The Kinetics And Pyrolysis Process Of Hy-drocarbon Fuels Cracked In Active Cooling Channels Under Supercritical Conditions

In recent years, with the development of aerospace technology, scramjet is ap-plicated more widely to achieve hypersonic flight speed. However, when the speedof aircraft is up to Mach5, its fuselage temperature will be up to thousands of degreesdue to the strong friction with air. But there are no materials that can ensure the nor-mal working of the aircraft in such extreme conditions in present time. However, itwill cause exceeded weight for vehicle by increasing circulation cooling system out-side of the aircraft. To solve this problem, researchers have proposed an effectivecooling system, called regenerative cooling method, which make use of the high heatsink value of endothermic hydrocarbon fuels to achieve effective cooling for the en-gine. The principle of this cooling method is that before it gets into the combustionchamber, the big molecules of hydrocarbon fuel crack into excellent energy-richsmall molecules by absorb the exothermic heat of the combustion chamber. Thenthese small can release a lot of heat when combusted in the combustion chamber, andthe released heat was absorbed by the fuel again to cracked into small moleculers. Bythe method, it is not only to improve the utilization percent of energy fule, and it canreduce the load of the vehicle. Therefore, the in-depth study of hydrocarbon fuelscracked in heat exchange tubes is necessary.In this work, the thermal cracking reations of n-alkanes (include n-octane,n-decane and n-dodecane), cycloalkanes (include JP-10, MCH, and DHN) and binarymixtures of alkanes (n-decane and DHN in accordance with the mass ratio of1:1,)were investigated in microchannels(i.d. Φ2mm) by a lab-made electric heating ex-perimental apparatu under the high-pressure supercritical conditions, respectively.The supercritical thermal cracking reactions of n-alkanes were studied underconditions of high pressure of5MPa and the temperature range of500to710°C.And the products distributions along the distance of tube were give, so were the themolar selectivities of typical products cracked by n-alkanes. The calculated residencetime along the distance of tube were given also. By the modified kinetic model ofsecondary reactions of intermediate fraction C5-C11, the PPD model proposed byWard et al. can be applied to high conversion conditions and also can predict theyields of aromatics in thermal cracking reactions under supercritical conditions.Under the conditions of4MPa and the feed rate for the0.6g/s, the study of thethermal cracking reactions of the cycloalkanes in the supercritical state was pro-ceeded. And the gas and liquid products distributions of cycloalkane under high conversion rates were obtained. According to the property data of materials providedby Supertrapp, the residence time of thermal cracking reations of cycloalkanes wascalculated by Fortune program, and macrokinetics equations were measured respec-tively.Accordance with the mass ratio of1:1ratio method, the binary mixture ofn-decane and DHN was prepaired. And under the conditions of4MPa and conversionrate (>80%), the thermal cracing reations of binary mixture was studied. On the ba-sis of experiments,1-nonene which was the main product of thermal crackedn-decane was disappeared in the products of thermal carcked binary mixture, but thealkenes which was not contained in the cracked DHN were found in the middle ofthe products of thermal cracked binary mixture. Comparied with the cracked DHN,along with the products of cracked binary mixture, the mole selectivity of alkenesincreased, but the mole selevtivity of cycloalkenes decresased sharply.