| Recently, scramjet engine research has become a hot issue in the filed ofhypersonic research. China RP-3aviation kerosene is an important commonhydrocarbon fuel preferred for supersonic scramjets, the study of chemical kineticmechanism about combustion of China RP-3aviation kerosene has become a hot issuein the filed of supersonic combustion research in recent years. Measuring the ignitiondelay time of kerosene under different temperature﹑stoichiometry and pressureconditions can not only serve as the important basis for validation of combustionreaction mechanism and simplification of the chemical kinetic model, but also canprovide the important basic data for the design and optimization of the combustionchamber of the scramjet engine. In ground tests of supersonic scramjet, thehigh-enthalpy airstream produced by burning hydrocarbon fuels often containscontaminants of water vapor and carbon dioxide. The contaminants may change theignition characteristics of fuels between ground tests and real flights. In order toproperly assess the influence of the contaminants on ignition characteristics of fuels, theeffect of water vapor and carbon dioxide on the ignition delay times of China RP-3aviation kerosene must be studied. At the same time, when China RP-3aviationkerosene was used in ground tests of supersonic scramjet, it was expected to addaluminum powder, which can make the secondary combustion with the products ofhydrocarbon fuels such as water vapor and carbon dioxide in the combustion chamber,to increase the engine thrust. Studying the ignition and combustion characteristics ofaluminum powder can not only serve as the important basis for validation ofcombustion reaction mechanism and simplification of the chemical kinetic model, butalso can provide the important basic data for the design and optimization of thecombustion chamber of the scramjet engine.Shock tube is the major laboratory equipment for studying the ignition andcombustion characteristics of fuels. It can make one-dimensional homogeneous mediumnon-isentropic adiabatic compression by the incident and reflected shock, which can geta wide range of temperature and pressure by adjusting the initial pressure shock wavevelocity and the experimental area gas. Combining the experimental research andnumerical simulation, the ignition characteristics of China RP-3aviation kerosene underlow-pressure conditions are investigated. Then the vitiation effects of water vapor and carbon dioxide on the autoignition characteristics of China RP-3aviation keroseneunder low-pressure conditions and the ignition and combustion characteristics ofultra-fine aluminum powder are explored. The main contents are summarized as below:(1) The ignition characteristics of China RP-3aviation kerosene were experimentalstudied in shock tube. Under low-pressure conditions, the experimental results ofignition delay times were correlated with the temperature, pressure, stoichiometry, andthe concentrations of kerosene and oxygen. The comparison between current data andthe previous high-pressure results shows that a critical temperature exists about theeffect of equivalence ratio on the ignition behavior of China RP-3aviation kerosene.For the higher temperature range above the critical temperature, ignition delay timesincrease with increasing equivalence ratio, but decrease with increasing equivalenceratio for the lower temperature range below the critical temperature. This criticaltemperature also rises with decreasing the pressure. Meanwhile, the ignition process ofkerosene was simulated by using three kinds of kerosene combustion models, and thecomparison was made between the experimental and calculated results. The resultsshow good agreement between experimental data and the prediction based on the modelof Honnet et al. at high pressure of2.2MPa. The sensitivity analyses indicate that mostof the elementary reactions, which have a promoting effect, are the chain transfer andbranch reactions. The most obvious reaction is H+O2=O+OH. The sensitivity analysesfor different pressures also indicate that most of the elementary reactions, which havean inhibitory effect, are the chain termination reactions which consuming the freeradicals. The most obvious reaction is HO2+OH=H2O+O2.(2) The vitiation effects of water vapor and carbon dioxide on the ignition delaytimes of China RP-3kerosene was studied based on the measurement of ignition delaytime of China RP-3aviation kerosene. The experimental results show that water vaporor/and carbon dioxide have almost no effect at pressure of0.1MPa. However, atpressure of0.05and0.2MPa, water vapor appears to accelerate the ignition process,whereas carbon dioxide produces an inhibiting effect. At pressure of0.05and0.2MPa,an obvious promoting effect appears over a wide temperature range when water vaporand carbon dioxide exist together. Comparison between simulation and experimentalresults show the simulation results on the evaluation of the vitiation effects on keroseneignition consistent with the experimental trends. The sensitivity analyses indicate thatthe elementary reaction H2O+O2=HO2+OH has a significant promoting effect onkerosene ignition when water vapor exist and the initial oxidation react of n-decane and oxygen plays a major promoting effect on kerosene ignition when carbon dioxide exist.(3) The ignition and combustion characteristics of50nm,200nm and6μmaluminum powders in three different oxidant environments of oxygen, carbon dioxideand water vapor were experimental studied in shock tube, respectively. The effects oftemperature, pressure and the oxidizer primary mole fraction on the ignition andcombustion characteristics of the three types of aluminum powders were studiedsystematically. The experimental results show that the aluminum powders of50nm and200nm in all three oxidant environments and aluminum powders of6μm in oxygenignite and burn in the chemical kinetic limit regime, but the aluminum powders of6μmin carbon dioxide and water vapor ignite and burn in diffusion limit regime. Theexperimental results of ignition delay times and burn time of50nm and200nmaluminum powders in three different oxidant environments of oxygen, carbon dioxideand water vapor were correlated with the ambient temperature, pressure, and theoxidizer primary mole fraction, respectively. |
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