment method can be applied to the heat-flux measurement of the sharp leading edge for its small size and high-heat flux. In this article, an experimental method based on the law of inverse conduction is proposed in this paper for the calculation of heat flux from the inner wall temperature of the sharp leading edge. This experimental method proposed includes the method of inner wall transient temperature acquisition, smoothing technique, and the Matlab and Fluent cosimulation postprocessor, where Fluent is used as a 3D unsteady heat conduction solver, and conjugate gradient method is applied for optimization. The effectiveness of the proposed method is verified by its application in the scramjet experiment for the heat-flux measurement on the strut-leading edge, which greatly helps the assessment of thermal environment with a total error of less than 5%.

Hydrogen-fueled scramjet cooling system investigation using combustor and regenerative cooling coupled model

A quasi-one-dimensional combustor model is developed using MacCormack’s method to solve simplified Navier–Stokes equations for the intention of simulating the flow parameters in the combustor. The combustor model is capable of predicting the flowfield of scramjet combustor. The Eckert reference technique is adopted in the heat transfer model of the regenerative cooling system. With these two models, the relationships between phenomena are investigated. Simulation results indicate that this coupled model of combustor and regenerative cooling system can be used to investigate the influence of the cooling channel geometry, flight Mach number and fuel equivalence ratio. This coupled model is useful for the pre-design of scramjet engines.

Off-Design Condition Cooling Capacity Analysis of Recooling Cycle for a Scramjet

Many methods have been widely carried out to increase fuel heat sink to meet the cooling requirement of an airbreathing hypersonic vehicle. In particular, the recooling cycle has been newly proposed for an actively cooled scramjet to increase fuel heat sink. Fuel heat sink (cooling capacity) is repeatedly used to indirectly increase the fuel heat sink through secondary cooling in recooling cycle. The performance of recooling at off-design conditions is evaluated based on a coupled heat transfer and flowmodel of a scramjet with recooling cycle. The design principle of the recooling cycle under off-design conditions with a great range of Mach numbers and equivalence ratios is determined. The results show that the recooling cycle possesses variable heat sink increment capacities, and it can meet heat sink requirement at all conditions.

Comparison During a Scramjet Regenerative Cooling and Recooling Cycle

A coupled heat-transfer and flow model of a scramjet with a recooling cycle is established, and it includes supersonic combustion, combustion heating, and fuel cooling with real scramjet engine geometry and operating parameters. Under the most insufficient heat sink condition, flow and heat transfer characteristics are compared under real operating conditions during the recooling cycle and regenerative cooling. The comparison results indicate that the total heat sink (physical and recooling) in the recooling cycle adequately meets the cooling requirements of a scramjet under the most insufficient heat sink condition, and overtemperature can be well avoided in the recooling cycle. However, theMach number constraint can be easily activated in the recooling cycle and, therefore, the design of the second cooling passage merits some special attention.

Comparison Analysis between Expander Cycle and Recooling Cycle for a Scramjet

AbstractAn expander cycle is one potential fuel feeding cycle for a scramjet, which has been successfully applied in the liquid rocket. However, very little literature exists about the fuel feeding cycle for a scramjet. A recooling cycle has been newly proposed for a scramjet to reduce the fuel flow for cooling, the secondary function of which acts as the fuel feeding cycle. To illustrate the difference between the expander cycle and the recooling cycle, the model of the components, the pump, the turbine, and the cooling-channel are proposed in terms of hydrodynamic, thermal, power balance, and Machnumber constraints. The applicability of expander cycle as the fuel feeding cycle for a scramjet is investigated, and then the differences in working principle, functions, components, performance, and so on between the expander cycle and the recooling cycle are discussed. Furthermore, the new limitations introduced by the recooling cycle are also analyzed.

Effects of Pressure on Heat Sink of n-Decane

Enhancing the chemical heat absorption capacity is an effective method to increase the total heat sink of the endothermic hydrocarbon fuels to meet the cooling requirements of future high-performance aircraft. Thermal cracking and endothermicity capacity of ndecane were studied under different pressures. The main gas products are small molecular hydrocarbons (methane, ethane, ethylene, etc) and hydrogen, ethylene and propylene are the most abundant components at current experimental conditions. It was found that the influence of pressure on the endothermicity of n-decane is not simple effect of promotion or inhibition. Increasing pressure increases the conversion of the fuel，meanwhile，that also decreases the alkene/alkane ratio which is negative to improve the chemical heat sink of the fuel.

Experimental study on effect of pyrolysis on heat transfer of n-decane at different pressure

The heat transfer characteristics with pyrolysis of n-decane flowing through a horizontal mini circular tube of GH3128 were experimentally investigated at different supercritical pressures. The Reynolds number ranged from about 1600 to 51000. Both the outer wall temperature and the fuel temperature measured were fixed. The effect of pyrolysis on heat transfer was discussed under different pressure and the outer wall temperature distribution types were analyzed by CFD. The heat transfer coefficient distributions with length was analyzed. And the improved heat transfer regimes in pyrolysis temperature range were discussed. The experimental results indicated that the pyrolysis had a significant effect on the n-decane heat transfer behaviors.

Controlling the rule of Coke Depositions of Hydrocarbon Fuels in Channel to intensify Heat Transfer Under Supercritical Conditions

As the temperature in chamber of scramjet engine would be very high, for the moment, endothermic hydrocarbon fuels instead of the conventional aviation oils would be used in active cooling. However, when endothermic hydrocarbon fuels were heated, it would be occurred coke deposition on the in-wall of cooling channels. In this paper, the study is focused on the influence of coke depositions on heat transfer by experiments and numerical calculations. Along with the time of heating, the thickness of coke depositions in channel varied. At the beginning of heating, a few of cokes are deposited on the in-wall of channels. Heat transfer is intensified as a result of the roughness of coke. Then, the coke thickness increases, the efficiency of heat transfer gradually reduces. At this time, other conditions were varied to control the rule of coke depositions in order to increase the intensity of heat exchange. For example, the flux of fuels would be increased to overcome the clinging force between cokes and channel wall,and so on.