A numerical study of the counterflow diffusion flames of methane/air at both subcritical and supercritical pressures,which have very important applications in the air-breathing rocket and advanced gas turbine engines,is conducted to obtain fundamental understanding of the flame characteristics.The analysis is based on a general mathematical formulation and accommodates a unified treatment of general fluids thermodynamics and accurate calculations of thermophysical properties.Results reveal that the maximum flame temperature occurs on the fuel-rich side for low-pressure conditions and shifts toward the stoichiometric position when the pressure increases.The maximum flame temperature increases with an increasing pressure,but decreases with an increasing strain rate.The flame width is inversely proportional to the square root of the product of the pressure and strain rate as■■1 p·a2/1.The total heat release rate varies with the pressure and strain rate in a relationship of Q release ■(p·a)0.518.An increased pressure leads to a slightly more complete combustion process near the stoichiometric position,but its effect on NO production is minor.Under the test conditions,variations of the strain rate have significant impacts on the formation of major pollutants.An increased strain rate leads to the decreased mole fraction of CO in the fuel-rich region and significantly reduced NO near the stoichiometric position.
The regenerative cooling technology is a promising approach for effective thermal protection of propulsion and power-generation systems.A mathematical model has been used to examine fluid flows and heat transfer of the aviation kerosene RP-3 with endothermic fuel pyrolysis at a supercritical pressure of 5 MPa.A pyrolytic reaction mechanism,which consists of 18 species and 24 elementary reactions,is incorporated to account for fuel pyrolysis.Detailed model validations are conducted against a series of experimental data,including fluid temperature,fuel conversion rate,various product yields,and chemical heat sink,fully verifying the accuracy and reliability of the model.Effects of fuel pyrolysis and inlet flow velocity on flow dynamics and heat transfer characteristics of RP-3 are investigated.Results reveal that the endothermic fuel pyrolysis significantly improves the heat transfer process in the high fluid temperature region.During the supercritical-pressure heat transfer process,the flow velocity significantly increases,caused by the drastic variations of thermophysical properties.Under all the tested conditions,the Nusselt number initially increases,consistent with the increased flow velocity,and then slightly decreases in the high fluid temperature region,mainly owing to the decreased heat absorption rate from the endothermic pyrolytic chemical reactions.
Aviation kerosene is commonly used in combustion and regenerative engine cooling processes in propulsion and power-generation systems,including rocket,scramjet,and advanced gas turbine engines.In this paper,many surrogate models proposed in the open literature are examined for their applicability and accuracy in calculating thermodynamic and transport properties of the China aviation kerosene RP-3 at supercritical pressures,based on the extended corresponding-states methods.The enthalpy change from endothermic decomposition and low heating value from combustion of the jet fuel are also evaluated.Results from a number of simple and representative surrogate models,which contain species components ranging from 1 to10,are analyzed in detail.Data analyses indicate that a surrogate model with four species is the best choice for thermophysical property calculations under the tested conditions,with fluid temperature up to 650 K at various supercritical pressures.The surrogate model is particularly accurate in predicting the pseudo-critical temperature of aviation kerosene RP-3 at a supercritical pressure.A simple surrogate model containing the n-decane species and a surrogate model containing 10 species are the other two acceptable options.The work conducted herein is of practical importance for theoretical analyses and numerical simulations of various physicochemical processes at engine operating conditions.
